Wall Insulation, Drill & Fill

Why walls are the hard one

An attic is an open floor you can walk on. A wall is a sealed box you cannot see into, and the only honest way to insulate it is either to open it up or to fill it through small holes. Opening it up means drywall, paint, trim and a month. Filling it means a drill, a hose and a day.

How the job runs

• We locate the studs and the fire blocking, because a cavity with a blocker halfway up is two cavities and needs two holes.
• Holes are drilled — from outside through siding or brick where we can, from inside where we must. Roughly two inches, one per bay per storey.
• Injection foam goes in wet and expands to fill the cavity, including around wiring and pipes where batts never could.
• Holes are plugged, and the siding, brick plug or drywall patch is made good.

When drill and fill is the wrong answer

We will tell you not to do it if the cavity is already insulated (foam will not push past existing batts), if the wall is a balloon frame with no fire blocking and no way to control the fill, if there is active water getting into the assembly, or if you are replacing the siding within a year — in which case exterior insulation done at the same time is a better assembly for less combined cost.

What the programme pays for walls

Walls are not on the no-assessment stream. Wall insulation only pays through the assessment pathway, which needs an energy advisor before and after, and at least two upgrades together.

Wall upgrade	Maximum rebate
Exterior wall, greater than R–20 added	$3,600
Exterior wall, R–12 to R–20 added	$2,100
Exterior wall, R–7.5 to R–12 added	$1,200
Basement wall, greater than R–22	$1,500
Basement wall, R–10 to R–22	$900
Foundation header (rim joist)	$300

Amounts are set by Enbridge Gas and Save on Energy, quoted here from the programme pages — attic stream and assessment stream — checked 17 September 2026. Programme terms change without notice.

Injection foam into a typical empty 2x4 cavity lands in the R–12 to R–20 band. The higher band generally needs insulation added on the outside of the sheathing, which is a re-cladding job, not a drill-and-fill.

Common questions