Insulated Crawl Space. Poured Concrete w/ 1-1/2in. Exterior Rigid Foam

Foundations, Floors, and Walls Are Critical Green Connections

Air sealing is imperative. The connection between concrete foundations and wood framing is a place prone to air leaks and moisture problems. Wood is often warped, and concrete is rarely flat. There are at least three places for air to leak in and probably a lot more. Leaky connections can mean energy, moisture, comfort, and IAQIndoor air quality. Healthfulness of an interior environment; IAQ is affected by such factors as moisture and mold, emissions of volatile organic compounds from paints and finishes, formaldehyde emissions from cabinets, and ventilation effectiveness. problems. Extending the wall sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. past these connections is a good first step whenever practical. Caulks, adhesives, spray foam, and gaskets can seal them up tightly.

Keep water at bay

Unless you live in the desert, the ground is always wet; and that ground water is always pushing its way in. Footing drains can carry away bulk groundwater, but foundations also have to disrupt capillarity. Water in the soil will wick all the way up to the roof framing if you let it. CapillaryForces that lift water or pull it through porous materials, such as concrete. The tendency of a material to wick water due to the surface tension of the water molecules. breaks such as brush-on damp-proofing, sill sealer, and rigid insulation block this process. A foundation is a bad place to cut corners because problems are expensive and complicated to fix after a house is finished.

Foundation walls cannot dry to the outside

Because crawl spaces are mostly buried in the ground, it's important to keep them from getting wet. Brush-on damp-proofing — or even better, dimple mats — help keep basement walls dry. Basement walls should be backfilled with coarse granular material to interrupt capillarity and to help ground- and stormwater flow toward the footing drains.

Many building experts recommend against crawl spaces

Crawl spaces have all of the disadvantages of basements and few of their advantages: they provide all of the moisture, mold, and air leaks without providing any living space in return. Still, a crawl space sometimes makes sense. Crawl space walls should be insulated at the perimeter with rigid foam, and sealed rather than vented. The best current practice is to make a crawl space a conditioned area like the rest of the house. This is permitted by newer versions of most building codes, and is much better for the house and the people who live there.

Insulation on the inside or outside? Crawl space foundations need insulation on either the inside or the outside. Placing insulation on the outside puts the thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. where it can do the most good — inside the thermal envelope. But the above-grade portions of exterior insulation need to be covered for aesthetic and functional reasons; providing this protection is an added hassle and expense. Insulating the inside allows the insulation to be continuous from the slab to the floor framing, but puts the thermal mass outside the insulation.

Learn more in the Green Building Encyclopedia

Enclosure overview
Crawl spaces
Footing Drains

DRAWING DETAIL

Download: PDF | DWG

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