Existing band joist insulation retrofit with 1 1/2" rigid insulation

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.

RIGID INSULATION

Rigid foam is a versatile and effective type of insulation that can be used in walls, roofs and foundations. Even the least thermally efficient variety of foam has a higher R-value than fiberglass or cotton batts and blown-in fiberglass or cellulose.

There are three types of foam board—expanded polystyrene, extruded polystyrene and polyisocyanurate. Key differences are R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. per inch, water resistance, compressive strength, how permeable they are to water vapor, available facings and, of course, their cost.

Board insulation is manufactured with the help of a “blowing agent” that creates tiny bubbles in the foam which slow down the flow of heat. Manufacturers of expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.) and polyiso board use hydrocarbon blowing agents that don’t damage the earth’s ozone layer. A switch away from the ozone-damaging hydrofluorochlorocarbons (HFCFs) used to make extruded polystyrene (XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation.)is not expected to take place until 2010, giving this type an environmental disadvantage for the time being.

Expanded polystyrene. The least expensive of the three, EPS can be manufactured in different densities to increase its compressive strength but it’s still not as strong as extruded board and it’s more susceptible to crumbling at the edges and to other job-site damage.

R-value: About 4 per in.

Permeance: 2 to 5, depending on the density of the board.

Extruded polystyrene. Because of it shigher strength and water resistance, XPS is often used below grade to in-sulate slabs and foundation walls.

R-value: About 5 per in.

Permeance: 1.1 per in. up to 2 in. then 0.55 per in.

Polyiso. With higher insulating values and no ozone-depleting blowing agents, polyiso board has some advantages over XPS for above-grade use (it’s not recommended for below-grade applications because it can absorb water). Polyiso often comes with a foil facing, which gives the material a very low vapor permeance.

R-value: up to 6.5 per in.

Permeance: 0.03