By Trevor Parsons
Most homes and buildings are constructed from a palette of building components. After a cast concrete foundation come a dimensional lumber platform, walls, trusses and roof. The choice of traditional building components comes from hundreds of years of building experience. Similarly, basic building efficiency is achieved using many basic components used knowledgably in combination. Much has been written on ideal sets of components for very low-energy buildings. This article focuses on a few common problem areas often found in existing homes.
A foundation or slab edge is one of the most effective places to add insulation. Concrete and stone make terrible insulation, yet are often uninsulated. The most recent Vermont Residential Building Energy Code insists on R-15 (3” of extruded polystyrene) a full four feet down from top of slab. New denser mineral-wool products from Roxul and foamglass provide wonderful non-foam alternatives, both above and below grade. Older homes may require soil assessment and site drainage may need to be addressed. Once drainage concerns are met, two-part spray foam makes for a form-fitting seal.
Box sills, where the floor joists intersect the exterior walls, are crucial. In the past, stuffing some pink fluffy stuff in was considered sufficient. Insulating the box sill with foam improves both insulation and air sealing greatly. A common method in new construction is to use two-part spray foam to insulate and seal the box. A method I’ve used on numerous personal projects is cutting and fitting pieces of high-R foam board a full inch undersized in both directions, allowing me to apply a picture-frame of spray foam for the final seal.
Many buildings have internal walls dividing heated and unheated space. Two examples are the wall dividing the heated part of a house from an attached garage and a floor extending over an unheated space. These walls are often poorly insulated. A variation on the same theme can be found on raised ranches where the second floor protrudes over the first. Often those bays have little air sealing and are insulated only with fiberglass. High-R board foam can be inserted into each bay and sealed with caulk or expanding foam.
Knee walls on second story homes are often worth improving. Roof insulation should extend to the true exterior wall. A common symptom of a poorly insulated knee wall is spots in the snow on the roof melting, or even ice dams.
Adding attic insulation is a clear way to improve a house’s energy profile. Air sealing the attic plane is essential to guarantee that savings are realized and moisture problems avoided. All penetrations through the attic floor should be sealed using expanding foam or caulk. Large chases such as wet walls or plumbing chases should be sealed with board foam. All electrical boxes should be sealed using expanding foam. Occasionally you will find a balloon-framed wall passing through the attic floor; those cavities should be plugged with board foam and expanding foam. Remember, loose fill insulation acts only as an air filter, not as an air barrier. Attic hatches should be weather-stripped and fitted with foam board to same level of insulation as the attic floor.
Trevor Parsons works for Housing Vermont, a statewide non-profit affordable housing developer. Green Energy Times is grateful for both his help to us and his commitment to energy efficiency. Buildings are one of the two biggest contributors to the CO2 in our atmosphere. Making them efficient is of utmost importance for both the planet and your wallet!