The Air Barrier Comes Free With The Insulation
On a conventional build the insulation and the air barrier are separate things installed by separate trades, and the air barrier is a sheet product that has to be lapped, taped and kept intact through the rest of the build.
Every service penetration afterwards is a hole in it. Every trade on site is a chance to tear it.
Foam is an air barrier as it is installed. It goes in as a liquid, expands into the actual shape of every cavity, and hardens there. The airtightness result is a property of the insulation rather than something chased afterwards with tape.
Zone 6, And What The Targets Ask For
New Brunswick is in climate zone 6. Current residential energy provisions push on both insulation levels and airtightness, and the airtightness side is the harder one to hit with conventional assemblies.
Where the build is being assessed on measured airtightness, foam is the straightforward route to the number, because the assembly is continuous by the time the gun leaves the room.
We specify depth against the target and the cavity available, and we put the assumed depth on the quote next to the R-value. Anybody quoting an assembly R-value without the depth it assumes is quoting a wish.
Hybrid Assemblies
Full-depth foam is not always the best value in a new wall.
A common approach is a flash coat of closed cell against the sheathing, thick enough to act as the air and vapour control, with the rest of the cavity filled with something cheaper.
That gets the continuous air barrier and the vapour control where they belong, at the cold side, and puts the remaining R-value in at lower cost. Whether it suits a given wall depends on the assembly and the target, and we will run both options past you rather than defaulting to the larger job.
Sequencing, Which Matters More Than The Product
Foam goes in after rough-in and before boarding. That window is narrow and everything downstream depends on it.
We book against the framing schedule rather than a date picked in advance, and we would rather be told a week late than have a crew arrive to a building that is not ready.
Roof deck, walls, rim joists and any cantilevered floor should be planned together. Doing them as separate visits costs more and leaves joins between them.