Basement Backfill Requirements

(2006 IRC)

RESIDENTIAL BASEMENT WALLS

(Revised 10/12/10)

2006 V.U.S.B.C. section 101.2 and section 310.3 state that One & Two Family Dwellings and multiple Single-Family Dwellings (townhouses) not more than 3 stories in height will be reviewed per the 2006 International Residential Code. This code became effective as of May 1^st, 2008.

Note: The maximum number of stories could be exceeded where the dwelling has a basement and finishable attic area per the two conditions listed below.

1. The upper attic floor level is built within roof rafters or roof trusses. This roofed-in finishable floor area will be considered a story above grade when its finishable floor area exceeds the area allowed per the definition of a mezzanine. A mezzanine is defined as a floor area that is not more than 1/3 of the individual room or space that it serves.
2. The basement floor level shall meet the definition of a basement below grade or be defined as a story above grade per the definition below.

Story above grade: A basement shall be considered a story above grade where the finished surface of the floor above the basement is:

1. More than 6′ above grade plane, or
2. More than 6′ above the finished ground level for more than 50% of the total building perimeter, or
3. More than 12′ above the finished ground level at any point.

The building designer and/or permit applicant shall verify that the basement is a true basement below grade or is a story above grade. This distinction shall be noted on the basement wall section of each building permit application plan.

Note: Please note that 2006 IRC table R602.3 (5) requires 2×6’s 16″ o.c. where the bearing wall framing supports “two stories and a roof and ceiling”. This includes the exterior bearing wall framing on the first story of houses that support a second story and finishable attic area and/or room trusses above.

True 4-story buildings shall be reviewed under the 2006 International Building Code by the commercial plan review division of our department.

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The following 2006 IRC Code requirements are for your reference when designing residential basement walls.

The 2006 IRC code section R404 provides prescriptive, structural requirements for properly constructing and backfilling basement walls. The building permit application construction documents must provide enough information for the plan reviewer to verify compliance with code section R404.

All residential permit application plans, with exterior foundation walls retaining more than 4 feet of unbalanced fill (i.e. the basement floor slab is at least 4 feet below grade), shall provide the following information:

All four building elevations shall show:

1. Approximate grade,
2. Exterior door and window openings in the foundation wall,
3. Window wells, if appropriate.

The typical basement wall section shall provide details of the foundation wall design using one of the three options listed below:

1. IRC Section R404.1: Engineered Design – A registered design professional may design the basement wall, including wall systems such as Superior Wall or ICF walls. An engineered design is required for all sites identified with high shrink/swell soils noted as (MH, CH, OH or PT – code prescriptive requirements to not apply). The design shall include:

1. Dimensions from the top of the basement slab or crawl space grade, as applicable, to the underside of the first floor framing,
2. Maximum backfill height and what material(s) may be used as backfill against the wall,
3. Reinforcement details (horizontal and vertical),
4. Wall thickness and material(s).
5. Foundation draintile system and waterproofing.

2. IRC Section R404.1: Prescriptive Requirements using Granular Fill – IRC table R404.1.1(1) may be used for un-reinforced masonry foundation wall design using the column for drainable soil types marked as GW, GP, SW, SP, GM, SM, GC, SC, ML, CL, and OL. The soil type should be identified on the soils report or identified by a soils scientist or engineer. Gravel backfill can be approved by the plan reviewer. The contractor shall provide a foundation wall section (similar to the one attached). The basement wall section shall include:

1. Dimensions from the top of the basement slab or crawl space grade, as applicable, to the underside of the first floor framing,
2. Maximum backfill height and granular fill against the wall,
3. Masonry or concrete wall thickness (and all reinforcing if any),
4. Foundation draintile system and waterproofing,
5. Granular fill material shall extend from the top of the footing projection to a height that is within 12 inches of the exterior finished grade and shall be #57 stone (or other granular material, such that less than 5% of the material will pass a # 200 sieve),
6. Filter fabric shall be installed so as to cover the granular fill and,
7. The granular fill shall be placed such that it measures a minimum of 12 inches in width from the face of the foundation wall at the top of the footing projection and increases in width a sufficient amount to facilitate construction of the foundation wall.

3. IRC Section 404.1: Prescriptive Requirements with Soil Backfill – Provide the specific information required to comply with the requirements of IRC Section 404.1, and tables R404.1.1 (1)-(5). The basement wall section shall include:

1. Dimensions from the top of the basement slab or crawl space grade, as applicable, to the underside of the first floor framing,
2. Maximum unbalanced fill height against the wall.
3. The soil classification designation from IRC table R405.1 (GW, GP, SW, SP, GM, SM, GC, SC, ML, CL, OL), may be used where the site soils report identifies these types of soils or a soils engineer or scientist can identify the type of backfill soil. Designate whether the wall will be constructed of hollow masonry units, solid masonry units, grouted-solid masonry units or concrete.
4. Wall thickness.
5. Reinforcement if necessary (horizontal or vertical).
6. An approved foundation drainage board is required per IRC section R404.1.3. along with the waterproofing on the wall.
7. A foundation draintile system shall be provided as required by IRC section R405.1.

Notes:

1. The following inspections will be required and shall be performed by the Henrico County Department of Building Inspections:a. “Projection” inspection b. “Waterproofing/Draintile” inspection c. “Foundation” inspection
2. IRC code section R404.1.7 states that “backfill shall not be placed against the wall until the wall has sufficient strength and has been anchored to the floor above, or has been sufficiently braced to prevent damage by the backfill”. This includes pouring the basement slab within the basement wall, installing a keyed footing or installing wall reinforcing steel tied to the footing rebar.
3. Always consult with the manufacturer for specific backfill requirements for engineered products such as Insulating Concrete Form (ICF) or Superior Wall basement foundations.

See an example sketch showing minimum information required on a drawing for “granular fill design and foundation walls retaining more than 4 feet of unbalanced fill.”