<PAGE>

                                                                   EXHIBIT 10.57





                        LANDLORD: SSP ASSOCIATES, INC.

                                      And

                    TENANT: CONCENTRIC NETWORK CORPORATION

                           Dated: December 15, 1999
<PAGE>

                               TABLE OF CONTENTS
                               -----------------
<TABLE>
<CAPTION>
                                                           Page
                                                           ----
<S>          <C>                                            <C>

SECTION 1    SCHEDULE.....................................   1

SECTION 2    GRANT AND TERM...............................   2

             2.1 Demised Premises.........................   2
             2.2 Term.....................................   3
             2.3 Renewal Term.............................   3

SECTION 3    CONSTRUCTION OF DEMISED PREMISES.............   3

             3.1 Construction.............................   3
             3.2 Delays...................................   3
             3.3 Completion Date..........................   4
             3.4 Settlement of Disputes...................   4

SECTION 4    POSSESSION AND COMMENCEMENT OF TERM..........   4

             4.1 Possession and Commencement of Lease Term   4
             4.2 Landlord Not Liable For Delays...........   5
             4.3 Memorandum...............................   5

SECTION 5    BASE RENT....................................   5

             5.1 Base Rent................................   5
             5.2 Renewal Base Rent........................   6
             5.3 Rent Net of All Expenses.................   7
             5.4 Delinquency Charge.......................   7
             5.5 Lease Year...............................   7
             5.6 Default Charge...........................   7

SECTION 6    UTILITIES....................................   8

SECTION 7    TAXES AND ASSESSMENTS........................   8

             7.1 Obligation...............................   8
             7.2 Definition...............................   8
             7.3 Payments.................................   8
             7.4 Escrow...................................   9
             7.5 Right to Contest Taxes...................   9
             7.6 Tenant's Taxes...........................  10
             7.7 Surplus Taxes............................  10
</TABLE>

                                      -i-
<PAGE>

<TABLE>
<S>                  <C>                                             <C>
SECTION 8            USE OF DEMISED PREMISES.......................  10

                     8.1 Use of Demised Premises...................  10
                     8.2 Care of Demised Premises..................  10
                     8.3 Hazardous Substances......................  11
                     8.4 Obligation of Tenant......................  11

SECTION 9            INDEMNITY.....................................  11

                     9.1 Indemnity.................................  11
                     9.2 Liability Insurance.......................  12
                     9.3 Tenant's Contractor's Insurance...........  12
                     9.4 Delivery of Policy and Special Endorsement  12

SECTION 10           MAINTENANCE AND REPAIRS.......................  12

                     10.1 Maintenance And Repairs..................  12
                     10.2 Compliance With Laws.....................  13

SECTION 11           TENANT'S ALTERATIONS..........................  13

                     11.1 Alterations..............................  13
                     11.2 Construction Liens.......................  14

SECTION 12           PROPERTY INSURANCE, REBUILDING AND WAIVER
                     OF SUBROGATION................................  14

                     12.1 Property Insurance.......................  14
                     12.2 Rebuilding...............................  15
                     12.3 Tenant's Deposit for Rebuilding..........  16
                     12.4 Waiver of Subrogation....................  16

SECTION 13           EMINENT DOMAIN................................  16

                     13.1 Total Condemnation.......................  16
                     13.2 Partial Condemnation.....................  16
                     13.3 Landlord's and Tenant's Damages..........  17

SECTION 14           ACCESS TO PREMISES............................  17

SECTION 15           FIXTURES AND EQUIPMENT........................  18

SECTION 16           BANKRUPTCY AND INSOLVENCY OF TENANT...........  18

SECTION 17           RIGHT TO MORTGAGE.............................  19
</TABLE>

                                     -ii-
<PAGE>

<TABLE>
<S>                 <C>                                         <C>
SECTION 18          ASSIGNMENT, SUBLETTING AND TRANSFERS
                     BY TENANT................................  19

SECTION 19          SALE OR TRANSFER..........................  20

SECTION 20          DEFAULT, RE-ENTRY AND DAMAGES.............  20

                    20.1 Default..............................  20
                    20.2 Re-Entry and Damages.................  20
                    20.3 Waiver of Landlord's Liability.......  21
                    20.4 Landlord's Rights Cumulative.........  21
                    20.5 Waiver of Jury Trial and Counterclaim  21
                    20.6 Non-Liability........................  21

SECTION 21          LANDLORD'S RIGHT TO CURE DEFAULTS.........  22

SECTION 22          QUIET ENJOYMENT...........................  22

SECTION 23          HOLDING OVER..............................  22

SECTION 24          CUMULATIVE REMEDIES AND WAIVER............  22

                    24.1 Cumulative Remedies..................  22
                    24.2 Waiver...............................  23

SECTION 25          OPTION TO EXPAND BUILDING SPACE...........  23

SECTION 26          DEFINITION OF LANDLORD, LANDLORD'S
                     LIABILITY................................  23

SECTION 27          WASTE.....................................  24

SECTION 28          SIGNS.....................................  24

SECTION 29          SECURITY DEPOSIT..........................  24

SECTION 30          MISCELLANEOUS.............................  24

                    30.1 Condition of Demised Premises........  24
                    30.2 Lease Changes Required By Lender.....  25
                    30.3 Entire Agreement.....................  25
                    30.4 Modification.........................  25
                    30.5 Joint Venture, Mortgage..............  25
                    30.6 Notices..............................  25
                    30.7 Survival.............................  25
</TABLE>

                                     -iii-
<PAGE>

<TABLE>
               <S>                                   <C>
               30.8 Estoppel Certificate...........  26
               30.9 Gender.........................  26
               30.10 Captions and Section Numbers..  26
               30.11 Broker's Commission...........  26
               30.12 Recording.....................  26
               30.13 Execution of Lease............  26
               30.14 Construction..................  26
               30.15 Binding Effect................  27
</TABLE>

                                     -iv-
<PAGE>

                                     LEASE
                                     -----

                                   SECTION I

                                    SCHEDULE
                                    --------

LANDLORD:      NAME: SSP Associates, Inc.
               ADDRESS: 4509 Longmeadow Road, Saginaw, MI 48603

TENANT:        NAME: Concentric Network Corporation
               ADDRESS:
                Before Commencement Date:
                1400 Parkmoor Avenue
                San Jose, CA 95126
                Attn: Director of Administration

                After Commencement Date:
                1400 Parkmoor Avenue     and     The Premises
                                         ---
                San Jose, CA 95126               Attn: Facility Manager
                Attn: Director of Administration

DEMISED
PREMISES:      Land ("Site") as described in Exhibit A consisting of
               approximately 7.34 acres, and improvements to be constructed or
               installed thereon ("Project"), located at 1405 Tittabawassee,
               Carrollton Township, Saginaw County, Michigan, described as
               follows:

                    An office and computer facility consisting of approximately
                    40,000 square feet of office space, and including driveways,
                    parking areas and related improvements.

PLANS:         Plans and specifications ("Plans") for completion and
               construction of the Project, as approved and initialed by the
               parties, floor plan (Job No. 99-1334-60; 10/20/99) Sheet A1,
               Elevation (Job No. 99-1334-60; 11/8/99) Sheet A2, together with
               any subsequent plans and specifications approved in writing by
               the parties.

LEASE TERM:    12 years

RENEWAL TERM:  One 10-year term

COMMENCEMENT
DATE:          When built (Anticipated to be June 1, 2000)

                                       1
<PAGE>

TERMINATION
DATE:               May 30, 2012

ANNUAL BASE
RENT:               Lease Year               Annual Base Rent
                    ----------               ----------------

                    1 ($10.00 x sq. ft.)     $440,000.00
                    2 ($10.00 x sq. ft.)     $440,000.00
                    3-12 ($12.75 x sq. ft.)  $510,000.00

                    Renewal Term (13-22)     $CPI since 2000 with no one
                                              year exceeding 3.5% increase

MONTHLY
INSTALLMENT OF
BASE RENT:          Month of Lease Term       Monthly Installment of Base Rent
                    -------------------       --------------------------------

                         1-24                          $36,666.66
                         25-144                        $42,500.00

SECURITY
DEPOSIT:            None required at commencement

USE OF DEMISED
PREMISES:           Office/Computer Facility and other uses permitted under the
                    B-1 Zoning

DATED:              December 15, 1999

EXHIBITS
ATTACHED:           A - Legal Description of Demised Premises and Site Plan
                    B - Plans
                    C - Tenant Requirements


                                   SECTION 2

                                 GRANT AND TERM
                                 --------------

2.1  Demised Premises
     ----------------

     Landlord, in consideration of the rents to be paid and the covenants,
promises and agreements to be performed by Tenant, does hereby lease to Tenant
and Tenant hereby rents from Landlord, the Demised Premises described in
Section 1.

                                       2
<PAGE>

2.2  Term
     ----

     The term of this Lease shall be for the Lease Term stated in Section 1,
commencing on the Commencement Date stated in Section 1 and expiring on the
Termination Date stated in Section 1, unless delayed or sooner terminated as
herein set forth.

2.3  Renewal Term
     ------------

     Tenant is granted an option to renew the term of the Lease for one 10-year
term which shall be exercised, if at all, as follows:

     Not less than 270 days before the expiration of the Lease, Tenant will
     notify Landlord in writing of Tenant's election to renew the Lease for an
     additional term of ten years. The monthly rental charge is set out in
     Section 5.


                                   SECTION 3

                        CONSTRUCTION OF DEMISED PREMISES
                        --------------------------------

3.1  Construction
     ------------

     Landlord agrees, prior to the Commencement Date to construct and complete
the Project on the Site, in accordance with the Plans as described in Section 1,
at Landlord's sole cost and expense. Any changes made to the Plans, at the
request of Tenant, after the date of this Lease, which are acceptable to
Landlord in cost, character, nature and scope, shall be paid by Tenant to the
extent they increase the cost to complete the Project; one-half of such amount
at date of the request by Tenant and the balance to be paid on the Commencement
Date. Minor changes from such plans and specifications, which may be necessary
to accommodate construction and are reasonably approved by Tenant, shall not
affect, change or invalidate this Lease. The Project shall be constructed in a
good and workmanlike manner, free of all liens, and in accordance with the Plans
and all laws, statutes, ordinances, building codes, rules and regulations of any
federal, state or municipal body or other governmental agency having
jurisdiction thereof then in effect. Landlord warrants against structural
defects and further warrants that the entire Project will be free from defect in
materials or workmanship for one year.

3.2  Delays
     ------

     Landlord's obligations under this section shall not require Landlord to
incur overtime costs and expenses. In the event Landlord shall be delayed or
hindered in the construction of the Project or prevented from completing such
construction or prevented from delivering possession of the Demised Premises
because of any strike, lockout, labor dispute, fire, damage or destruction or
casualty, unavailability of material, weather, power failures, unavailability of
utilities, restrictive governmental laws or regulations, riots, insurrection,
war, or any other reason, beyond its control,

                                       3
<PAGE>

then Landlord shall be excused for the period of delay and the Commencement Date
shall be postponed for such period of delay until such time as the Demised
Premises are ready for occupancy, but no such failure to give Tenant occupancy,
shall extend the Termination Date.

3.3  Completion Date
     ---------------

     Subject to Section 3.2, the Project shall be substantially completed on or
before the Commencement Date. Substantially completed shall mean the date upon
which water, gas, electricity, sewer and other utilities at levels reasonably
required for the permitted use are available, Landlord has substantially
completed the Project (subject only to Punchlist Items or exterior seasonal
projects (e.g., blacktopping, landscaping, etc.)) and Landlord delivers a
Certificate of Occupancy which permits Tenant to occupy the Project and conduct
its business.

3.4  Settlement of Disputes
     ----------------------

     If any disagreement or dispute may arise between Landlord and Tenant with
reference to the work performed by Landlord with respect to the Exhibit B
(Plans) or Exhibit C (Tenant Requirements), such shall be decided by arbitration
in accordance with the Construction Industry Arbitration Rules of the American
Arbitration Association unless the parties mutually agree otherwise. Notice of
the demand for arbitration shall be filed in writing with the other party and
with the American Arbitration Association and shall be made within a reasonable
time after the dispute has arisen. The arbitrator's decision shall be final and
binding upon Landlord and Tenant and a judgment for enforcement thereof shall be
entered by a court in Saginaw County, Michigan. Landlord and Tenant shall agree
that all arbitration hearings shall be held in Saginaw County, Michigan, and
that any contractors, subcontractors, laborers, materialmen and other persons or
entities having responsibility for the claim or dispute may be joined to the
arbitration.


                                   SECTION 4

                      POSSESSION AND COMMENCEMENT OF TERM
                      -----------------------------------

4.1  Possession and Commencement of Lease Term
     -----------------------------------------

     Landlord shall deliver actual possession of the Demised Premises to Tenant
on or before the completion date specified in Section 3.3, but if delivery is
delayed by reason of Section 3.2 or by the Landlord for any reason whatsoever,
the date upon which such possession is delivered shall constitute the
"Commencement Date" in lieu of the date provided in Section 1; however, the
Termination Date provided in Section I shall not change. Landlord shall, when
construction progress so permits, notify Tenant of the anticipated completion
date specified in Section 3.3. By occupying the Demised Premises, Tenant will be
deemed to have accepted the Demised Premises and acknowledged that they are in
substantially the condition required under this Lease; except for incidental
items of uncompleted contract work that does not interfere with or diminish
Tenant's use of the Project of which Tenant shall notify Landlord in a writing
("Punchlist") within six (6) months after the Commencement Date. Landlord shall
diligently pursue completion of such items of

                                       4
<PAGE>

uncompleted contract work set forth in the Punchlist. The Rent, as defined
herein, due under this Lease and the term of this Lease shall commence on the
Commencement Date. If permission is given to Tenant to occupy all or part of the
Demised Premises prior to the Commencement Date, Tenant covenants and agrees
that such occupancy shall be governed by all terms and conditions of this Lease
(other than the obligation to pay rent), and the Termination Date shall not be
changed. Such early occupancy shall not interfere with Landlord's completion of
the Project. Tenant and its contractors shall have the right to install
equipment, trade fixtures, furnishings and decorations in the Demised Premises
for a period of 30 days prior to the Commencement Date, provided such does not
delay or interfere with Landlord's construction or delivery of possession and
any such delay or interference shall not postpone the Commencement Date or the
obligation to pay Rent.

4.2  Landlord Not Liable For Delays
     ------------------------------

     Under no circumstances shall Landlord be liable for any delays in the
delivery of possession to Tenant on the Commencement Date.

4.3  Memorandum
     ----------

     Within 30 days after the delivery of possession to Tenant, Tenant shall
join with Landlord in the execution of a written memorandum confirming the
Commencement Date and Termination Date of the Lease Term. Tenant's failure to
execute the Memorandum shall be a violation by Tenant under this Lease and
Landlord's default under this Lease shall not relieve Tenant of the obligation
to execute the Memorandum within such 30-day period.


                                   SECTION 5

                                   BASE RENT
                                   ---------

5.1  Base Rent
     ---------

     Tenant shall pay to Landlord the Annual Base Rent stated in Section 1, for
the Demised Premises during the Lease Term. The Annual Base Rent shall be
payable in monthly installments equal to the Monthly Installment of Base Rent
stated in Section 1, paid in advance, on the first day of each and every
calendar month during the Lease Term, without any set-off or deduction
whatsoever (except as expressly set forth herein), at the office of Landlord
stated in Section 1, or at such other place as Landlord may designate from time
to time in writing. The first Monthly Installment of Base Rent shall be due and
payable at the time of the execution of this Lease. If the Lease Term shall
commence on a day other than the first day of a calendar month, or shall end on
other than the last day of a calendar month, then the Monthly Installment of
Base Rent due for such partial month shall be prorated.

                                       5
<PAGE>

5.2  Renewal Base Rent
     -----------------

          A.  If Tenant elects to continue the Lease for an additional ten-year
     term, the Annual Base Rent for each year of the Renewal Term (ten years)
     shall be increased on June 1, 2012 ("Adjustment Date"), to an amount equal
     to the product obtained by multiplying Five Hundred Ten Thousand
     ($510,000.00) Dollars by the sum of each calendar year percent change
     (positive or negative) in the Consumer Price Index-Detroit All Items (1992-
     1984 = 100), published by the Bureau of Labor Statistics of the United
     States Department of Labor during the lease term. For each year that the
     Consumer Price Index exceeds a percent change greater than 3.5% (positive
     or negative), the figure of 3.5% shall be used instead of the actual
     figure. In no event shall the Annual Base Rent as adjusted be less than the
     Annual Base Rent for the previous lease year. The Monthly Installment of
     Base Rent shall be increased on each Adjustment Date to an amount equal to
     one-twelfth (1/12) of the Annual Base Rent as increased on such Adjustment
     Date. References in this Lease to Annual Base Rent shall include
     adjustments thereto pursuant to this Section. An example of how the
     adjustment of Base Rent shall be calculated in the year 2012, shall be as
     follows:

          Assume the following annual percent increase in CPI Detroit All Items:

                 00    2.1%        06   3.0%
                 01    2.7%        07   2.8%
                 02    4.6%        08   2.3%
                 03    5.2%        09   2.0%
                 04    4.0%        10   2.1%
                 05    3.4%        11  -2.0%

          Sum total percent increase without adjustment for the lease
                                     ------------------
          term = 32.2%

          Sum total percent increase with adjustment (e.g., 3.5% cap)
                                     ---------------
          to use for ten-year Renewal Term = 28.9%

          $510,000.00 x 1.289 = $657,390.00 / 12 = $54,782.50 per month
          for each month often-year Renewal Term

          B.  The Landlord shall, within a reasonable time after obtaining the
     appropriate data necessary for computing such increase, give Tenant written
     notice of any such increase, and Tenant shall commence paying the Monthly
     Installment of Base Rent as increased with the next Monthly Installment of
     Base Rent due hereunder. In the event the determination is made after the
     Adjustment Date, then Tenant shall pay the increase allocated for any prior
     periods with the next Monthly Installment of Base Rent payment or within
     thirty (30) business days after such notice of the increase, whichever
     occurs last.

          C.  In the event the CPI Detroit (All Items) is discontinued and not
     replaced by a successor index by the Bureau of Labor Statistics, the
     adjustments to be made hereunder

                                       6
<PAGE>

     shall be made based upon such comparable statistics on the cost of living
     for the Detroit region which shall carry out the intent of this paragraph.

          D.  In the event of any dispute between Landlord and Tenant with
     regard to such adjustment, such dispute shall be determined by arbitration
     under the then prevailing commercial arbitration rules of the American
     Arbitration Association. Such arbitration shall be final and binding upon
     the parties and a judgment may be entered upon it in accordance with the
     applicable law in any court having jurisdiction thereof.

5.3  Rent Net of all Expenses
     ------------------------

     Landlord and Tenant intend that the Annual Base Rent due hereunder,
together with any adjustments during the Lease Term shall be absolutely net of
all operating costs, expenses, taxes (real and personal) and charges.

5.4  Additional Rent
     ---------------

     All amounts due from Tenant and payable to Landlord, excluding Annual Base
Rent, including, without limitation, if applicable, taxes and assessments
pursuant to Section 7 hereof and insurance premiums pursuant to Section 9 and 12
hereof, shall be deemed to be Additional Rent and upon Tenant's failure to pay
any such amount, Landlord, in addition to any other remedies, shall have the
same remedies provided for Tenant's failure to pay the Annual Base Rent (the
Annual Base Rent, together with the Additional Rent, shall be collectively
referred to as "Rent"). Tenant shall pay any and all sums of money or charges
required to be paid by Tenant under this Lease promptly when the same are due,
without any deductions or setoff whatsoever (except as expressly set forth
herein).

5.5  Delinquency Charge
     ------------------

     If Tenant shall fail to pay all or any portion of a Monthly Installment of
Base Rent, as and within five (5) days after the date the same is due, in
addition to the Monthly Installment of Base Rent, Tenant shall pay a delinquency
charge equal to 5 percent of the amount unpaid per month outstanding to
reimburse the Landlord for the costs incurred as the result of such late
payment. Such delinquency charge shall be paid with the next Monthly Installment
of Base Rent.

5.6  Default Charge
     --------------

     If Tenant shall default in any payment or expenditure other than Annual
Base Rent required to be paid or expended by Tenant under the terms hereof, then
Landlord may, at its option, make such payment or expenditure in accordance with
Section 21. In such event, the amount thereof shall be due and payable as
Additional Rent to Landlord by Tenant with the next Monthly Installment of Base
Rent, together with interest thereon at a rate equal to the sum of the then
prevailing "prime interest rate" (as hereinafter defined) plus 2% from the date
of such payment or expenditure by Landlord until the date of the payment by
Tenant, to cover Landlord's loss of the use of the funds and administrative
costs resulting from Tenant's failure. Upon Tenant's failure to

                                       7
<PAGE>

pay said Additional Rent together with interest, such interest shall continue
for each month or portion thereof outstanding until the date of payment. The
"prime interest rate" for purposes of this Lease shall mean the rate of interest
announced by Wall Street Journal as the "prime interest rate". The "prime
interest rate" shall be determined as of the date of Landlord's payment or
expenditure. If the Wall Street Journal ceases to publish its "prime interest
rate", the most comparable interest rate to that known as the "prime interest
rate" shall be used.


                              SECTION 6

                              UTILITIES
                              ---------

     Tenant agrees to pay all charges made against the Demised Premises for gas,
heat, water, air conditioning, electricity, sanitary and storm sewage
disposition, telephone and all other utilities during the Lease Term as the same
shall become due. Landlord shall not be liable to Tenant for the quality or
quantity of any such utilities, or for any interruption in the supply of any
such utilities.


                                   SECTION 7

                             TAXES AND ASSESSMENTS
                             ---------------------

7.1  Obligation
     ----------

     Tenant agrees to pay all Taxes, as defined in Section 7.2, on the Demised
Premises for each lease year or partial lease years during the Lease Term. At
the start of the Lease, taxes shall be prorated and treated as if paid in
arrears with Landlord responsible for payment of taxes from January 1, 2000, to
the Commencement Date. Thereafter, Tenant will be responsible for taxes each
year including the year of termination. At termination, Tenant shall pay for
taxes from January 1 through the date the premises have been turned over to
Landlord.

7.2  Definition
     ----------

     "Taxes" shall be defined as: (a) all taxes (either real or personal),
assessments (general or specific), all water and sewer charges, and all other
governmental impositions, which may be levied during the Lease Term upon the
land, buildings or improvements comprising the Demised Premises or any part
thereof; (b) a tax or surcharge of any kind or nature upon, against or with
respect to the parking areas or the number of parking spaces on the Demised
Premises; and (c) all costs and expenses incurred by Landlord during
negotiations for or contests of the amount of such taxes and assessments,
without regard to the result, including, without limitation, actual attorneys'
fees.

7.3  Payments
     --------

     Taxes on the Demised Premises levied or assessed for or during the Lease
Term shall be paid before any penalty interest is imposed or within thirty (30)
days of issuance of a tax bill to the

                                       8
<PAGE>

Tenant (whichever occurs later). In the event a refund of Taxes previously paid
is obtained, Landlord shall credit the portion which relates to the Demised
Premises to the next payment due under this Section or after the termination of
the Lease, refund such amounts to Tenant. A copy of a tax bill or assessment
bill submitted by Landlord to Tenant shall at all times be sufficient evidence
of the amount of Taxes assessed or levied against the property to which such
bill or return relates.

7.4  Escrow
     ------

     If Tenant fails to pay taxes within applicable notice and cure periods on
more than two occasions during the term of the Lease, Landlord may, at its
option and upon written notice to Tenant, require that Taxes shall be paid to
Landlord in monthly installments on or before the first day of each calendar
month, in advance, in an amount estimated by Landlord; provided, that in the
event Landlord is required under any mortgage covering the demised Premises, or
any portion thereof, to escrow Real Estate Taxes, Landlord may, but shall not be
obligated to, use the amount required to be so escrowed as a basis for its
estimate of the monthly installments due from Tenant hereunder. If Landlord
elects to require monthly installments, upon making such election, Tenant shall
pay to Landlord an amount which, when added to the installment payments to be
paid by Tenant, will be sufficient to provide Landlord with the amount required
to pay the Taxes thirty (30) days before the Taxes are due. Subsequent to the
end of each lease year or partial lease, Landlord shall furnish Tenant with a
written statement of the actual amount of the Taxes on the Demised Premises. In
the event no tax bill is available, Landlord will compute the amount of such
tax. If the total amount paid by Tenant under this Section 7.4 for any lease
year during the Lease Term shall be less than the actual amount due from Tenant
for such year, as shown on such statement, Tenant shall pay to Landlord the
difference between the amount paid by Tenant and the actual amount due, such
deficiency to be paid within thirty (30) days after demand therefor by Landlord;
and if the total amount paid by Tenant hereunder for any such year shall exceed
such actual amount due from Tenant for such year, such excess shall be credited
against the next installment of taxes and assessments due from Tenant to
Landlord hereunder or after the termination of the Lease, refund such amounts to
Tenant. In the event a refund of Taxes previously paid is obtained, Landlord
shall credit the portion which relates to the Demised Premises to the next
installments due under this Section.

7.5  Right to Contest Taxes
     ----------------------

     In the event the amount of the Taxes are not contested by Landlord, then
Tenant, upon written notice to Landlord, shall have the right to contest the
amount of the Taxes at Tenant's sole cost and expense, by the appropriate
proceedings diligently contest in good faith and shall immediately pay any
increases in the Taxes or shall be given a credit against monthly installments
thereof subsequently due (or, after the termination of the Lease, a refund) in
the amount of any reductions in the Taxes. Notwithstanding such proceedings,
Tenant shall promptly pay and discharge such Taxes and any penalties or interest
assessed thereon, unless such proceedings and the posting of a bond or other
security shall (a) operate to prevent or stay the collection of the Taxes and
secure any accruing penalties or interest and (b) operate to cure Landlord's
default in the payment of Taxes required under any mortgage upon the Demised
Premises. Landlord agrees to

                                       9
<PAGE>

join Tenant in such proceedings, if necessary, provided Tenant pays all costs
and expenses incurred by Landlord, including actual attorneys' fees.

7.6  Tenant's Taxes
     --------------

     Tenant shall pay all real and personal property taxes levied or assessed
against Tenant's property and improvements upon or affixed to the Demised
Premises, including taxes attributable to all alterations, additions, or
improvements made by Tenant.

7.7  Surplus Taxes
     -------------

     Landlord's obligation to refund overpayment of Taxes shall survive the
termination of this Lease.


                                   SECTION 8

                            USE OF DEMISED PREMISES
                            -----------------------

8.1  Use of Demised Premises
     -----------------------

     Tenant may use and occupy the Demised Premises during the Lease Term only
for the purpose stated in Section 1, and attendant office use and other legal,
related uses and for no other purpose without the prior written consent of the
Landlord. Tenant shall not use or permit any person to use the Demised Premises
or any part thereof for any use or purpose other than the use stated in Section
1 or in violation of any law, statute, order, ordinance, code, rule or
regulation of any federal, state or municipal body or other governmental agency
or authority having jurisdiction thereof, including, without limitation,
occupational safety and health requirements, community right-to-know
requirements, requirements pertaining to the possession, generation,
transportation, treatment and disposal of hazardous substances and hazardous
wastes, or pollution standards or requirements ("Laws"), or any building and use
restrictions ("Restrictions") affecting the Demised Premises, if any. Subjection
to Section 10.2, Tenant shall comply with all such present and future Laws and
Restrictions affecting the Demised Premises and the cleanliness, safety,
occupation and use of the same, at Tenant's sole cost and expense. Tenant shall
promptly notify Landlord of, and provide Landlord with copies of, all notices,
requests, orders, complaints or other correspondence directed to Tenant from any
federal, state or municipal body or governmental agency or authority pertaining
to any actual or alleged violation of Laws or Restrictions.

8.2  Care of Demised Premises
     ------------------------

     Tenant shall keep the Demised Premises orderly, neat, safe and clean and
free from rubbish and dirt at all times and shall store all inventory, supplies,
trash and garbage within the building or approved containers on the Demised
Premises. Tenant shall maintain the landscaping on the Demised Premises and keep
the driveways and walkways within the Demised Premises free from snow and ice,
and shall arrange for the regular removal of snow during the winter months at
Tenant's expense and the pick up of trash and garbage at Tenant's expense.
Tenant shall not burn

                                       10
<PAGE>

any trash or garbage at any time in or about the Demised Premises. At the
expiration of the term of this Lease, or the sooner termination thereof, Tenant
shall surrender the Demised Premises in as good condition and repair as existed
at the time Tenant took possession, reasonable wear and tear excepted.

8.3  Hazardous Substances
     --------------------

     Tenant and its agents, employees and contractors shall not generate,
manufacture, refine, transport, treat, store, handle, dispose, transfer, produce
or process on or about the Demised Premises hazardous substances as defined in
Section 101(14) of the Comprehensive Environmental Response, Compensation, and
Liability Act, as amended, 42 U.S.C. (S)9601(14), hazardous wastes as defined in
Section 1004(5) of the Resource Conservation and Recovery Act, as amended, 42
U.S.C. (S)6903(5) and implementing regulations, hazardous wastes as defined in
the Michigan Hazardous Waste Management Act, as amended, MCL (S)299.501 et seq,
                                                                        -- ---
or extremely hazardous substances as defined in the Emergency Planning and
Community Right-To-Know Act of 1986, 42 U.S.C. (S)11001 et seq. (hereinafter
                                                        -- ---
collectively referred to as "Hazardous Substances") without Landlord's prior
written consent. Landlord hereby approves Tenant's use of diesel fuel for its
generator if said use of diesel fuel is in compliance with Federal, State and
local laws.

8.4  Obligation of Tenant
     --------------------

     The obligations and liabilities of Tenant and Landlord, under Sections 8.1
- 8.3, shall survive termination of this Lease.


                                   SECTION 9

                                   INDEMNITY
                                   ---------

9.1    Indemnity
       ---------

     Tenant shall defend, indemnify and hold harmless Landlord and Landlord's
officers, directors, employees and agents, from and against any and all claims,
suits, liabilities, damages, losses, costs or expenses, including, without
limitation, reasonable legal, accounting, consulting, engineering and other
expenses which may be imposed upon, incurred by, or asserted against Landlord or
Landlord's officers, directors, employees or agents, for personal injuries,
death or property damage, damage to natural resources or environmental
contamination ("Damages") occurring or originating on or about the Demised
Premises from and after the Commencement Date and during the Lease Term, to the
extent due to the negligence or willful misconduct by Tenant or its agents,
employees or contractors due to Tenant's violation of any law, order or
regulation, or breach of Tenant's obligations or representations under the
Lease. The indemnities provided herein shall include attorneys' fees incurred by
Landlord or Landlord's officers, directors, employees and agents in connection
with such Damages or to enforce the indemnity given hereunder.

                                       11
<PAGE>

9.2  Liability Insurance
     -------------------

     Tenant shall procure and keep in effect during the Lease Term, for the
benefit of Landlord and any mortgagee of the Demised Premises, commercial
general liability insurance, including blanket contractual coverage in the
amount of One Million ($1,000,000.00) Dollars for personal injury or death
resulting from one occurrence and the sum of Five Hundred Thousand ($500,000.00)
Dollars for property damage resulting from any one occurrence. In addition,
Tenant shall maintain excess insurance or "umbrella" coverage in the amount of
Two Million ($2,000,000.00) Dollars. Such insurance policies shall name Landlord
and any mortgagee of the Demised Premises (at Landlord's request) as additional
insureds by specific endorsement.

9.3  Tenant's Contractor's Insurance
     -------------------------------

     Tenant shall require any contractor of Tenant performing work on the
Demised Premises to take out and keep in force, at no expense to Landlord, (a)
commercial general Liability insurance, including contractor's liability
coverage, contractual liability coverage, completed operations coverage, broad
form property damage endorsement and contractor's protective liability coverage,
to afford protection to the limit, for each occurrence, of not less than Two
Million ($2,000,000.00) Dollars with respect to personal injury or death and
Five Hundred Thousand ($500,000.00) Dollars with respect to property damage; and
(b) worker's compensation or similar insurance in form and amounts required by
law. The liability insurance shall name Landlord and any mortgagee of the
Demised Premises, or any portion thereof, as additional insureds by specific
endorsement.

9.4  Delivery of Policy and Special Endorsement
     ------------------------------------------

     The insurance policies required by this Section 10 shall contain provisions
or special endorsements satisfactory to Landlord and Landlord's mortgagee, if
any, prohibiting cancellation, deletions or reductions in coverage either at the
instance of Tenant or the insurance company issuing the policy, without at least
30 days prior written notice having been given to Landlord at the address stated
above. Original Insurance Certificates including declaration page showing all
coverages and amounts of coverage, together with receipts evidencing payment in
full of the premiums thereon, shall be delivered promptly to Landlord and in no
event less than 30 days prior to expiration of such insurance.


                                   SECTION 10

                            MAINTENANCE AND REPAIRS
                            -----------------------

10.1  Maintenance And Repairs
      -----------------------

     Tenant shall, at its sole cost and expense, during the Lease Term, maintain
and repair and keep neat and in good appearance and condition the Demised
Premises, including, but not limited to, the roof (e.g., removal of snow),
exterior, interior, ceiling, electrical system, plumbing system,

                                       12
<PAGE>

H.V.A.C. system, storm sewers, sanitary sewers, water main, the driveways,
walkways, parking area, lighting facilities, landscaping and land, which are
part of the Demised Premises. The plumbing system, including the sewage
facility, serving the Demised Premises shall not be used for any purpose other
than for which it was constructed and Tenant shall not introduce any matter
therein which results in blocking such system. Tenant shall, at its sole cost
and expense, also repair or replace the driveways, walkways, parking areas, or
landscaping on the Demised Premises. Tenant shall, at its sole cost and expense,
contract with contractors acceptable to Landlord for the performance of all
maintenance and repairs required of Tenant under this Lease. Tenant shall
perform such maintenance and repair so as to maintain the Demised Premises in a
first-class condition. The maintenance and repair obligations of Tenant
hereunder arising during the term of the Lease, shall survive termination of
this Lease. All warranties provided by the contractor will be assigned to Tenant
for benefit of Tenant at commencement of the Lease.

10.2  Compliance With Laws
      --------------------

     During the term of this Lease, Tenant shall make any repairs, additions,
modifications or alterations to the Demised Premises, regardless of the nature
thereof, which are required by any Laws or Restrictions (as defined in Section
8.1) or required by the insurance carrier to maintain the insurance required
under this Lease.


                                   SECTION 11

                              TENANT'S ALTERATIONS
                              --------------------

11.1  Alterations
      -----------

     Tenant shall not make any alterations, additions, modifications or
improvements ("Alterations") to the Demised Premises without the prior written
consent of Landlord. Landlord will not unreasonably withhold its consent with
respect to Alterations. All Alterations made by either Landlord or Tenant to the
Demised Premises shall become the property of Landlord, shall remain upon and be
surrendered with the Demised Premises at the termination of this Lease, without
molestation or injury; unless Landlord consents in writing to Tenant's removal
of such alterations and Tenant repairs any damage or injury caused thereby in a
good and workmanlike manner. Notwithstanding anything to the contrary herein,
Landlord, at its option, may, at the time Landlord consents to an Alteration,
require Tenant, at Tenant's sole cost and expense, to remove any Alterations
made by Tenant during the Lease Term and to repair any damage or injury caused
thereby in a good and workmanlike manner at the expiration of the Lease Term.
All Alterations made by Tenant or the removal thereof shall be made free of all
liens and encumbrances and in compliance with all Laws and Restrictions. Tenant
hereby indemnities and holds Landlord harmless from and against any such liens,
encumbrances and violations of Laws and Restrictions. The filing of any lien or
encumbrance, or the violation of Laws or Restrictions, shall constitute a
violation hereunder. The repair obligations of Tenant hereunder shall survive
the termination of this Lease.

                                       13
<PAGE>

11.2  Construction Liens
      ------------------

      Tenant shall not permit any construction liens to be filed against the
Demised Premises or any part thereof by reason of work, labor, services or
materials supplied or claimed to have been supplied to Tenant or any part
thereof through or under Tenant. If any such construction lien shall at any time
be filed against the Demised Premises, Tenant shall cause the same to be
discharged of record within 20 days after the date of filing the same. If Tenant
shall fail to discharge such construction lien within such period, then, in
addition to any other right or remedy of Landlord, Landlord may,, but shall not
be obligated to, discharge the same either by paying the amount claimed to be
due or by procuring the discharge of such lien by deposit in court or by giving
security or in such other manner as is, or may be, prescribed by law. Any amount
paid by Landlord for any of the aforesaid purposes, and all actual legal and
other expenses of Landlord, including actual counsel fees, in or about procuring
the discharge of such lien, together with all necessary disbursements in
connection therewith, and together with interest thereon at the rate of prime
plus two (2%) percent per annum, but in no event higher than the legal limit,
from the date of payment, shall be repaid by Tenant to Landlord on demand, and
if unpaid may be treated as Additional Rent. Nothing herein contained shall
imply any consent or agreement on the part of Landlord to subject Landlord's
estate to liability under any construction lien law.


                                  SECTION 12

                        PROPERTY INSURANCE, REBUILDING
                           AND WAIVER OF SUBROGATION
                           -------------------------

12.1  Property Insurance
      ------------------

          A.  Tenant shall, during the Lease Term, carry at its expense
     insurance for the benefit of Landlord and any mortgagee of the Demised
     Premises, or a portion thereof, against fire, vandalism, malicious mischief
     and such other perils as are from time to time included in a policy of "all
     risk" insurance, insuring the Demised Premises in an amount equal to the
     full replacement and reconstruction cost and valued on a replacement cost
     basis of the building and improvements which are a part of the Demised
     Premises. If Tenant fails to maintain such insurance coverage, Landlord
     may, at its option, procure such insurance for the account of Tenant and
     the cost thereof shall be paid by Tenant to Landlord upon delivery to
     Tenant of bills therefor. The insurer or insurers shall be such as may from
     time to time be approved by Landlord. The policies of all such insurance
     and all renewals thereof, together with receipts evidencing payment in full
     of the premiums thereon, shall be delivered promptly to Landlord and in no
     event less than 30 days prior to the expiration of such insurance. The
     terms and conditions of all policies and endorsements thereto shall be in
     form and content satisfactory to Landlord. All of the required policies of
     insurance shall contain provisions satisfactory to Landlord prohibiting
     cancellation, deletions or reductions in coverage, either at the instance
     of the Tenant or of the insurance company issuing the policy, without at
     least 30 days prior written notice having been given to Landlord at the
     address of Landlord stated above, and shall name Landlord as a loss payee
     and any

                                       14
<PAGE>

     mortgagee of the Demised Premises as a loss payee under the standard
     mortgage loss payable endorsement. Tenant shall not, without the prior
     written consent of Landlord, cancel, alter, change, amend, modify, delete
     or reduce the coverage of any required policy of insurance which results in
     Tenant failing to have insurance coverage as required hereby. In the event
     of loss or damage, the proceeds of the insurance shall be paid to Landlord
     and such mortgagee alone. Landlord is authorized to adjust and compromise
     such loss without the consent of Tenant, to collect, receive and receipt
     for such proceeds in the name of Landlord and Tenant. The power granted
     hereby shall be deemed to be coupled with an interest and shall be
     irrevocable.

          B.  Tenant shall, during the Lease Term, carry rental interruption
     insurance naming Landlord as the insured party, which insurance shall be
     carried in amounts equal to Tenant's Annual Base Rent for twelve (12) full
     months under this Lease plus the total of the estimated costs to Tenant of
     taxes, assessments, utilities, insurance premiums and common facilities
     maintenance costs for such 12-month period with proceeds payable to
     Landlord.

          C.  Tenant shall, during the Lease Term, carry, at its expense,
     insurance against fire, vandalism, windstorm, explosion, smoke damage,
     malicious mischief, and such other perils as are from time to time included
     in an "all risk" policy of insurance, insuring Tenant's merchandise, trade
     fixtures, furnishings, equipment and all other items of personal property
     of Tenant located on or within the Demised Premises, in an amount equal to
     not less than 80 percent of the actual replacement cost thereof and furnish
     Landlord with a certificate evidencing such coverage. If Tenant fails to
     maintain such insurance coverage, Landlord may, at its option, procure such
     insurance for the account of Tenant and the cost thereof shall be paid by
     Tenant to Landlord upon delivery to Tenant of bills therefor.

12.2  Rebuilding
      ----------

     In the event, during the Lease Term, the improvements on the Demised
Premises are damaged or destroyed in whole or in part by fire or other casualty
insured under the insurance carried by Tenant pursuant to Section 12., then
Landlord shall, after the adjustment of the insurance loss, immediately commence
and diligently pursue the restoration of such improvements to good and
tenantable condition unless Landlord shall elect not to rebuild as hereinafter
provided. If: (a) the insurance proceeds are insufficient to pay the full cost
of the repairs (unless Tenant deposits sufficient funds with Landlord pursuant
to Section 13.3 to pay the full cost of the repairs), (b) more than 35 percent
of the improvements on the Demised Premises shall be destroyed by fire or other
casualty, or (c) during the last 24 months of the Lease Term, more than 20
percent of the improvements on the Demised Premises shall be destroyed by fire
or other casualty, Landlord may, at its option, terminate this Lease by notice
in writing delivered to Tenant within 120 days after the occurrence of such fire
or other casualty or repair to the improvements on the Demised Premises. If
Landlord is obligated, or elects, to perform such repairs, the improvements on
the Demised Premises are partially or totally untenable, then the Rent shall be
proportionately reduced during the period of rebuilding, based upon the extent
to which Tenant's use of the Demised Premises is diminished. During such time
period, Tenant shall have in effect

                                       15
<PAGE>

renter's insurance which pays to Landlord an amount equal to the monthly rental
payment as set forth in Section 12.1 (b) of this Lease.

12.3  Tenant's Deposit for Rebuilding
      -------------------------------

      If the insurance proceeds available for rebuilding are insufficient to
cover the cost of repair or restoration of the Demised Premises as required
hereunder, Tenant, so long as Tenant is not in default, may elect to deposit
with Landlord an amount which in combination with the insurance proceeds shall
be sufficient for such repairs or restorations. In the event Tenant elects not
to deposit such funds, then Landlord shall be relieved of any obligation to
repair or restore the Demised Premises.

12.4  Waiver of Subrogation
      ---------------------

      Any insurance policy carried by Landlord or Tenant or any policy covering
both the interest of Landlord or Tenant under this Section 12 shall include a
provision under which the insurance company waives all right of recovery by way
of subrogation against Landlord or Tenant in connection with any loss or damage
covered by any such policy. Landlord or Tenant hereby release and discharge each
other from any liability whatsoever arising from any loss, damage or injury
caused by fire or other casualty to the extent of the paid insurance proceeds
coverting such loss, damage or injury.


                                  SECTION 13

                                EMINENT DOMAIN
                                --------------

13.1  Total Condemnation
      ------------------

      If the whole of the Demised Premises shall be taken by any condemning
authority under the power of eminent domain, then the term of this Lease shall
cease as of the date actual physical possession of the Demised Premises is
transferred to such condemning authority and the Rent shall be paid up to that
day with a proportionate refund by Landlord of such Rent as may have been paid
in advance for a period subsequent to the date of the transfer of actual
physical possession.

13.2  Partial Condemnation
      --------------------

     If only a part of the Demised Premises shall be taken by any condemning
authority under the power of eminent domain, then, except as otherwise provided
in this Section, this Lease and the term shall continue in full force and effect
and there shall be no reduction in the Rent. From and after the date actual
physical possession of a portion of the building or parking area on the Demised
Premises is transferred to such condemning authority, the Rent shall be reduced
based on the extent to which Tenant's use of the Demised Premises is diminished.
If (a) more than 20 percent of the floor area of all buildings on the Demised
Premises shall be taken under eminent

                                       16
<PAGE>

domain, or (b) more than 20 percent of the parking spaces on the Demised
Premises shall be taken under eminent domain and Landlord is unable to provide
parking spaces on land immediately contiguous to the Demised Premises equal to
one-half of the number of parking spaces taken, Tenant shall have the right to
terminate this Lease and declare the same null and void, by written notice of
such intention to the other party within 30 days after the date the order is
entered in such eminent domain proceeding establishing the date upon which
actual physical possession shall be transferred to the condemning authority. In
the event Tenant does not exercise said right of termination, the Lease Term
shall cease only on the part of the Demised Premises so taken as of the date
actual physical possession is transferred to the condemning authority and Tenant
shall pay Annual Base Rent and Additional Rent up to that day, with appropriate
refund by Landlord of such Rent as may have been paid in advance for a period
subsequent to the date actual physical possession is transferred, and thereafter
all the terms herein provided shall continue in effect, except that the Rent
shall be reduced in the proportion stated above and Landlord shall, at its own
cost and expense, make all the necessary repairs or alterations to the remaining
Demised Premises so as to cause it to be a complete architectural unit.

13.3  Landlord's and Tenant's Damages
      -------------------------------

      All damages awarded for such taking under the power of eminent domain,
whether for the whole or a part of the Demised Premises, shall belong to and be
the property of Landlord whether such damages shall be awarded as compensation
for diminution in value to the leasehold or to the fee of the Demised Premises;
provided, however, that Landlord shall not be entitled to the award made for
depreciation to, and cost of removal of, Tenant's stock and fixtures, Tenant's
relocation costs, lost goodwill, the unamortized value of improvements paid for
by Tenant and any "bonus value" under the Lease.


                                  SECTION 14

                              ACCESS TO PREMISES
                              ------------------

      Landlord or Landlord's agent shall have the right to enter the Demised
Premises at all reasonable times to inspect or examine the same, and to show
them to prospective purchasers or mortgagees of the Demised Premises and to make
such tests, repairs, alterations, improvements or additions as Landlord may deem
necessary or desirable, and Landlord shall be allowed to take all material into
and upon the Demised Premises that may be required therefor without the same
constituting an eviction of Tenant in whole or in part, and the Annual Base Rent
and Additional Rent shall in no way abate while said repairs, alterations,
improvements, or additions are being made, by reason of loss or interruption of
the business of Tenant, or otherwise. During the six months prior to the
expiration of the Lease Term or any renewal term, Landlord may exhibit the
Demised Premises to prospective lessees and place upon the Demised Premises the
usual notices of "For Sale", "For Lease" or "For Rent" signs advertising the
space which will be available three (3) months prior to vacancy.

                                       17
<PAGE>

                                  SECTION 15

                            FIXTURES AND EQUIPMENT
                            ----------------------

      Subject to Section 11.1, all fixtures and equipment installed by Tenant
during the term of this Lease which are incorporated and affixed to the
buildings or improvements and cannot be removed without substantial damage or
injury to the buildings or improvements shall not be removed without Landlord's
consent, and all fixtures and equipment not removed shall remain the property of
Landlord at the termination of the Lease Term. In the event Landlord consents to
such removal, Tenant shall remove such fixtures in accordance with all
applicable Laws and Restrictions and shall repair any such damage or injury in a
good and workmanlike manner.


                                  SECTION 16

                      BANKRUPTCY AND INSOLVENCY OF TENANT
                      -----------------------------------

      If the estate created hereby shall be taken in execution or by other
process of law, or if Tenant shall be declared bankrupt or insolvent, according
to law, or if any receiver be appointed for the business and property of Tenant
or if any assignment shall be made of Tenant's property for the benefit of
creditors (and as to such matters involuntarily taken against Tenant, Tenant,
has not within 60 days thereof obtained release or discharge therefrom), then
this Lease may be cancelled at the option of Landlord. If, as a matter of law,
Landlord has no right upon the bankruptcy of Tenant, to terminate this Lease,
then the rights of Tenant, as debtor, or its trustee, shall be deemed abandoned
or rejected unless Tenant, as debtor or its trustee, (a) within 60 days after
the date of the Order for Relief under Chapter 7 of the Bankruptcy Code or 60
days after the date the Petition is filed under Chapter 11 of the Bankruptcy
Code assumes in writing the obligations under this Lease (b) cures or adequately
assures the cure of all defaults existing under this Lease on Tenant's part
within 60 days and (c) furnishes adequate assurances of future performance of
the obligations of Tenant under this Lease within such 60 days. Adequate
assurance of curing defaults means the posting with Landlord of a sum in cash
sufficient to defray the costs of such cure. Adequate assurance of future
performance of the Tenant's obligations under this Lease means increasing any
existing security deposit or creating a security deposit in an amount equal to
three Monthly Installments of Base Rent.

      Tenant shall not be permitted to assume and assign this Lease in
connection with any bankruptcy or insolvency proceedings without full and
complete compliance with the following provisions: (a) Landlord is provided with
the following information regarding the party desiring to assume the Lease
("Assumptor") which Landlord in its reasonable discretion deems sufficient (1)
organizational information regarding the Assumptor (2) audited financial
statements for the three most recent fiscal years, and (3) such other
information as Landlord deems appropriate, (b) Landlord determines that the use
of the Demised Premises by the intended Assignee is compatible with the
character of the Building, (c) all existing defaults under this Lease are cured
at least ten days prior to any hearings in connection with Tenant's request to
assume and assign the Lease, (d) the Assumptor at any such hearing provides
adequate assurance of its future performance of the

                                       18
<PAGE>

Lease as determined by Landlord in its reasonable discretion, which adequately
assurance shall include at least the following: (1) posting of security deposit
equal to three Monthly Installments of Base Rent, if such was not already posted
by Tenant, (2) establishing with Landlord an escrow for the full cost of all
real estate taxes, insurance, and common area maintenance charges as required
under the Lease for the next 12 months of the Lease and thereafter on an annual
basis in advance, and (3) the Assumptor executes a written agreement assuming
the Lease and such Lease amendments as are necessary, which agreements and
amendments are satisfactory to Landlord in its reasonable discretion.


                                  SECTION 17

                               RIGHT TO MORTGAGE
                               -----------------

      Landlord reserves the absolute right to subject and subordinate this
Lease, at all times, to the lien of any mortgage or mortgages now or hereafter
placed upon the Demised Premises; provided Tenant's right of possession will not
disturbed by the mortgagee of any mortgage upon the Demised Premises in
connection with any mortgage foreclosure proceedings so long as Tenant is in not
default hereunder. In the event Landlord exercises its right hereunder, Tenant
hereby agrees to execute and deliver, or join in the execution and delivery of
an agreement which shall provide, among other things, (a) that this Lease is
subordinate to the lien of any mortgage or mortgages upon the Demised Premises,
(b) that the Tenant's right of possession will not be disturbed by the mortgagee
in connection with any mortgage foreclosure proceedings, so long as Tenant is
not in default, and (c) that the Tenant shall attorn to any foreclosing
mortgagee or purchaser at the foreclosure sale.


                                  SECTION 18

                ASSIGNMENT, SUBLETTING AND TRANSFERS BY TENANT
                ----------------------------------------------

      Tenant shall not sell, assign, sublet, hypothecate, encumber, mortgage or
in any manner transfer this Lease or any estate or interest therein (including
any transfer by operation of law or otherwise), the Demised Premises or any part
thereof or permit the use of the Demised Premises by any Third Party
(collectively "Transfer") without the prior written consent of the Landlord
which shall not be reasonably withheld.

      The acceptance of Rent or Additional Rent from an assignee, subtenant or
occupant shall not constitute a release of Tenant from the obligations and
covenants in this Lease. Tenant shall remain liable under this Lease until
Landlord executes and delivers a written release of such liability. Landlord's
consent hereunder shall not be unreasonably withheld. In the event of a Transfer
by Tenant, with or without Landlord's consent, then fifty (50%) per cent of all
Rent, sums of money or other economic considerations owed to or received by
Tenant, which exceed, in the aggregate, the total sums of Rent, Additional Rent
or otherwise which Tenant is obligated to pay Landlord under this Lease, after
first deducting therefrom Tenant's actual costs to effect

                                       19
<PAGE>

the transfer, shall be payable to Landlord as Additional Rent under this Lease
without affecting or reducing any obligations of Tenant hereunder.


                                  SECTION 19

                               SALE OR TRANSFER
                               ----------------

     Landlord shall have the right to sell, transfer or assign the Demised
Premise ("Conveyance"). In the event of Conveyance, Tenant shall attorn to the
purchaser, transferee or assignee ("Transferee") and recognize such Transferee
as Landlord under this Lease and Landlord shall be relieved from all subsequent
obligations and liabilities under this Lease, provided such obligations are
assumed in writing by such Transferee and a copy thereof is provided to Tenant.


                                  SECTION 20

                         DEFAULT. RE-ENTRY AND DAMAGES
                         -----------------------------

20.1  Default
      -------

      The following shall constitute a default under this Lease: (a) Failure to
pay when due any Annual Base Rent or Additional Rent due hereunder on the day
the same shall be due and such failure remains uncured for five (5) days
following written notice; (b) Failure to perform any of the terms and conditions
under this Lease, other than the payment of Annual Base Rent or Additional Rent,
and such failure remains uncured for thirty (30) days following written notice
or such longer period as may be reasonably required to effect such cure provided
Tenant diligently pursues such cure; (c) Landlord has elected to cure Tenant's
default under Section 21 and Tenant has failed to pay Landlord the cost and
expenses incurred to cure such default within 15 days after demand; or (d) an
event of bankruptcy or insolvency in violation of Section 16 has occurred;

20.2  Re-Entry and Damages
      --------------------

      In the event of Tenant's default, Landlord shall, in addition to all of
its other remedies under this Lease, or permitted in law or equity, have the
right to re-enter the Demised Premises, with process of law, to remove all
persons and property therefrom. Upon such default, Landlord, at its option, may
terminate this Lease, or without terminating this Lease, relet the Premises or
any part thereof on such reasonable terms and reasonable conditions.

      No re-entry or taking possession of the Demised Premises by Landlord shall
be construed as an election on its part to terminate this Lease unless written
notice of such intention is given to Tenant. It is understood between the
parties that the Tenant shall not be liable for any damages caused by a third-
party entering into a Lease with Landlord in replacement of Tenant. At all times
herein, Landlord shall have the duty to mitigate damages.

                                       20
<PAGE>

      In the event Landlord elects to terminate this Lease, then Landlord shall
have the right to accelerate all of the Annual Base Rent and Additional Rent due
hereunder for the balance of the term of this Lease and Tenant shall forthwith
pay to Landlord upon demand, as liquidated damages, the deficiency between the
present value of the amount of said accelerated rent and the proceeds of
reletting, if any, for what would have otherwise constituted the balance of the
Lease Term or the reasonable rental value of the Demised Premises for such
balance of the Lease Term if the Demised Premises are not relet by Landlord
within 30 days following Tenant's default. Upon acceleration, for the purpose of
determining the Additional Rent for the remainder of the Lease Term, the
Additional Rent paid during the 12 months immediately preceding the date of
acceleration shall be assumed to be the amount of Additional Rent which Tenant
would have paid during the remainder of the Lease Term. In computing such
liquidated damages there shall be added to such deficiency any expenses incurred
in connection with obtaining possession of the Demised Premises and reletting
the Demised Premises (to the extent allocable to the remainder of the term),
whether such reletting is successful or not, which expenses include, but are not
limited to, actual attorney fees, brokerage fees and expenses, advertising
expenses, reasonable alterations and repairs to the Demised Premises, and
inspection fees.

20.3  Waiver of Landlord's Liability
      ------------------------------

      Whether or not Landlord terminates the Lease because of Tenant's default,
Landlord shall have no liability or responsibility in any way whatsoever for its
failure to relet the Demised Premises or, in the event of reletting, for failure
to collect the Rent under such reletting. The failure of Landlord to relet the
Demised Premises or any part thereof shall not release or affect Tenant's
liability for Rent or damages.

20.4  Landlord's Rights Cumulative
      ----------------------------

      All the rights and remedies of Landlord hereunder shall be cumulative and
in addition to all other rights and remedies allowed by law or equity and may be
exercised separately or jointly without constituting an election of remedies.

20.5  Waiver of Jury Trial and Counterclaim
      -------------------------------------

      (Deleted upon agreement of parties.)

20.6  Non-Liability
      -------------

      Subject to Sections 9.1 and 9.3, Landlord shall not be responsible or
liable to Tenant for any loss or damage that may be occasioned by or through the
acts or omissions of persons occupying adjoining premises or for any loss or
damage resulting to Tenant or its property from burst, stopped or leaking water,
gas, sewer or steam pipes, or for any damage or loss of property within the
Demised Premises from any cause whatsoever, and no such occurrence shall be
deemed to be an actual or constructive eviction from the Demised Premises or
result in an abatement of rental.

                                       21
<PAGE>

                                  SECTION 21

                            RIGHT TO CURE DEFAULTS
                            ----------------------

      If Tenant defaults in the performance of any provision of this Lease,
Landlord shall have the right (but not the obligation) in addition to any and
other rights and remedies in the event of default, to cure such default for the
account of Tenant, without prior notice to Tenant, and Tenant shall upon receipt
of notice thereof and demand for payment from Landlord pay any payment or
expenditure made by Landlord with the next Monthly Installment of Base Rent,
together with interest at the "prime interest rate" as defined in Section 5.6
plus 2%.


                                  SECTION 22

                                QUIET ENJOYMENT
                                ---------------

      Landlord covenants that so long as Tenant is not in default the terms and
conditions of this Lease, Tenant may peacefully and quietly hold and enjoy the
Demised Premises for the Lease term without interference by Landlord or any
person claiming by, through or under Landlord.


                                  SECTION 23

                                 HOLDING OVER
                                 ------------

      In the event of Tenant holding over after the expiration of the Term of
this Lease, then the tenancy shall continue from month-to-month in the absence
of a written agreement to the contrary, subject to all the terms and provisions
hereof, except the Monthly Installment of Base Rent shall be equal to one
hundred twenty-five (125%) percent of the Monthly Installment of Base Rent, due
in the last full month of the lease Term.


                                  SECTION 24

                        CUMULATIVE REMEDIES AND WAIVER

24.1  Cumulative Remedies
      -------------------

      Each and every right, remedy and benefit provided by this Lease to
Landlord shall be cumulative and shall not be exclusive of any other right,
remedy or benefit allowed by law. These remedies may be exercised jointly or
severally without constituting an election of remedies.

                                       22
<PAGE>

24.2  Waiver
      ------

      One or more waivers by Landlord of any term and condition hereunder or
default by Tenant hereunder shall not be construed as a waiver of such term and
condition or default in the future or any subsequent default for the same cause.
Any consent or approval given by Landlord requiring such consent or approval
shall not constitute consent or approval to any subsequent similar act by
Tenant.

      No payment by Tenant or receipt by Landlord of a lesser amount than the
Monthly Installment of Base Rent shall be deemed to be other than on account of
the earliest stipulated Rent, nor shall any endorsement or statement on any
check or any letter accompanying any check or payment of Rent be deemed an
accord and satisfaction, and Landlord shall accept such check or payment without
prejudice to Landlord's right to recover the balance of such Rent or pursue any
other remedy in this Lease provided.


                                  SECTION 25

                        OPTION TO EXPAND BUILDING SPACE
                        -------------------------------

      In the event the parties desire to expand the building space, the parties
shall amend this lease agreement to provide for such expansion.


                                  SECTION 26

                                 DEFINITION OF
                                 -------------
                              LANDLORD'S LIABILITY
                              --------------------

      The term "Landlord" as used in this Lease so far as covenants or
obligations on the part of Landlord are concerned shall be limited to mean and
include only the owner or owners at the time in question of the fee of the
Demised Premises, and in the event of any transfer or transfers of the title to
such fee (and the written assumption by such transferee of Landlord's
obligations hereunder) Landlord herein named (and in case of any subsequent
transfers or conveyances, the then grantor) shall be automatically freed and
relieved from and after the date of such transfer or conveyance of all personal
Liability as respects to the performance of any covenants or obligations on the
part of Landlord contained in this Lease thereafter to be performed, provided
that any funds in the hands of such Landlord or the then grantor at the time of
such transfer in which Tenant has an interest, shall be turned over to the
grantee and any amount then due and payable to Tenant by Landlord or the then
grantor under any provision of this Lease, shall be paid to Tenant, it being
intended hereby that the covenants and obligations contained in this Lease on
the part of Landlord shall, subject as aforesaid, be binding on Landlord, its
successors and assigns, only during and in respect of their respective
successive periods of ownership.

                                       23
<PAGE>

     If Landlord shall fail to perform any covenant, term or condition of this
Lease upon Landlord's part to be performed, and if as a consequence of such
default Tenant shall recover a money judgment against Landlord, such judgment
shall be limited to Landlord's interest in the Project, including any sale,
insurance or condemnation proceeds thereof, and Landlord shall not be liable for
any deficiency.


                                  SECTION 27

                                     WASTE
                                     -----

     Tenant and its employees and agents shall not commit any waste upon the
Demised Premises.


                                  SECTION 28

                                     SIGNS
                                     -----

     Tenant will not place or cause to be placed or maintained any sign or
advertising matter of any kind anywhere on the Demised Premises, except as
agreed upon by both parties. Tenant further agrees to maintain in good condition
and repair at all times any such sign or advertising matter of any kind which
has been approved by Landlord for use by Tenant.


                                  SECTION 29

                               SECURITY DEPOSIT
                               ----------------

     The Landlord herewith acknowledges that no Security Deposit is needed.
However, if Tenant is more than five (5) days late with rent payments on three
or more occasions during a calendar year, then Landlord may elect to require
Tenant to provide a security deposit equal to one month's rent. Said Security
Deposit shall be paid at the time of the next rent payment.


                                  SECTION 30

                                 MISCELLANEOUS
                                 -------------

30.1  Condition of Demised Premises
      -----------------------------

     Tenant is fully familiar with the proposed plans and the intended physical
conditions of the Demised Premises and except as expressly set forth herein,
Landlord has made no representations of whatever nature in connection with the
condition of the Demised Premises.

                                       24
<PAGE>

30.2  Lease Changes Required By Lender
      --------------------------------

     (This section is blank by agreement of the parties)

30.3  Entire Agreement
      ----------------

     This Lease and exhibits attached hereto and forming a part hereof, set
forth all of the covenants, agreements, stipulations, promises, conditions,
understandings and representations, hereinafter collectively "Representations"
between Landlord and Tenant concerning the Demised Premises and the buildings
and improvements to be constructed thereon. Landlord and Tenant agree that there
are no Representations other than set forth herein and agree to make no claims
against each other based upon Representations not set forth herein.

30.4  Modification
      ------------

     This Lease shall not be modified or amended unless by a writing signed by
Landlord and Tenant.

30.5  Joint Venture, Mortgage
      -----------------------

     Nothing contained herein shall be deemed or construed by the parties
hereto, nor by any third party, as creating relationship of mortgagor and
mortgagee, principal and agent or of partnership or of joint venture between the
parties hereto, it being understood and agreed that neither this method of
computation of Rent, nor any other provision contained herein, nor any acts of
the parties herein, shall be deemed to create any relationship between the
parties hereto other than the relationship of lessor and lessee.

30.6  Notices
      -------

     Except as specifically provided otherwise in this Lease, any notices or
demands required under this Lease shall be given in writing and either delivered
personally or sent by certified mail, return receipt requested, postage prepaid
and addressed to the address of Landlord or Tenant as set forth in Section 1
hereof or such other address as Landlord or Tenant shall designate from time to
time by written notice to the other and shall be deemed received three days
after being deposited in the mail or upon personal hand-delivery.

30.7  Survival
      --------

     Any obligation of Tenant under this Lease which is not performed in full
prior to the termination of this Lease shall survive the termination of this
Lease and continue in full force and effect until performed in full.

                                       25
<PAGE>

30.8  Estoppel Certificate
      --------------------

     Upon request by Landlord, Tenant shall, from time to time, execute,
acknowledge and deliver to Landlord a written statement certifying that this
Lease is in full force and effect and unmodified (or if modified specifying the
nature of the modification), the dates to which Rent and other charges have been
paid, that Landlord is not in default hereunder (or if in default, specifying
the nature of any default) and such other matters pertaining to the Lease and
Tenant's occupancy of the Demised Premises as Landlord may reasonably request.
It is understood that such statement may be relied upon by Landlord, a
prospective purchaser, mortgagee or assignee of any mortgagee of Landlord's
interest in the Demised Premises or this Lease.

30.9  Gender
      ------

     Whenever the singular is used herein, the same shall include the plural
and the masculine, feminine and neuter genders.

30.10 Captions and Section Numbers
      ----------------------------

     The captions, section numbers, article numbers, and index appearing in
this Lease are inserted only as a matter of convenience and in no way define,
limit, construe, or describe the scope or intent of such sections or articles of
this Lease nor in any way affect this Lease.

30.11 Broker's Commission
      -------------------

     A real estate commission is owed to Spallino Reid, Corporate Real Estate
Services and The Miller Group payable by the Landlord. Tenant shall have no
liability for payment of any broker commissions..

30.12 Recording
      ---------

     Landlord and Tenant shall record a memorandum of this Lease promptly on
Lease execution.

30.13 Execution of Lease
      ------------------

     The submission of this Lease for examination does not constitute a
reservation of, or option for, the Demised Premises, and this Lease shall become
effective as a lease only upon execution and delivery thereof by Landlord and
Tenant.

30.14 Construction
      ------------

     This Lease shall be construed and enforced in accordance with the laws of
the State of Michigan. If any provision of this Lease, or the application
thereof to any person or circumstances, shall, to any extent be invalid or
unenforceable, the remaining provisions of this Lease shall not be affected
thereby and shall be valid and enforceable.

                                       26
<PAGE>

30.15  Binding Effect
       --------------


     This Lease shall be binding upon and inure to the benefit of the parties
hereto and their respective heirs, legal representatives, successors, assigns
and permitted transferees..

     IN WITNESS WHEREOF, Landlord and Tenant have executed this Lease on the day
and year first above written.

IN THE PRESENCE OF:               LANDLORD:  SSP ASSOCIATES, INC.,
                                             A Michigan Corporation

 /s/ [ILLEGIBLE]^^                By: /s/ [ILLEGIBLE]^^
--------------------------           ----------------------------------
                                     Its: President


                                  TENANT:  CONCENTRIC NETWORK
                                             CORPORATION

 /s/ [ILLEGIBLE]^^                By: /s/ Henry R. Nothhaft
--------------------------           ----------------------------------
                                  Its: Chairman, President, & CEO

PREPARED BY:
ROBERT A. JAREMA (P31537)
Smith, Bovill, Fisher, Meyer
 & Borchard, P.C.
200 St. Andrews Road
Saginaw, MI 48603
(517) 792-9641

                                       27
<PAGE>

                                   EXHIBIT A

          11/30/99

          LEGAL DESCRIPTION FOR CONCENTRIC PARCEL

          Beginning 330 feet North 89 deg 18 mm 00 sec West and
          561.80 feet South 0 deg 09 min 30 sec East of the North 1/4 Corner of
          Section 1,
          T12N, R4E, Carrollton Township, Saginaw County, Michigan;
          Thence South 0 deg 09 min 30 sec East 707.15 feet;
          Thence North 89 deg 47 min 00 sec West 191 feet;
          Thence North 0 deg 09 min 30 sec West 99 feet;
          Thence North 89 deg 47 min 00 sec West 304 feet;
          Thence North 0 deg 09 min 30 sec West 608.15 feet;
          Thence South 89 deg 47 min 00 sec East 495 feet to the place of
          beginning
          Consisting of 7.34 acres.


          PARCEL INCLUDES 80,000 SQ FEET OF BUILDING AND THE REQUIRED PARKING.
          DETENTION POND AND THE DRAIN ARE NOT INCLUDED.

          Jerry Schafer
          631 1245
<PAGE>

                                  [FLOORPLAN]
<PAGE>

                                   EXHIBIT C

                              TENANT REQUIREMENTS
                              -------------------

The following is an itemized list of the tenant improvements required for
Concentric Network Incorporated. The proposal shall address but shall not be
limited to the improvements described herein for your reference.

Hard Walls
- 4 Conference Rooms (accommodate 4-6 people and strategically located
throughout the facility).
- 2 Large Conference Rooms (approx. 12x30)
- 3-5 Private Offices (approx. 12x12)
- 1 Executive Office (approx. 12x16)
- 1 Reception Area to accommodate two people with side room for storage, mail,
copy, fax
**All offices require a front glass wall, and some form of sound proofing

- 4 Supply rooms (approx. 8x10)
- 1 Employee lounge area (approx. 20x20) and located by the kitchen area.
- 1 Kitchen Area (approx. 30x30)
- 2 Coffee Stations strategically located
- 3 Training Rooms (approx. 16x30)
- 4 Telecommunication Rooms;
     One (1) room which contains fiber, data and voice equipment centrally
     located in the facility (approx. 25x40)
     Three (3) smaller rooms for commercial power service entry and main
     distribution
     (Size of these Telecom room; to be determined)
- 4 Electrical Rooms
     One (1) main room for commercial power service entry and main distribution
     Three (3) Smaller rooms for secondary, distribution of UPS and commercial
power
     (Size of these Electrical rooms to be determined)
- UPS supply room
- 1 System Lab/Repair and Testing center for client server systems (approx.
14x16)

Electrical Requirements:
- Power Distribution throughout facility and to all offices
- Commercial Power (1600 amps/208v/3Phase)
- UPS power distribution (200 kva/208v/3Phase)
One Generator external to facility (approx. 400 kva/208v/3phase)
     Emergency power to UPS, HVAC, and commercial power distribution
- Soft fluorescent lighting (suspended-indirect) throughout the facility

HVAC Requirements:
- Dedicated Units in all conference rooms, training rooms, UPS and
telecommunications rooms
- All units must be centrally controlled via computer and have remote alarming
capabilities
<PAGE>

                            FIRST ADDENDUM TO LEASE
                            -----------------------

     THIS FIRST ADDENDUM TO LEASE (this "Addendum") is made by and between SSP
ASSOCIATES, INC. ("Landlord"), and CONCENTRIC NETWORK CORPORATION ("Tenant"), to
be a part of that certain Lease of even date herewith between Landlord and
Tenant (the "Lease") concerning an approximately 40,000 square foot building and
related land and improvements located at 1405 Tittabawassee, Carrollton
Township, Saginaw County, Michigan (the "Demised Premises"). Landlord and Tenant
agree that, notwithstanding anything to the contrary in the Lease, the Lease is
hereby modified and supplemented as set forth below.

     2.2  Term. The Lease shall commence on the date by which Landlord has
          ----
substantially completed the Project in accordance with the Lease and delivered
possession of the Project to Tenant. If the Commencement Date has not occurred
for any reason whatsoever on or before (i) July 1, 2000, then the date Tenant is
otherwise obliged to commence payment of rent shall be delayed by one day for
each day that the Commencement Date is delayed beyond such date; or (ii) August
1, 2000, then, in addition to Tenant's other rights or remedies, Tenant may
terminate the Lease by written notice to Landlord, whereupon any monies
previously paid by Tenant shall be reimbursed to Tenant.

     3.1  Construction. Notwithstanding anything to the contrary herein,
          ------------
effective upon the Commencement Date, Landlord does hereby warrant that (a) the
construction of the Project was performed in accordance with all Laws and
Restrictions, in accordance with the Plans, and in a good and workman-like
manner, (b) all material and equipment installed therein conformed to the Plans
and was new and otherwise of good quality, (c) the electrical, plumbing, and
mechanical systems servicing the Demised Premises are in working order and in
good condition, and (d) the roof is in good condition and water tight. Prior to
the Commencement Date, Landlord shall cause the roadway into the Demised
Premises to be named Concentric Boulevard, if the Township will allow such name
to be used.

     4.1  Possession. Landlord shall diligently complete the Project; provided,
          ----------
however, Landlord shall not be held liable for any loss, damage or delay due to
fire, strike, civil disturbance, military riot, insurrection, casualty loss
including, but not limited to, tornado, high winds or extraordinary winter
conditions defined as seven (7) consecutive business days with the average
temperature below 15(degrees) Fahrenheit nor seven (7) consecutive business days
with average precipitation in excess of 1/2 inch as measured at the Site.
Notwithstanding the forgoing, in the event Landlord is delayed in meeting any of
the Milestone Dates (defined below) in constructing the Project by more than
sixty (60) days for any reason (other than Tenant's delay), Tenant shall have
the right to terminate this Lease by delivery of written notice thereof to
Landlord, whereupon any monies previously paid by Tenant to Landlord shall be
reimbursed to Tenant. As used herein, "Milestone Dates" shall mean the following
dates: (a) January 17, 2000 for completion of the foundation on the Project; and
(b) March 17, 2000 for the building to be "under-roof" and "roughed- in".
Promptly upon substantial completion of the Project, Landlord shall deliver
possession of the Demised Premises to Tenant in good, broom clean condition,
with all building systems in good working order and in compliance with all
ordinances and laws.

     6    Utilities. Landlord represents that, on the Commencement Date, the
          ---------
Demised Premises shall be served by water, electricity, gas, telephone, sewer
and other utilities pursuant to Tenant's specifications for the Demised
Premises. If the Demised Premises should not be reasonably suitable for Tenant's
use as a consequence of cessation of utilities or other services, interference
with access to the Demised Premises, legal restrictions or the presence of any
Hazardous Substance, which in any such case does not result from Tenant's
negligence or willful misconduct, and if any of the foregoing causes a
substantial interference with Tenant's use of the Demised Premises and prevents
Tenant from using the Demised Premises for its intended purpose for fourteen
(14) days, then Tenant shall be entitled to an equitable abatement of rent. If
such

                                      -1-
<PAGE>

interference persists for more than one hundred eighty (180) days, Tenant shall
have the right to terminate the Lease.

     7.2  Taxes. "Taxes" shall not include and Tenant shall not be required to
          -----
pay any portion of any tax or assessment expense or any increase therein (a) in
excess of the amount which would be payable if such tax or assessment expense
were paid in installments over the longest permitted term or (b) resulting from
a change of ownership or transfer of any or all of the Demised Premises.

     8.2  Care of Demised Premises. Tenant's obligations with respect to the
          ------------------------
surrender of the Demised Premises shall be fulfilled if Tenant surrenders
possession of the Demised Premises in the condition existing at the Commencement
Date, ordinary wear and tear, condemnation, Hazardous Substances (other than
those released or emitted by Tenant), and alterations or other interior
improvements which Tenant is permitted to surrender at the termination of the
Lease, excepted, and subject to Section 12 of the Lease.

     8.3  Hazardous Substances. To the best knowledge of Landlord, (a) no
          --------------------
Hazardous Substance is present on the Land or the soil, surface water or
groundwater thereof, (b) no underground storage tanks are present on the Land,
and (c) no action, proceeding or claim is pending or threatened regarding the
Land concerning any Hazardous Substance or pursuant to any environmental law.
Under no circumstance shall Tenant be liable for, and Landlord shall indemnify,
defend, protect and hold harmless Tenant, its agents, contractors, stockholders,
directors, successors, representatives, and assigns from and against, all
losses, costs, claims, liabilities and damages (including attorneys' and
consultants' fees) of every type and nature, directly or indirectly arising out
of or in connection with any Hazardous Substance present at any time on or about
the land, or the soil, air, improvements, groundwater or surface water thereof,
or the violation of any laws, orders or regulations, relating to any such
Hazardous Substance, except to the extent that any of the foregoing actually
results from the release or emission of Hazardous Substance by Tenant or its
agents or employees in violation of applicable environmental laws. This section
and Section 8.3 of the Lease constitute the entire agreement of Landlord and
Tenant regarding Hazardous Substances. No other provision of the Lease shall be
deemed to apply thereto.

     9.1  Indemnity. Landlord shall not be released or indemnified from, and
          ---------
shall indemnify, defend, protect and hold harmless Tenant from, all losses,
damages, liabilities, claims, attorneys' fees, costs and expenses arising from
the negligence or willful misconduct of Landlord or its agents, contractors,
licensees or invitees, Landlord's violation of any law, order or regulation, or
a breach of Landlord's obligations or representations under the Lease.

     10.1 Maintenance and Repairs. Landlord shall perform and construct, and
          -----------------------
Tenant shall have no responsibility to perform or construct, any repair,
maintenance or improvements (a) necessitated by the acts or omissions of
Landlord or its agents, employees or contractors, (b) which are the subject of a
warranty in Landlord's favor, (c) to the structural portions of the Demised
Premises, which are defined as the roof, sidewalls and foundation, but excluding
any windows, doors, roof-top heating ventilating and air conditioning units, and
any required snow removal from the roof or (d) which would be treated as a
capital expenditure under generally accepted accounting principles.
Notwithstanding the foregoing, Landlord shall amortize the cost of any "capital
expenditure" over its useful life as reasonably determined by Landlord in
accordance with generally accepted accounting principles and Tenant shall pay
the monthly amortized amount thereof together with interest at the rate of the
prime rate plus two percent (2%) per annum with each monthly installment of base
rent. Landlord shall, at its sole cost, maintain in good condition and free of
snow the roadway (Concentric Boulevard) leading to the Demised Premises.

     10.2 Compliance with Laws. Tenant shall not be required to comply with or
          --------------------
cause the Demised Premises to comply with any Laws or Restrictions requiring the
construction of alterations unless such compliance is necessitated solely due to
Tenant's particular use of the Demised Premises.

                                      -2-
<PAGE>

     11.1  Alterations. Tenant may construct non-structural alterations,
           -----------
additions and improvements in the Demised Premises without Landlord's prior
approval, if the cost of any such work does not exceed Twenty-Five Thousand
Dollars ($25,000). Alterations and Tenant's trade fixtures, furniture, equipment
and other personal property installed in the Demised Premises ("Tenant's
Property") shall at all times be and remain Tenant's property. Except for
Alterations which cannot be removed without structural injury to the Demised
Premises, at any time Tenant may remove Tenant's Property from the Demised
Premises, provided that Tenant repairs all damage caused by such removal.
Landlord shall have no lien or other interest in any item of Tenant's Property.
Landlord shall have the right to require Tenant to remove any alterations within
the Demised Premises unless Landlord notifies Tenant at the time Landlord
consents to such alteration that Landlord shall not require such alteration to
be removed. Upon request by Tenant, Landlord shall inform Tenant at the time
Landlord consents to any alterations whether Tenant shall be required to remove
such alterations.

     12.2  Damage. If the Demised Premises are damaged by any peril and Landlord
           ------
does not terminate the Lease, then Tenant shall have the option to terminate the
Lease if the Demised Premises cannot be, or are not in fact, fully restored by
Landlord to their prior condition within one hundred eighty (180) days after the
damage. Landlord shall not have the right to terminate the Lease if (a) the
damage to the Demised Premises is (i) due to a risk required to be insured
against under Section 12.1 of the Lease (provided Tenant has maintained such
insurance in place) or (ii) relatively minor (e.g., repair or restoration would
cost less than ten percent (10%) of the replacement cost of the Demised
Premises) or (b) Tenant pays any uninsured amounts.

     12.4  Waiver of Subrogation. Notwithstanding anything to the contrary
           ---------------------
herein, the parties hereto release each other and their respective agents,
employees, successors, assignees and subtenants from all liability for injury to
any person or damage to any property that is caused by or results from a risk
which is actually insured against without regard to the negligence or willful
misconduct of the entity so released. All of Landlord's and Tenant's repair and
indemnity obligations under the Lease shall be subject to the waiver contained
in this paragraph.

     14    Access to Premises. Landlord and Landlord's agents, except in the
           ------------------
case of emergency, shall provide Tenant with one (1) business day notice prior
to entry of the Demised Premises. Any entry by Landlord and Landlord's agents
shall not impair Tenant's operations more than reasonably necessary, and shall
comply with Tenant's reasonable security measures.

     17    Right to Mortgage. Landlord represents that there is not currently a
           -----------------
mortgage or deed of trust encumbering the Demised Premises. Prior to Landlord's
execution of a mortgage or deed of trust as to the Demised Premises, Landlord
shall obtain from any lender of the Demised Premises a written agreement on
commercially reasonable terms providing for recognition of Tenant's interests
under the Lease in the event of a foreclosure of the lender's security interest.
Further, as a condition to the subordination of Tenant's leasehold interest,
Landlord shall obtain from any lenders a non-disturbance agreement recognizing
Tenant's leasehold interest and the ability of Tenant to continue its leasehold
interest in the Demised Premises as long as Tenant is not in default hereunder,
after expiration of applicable notice and cure periods.

     18    Assignment and Subletting. Tenant may, without Landlord's prior
           -------------------------
written consent, sublet the Demised Premises or assign the Lease to (a) a
publicly-traded entity controlling, controlled by or under common control with
Tenant, or (b) a successor publicly-traded entity related to Tenant by merger,
consolidation, non-bankruptcy reorganization or government action. In addition
to the foregoing Tenant may, without Landlord's prior written consent, sublet
the Demised Premises or assign the Lease to (i) a non-public entity controlling,
controlled by or under common control with Tenant, (ii) a non-public successor
entity related to Tenant by merger, consolidation, nonbankruptcy reorganization,
or government action, or (iii) a purchaser of substantially all of Tenant's
assets; provided, however, that in any such case, such entity

                                      -3-
<PAGE>

shall have a net worth equal to or greater than Tenant's net worth immediately
prior to the proposed assignment or sublease. A sale or transfer of Tenant's
capital stock shall not be deemed an assignment, subletting or any other
transfer of the Lease or the Demised Premises.

     21  Right to Cure Defaults. In the event Landlord fails to perform any of
         ----------------------
its obligations under the Lease and (except in case of a roof leak or similar
emergency posing an immediate threat to persons or property, in which case only
three (3) days prior notice shall be required) fails to cure such default within
thirty (30) days after written notice from Tenant specifying the nature of such
default (where such default could reasonably be cured within said thirty (30)
day period), or fails to commence such cure within said thirty (30) day period
and thereafter continuously with due diligence prosecute such cure to completion
(where such default could not reasonably be cured within said thirty (30) day
period), then Tenant may, in addition to its other remedies, cure any default of
Landlord at Landlord's cost and deduct the reasonable cost of such cure from
rent.

     28  Signs. Landlord hereby approves Tenant's signage as described in
         -----
Exhibit _____ hereto. Landlord shall contract, at its sole cost, a monument sign
base at the street entrance to the driveway of the Demised Premises as allowed
by Township ordinance, in accordance with plans and at a location reasonably
acceptable to Tenant. Tenant shall be entitled, at its sole cost, to install
thereon Tenant's signage. Tenant shall also be entitled to install, at its sole
cost, signage on the building in compliance with all applicable laws. Tenant
shall further have the right, at its sole cost, to install on the Demised
Premises in front of the building flag poles and to fly Tenant's flag thereon.

     30.16  Approvals. Whenever the Lease requires an approval, consent,
            ---------
determination, selection or judgment by either Landlord or Tenant, unless
another standard is expressly set forth, such approval, consent, determination,
selection or judgment and any conditions imposed thereby shall be reasonable and
shall not be unreasonably withheld or delayed and, in exercising any right or
remedy hereunder, each party shall at all times act reasonably and in good
faith.

     30.17  Reasonable Expenditures. Any expenditure by a party permitted or
            -----------------------
required under the Lease, for which such party demands reimbursement from the
other party, and while the Lease is not in default (after expiration of
applicable notice and cure periods), shall be limited to the fair market value
of the goods and services involved, shall be reasonably incurred, and shall be
substantiated by documentary evidence available for inspection and review by the
other party upon request.

     Effect of Addendum. All terms with initial capital letters used herein as
     ------------------
defined terms shall have the meanings ascribed to them in the Lease unless
specifically defined herein. In the event of any inconsistency between this
Addendum and the Lease, the terms of this Addendum shall prevail.

     In witness whereof, said parties hereunto subscribe their names.

LANDLORD:                                    TENANT:

SSP ASSOCIATES, INC.                         CONCENTRIC NETWORK CORPORATION

By /s/ [ILLEGIBLE]^^                         By /s/ Henry R. Nothhaft
  ----------------------                       -------------------------
Name [ILLEGIBLE]^^                                  Henry R. Nothhaft
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Its  President                                      Chairman, President & CEO
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