Attic Insulation In Cape Breton, Nova Scotia

Cold Attic Or Warm Attic

The first approach leaves the attic vented and cold. Every penetration through the ceiling below is sealed, then insulation goes over the top. It suits a straightforward roof with nothing mechanical stored above the ceiling.

The second folds the roof space into the warm building. Foam goes beneath the sheathing and up the gable ends, and the venting is shut off.

Go warm where ducting or an air handler lives above the ceiling, where dormers and valleys chop the roof into sections, where knee wall space hides behind a finished room, or where ice returns to the overhang year after year.

Which one your roof wants is a decision made after somebody has been inside it.

The Overhang Is Where Vented Attics Come Undone

There is a failure that shows up hard on exposed sites. Outside air enters at the soffit and works through and around loose fill and batts, worst of all at the overhang, where the material tapers to almost nothing.

Wind washing is the term. The material is still sitting where it was installed. It is no longer doing much.

Foam is not vulnerable to it, because air cannot travel through the material. Applied under the sheathing, there is no vented attic for wind to reach. Where a cold attic is the correct approach, we baffle each rafter bay and seal the overhang so incoming air stays in its channel.

Ice At The Overhang Is A Heat Problem

Ice at the edge of a roof is not a drainage fault. Warm air escaping into the attic melts snow higher up, the meltwater runs down onto the unheated overhang and freezes there, the ridge of ice grows, and water starts backing up beneath the shingles.

Piling on more insulation does not always cure it, because the mechanism is escaping air rather than conducted heat. Sealing the ceiling below, or shifting the insulation up to the sheathing, removes the heat that starts it.

Ice in the same place two winters running is worth investigating properly.

Depth, Resistance And Straight Answers

Closed cell delivers roughly R-6 to R-7 an inch, easing toward R-6.5 with age. Open cell delivers roughly R-3.5 to R-3.8.

This province sits in climate zone 6, and current residential targets are demanding, so the depth follows from the target and the space available rather than from a figure chosen in advance.

We will not give you an assembly resistance figure without telling you the depth it assumes. If anyone else does, that is worth questioning.