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Indoor airPLUS

Technical Guidance to the Indoor airPLUS Construction Specifications

1. Moisture Control

Sections 1.1 - 1.4: Water-Managed Site and Foundation

1.1 Site and Foundation Drainage

Provide site and foundation drainage as follows:

1.1 a. Slope patio slabs, walks and driveways a minimum of ¼ in. per ft. away from house, tamp back-fill to prevent settling, AND slope the final grade away from the foundation at a rate of ½ in. per ft. over a minimum distance of 10 ft.
Where setbacks limit space to less than 10 ft., provide swales or drains designed to carry water away from the foundation. Back-fill tamping is not required if proper drainage can be achieved using non-settling compact soils, as determined by a certified hydrologist, soil scientist, or engineer.

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Building Site Drainage*


Building Site Drainage

Installation of Above-grade Drains From Guttering

Installation of Above-grade Drains From Gutterings

Lateral Drainage From Guttering

Lateral Drainage From Guttering
* Source: "Residential Rehabilitation Inspection Guide"; U.S. Dept. of Housing and Urban Development, Office of Policy Development and Research; February, 2000.

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1.1 a.: Why

Wet foundations, basements and crawl spaces are all too common. They present major problems for homeowners and can result in costly repairs for builders. Foundations can be compromised by (1) surface water from rain and snow that drains from the yard toward the foundation because of incorrect grading and (2) water that drains from the roof and is deposited next to the home's foundation instead of being carried away.

Poor final grading of the yard can result in tremendous quantities of water being absorbed in soils adjacent to foundation walls. Sloping the finish grade of lawns or impervious surfaces such as concrete or blacktop away from the house is the first line of defense. A drainage plan should be developed for the site. The grading should incorporate swales when necessary to move the drainage water to an appropriate area of the site, or off the site altogether. It is also important to plan for the inevitable settlement of soil that was removed temporarily during the construction of the foundation and then returned as backfill to create the final grade next to the house. It is not uncommon to find the soil next to a home's foundation has settled a year or so after the home's completion. If backfill is not compacted properly, the ground can settle and create a depression that can collect surface water from the yard when it rains. Proper backfilling reduces the amount of future settlement and provides enough extra soil to maintain an effective grade after the unavoidable minor settlement of the soil.

Large amounts of water can run off a home's roof from either a short, intense period of heavy rain, or a steady, moderate rainfall lasting for a day or more. A couple of inches of rain falling on the roof of an average-sized house can produce several thousand gallons of runoff; if not drained away from the home's perimeter by a gutter system (see Specification. 1.7) and proper grading, this water can percolate along the foundation, overwhelm the drainage capacity of the soil, and leak into the home.

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1.1 a.: How

Tamping soil back-filled in 6-inch layers minimizes settlement.

image: Tamping soil back-filled in 6-inch layers minimizes settlement.

When determining the location of a new home on a site, the builder should at the same time develop a plan for how surface water will be drained away from the foundation. It is essential that the top of the home’s foundation be of sufficient elevation to allow for a final minimum grade of 1/2 in. per ft., or 5 in. over a distance of 10 ft. If property lines are a limiting factor, increase the slope and use swales or underground piping to accomplish the drainage. Work closely with the excavation contractor to ensure that this grading is accomplished.

The best way to avoid or minimize settlement of soil backfilled around the foundation is to add the soil in approximately 6-in. layers and tamp each layer before the next is added. Make sure the wall is structurally sound and loaded before backfilling (see IRC, R404.1.7, Backfill placement). Workers should be cautious if operating a power soil compactor since misuse can fracture block walls.


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1.1 b. Install protected drain tile at the footings of basement and crawl space walls, level or sloped to discharge to outside grade (daylight) or to a sump pump.
The top of each drain tile pipe must always be below the bottom of the concrete slab or crawl space floor. Each pipe shall be surrounded with at least 6 in. of 1/2 to 3/4 in. washed or clean gravel. The gravel layer shall be fully wrapped with fabric cloth to prevent fouling of the drain tile. If a drain tile discharges to daylight and radon-resistant features are required (see Specification 2.1), install a check valve at the drain tile outfall.

1.1 b: Detailed Illustrations

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Foundation Drainage Pipes - "To Daylight"

Foundation Drainage Pipes - To Daylight

Foundation Drainage Pipes - to Sump

Foundation Drainage Pipes - to Sump

Sump Pump Removal of Water


Sump Pump Removal of Water

1.1 b.: Why

Drain tile (corrugated plastic pipe or the equivalent) placed beside the footing helps to divert water away from the bottom of foundations. The system of perforated drainpipes surrounding the foundation works with the gravel layer under the concrete slab to prevent liquid water from coming into contact with the slab, thus helping to keep the basement or crawl space floor dry. Any water that finds its way to the footing area will be carried away by the system. If water occurs under the slab, the gravel layer provides easy drainage to the pipe system; the gravel also provides a capillary break, preventing water from contacting the underside of the slab. Poor installation of the pipe system often prevents it from accomplishing this drainage function.

Uncovered sump pump pits (crocks or vaults) can be a source of several pollutants, including radon, other soil gasses, and water vapor. Without an effective cover, these pollutants can enter basements and crawl spaces and then mix with the air inside the home. A sump cover, especially one equipped with a gasket and screwed to the vault, can help prevent these pollutants from entering living spaces.

1.1 b.: How

The top of the drainage pipe must be below the bottom of the slab or the gravel layer could be saturated with water and wick into the concrete slab. The pipe must be laid flat (with no sagging areas) or with a slight slope towards the drain termination point (either surface grade at a lower elevation on the property or to a sump pump). It must also be surrounded with clean gravel that is wrapped in filter fabric cloth or the perforated pipe will quickly clog with dirt, interfering with its drainage function.

Effective installation of footing drains and sump pits requires:

  • Clear detailing and specification of the drainage system.
  • Inspection during installation to ensure proper drain location and slope of the drain tile, proper quality and location of the surrounding gravel layer, proper location and installation of protective filter fabric and proper location and details of the sump pump system, if present.
  • The inspection must be done while the drainage system is being installed, before backfilling begins.

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1.1 c. Install a drain or sump in basement and crawl space floors, discharging to daylight at least 10 ft. outside the foundation or into an approved sewer system.
Floor drains are not required for slab-on-grade foundations. Please refer to the Construction Specifications 1.1 Provide site and foundation drainage..."

1.1 c.: Detailed Illustrations

Click on the images for a full-page version

Foundation Drainage Pipes - "To Daylight"

Foundation Drainage Pipes - To Daylight

Sump Pump Removal of Water

Sump Pump Removal of Water

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References/Additional Information

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