CHAPTER 2 - SITE ACCEPTABILITY CRITERIA

**200. GENERAL.** Before approval of the site can begin, preliminary
information about the site must be provided. Information to be provided
appears in Appendix E.

**201. SITE SUITABILITY.** Site conditions can determine whether a given
foundation design will be suitable for the manufactured home. Problem
soils, flood-prone building sites, sloping sites, and ground-water level
can affect decisions about foundation design. An investigation of the
problem site by a qualified geotechnical engineer is recommended to
assure that site conditions will not adversely affect foundation
performance.

**201-1. EXISTING GRADE ELEVATION(S)** must be provided using a level
and known benchmarks if any of the following are true:

**A**. The elevation is to be altered by grading or fill; or

**B.** The site is near a flood zone (e.g. lakes, rivers, streams, or
coastal areas); or

**C**. The site is or will be incorporated in subdivisions and
communities.

**201-2. FLOOD-PRONE SITES.** Building sites near lakes, rivers, streams
and oceans are likely flood-prone areas. Information about whether the
site is flood-prone should be obtained from FEMA Flood Maps. Determine
whether the building site is in a flood zone. Refer also to the map
showing distribution of great floods in the United States, page H‑3.

**A. Sites in Flood Zones.** If the building site is within a flood
zone, the finish grade of the building site must be located above the
100-year return frequency flood elevation, and in accordance with *HUD
Handbooks 4135.1 REV.2* and *4145.1*.

**B. Elevated Homes** within flood zones can be built on
specially-designed elevated foundations.

1\. Refer to *Manufactured Home Installation in Flood-Hazard Areas*,
FEMA-85 / Sept. 1985.

2\. Homes built on elevated foundations must comply with requirements of
the National Flood Insurance Program to qualify for flood insurance.
(N.F.I.P.)

**201-3. FROST PENETRATION DEPTH.** Verify the frost penetration depth
with local building code department. Refer to the Maximum Annual Frost
Penetration map on page H‑4. The base of the foundation footing must be
below the maximum frost penetration depth. Foundations in permafrost
must be designed by an engineer registered in Alaska.

**201-4. GROUND WATER TABLE ELEVATION.** Water table elevations vary
from season to season and/or by locations. Building structures, streets,
paved areas, and utilities shall be located or engineered to minimize
the adverse effects of a high water table.

**A. Subdivisions.** A subsurface investigation by a Geotechnical
Engineer is required to determine water table elevation.

1\. Developed portions of a site which can be adversely affected by a
potentially high ground water table shall be drained where possible
(based on recommendations by Geotechnical Engineer) by subsurface
drainage facilities adequate for the disposal of excess ground water or
by provision of surface drainage and surface ponds.

2\. A Geotechnical Engineering Report shall be submitted in subdivision
applications.

**B. Exceptions.** For individually-sited homes, the water table
elevation may be based on local records if available; otherwise,
determine by subsurface investigation.

**202. SOIL BEARING CAPACITY**

**202-1. GENERAL.** Soil conditions typically vary with depth.
Subsurface investigations to a minimum recommended depth below the
footing depth by a Geotechnical Engineer, using appropriate laboratory
tests, are recommended to identify soil type and bearing capacity.

**202-2. REQUIRED SUBSURFACE INVESTIGATION.** For subdivisions and
communities, a subsurface investigation is required.

**A. Preliminary Design.** Other sources may be consulted for
presumptive bearing pressures for preliminary design purposes.

1\. Allowable bearing pressures based on national model codes:

a\. BOCA - Basic National Building Code

b\. SBCC - Standard Building Code

c\. ICBO - Uniform Building Code

d\. CABO - One and Two Family Dwelling Code

2\. Local authority having jurisdiction

3\. Soil Conservation District

4\. United States Geological Survey

5\. Soil Conservation Service of the U.S. Dept. of Agriculture

6\. Highway Department

7\. Utility Company Records

**B. Exceptions.** For individually-sited homes, the bearing capacity
may be determined based on local building codes, unless the site is
located in an area of known or suspected adverse soil conditions (as
defined in Section 203), then a subsurface investigation may be
required.

**203. PROBLEM SOIL AND SITE CONDITIONS**

**203-1. ORGANIC SOILS**

**A . Soil Identification.** If any of the following soil types is
identified at the proposed site by a Geotechnical Engineer (or soil
conservation maps), removal of the problem soil type and replacement
with an engineered fill is permitted if submitted and approved by a
Geotechnical Engineer.

1\. *Loess*. Deposits of windblown organic silts. Susceptible to
moisture and frost action and excessive settlement.

2\. *Peat*. River or water deposits of organic matter and silts,
susceptible to excessive settlement.

3\. *Topsoil*. Top organic layer of soil, susceptible to excessive
settlement.

4\. *Others* (As defined by Geotechnical Engineer). Refer to overview
map of expansive soils, Appendix F.

**203-2. UNSTABLE CLAYS** have potential for large movements.

**A. Conditions Causing Instability:**

1\. Expansive characteristics

2\. Highly plastic characteristics

3\. High compressibility

4\. Other conditions as noted by Geotechnical Engineer.

**B. Foundations for Unstable Clays.** The presence of unstable clays
indicates that special foundation treatment as recommended by a
Geotechnical Engineer be included in the approval plan.

**203-3. SLOPING SITES**

**A. General.** There is the potential for slope instability and soil
movement if the following conditions occur:

1\. Loading on the slope by fill, home, or foundation.

2\. Removal of lateral supports by construction.

3\. Inherent characteristics of soil material and slope geometry.

4\. Changes in the water content of the soil.

5\. Refer to overview map of landslide problems on pages H‑6 and H‑7,
and National Academy of Sciences Report *Reducing Losses from
Landsliding in the United States*.

**B. Local Records.** Refer to local Geotechnical records and ordinances
for guidance.

**C. Identification.** Subsurface investigation by a Geotechnical
Engineer is recommended for sloping sites. This is the primary method of
determining slope instability.

**203-4. SUBSIDENCE**

**A. General.** Subsidence refers to the potential for lowering or
collapse of the land surface. Its causes are:

1\. Dissolving of soluble materials below the surface to form cavities.

2\. Underground mining.

3\. Withdrawal of gas, oil, and water from subterranean cavities

4\. Other causes as noted by Geotechnical Engineer.

**B. Identification.** Areas where subsidence occurs can be identified
by local geological records or by subsurface investigation by a
Geotechnical Engineer. Refer to the maps showing cave locations and coal
field locations on pages H‑8 and H‑9, NBSIR 81‑2215 *Construction of
Housing in Mine Subsidence Areas*, and National Academy of Sciences
Report *Mitigating Losses from Land Subsidence in the United States*.

**C. Stipulations.** Construction on the site should be determined by a
Geotechnical Engineer.

**203-5. TERMITE HAZARD.** Refer to the map on page H‑10 for locations
and intensity of termite infestation. Wood selection and treatment, and
wood members in close proximity to the ground shall be in accordance
with CABO *One & Two Family Dwelling Code* (all provisions listed in
section R‑309) or with local ordinances.