New Home Air Barrier Checklist for Ontario: The Air Barrier Drawn as One Continuous Line, the Details at the Rim, the Windows, the Ceiling and the Service Penetrations, and the Blower Door Target to Write Into the Contract

Three places the pencil lifts on every frame house

The rim joist, the top of the wall, and the windows. The rim joist is the band of lumber between the foundation and the first floor, with the floor joists running into it, and on a 1,000 sq ft footprint it is 128 linear feet of joints between wood, concrete and more wood. The top of the wall is where the wall poly is supposed to meet the ceiling poly and almost never does, because the partitions went up first and the ceiling poly was cut around them. The windows are where the wall’s air barrier has to turn the corner, meet the window frame and be sealed to it, and most of the time a bead of low-expansion foam is counted as sealed.

The blower door guide explains why these three are where most of a new house’s ACH50 comes from, and the three-layers page explains why the air barrier does not have to be the poly: taped sheathing on the outside is easier to make continuous, and the poly can go back to being just the vapour barrier.

The checklist, footing to ridge

1. Under the slab. 6 mil poly over the under-slab foam, lapped and taped, turned up and sealed to the foundation wall, sealed around the sump and every pipe through the slab. This is also the radon barrier; the radon rough-in page covers the rough-in the OBC requires and why the slab edge matters.
2. The sill plate. A foam sill gasket under the plate, and acoustical sealant or a bead of foam between the plate and the concrete on the inside. On ICF the plate sits in the concrete and the joint is the one seam to seal.
3. The rim joist. 2 in. of closed-cell foam over the whole band, the joist ends and the top of the foundation wall, $4 to $7 a linear foot, default $5.50; 128 lf is $704. Batts stuffed in the rim bays are insulation over a hole. The basement section has the cut-and-cobble alternative.
4. The wall. Either the sheathing taped at every seam and sealed to the sill and the top plate, or the poly inside sealed at every lap, plate and box with acoustical sealant and tape, $0.50 a square foot. Pick one and finish it. Both, half done, is neither.
5. Every window and door. The rough opening sealed to the frame all the way around with low-expansion foam, and then the inside face of that foam sealed to the wall’s air barrier with tape or sealant. The foam alone shrinks and cracks; the tape is the seal.
6. Electrical boxes on exterior walls and the ceiling. Airtight boxes with a flange the poly seals to, or poly hats behind standard boxes sealed to the sheet, $4 a box in gaskets at the very least. Thirty boxes is the equivalent of a fist-sized hole if they are left alone.
7. The top of the wall and the partitions. A strip of poly laid over every partition top plate before the partition goes up, so the ceiling poly can lap onto it and be sealed. This one costs an hour of forethought and is the single detail that separates a 2.5 house from a 4.
8. The ceiling. 6 mil poly over the whole ceiling under the trusses, sealed to the wall poly or the top plates, sealed at every duct boot, bath fan, plumbing stack, wire and pot light. IC-rated airtight pot lights or none; the attic section covers the fixtures and the hatch.
9. The attic hatch or stair. Gasketed, latched, insulated to the attic value. A pull-down stair gets an insulated box over it, $350.
10. The garage wall and ceiling. The garage is outside. The wall between it and the house, and the ceiling under a bedroom over it, get the full air barrier plus the fire separation, and the door gets weatherstripping and a closer. This wall leaks exhaust into bedrooms when it is done badly.
11. Service penetrations. The gas line, the hydro mast, the water service, the dryer vent, the HRV ducts, the range hood, the central vac, the outdoor taps: each one sealed where it crosses the barrier, not just where it crosses the siding.
12. The chimney and flue chase. Sheet metal collar at the ceiling, sealed to the poly with high-temperature sealant, with the insulation held 3 in. (75 mm) off the flue by a metal dam.

What the test should read, and when to run it

SB-12 lets a builder take an air-tightness credit in the compliance package, and the credit is earned with a blower door at or near completion reading about 2.5 to 3.0 ACH50; ENERGY STAR for New Homes wants 2.5. Those are the numbers to write into the contract: “blower door test at completion, result at or below 3.0 ACH50, report to the owner”. A builder who will not sign that is telling you something. The ICF houses I build test well under 2, and the number is in the contract because concrete walls make it an easy promise.

Run a rough test too, with the windows in, the ceiling poly up and the rim foamed, before the drywall. It costs $300 to $450 and it is the last day the holes can be reached with a caulking gun instead of a drywall saw. The technician walks the house with the fan on and a smoke pencil and the crew follows with the sealant. The finished-house number is always better than the rough one. Then the heat-loss design gets the tested number: air leakage is an input, and OntarioHeatLoss.ca sizes the furnace or heat pump and the HRV from it rather than from a rule of thumb.

Where builders go wrong, in order of how often I see it

The partition tops with no poly strip, so the ceiling poly is cut around every interior wall and taped to nothing. The window foam with no tape over it. The rim joist stuffed with batts because the foam crew was not booked and the floor went on. Poly on the walls sealed with staples and good intentions. The hatch with no gasket. The garage door to the house with no weatherstrip. None of these are expensive to do right on the day; all of them are expensive a year later. The SB-12 page explains the compliance sheet that names the package, and that sheet is where you check whether the credit was taken, because if it was, the test is owed.

On a frame house the air barrier is a hundred decisions by six trades. On an ICF house it is one pour and a lid. That is the honest reason my houses test where they do, and it is most of what the ICF air sealing article is about.

Questions people ask

Sources and further reading

• Ontario’s Building Code: the official page with the current regulation; vapour barriers are 9.25, attic ventilation 9.19, thermal barriers over foam 9.10.17, radon 9.13.
• Ontario’s Building Code, Supplementary Standard SB-12: the energy-efficiency packages that set the R-values for attics, walls, basements and slabs in a new or renovated Ontario house.
• Keeping the Heat In: Natural Resources Canada: the plain-language Canadian guide to air sealing, insulation materials, basements, walls and ventilation.