Can New Brunswick walls be filled from outside?

Yes, NB walls can absolutely be filled from the outside — this is called exterior drill-and-fill, and it's one of the most common wall insulation retrofit methods used in New Brunswick.

The process involves drilling a series of holes through the exterior siding (typically 1.5 to 2 inches in diameter), inserting a fill tube into each stud cavity, and blowing dense-pack cellulose or fibreglass at high density until the cavity is completely packed. The holes are then plugged and the siding is patched. When done properly, the repair is nearly invisible on most siding types.

Why exterior drill-and-fill works well in NB

Dense-pack cellulose is the most popular material for this application in New Brunswick. Blown in at 3.5 pounds per cubic foot or higher, it fills every corner of the stud cavity, conforms around wiring and blocking, and provides meaningful air sealing in addition to the R-value — typically R-13 to R-15 in a standard 2x4 wall cavity, or R-20 to R-22 in a 2x6 wall. That air sealing benefit is significant in NB's cold Maritime climate, where wind-driven infiltration through unsealed wall cavities is a major source of heat loss and discomfort.

The exterior approach is almost always preferred over drilling from the interior because it avoids disturbing drywall, paint, trim, and interior finishes. In a lived-in NB home, that's a major practical advantage. The trade-off is that the siding must be in reasonable condition and compatible with the drilling and patching process.

Siding compatibility matters

Wood clapboard, vinyl, and fibre cement siding all handle exterior drill-and-fill reasonably well. Vinyl siding is actually the easiest — the contractor can often remove individual boards temporarily, drill the sheathing behind them, fill the cavities, and reinstall the boards without any visible patching at all. Wood clapboard requires careful drilling and colour-matched plugs. Brick veneer is more complex — holes must be drilled through the mortar joints, which requires a skilled contractor and careful patching to maintain the appearance.

One important building science note for NB homes

When filling walls from the exterior, the existing vapour barrier on the interior side of the wall (if there is one) remains in place — which is exactly where it should be in Climate Zone 6. The dense-pack cellulose goes into the cavity between the vapour barrier and the exterior sheathing, which is the correct assembly for NB's cold climate. If your home was built without a proper interior vapour barrier (common in pre-1970s NB construction), discuss this with your contractor before proceeding — the wall assembly needs to be able to manage moisture, and the solution may involve a smart vapour retarder or a different approach depending on the wall construction.

What to expect cost-wise

Exterior drill-and-fill for a typical two-storey NB home runs roughly $2,500 to $6,000 depending on house size, siding type, and access. This is significantly less expensive than adding exterior continuous insulation with new siding, which can run $15,000 to $35,000 or more. For most NB homeowners who aren't planning to replace their siding, drill-and-fill is the most cost-effective way to get insulation into existing walls.

This work also qualifies for NB Power's Total Home Energy Savings Program and the Canada Greener Homes Grant — but you must get your pre-retrofit EnerGuide evaluation completed before any work begins. Don't skip that step or you'll lose eligibility for up to $10,000 in combined rebates.

Exterior drill-and-fill is a job for an experienced professional with the right blowing equipment to achieve proper density — underblown cavities settle and leave voids that defeat the purpose. New Brunswick Insulation can match you with local contractors who specialize in this type of retrofit through the New Brunswick Construction Network directory at newbrunswickconstructionnetwork.com/directory?category=insulation.