<PAGE>

                                                                   EXHIBIT 10.53

                               TRI-PARTY AGREEMENT

      This TRI-PARTY AGREEMENT (this "Agreement") dated as of December 4, 2003
made by and among SNH ALT Mortgaged Properties Trust, a Maryland real estate
investment trust ("SNH Mortgagee"); SNH ALT Leased Properties Trust, a Maryland
real estate investment trust ("SNH Lessor," and together with SNH Mortgagee,
collectively, the "SNH Parties"); FIT-ALT SNH Loan LLC, a Delaware limited
liability company ("FIT"); Pomacy Corporation, a Delaware corporation
("Pomacy"); AHC Trailside, Inc., a Delaware corporation ("Trailside"); and
Alterra Healthcare Corporation, a Delaware corporation ("Alterra," and together
with Pomacy and Trailside, collectively, the "Alterra Parties").

      WHEREAS, SNH Mortgagee made a Loan to Pomacy on February 28, 2003 in the
original principal amount of $6,900,000 (the "Loan"), which Loan is evidenced by
the Loan Agreement and the Promissory Note and secured by the Security
Instruments, as such agreements are described and defined in Exhibit A attached
hereto (collectively, the "Loan Documents");

      WHEREAS, SNH Lessor leases certain properties to Trailside pursuant to a
Lease Agreement dated February 28, 2003 (the "Lease");

      WHEREAS, pursuant to a Guaranty Agreement in favor of SNH Lessor dated
February 28, 2003 (the "Pomacy Guaranty"), Pomacy has guaranteed the obligations
of Trailside under the Lease, which Pomacy Guaranty is secured by certain of the
Pomacy Security Instruments (as defined in Exhibit A);

      WHEREAS, pursuant to a Guaranty Agreement in favor of SNH Mortgagee dated
February 28, 2003 (the "Trailside Guaranty"), Trailside has guaranteed the
obligations of Pomacy under the Loan Documents, which Trailside Guaranty is
secured by the Trailside Security Instruments (as defined in Exhibit A);

      WHEREAS, in connection with the Order entered November 26, 2003
confirming the Plan of Reorganization (the "Plan of Reorganization") in
Alterra's Chapter 11 Case No. 03-10254 in the Untied States Bankruptcy Court for
the District of Delaware, SNH Mortgagee has agreed to sell, and FIT has agreed
to purchase, the Loan on the terms and conditions set forth herein;

      WHEREAS, to facilitate the sale of the Loan to FIT, the parties to the
Loan Documents wish to eliminate the cross-collateralization and
cross-defaulting between the Loan Documents and the Lease by terminating and/or
releasing the Pomacy Guaranty, the Trailside Guaranty, the Trailside Security
Instruments and the Alterra Second Security Agreement (as defined in Exhibit A)
and by modifying the remaining Loan Documents (to the extent applicable) to
delete the cross-collateralizing and cross-defaulting provisions.

      NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto do hereby agree as follows:

<PAGE>

      1.    Sale of the Loan. Subject to the terms and conditions of this
            Agreement, effective on the Effective Date of the Plan of
            Reorganization (the "Effective Date") and receipt of the Purchase
            Price (as hereinafter defined), (a) SNH Mortgagee hereby sells,
            transfers and assigns to FIT all right, title and interest of SNH
            Mortgagee in, to and under the Loan, the Promissory Note and the
            Loan Agreement, as amended hereby, and (b) SNH Mortgagee and SNH
            Lessor hereby sell, assign and transfer to FIT all their respective
            right, title and interest in, to and under (i) each of the Pomacy
            Security Instruments, as amended hereby and by the assignment and
            modification agreements executed and delivered in connection
            herewith, and (ii) all stock certificates, related stock powers,
            opinions, title policies and any other agreements and documents
            delivered by Pomacy and/or Alterra in connection with the Loan (the
            rights, title and interests assigned pursuant to clauses (a) and (b)
            are collectively referred to herein as the "Assigned Rights"), in
            each case to the extent assignable.

      2.    Purchase Price. In consideration for the sale, transfer and
            assignment by SNH Mortgagee and SNH Lessor to FIT of the Assigned
            Rights, FIT will pay to SNH Mortgagee an amount equal to the
            outstanding principal balance of the Loan plus accrued and unpaid
            interest thereon as of the Effective Date. FIT shall pay the
            Purchase Price on the Effective Date by wire transfer of immediately
            available federal funds to the account designated by SNH Mortgagee.

      3.    Modification of Loan Documents. Effective upon sale of the Loan
            pursuant to Section 1 of this Agreement, the following Loan
            Documents are modified as follows:

            a.    Loan Agreement.

                  i.    Section 1.32 of the Loan Agreement is amended by
                        deleting the word "Tenant" from the definition of
                        "Guarantor."

                  ii.   Section 6.1.1 of the Loan Agreement is amended by
                        deleting the words "or any payment of Minimum Rent or
                        Additional Rent (as such terms are defined in the Lease)
                        under the Lease" from clause (a) thereof and by deleting
                        the words "or the Lease Documents" from clause (b)
                        thereof.

                  iii.  Section 6.1.6 of the Loan Agreement is amended by
                        deleting the words "or any Lease Document" from both the
                        second line and the fourth line thereof.

                  iv.   Section 8.1(c) of the Loan Agreement is amended by
                        deleting the notice address for Senior Housing
                        Properties Trust and its counsel and by substituting
                        therefor as the address for Lender:

                                       2
<PAGE>

                                       c/o Fortress Investment Group LLC
                                           1251 Avenue of the Americas, 16th Fl.
                                           New York, New York  10019
                                           Attn:  Randal Nardone
                                           Facsimile:  (212) 798-6120

                                           With a copy to:

                                           Sidley Austin Brown & Wood LLP
                                           787 Seventh Avenue
                                           New York, New York  10019
                                           Attn:  Scott M. Freeman
                                           Facsimile:  (212) 839-5599

            b.    Stock Pledge Agreement (Pomacy Corporation).

                  i.    Section 3 of the Stock Pledge Agreement (Pomacy
                        Corporation) is amended by deleting clauses (ii), (iii)
                        and (v) thereof and renumbering the remaining clauses in
                        numerical order.

                  ii.   Section 8 of the Stock Pledge Agreement (Pomacy
                        Corporation) is amended by deleting the words "the
                        Purchase Agreement or the Lease" from clause (a) thereof
                        and by deleting the words "or the Landlord Guaranty"
                        from clause (b) thereof.

                  iii.  Section 15(c) of the Stock Pledge Agreement (Pomacy
                        Corporation) is amended by deleting the notice address
                        for Senior Housing Properties Trust and its counsel and
                        by substituting therefor:

                                           Fortress Investment Group LLC
                                           1251 Avenue of the Americas, 16th Fl.
                                           New York, NY  10019
                                           Attn:  Randal Nardone
                                           Facsimile:  (212) 798-6120

                                           With a copy to:

                                           Sidley Austin Brown & Wood LLP
                                           787 Seventh Avenue
                                           New York, NY  10019
                                           Attn:  Scott M. Freeman
                                           Facsimile:  (212) 839-5599

            c.    Assignment of Contracts, Licenses and Permits.

                  i.    Section 1 of each Assignment of Contracts, Licenses and
                        Permits is amended by deleting the words "or in the
                        Pomacy Guaranty" from the first paragraph thereof.

                                       3
<PAGE>

                  ii.   Section 2 of each Assignment of Contracts, Licenses and
                        Permits is amended by deleting the words "or the Pomacy
                        Guaranty" from both paragraphs thereof.

                  iii.  Section 5 of each Assignment of Contracts, Licenses and
                        Permits is amended by deleting the language of clause
                        (d) thereof and substituting the words "Intentionally
                        omitted."

      4.    Closing Documents. On the Effective Date, the following documents
            shall be executed and delivered to FIT by the party indicated:

            a.    SNH Lessor shall deliver a termination of the Pomacy Guaranty;

            b.    SNH Mortgagee shall deliver a termination of the Trailside
                  Guaranty, the Trailside Security Instruments and the Alterra
                  Second Security Agreement;

            c.    SNH Mortgagee shall deliver the original Promissory Note,
                  endorsed by SNH Mortgagee in the following form: pay to the
                  order of FIT-ALT SNH Loan, LLC, its successors and assigns,
                  without recourse or warranty except as set forth in the
                  Tri-Party Agreement dated as of December ___, 2003 among SNH
                  ALT Mortgaged Properties Trust, SNH ALT Leased Properties
                  Trust, FIT-ALT SNH Loan LLC, Pomacy Corporation, AHC
                  Trailside, Inc. and Alterra Healthcare Corporation.

            d.    SNH Mortgagee and SNH Lessor shall deliver the originals of
                  all Loan Documents in their respective possession;

            e.    SNH Mortgagee, SNH Lessor and Pomacy shall deliver an
                  Assignment and Amendment in the form of Exhibit B attached
                  hereto with respect to each Mortgage listed in Exhibit A, duly
                  executed and in proper form for recording;

            f.    SNH Mortgagee, SNH Lessor and Pomacy shall deliver an
                  Assignment and Amendment in the form of Exhibit C attached
                  hereto with respect to each Assignment Leases and Rents listed
                  in Exhibit A, duly executed and in proper form for recording;

            g.    SNH Mortgagee and SNH Lessor shall deliver assignments to FIT
                  of the Uniform Commercial Code Financing Statements listed in
                  Exhibit A, and SNH Mortgagee shall deliver terminations of all
                  Uniform Commercial Code Financing Statements filed by SNH
                  Mortgagee, as secured party against Trailside and/or Alterra,
                  as debtor;

            h.    SNH Mortgagee and SNH Lessor shall deliver the original Title
                  Policy issued with respect to each Mortgage (to the extent
                  that such Title Policies have been delivered to SNH Mortgagee
                  and

                                       4
<PAGE>

                  SNH Lessor) or the original Commitment for title insurance
                  marked and initialed by Chicago Title Insurance Company (to
                  the extent that such Title Policies have not been delivered to
                  SNH Mortgagee and SNH Lessor);

            i.    SNH Mortgagee shall deliver the original stock certificate(s)
                  of Pomacy Corporation and related Stock Powers and copies of
                  all other certificates, opinions and other agreements and
                  documents delivered in connection with closing of the Loan;
                  and

      5.    Conditions to Closing.

            a.    Conditions to FIT's Obligation to Close. FIT's obligation to
                  consummate the transactions contemplated hereunder is subject
                  to satisfaction by SNH and the Alterra Parties, or waiver by
                  FIT, of the following conditions:

                  i.    SNH shall have complied in all material respects with
                        all terms and conditions of this Agreement required to
                        be performed by SNH on or before the Effective Date.

                  ii.   On or before the Effective Date, FIT shall have received
                        the documents and instruments required to be executed,
                        endorsed or delivered by the SNH Parties and the Alterra
                        Parties pursuant to Section 4 above, in accordance with
                        the requirements of Section 4 above.

                  iii.  The representations and warranties of the SNH Parties
                        and the Alterra Parties shall be true and correct in all
                        material respects as of the Effective Date.

                  iv.   SNH Lessor and Trailside shall have entered into the
                        First Amendment of Lease in the form of Exhibit E
                        hereto.

            b.    Conditions to SNH's Obligation to Close. SNH's obligation to
                  consummate the transactions contemplated hereunder and for the
                  Effective Date to occur is subject to satisfaction by FIT and
                  the Alterra Parties, or waiver by SNH, of the following
                  conditions:

                  i.    FIT and the Alterra Parties shall have complied in all
                        material respects with all terms and conditions of this
                        Agreement required to be performed by FIT and the
                        Alterra Parties on or before the Effective Date,
                        including, without limitation, payment of the amounts
                        required to be paid on or prior to the Effective Date
                        under Sections 2 and 5 hereof.

                  ii.   On or before the Effective Date, SNH shall have received
                        the documents to be executed and delivered by FIT and
                        the Alterra Parties pursuant to Sections 4 and 5 hereof
                        and all other documents that need to be executed in
                        connection with this

                                       5
<PAGE>

                        Agreement, including, without limitation, all amendments
                        to those documents that secure Trailside's payment and
                        performance obligations under the Lease.

                  iii.  The representations and warranties of FIT shall be true
                        and correct in all material respects as of the Effective
                        Date.

                  iv.   On or before the Effective Date, Alterra shall have
                        delivered to SNH Lessor the amount of $1,000,000 (the
                        "Payment Amount") in immediately available federal
                        funds, which Payment Amount is solely in
                        consideration of the parties' agreements contained
                        herein and is not a credit against amounts now or
                        hereafter owed by Trailside to SNH Lessor or any
                        Affiliated Person (as defined in the Lease) of SNH
                        Lessor under the Lease or any other Lease Document (as
                        defined in the Lease), and Alterra expressly
                        acknowledges and agrees that it does not elect, and
                        hereby expressly waives any right it may have to elect,
                        to convey the so-called "Fon-du-lac residence" to SNH
                        Lessor in lieu of payment of the Payment Amount.

                  v.    On or before the Effective Date, Alterra shall have
                        delivered to SNH the amount of $2,500,000 in immediately
                        available federal funds, which amount shall be in
                        satisfaction of the Allowed Administrative Claim that
                        SNH has against Alterra.

      6.    Recording Fees and Transfer Fees; Costs and Expenses. Each party
            shall be responsible for the payment of its legal and other costs
            and expenses for preparing, negotiating, executing and implementing
            this Agreement and any related documents and consummating the
            transactions contemplated hereunder. Any filing, recording or
            transfer fees or taxes shall be paid by FIT or the Alterra Parties.

      7.    FIT's Representations. FIT hereby represents, warrants, and
            acknowledges as of the Effective Date:

            a.    FIT has the legal capacity and authority to enter into and
                  perform its obligations under this Agreement.

            b.    The execution and delivery by FIT of this Agreement, and the
                  other agreements and instruments to be executed by FIT as
                  contemplated hereby and the performance and compliance by FIT
                  with the terms hereof and thereof, are within FIT's power and
                  authority; this Agreement, assuming due authorization,
                  execution and delivery by the other parties hereto,
                  constitutes, and the other agreements and instruments to be
                  executed by FIT as contemplated hereby will constitute legal,
                  valid and binding obligations of FIT, enforceable against FIT
                  in accordance with their respective terms.

            c.    The execution and delivery of this Agreement and the
                  performance of FIT's obligations hereunder by FIT will not
                  conflict with any provision of any law, regulation, or order
                  to which FIT is subject,

                                       6
<PAGE>

                  or conflict with or result in a breach of or constitute a
                  default under any of the material terms, conditions, or
                  provisions of any material agreement or instrument to which
                  FIT is a party or by which FIT is bound.

            d.    No license, consent, approval, authorization or order of, or
                  registration or filing with, or notice to any court or
                  governmental authority, is required for the execution,
                  delivery or performance by FIT of this Agreement and the other
                  agreements and instruments to be executed by FIT as
                  contemplated hereby.

            e.    FIT is (i) an entity which is in the business of buying,
                  entering into, or originating loans of the type being
                  purchased pursuant to this Agreement, or which otherwise deals
                  in such instruments in the ordinary course of its business; or
                  (ii) an entity which is defined as an "accredited investor"
                  under the Securities Act of 1933, 15 U.S.C Section 77a et
                  seq., and the rules and regulations promulgated thereunder
                  (the "33 Act").

            f.    FIT understands that none of the Loan Documents have been
                  registered under the 33 Act or the securities laws of any
                  state. Without characterizing any of the Loan Documents as a
                  "security" with the meaning of applicable securities laws, FIT
                  is not purchasing the Assigned Rights with a view towards a
                  sale or redistribution in violation of the 33 Act; provided
                  that FIT may resell the Assigned Rights or any portion thereof
                  if such resale does not violate the 33 Act.

      The representations and warranties set forth in this Section 7 shall
survive the execution, delivery, performance and closing of this Agreement for a
period of six (6) months from and after the Effective Date. Except as expressly
set forth in this Section 7, FIT makes no representations or warranties, express
or implied.

      8.    SNH Mortgagee Representations. SNH Mortgagee hereby represents,
            warrants, and acknowledges as of the Effective Date:

            a.    SNH Mortgagee has the legal capacity and authority to enter
                  into and perform its obligations under this Agreement.

            b.    The execution and delivery by SNH Mortgagee of this Agreement,
                  and the other agreements and instruments to be executed by SNH
                  Mortgagee as contemplated hereby and the performance and
                  compliance by SNH Mortgagee with the terms hereof and thereof,
                  are within the power and authority of SNH Mortgagee; this
                  Agreement, assuming due authorization, execution and delivery
                  by the other parties hereto, constitutes, and the other
                  agreements and instruments to be executed by SNH Mortgagee as
                  contemplated hereby constitute legal, valid and binding
                  obligations of SNH Mortgagee, enforceable against SNH
                  Mortgagee in accordance with their respective terms.

                                       7
<PAGE>

            c.    The execution and delivery of this Agreement and the
                  performance by SNH Mortgagee of its obligations hereunder will
                  not conflict with any provision of any law, regulation, or
                  order to which SNH Mortgagee is subject, or conflict with or
                  result in a breach of or constitute a default under any of the
                  material terms, conditions, or provisions of any material
                  agreement or instrument to which SNH Mortgagee is a party or
                  by which SNH Mortgagee is bound.

            d.    No license, consent, approval, authorization or order of, or
                  registration or filing with, or notice to any court or
                  governmental authority, is required for the execution,
                  delivery or performance by SNH Mortgagee of this Agreement and
                  the other agreements and instruments to be executed by SNH
                  Mortgagee as contemplated hereby.

            e.    The outstanding principal amount of, and accrued and unpaid
                  interest on, the Loan as of December 4, 2003 is Six Million
                  Fifty Six Thousand Five Hundred Ninety Two Dollars and Seventy
                  Six Cents ($6,056,592.76). Interest accrues at $1,344.71 per
                  diem.

            f.    The Promissory Note delivered pursuant to Section 4 is an
                  original instrument, and the Loan Documents have not been
                  modified or amended except as provided in this Agreement or as
                  contemplated hereby.

            g.    The Assigned Rights have not been assigned or pledged by SNH
                  Mortgagee.

            h.    All taxes due or required to be paid by SNH Mortgagee on or
                  prior to the Effective Date with respect to the Promissory
                  Note have been paid.

      The representations and warranties set forth in this Section 8 shall
survive the execution, delivery, performance and closing of this Agreement for a
period of six (6) months from and after the Effective Date. Except as expressly
set forth in this Section 8, SNH Mortgagee makes no representations or
warranties, express or implied.

      9.    SNH Lessor Representations. SNH Lessor hereby represents, warrants,
            and acknowledges as of the Effective Date:

            a.    SNH Lessor has the legal capacity and authority to enter into
                  and perform its obligations under this Agreement.

            b.    The execution and delivery by SNH Lessor of this Agreement,
                  and the other agreements and instruments to be executed by SNH
                  Lessor as contemplated hereby and the performance and
                  compliance by SNH Lessor with the terms hereof and thereof,
                  are within the power and authority of SNH Lessor; this
                  Agreement, assuming due authorization, execution and delivery
                  by the other

                                       8
<PAGE>

                  parties hereto, constitutes, and the other agreements and
                  instruments to be executed by SNH Lessor as contemplated
                  hereby constitute legal, valid and binding obligations of SNH
                  Lessor, enforceable against SNH Lessor or in accordance with
                  their respective terms.

            c.    The execution and delivery of this Agreement and the
                  performance by SNH Lessor of its obligations hereunder will
                  not conflict with any provision of any law, regulation, or
                  order to which SNH Lessor is subject, or conflict with or
                  result in a breach of or constitute a default under any of the
                  material terms, conditions, or provisions of any material
                  agreement or instrument to which SNH Lessor is a party or by
                  which SNH Lessor is bound.

            d.    No license, consent, approval, authorization or order of, or
                  registration or filing with, or notice to any court or
                  governmental authority, is required for the execution,
                  delivery or performance by SNH Lessor of this Agreement and
                  the other agreements and instruments to be executed by SNH
                  Lessor as contemplated hereby.

            e.    The Assigned Rights have not been assigned or pledged by SNH
                  Lessor.

      The representations and warranties set forth in this Section 9 shall
survive the execution, delivery, performance and closing of this Agreement for a
period of six (6) months from and after the Effective Date. Except as expressly
set forth in this Section 9, SNH Lessor makes no representations or warranties,
express or implied.

      10.   Alterra Parties' Representations. The Alterra Parties hereby
            represent, warrant, and acknowledge as of the Effective Date:

            a.    The Alterra Parties have the legal capacity and authority to
                  enter into and perform their respective obligations under this
                  Agreement.

            b.    The execution and delivery by the Alterra Parties of this
                  Agreement, and the other agreements and instruments to be
                  executed by the Alterra Parties as contemplated hereby and the
                  performance and compliance by the Alterra Parties with the
                  terms hereof and thereof, are within the power and authority
                  of the Alterra Parties; this Agreement, assuming due
                  authorization, execution and delivery by the other parties
                  hereto, constitutes, and the other agreements and instruments
                  to be executed by the Alterra Parties (or any of them) as
                  contemplated hereby constitute legal, valid and binding
                  obligations of such Alterra Party, enforceable against such
                  Alterra Party in accordance with their respective terms.

            c.    The execution and delivery of this Agreement and the
                  performance by the Alterra Parties of their obligations
                  hereunder will not conflict with any provision of any law,
                  regulation, or order to

                                       9
<PAGE>

                  which any Alterra Party is subject, or conflict with or result
                  in a breach of or constitute a default under any of the
                  material terms, conditions, or provisions of any material
                  agreement or instrument to which any Alterra Party is a party
                  or by which any Alterra Party is bound.

            d.    No license, consent, approval, authorization or order of, or
                  registration or filing with, or notice to any court or
                  governmental authority, is required for the execution,
                  delivery or performance by any Alterra Party of this Agreement
                  and the other agreements and instruments to be executed by any
                  Alterra Party as contemplated hereby.

            e.    The outstanding principal amount of, and accrued interest on,
                  the Loan as of December 4, 2003 is Six Million Fifty Six
                  Thousand Five Hundred Ninety Two Dollars and Seventy Six Cents
                  ($6,056,592.76). Interest accrues at $1,344.71 per diem.

            f.    The Loan Documents have not been modified or amended except as
                  provided in this Agreement or as contemplated hereby.

      The representations and warranties set forth in this Section 10 shall
survive the execution, delivery, performance and closing of this Agreement for a
period of six (6) months from and after the Effective Date. Except as expressly
set forth in this Section 10, the Alterra Parties make no representations or
warranties, express or implied.

      11.   Governing Law. This Agreement shall be governed by the laws of the
            State of Delaware without regard to conflicts of law principles.

      12.   Miscellaneous.

            a.    Each of the parties hereto shall execute and deliver all such
                  documents and perform all such acts as reasonably requested by
                  any other party hereto from time to time, after the date
                  hereof, to carry out the matters contemplated by this
                  Agreement.

            b.    The provisions of this Agreement run to the benefit of the
                  parties hereto and their respective successors and assigns.

            c.    This Agreement constitutes the entire agreement of the parties
                  hereto with regard to the Loan, and this Agreement may be
                  amended only by a writing executed by all parties hereto.
                  Excuse or waiver of the performance by any party of any
                  obligation under this Agreement shall only be effective if
                  evidenced by a written statement signed by the party so
                  waiving. No delay in exercising any right or remedy shall
                  constitute a waiver thereof, and no waiver by any party of the
                  breach of any covenant of this Agreement shall be construed as
                  a waiver of any preceding or

                                       10
<PAGE>

                  succeeding breach of the same or any other covenant or
                  condition of this Agreement.

            d.    This Agreement shall not be construed as if it had been
                  prepared by one of the parties, but rather as if all of the
                  parties had prepared the same.

            e.    Except as otherwise expressly stated, nothing in this
                  Agreement shall affect, modify, release, limit or otherwise
                  impair any rights or obligations of any of the parties hereto
                  under the Lease, the Lease Documents (as defined in the
                  Lease), the Loan Agreement, the Loan Documents or any document
                  executed in connection therewith.

      13.   Counterparts. This Agreement may be executed in any number of
            counterparts, each of which counterparts shall be deemed to be an
            original, and all of which counterparts shall constitute but one and
            the same instrument. Signature pages may be detached and reattached
            to physically form one instrument. Delivery of an executed
            counterpart of a signature page to this Agreement via facsimile
            transmission shall be effective as delivery of a manually executed
            counterpart of this Agreement.

      14.   Notices. All notices, requests or other communications desired or
            required to be given under this Agreement shall be in writing and
            shall be sent by (a) certified or registered mail, return receipt
            requested, postage prepaid, (b) national prepaid overnight delivery
            service, (c) telecopy or other facsimile transmission (following
            with hard copies to be sent by national prepaid overnight delivery
            service) or (d) personal delivery with receipt acknowledged in
            writing, as follows:

if to SNH:

c/o Senior Housing Properties Trust
400 Centre Street
Newton, Massachusetts  02458
Attn:  Mr. David J. Hegarty
Facsimile:  (617) 796-8349

with a copy to:

Sullivan & Worcester LLP
One Post Office Square
Boston, Massachusetts  02109
Attn:  Nancy S. Grodberg, Esq.
Facsimile:  (617) 338-2880

if to FIT:

c/o Fortress Investment Group LLC

                                       11
<PAGE>

1251 Avenue of the Americas
New York, New York  10019
Attn:  Randal Nardone
Facsimile:  (212) 798-6120

with a copy to:

Sidley Austin Brown & Wood LLP
787 Seventh Avenue
New York, New York  10019
Attn:  Scott M. Freeman
Facsimile:  (212) 839-5599

if to Pomacy, Trailside or Alterra:

c/o Alterra Healthcare Corporation
10000 Innovation Drive
Milwaukee, Wisconsin  53227
Attn:  Mr. Mark W. Ohlendorf
Facsimile:  (414) 918-5055

with a copy to:

Rogers & Hardin LLP
2700 International Tower
229 Peachtree Street, N.E.
Atlanta, Georgia  30303-1601
Attn:  Carolyn B. Dobbins, Esq.
Facsimile:  (404) 525-2224

            All notices and demands shall be deemed to have been given either at
            the time of the delivery thereof to the party entitled to receive
            such notices and demands at the address of such party for notices
            hereunder, or on the third day after the mailing thereof to such
            address, as the case may be.

                         [Signatures on following page.]

                                       12
<PAGE>

      IN WITNESS WHEREOF, the undersigned parties have executed this Agreement
to be effective as of the Effective Date.

                                         SNH MORTGAGEE:

                                         SNH ALT MORTGAGED PROPERTIES TRUST,
                                         a Maryland real estate investment trust

                                         By: /s/ John R. Hoadley
                                             ----------------------------------
                                             Name:  John R. Hoadley
                                             Title: Treasurer

                                         SNH LESSOR:

                                         SNH ALT LEASED PROPERTIES TRUST,
                                         a Maryland real estate investment trust

                                         By: /s/ John R. Hoadley
                                             ----------------------------------
                                             Name:  John R. Hoadley
                                             Title: Treasurer

                             [Signatures continued]

                                       13
<PAGE>

                                        FIT:

                                        FIT-ALT SNH LOAN LLC, a Delaware limited
                                        liability company

                                        By: /s/ Darryl W. Copeland, Jr.
                                            -----------------------------
                                            Name:  Darryl W. Copeland, Jr.
                                            Title: Vice President

                             [Signatures continued]

                                       14
<PAGE>

                                     POMACY:

                                     POMACY CORPORATION, a Delaware
                                     corporation

                                     By: /s/ Kristin Ferge
                                         ----------------------------------
                                         Name: Kristin Ferge
                                         Title: Vice President

                                     TRAILSIDE:

                                     AHC TRAILSIDE, INC., a Delaware corporation

                                     By: /s/ Kristin Ferge
                                         ----------------------------------
                                         Name: Kristin Ferge
                                         Title: Vice President

                                     ALTERRA:

                                     ALTERRA HEALTHCARE CORPORATION, a
                                     Delaware corporation

                                     By: /s/ Kristin Ferge
                                         ----------------------------------
                                         Name:  Kristin Ferge
                                         Title: Vice President

                                       15
<PAGE>

                                    Exhibit A

"Loan Documents" shall mean the following, each dated February 28, 2003:

      (a)   Loan Agreement by and between Pomacy Corporation and SNH ALT
            Mortgaged Properties Trust

      (b)   Promissory Note executed by Pomacy Corporation in favor of SNH ALT
            Mortgaged Properties Trust in the original principal amount of
            $6,900,000.00

      (c)   Security Instruments (as defined below)

"Security Instruments" shall mean the following, each dated February 28, 2003:

      (a)   Pomacy Security Instruments (as defined below)

      (b)   Trailside Security Instruments (as defined below)

      (c)   Alterra Second Security Agreement (as defined below)

"Pomacy Security Instruments" shall mean the following, each dated February 28,
2003:

      (a)   Guaranty Agreement made by Alterra Healthcare Corporation for the
            benefit of SNH ALT Mortgaged Properties Trust

      (b)   Environmental Indemnity by Alterra Healthcare Corporation and Pomacy
            Corporation for the benefit of SNH ALT Mortgaged Properties Trust
            and SNH ALT Leased Properties Trust

      (c)   Stock Pledge Agreement (Pomacy Corporation) by Alterra Healthcare
            Corporation for the benefit of SNH ALT Mortgaged Properties Trust
            and SNH ALT Leased Properties Trust

      (d)   The following mortgages or deeds of trusts, each dated February 28,
            2003 (the "Mortgages"):

            (i)   Mortgage, Assignment of Leases and Rents, Security Agreement
                  and Financing Statement from Pomacy Corporation to SNH ALT
                  Mortgaged Properties Trust and SNH ALT Leased Properties Trust
                  (Oviedo, Florida)

            (ii)  Mortgage, Assignment of Leases and Rents, Security Agreement
                  and Financing Statement from Pomacy Corporation to SNH ALT
                  Mortgaged Properties Trust and SNH ALT Leased Properties Trust
                  (Brandon, Florida)

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<PAGE>

            (iii) Mortgage, Assignment of Leases and Rents, Security Agreement
                  and Financing Statement from Pomacy Corporation to SNH ALT
                  Mortgaged Properties Trust and SNH ALT Leased Properties Trust
                  (Battle Creek, Michigan)

      (e)   the following Assignment of Leases and Rents, each dated February
            28, 2003 (the "Assignments of Leases and Rents"):

            (i)   Assignment of Leases and Rents from Pomacy Corporation to SNH
                  ALT Mortgaged Properties Trust and SNH ALT Leased Properties
                  Trust (Oviedo, Florida)

            (ii)  Assignment of Leases and Rents from Pomacy Corporation to SNH
                  ALT Mortgaged Properties Trust and SNH ALT Leased Properties
                  Trust (Brandon, Florida)

            (iii) Assignment of Leases and Rents from Pomacy Corporation to SNH
                  ALT Mortgaged Properties Trust and SNH ALT Leased Properties
                  Trust (Battle Creek, Michigan)

      (f)   the following Subordination of Management Agreements, each dated
            February 28, 2003:

            (i)   Subordination of Management Agreement by Alterra Healthcare
                  Corporation in favor of SNH ALT Mortgaged Properties Trust
                  (Oviedo, Florida)

            (ii)  Subordination of Management Agreement by Alterra Healthcare
                  Corporation in favor of SNH ALT Mortgaged Properties Trust
                  (Brandon, Florida)

            (iii) Subordination of Management Agreement by Alterra Healthcare
                  Corporation in favor of SNH ALT Mortgaged Properties Trust
                  (Battle Creek, Michigan)

      (g)   the following Assignment of Contracts, Licenses and Permits, each
            dated February 28, 2003 (the "Assignment of Licenses, Contracts and
            Permits"):

            (i)   Assignment of Contracts, Licenses and Permits by Pomacy
                  Corporation to SNH ALT Mortgaged Properties Trust and SNH ALT
                  Leased Properties Trust (Oviedo, Florida)

            (ii)  Assignment of Contracts, Licenses and Permits by Pomacy
                  Corporation to SNH ALT Mortgaged Properties Trust and SNH ALT
                  Leased Properties Trust (Brandon, Florida)

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<PAGE>

            (iii) Assignment of Contracts, Licenses and Permits by Pomacy
                  Corporation to SNH ALT Mortgaged Properties Trust and SNH ALT
                  Leased Properties Trust (Battle Creek, Michigan)

      (h)   the following Uniform Commercial Code Financing Statements, each
            delivered as of February 28, 2003 (the "UCC's"):

            (i)      UCC Financing Statement filed for record March 5, 2003,
                        recorded in Book 04732, Page 1280, Clerk's No.
                        2003038576, Seminole County, Florida (Oviedo, Florida)

            (ii)     UCC Financing Statement filed for record March 5, 2003,
                        recorded in Official Book 12407, Page 1282, Hillsborough
                        County, Florida (Brandon, Florida)

            (iii)    UCC Financing Statement filed for record March 8, 2003,
                        recorded in Liber 2596, Page 788, Calhoun County,
                        Michigan (Battle Creek, Michigan)

            (iv)     UCC Financing Statement filed for record March 4, 2003,
                        Initial Filing Number 3051809 5, Delaware Department of
                        State UCC Filing Section

"Trailside Security Instruments" shall mean the following, each dated February
28, 2003:

      (a)   Second Assignment of Sublease and Rents by and between AHC
            Trailside, Inc. and SNH ALT Mortgaged Properties Trust

      (b)   Second Security Agreement by and between AHC Trailside, Inc. and SNH
            ALT Mortgaged Properties Trust

"Alterra Second Security Agreement" shall mean the following, dated February 28,
2003:

      (a)   Second Security Agreement by and between Alterra Healthcare
            Corporation and SNH ALT Mortgaged Properties

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