Can I blow insulation into my wall cavities through small holes in Saint John NB? | Insulation IQ?

Yes — blowing insulation into existing wall cavities through small holes is a well-established retrofit technique used widely in older Saint John homes and throughout New Brunswick. It's called dense-pack insulation when done properly, and when executed correctly it's one of the most cost-effective ways to improve the thermal performance of an older home without a major interior or exterior renovation.

The most common materials used for this application are blown-in fibreglass (such as Spider or similar loose-fill products), dense-pack cellulose, and injection foam (two-component slow-rise polyurethane). Each has a different performance profile and is suited to different situations.

Dense-pack cellulose is the most widely used option for this type of retrofit in Atlantic Canada. It's made from recycled paper fibre treated with borate for fire resistance and mould inhibition. When blown into a closed wall cavity at high density — typically 55 to 65 kg/m³ — it creates a mass that resists further settling and provides meaningful air resistance in addition to its thermal properties. Cellulose achieves roughly R-3.5 per inch, so a standard 3.5-inch (89mm) 2x4 cavity achieves R-12 to R-13, and a 5.5-inch (140mm) 2x6 cavity achieves R-18 to R-19. This is a significant improvement over an empty or minimally insulated cavity.

Dense-pack fibreglass (not the same as loose-fill attic fibreglass) is blown at similar density and performs at roughly R-4.2 per inch — slightly better thermally than cellulose and less susceptible to moisture absorption, which is relevant in Saint John's coastal climate with its higher humidity levels and salt-air exposure. It's generally slightly more expensive than cellulose but preferred by many contractors for below-grade or high-moisture adjacent assemblies.

Injection foam (slow-rise two-component foam) fills cavities completely with nearly zero settling and excellent air sealing. It achieves R-4 to R-5 per inch and is particularly well-suited for complex cavity geometries with fire blocking, cross-bracing, or irregular framing — common in Saint John's older Victorian and Century homes. It's the most expensive of the three options but delivers the most complete coverage.

The process involves drilling 50mm to 63mm holes at regular intervals — typically every 400mm to 600mm between studs, at mid-wall height — through either the exterior siding (from outside) or the interior drywall (from inside). The installer inserts a fill tube, blows the material to density, withdraws the tube, and plugs the holes. When done from the exterior through wood siding or clapboard, the patches are typically painted over and nearly invisible. Vinyl siding can often be temporarily removed and reinstalled. Drilling from the interior through drywall requires patching and repainting but avoids exterior weather exposure.

Before drilling, a competent contractor should perform a thermal imaging inspection (ideally on a cold day) and sometimes a borescope inspection — inserting a small camera through a test hole — to identify what's in the cavity. Saint John's older housing stock frequently has surprises: knob-and-tube wiring requiring clearance before insulation, fire blocking (horizontal wood blocking midway up the cavity) requiring additional holes, settled or partial insulation already present, and moisture issues that need addressing first. Blowing insulation over active moisture problems can trap moisture and accelerate rot.

Costs in New Brunswick typically range from $2.50 to $5.50 per square foot of wall area for blown-in wall insulation, depending on material choice, access method (interior vs. exterior), cavity dimensions, and the complexity of the existing framing. A typical Saint John two-storey home with 1,200 to 1,500 square feet of exterior wall area might expect a total project cost of $3,500 to $8,000.

The Canada Greener Homes Grant can offset costs for wall insulation improvements when combined with an EnerGuide assessment, and NB Power rebates may apply. Given Saint John's significant heating load and the large stock of older, under-insulated housing, the payback on this type of project is often 8 to 12 years even without grants factored in.

For Saint John homeowners considering blown-in wall insulation, the listings on New Brunswick Insulation connect you with contractors experienced in retrofit insulation techniques suited to the city's unique older housing stock.

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Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• 3Tone Construction Ltd
• Brunswick insulation & roofing
• Thirty Four Renovations
• Gionetterenovations
• Arctic Fox Construction Inc.