Basement Insulation Retrofit. 3/4-in. Rigid Foam and Insulated Framed Wall (2x4)

The toughest details are those that have to match up with someone else's work, or those done — even done well — when energy was really cheap. These details are a collection of some common — and tough — dovetails of existing work with retrofits or additions. Bear in mind that green remodeling means creating a new operating regime that is better, not worse, than the one that may well have been working just fine before. Integration of energy efficiency, moisture management, and indoor air quality is much more important and challenging in remodeling than in new construction.

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.

Manage the moisture in an old house

Existing foundation walls (and basement floors) are sometimes wet, usually damp, and seldom dry. Rarely do they have perimeter drainage systems, 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 between masonry and wood (or soil) or insulation. To raise the performance of existing foundation and basement floors, you have to make them manage moisture BETTER than they currently do because you are going to insulate and air seal them, significantly decreasing their drying potential. shows more than a half dozen different retrofit basement wall insulation systems. The critical aspect is almost always what level of water or vapor the wall must manage as it increases thermal performance of the basement.

Foundation walls cannot dry to the outside

Because basements 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.

Basements are likely to become living space

Even if a basement is not intended to be used as a finished space, it's best to assume that it may be finished in the future. That's why it's a good investment to upgrade from damp-proofing to a true waterproofing system when the basement is built. Part of this is insulating under the slab for comfort, condensation reduction, and to save some energy.

Insulation on the inside or outside? Crawl space and basement 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 insulation on the outside needs to be covered for aesthetic and functional reasons. Insulating the inside allows the insulation to be continuous from slab to floor framing, but puts the thermal mass outside the insulation.

Learn more in the Green Building Encyclopedia

Enclosure overview
Footing Drains

Learn more in the Green Building Encyclopedia:

Water management
Enclosure Overview
Foundation Drains


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