To direct storm water runoff away from the foundation:
- Slope permeable surfaces away from the house at least 0.5 inch per foot for 10 feet.
- Tamp (mechanically compact) the back-fill to prevent later settling.
- If setbacks limit the space to less than 10 feet, install either swales or drains designed to carry water away from the foundation (ENERGY STAR).
See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Single-Family New Homes, and Indoor airPLUS.
Because no waterproofing system is 100% foolproof, the best defense against water intrusion through the foundation is to prevent water from saturating the soil around the foundation. This can be done by constructing the foundation and grading the site so that water drains away from the house on all sides (see Figure 1).
How to Grade the Site
- Grade to build up the site before construction, if needed, to create a slope that will carry water down and away from the foundation on all four sides.
- Excavate, install foundation footings, stem wall, and slab. Install footing drain pipe, waterproofing, and any exterior insulation.
- After construction, back-fill to the foundation walls, grade the slope, cap the top layer of the grade with 2 to 4 inches of silty clay, and mechanically compact the soils to prevent later settling.
The 2009, 2012, and 2015 International Residential Code require impervious surfaces within 10 feet of the building’s foundation to have a slope of 2% away from the foundation. ENERGY STAR Single-Family New Homes requires permeable surfaces sloped ≥ 0.5 inch per foot away from the home for ≥ 10 feet. ENERGY STAR also states:
- Tamping of the back-fill is not required if either: proper drainage can be achieved using non-settling compact soils, as determined by a certified hydrologist, soil scientist, or engineer; OR, the builder has scheduled a site visit to provide in-fill and final grading after settling has occurred (e.g., after the first rainy season).
- If setbacks limit the space on any side of the home to less than 10 feet, or if walls, slopes or other physical barriers prevent the construction of slopes away from the foundation, then install either swales or perimeter drains designed to carry water away from the foundation.
Visually inspect that back-fill has been tamped and permeable surfaces sloped ≥ 0.5 inches per foot away from the home for ≥ 10 feet. Where setbacks limit space to less than 10 feet, see that swales or drains are installed to carry water from the foundation.
Hurricane and High Wind Locations
In locations prone to heavy winds, follow all local codes regarding site stormwater management. In locations that experience frequent heavy rainfall events, in addition to grading the site, consider these other measures to help address rainwater management and to reduce ponding and erosion on site.
- Consider house designs with hip roofs and overhangs.
- Install gutters, kickout diverters, and downspouts adequately sized to handle large storm events. Direct water to an approved location such as a swale or drywell.
- Construct swales that drain to a French drain or drywell.
- Slope all hard surfaces away from the foundation, including patios, sidewalks, and driveways, or provide drains. Use open brickwork or porous paving as shown in Figure 2 when replacing a driveway or parking lot (FEMA 511 2005). Pervious pavers reduce runoff and allow slow percolation of water into the soil.
- Install rain barrels or cisterns that collect and hold rainwater for lawn and garden watering. This reduces both stormwater runoff and homeowner water bills (FEMA 511 2005).
- Construct rain gardens and plant them with native plants that soak up rainwater and have deep roots to improve filtration (see Figure 1). These gardens incorporate design features that can allow approximately 30% more water to soak into the ground than a conventional patch of lawn (FEMA 511 2005). Rain gardens should be installed more than 10 feet away from the house.
In areas prone to coastal flooding, consider building homes on pier foundations at least one foot above the base flood elevation.
Cold Climates and High Snow Load Areas
Snow melt from the roof can fall to the ground and freeze, creating an ice ridge around the foundation. This ice ridge may direct water from snow melt back to the foundation. Longer overhangs, steeper ground slope, and additional foundation water proofing protection can all help to reduce the likelihood of water leakage and or damage.
The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.
National Water Management System Builder Requirements
1. Water-Managed Site and Foundation.
1.2 Back-fill has been tamped, and permeable surfaces sloped ≥ 0.5 in. per ft. away from home for ≥ 10 ft. Alternatives in Footnote.3
Footnote 3) Swales or drains designed to carry water from foundation are permitted to be provided as an alternative to the slope requirements for any home, and shall be provided for a home where setbacks limit space to less than 10 ft. Also, tamping of back-fill is not required if either: proper drainage can be achieved using non-settling compact soils, as determined by a certified hydrologist, soil scientist, or engineer; OR, the builder has scheduled a site visit to provide in-fill and final grading after settling has occurred (e.g., after the first rainy season).
Please see the ENERGY STAR Single-Family New Homes Implementation Timeline for the program version and revision currently applicable in your state.
Exhibit 1 Mandatory Requirements.
Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.
Certified under ENERGY STAR Qualified Homes Version 3 or 3.1.
No additional Indoor airPLUS requirements.
The EPA WaterSense New Home Specification states that Slopes in excess of 4 feet of horizontal run per 1-foot vertical rise (4:1) shall be vegetated (EPA 2014).
Section R309.2 Carports: The area of floor used for parking automobiles shall be sloped to facilitate the movement of liquids to a drain or toward the main vehicle entry doorway.
Exception: Asphalt surfaces shall be permitted at ground level in carports
Exception: Where it is technically infeasible to comply because of site constraints, ramps shall have a slope of not more than 1-unit vertical in 8 units horizontal (12.5 percent).
Section R401.3 Drainage. This requires that surface water should drain to a storm sewer conveyance or another approved collection point that doesn’t create a hazard. Lots must be graded to drain water away from the foundation walls and the grade should fall at least 6 inches within the first 10 feet. If physical barriers such as walls, slopes, or the lot lines limit the ability to achieve 6 inches of slope within 10 feet of the foundation, then drainage can be achieved by installing drains or swales.
Section R405.1. Footing drains of drain tile, gravel, crushed stone, perforated pipe, or some other approved systems must be installed at the footing perimeter of any building with concrete or masonry foundations that has a basement. The drainage pipe must sit on a bed of gravel 2 or more inches thick that extends at least a foot from the edge of the footing. The drain pipe should be covered with an approved filter fabric then be topped with 6 or more inches of washed crushed gravel or crushed rock. This drain pipe must discharge by gravity or mechanical means into an approved drainage system. A drainage system is not required when the foundation is installed on well-drained ground or sand-gravel soils designated as Group 1 soils by the United Soil Classification System.
Table R405.1 describes the drainage characteristics and frost heave potential for soils classified by the unified soil classification system.
Section R408.6. Finished Grade, permits the finished grade of the crawlspace floor to be level with the bottom of the foundation wall footings. However, if there is evidence that the groundwater table can rise to within 6 inches of the finished floor of the building perimeter or if there is evidence that surface water is not readily draining from the building site, then level of the crawlspace dirt floor must be as high as the outside finished grade, unless an approved drainage system is provided.
Section R102.7.1 Additions, alterations, or repairs. Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with the requirements of this code, unless otherwise stated. (See code for additional requirements and exceptions.)
Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.
Section 1804.4 Site Grading: The ground immediately adjacent to the foundation shall be sloped away from the building at a slope of not less than one unit vertical in 20 units horizontal (5-percent slope) for a minimum distance of 10 feet (3048 mm) measured perpendicular to the face of the wall. If physical obstructions or lot lines prohibit 10 feet (3048 mm) of horizontal distance, a 5-percent slope shall be provided to an approved alternative method of diverting water away from the foundation. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped a minimum of 2 percent away from the building (Florida Building Code 2017).
Exception: Where climatic or soil conditions warrant, the slope of the ground away from the building foundation shall be permitted to be reduced to not less than one unit vertical in 48 units horizontal (2-percent slope). The procedure used to establish the final ground level adjacent to the foundation shall account for additional settlement of the backfill (Florida Building Code 2017).
Once a home has been constructed and concrete driveways and patios are poured, it is a difficult and expensive process to regrade the site should water issues arise due to negative slope on one or more sides of the home. Other options for dealing with water that wants to flow toward the house are to install footing drains if they don’t currently exist and to install damproofing and/or dimpled plastic moisture barrier on the exterior surface of the below-grade walls. Swales or other drainage systems can be constructed as described in the Description tab to carry water away from the home and to a drywell, stormwater sewer, or other drainage location downstream of the home. Drains can be installed at the base of driveways and patios that slope toward the house. Solid-surface driveways, patios, and walkways can be replaced with pervious surfaces such as pavers, gravel, or pebbles, to allow water to drain into the ground rather than flowing toward the house. Sometimes a combination of measures is needed to keep the basement or crawlspace dry. See the Description tab and these Building America Solution Center guides for additional guidance.
- Patio Slabs, Porch Slabs, Walks, and Driveways Slope Away from House
- Footing Drain Pipe
- Damp-Proof Exterior Surface of Below-Grade Walls
- Water Efficient Landscape Design.
The U.S. Department of Energy’s Standard Work Specifications has additional information on site drainage.
See Compliance tab.
Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.
The following authors and organizations contributed to the content in this Guide.
Ground water and rainwater can cause a lot of damage to a home. Building materials that are allowed to remain damp or saturated for long periods of time will eventually fail. Builders can take several steps to protect the home’s foundation. For example they can properly grade the site so water drains away from the home on all sides, install footing drains at the footing of the foundation walls that drain to daylight or to a French drain away from the home, build the foundation on a bed of aggregate rock, use a vapor barrier under slabs and on crawlspace floors, and damp-proof the exterior of foundation walls.