Drill and Fill Insulation for Older Homes in Canada: How Dense-Pack Cellulose Retrofits Work

Hey everyone, Russell here from Greenfoot Energy Solutions. I'm standing in front of an older Maritime home that has absolutely no wall insulation. The exterior is two-by-four rough lumber stud framing, the interior is the original plaster and lath, and the cladding is alpine clapboard. Tens of thousands of Canadian homes built before the 1960s look almost exactly like this one, and almost none of them have insulation in the walls. The good news: we can fix that in about a day, from the outside, without touching your interior finishes.

What Is Drill and Fill Insulation?

Drill and fill, sometimes called injection insulation or dense-pack retrofit, is a technique for adding insulation to existing wall cavities without removing the interior wall. The crew works from the exterior of the home, removes a single row of siding, drills small access holes into each stud bay, and blows loose-fill insulation under pressure until the cavity is packed solid. The holes are plugged, the siding goes back on, and from the curb you would never know we were there.

It is the standard retrofit method for older Canadian housing stock because it solves the one problem that stops most homeowners from insulating their walls: you do not have to tear out the plaster, the lath, the trim, or the wallpaper. Natural Resources Canada's Keeping the Heat In guide highlights wall cavity retrofits as one of the highest-impact upgrades available to older homes, and most rebate programs across NB, NS, PEI, NL, and BC will pay you back a meaningful chunk of the project.

Why Do So Many Older Canadian Homes Have No Wall Insulation?

Wall insulation simply was not part of standard Canadian home construction until the late 1950s and early 1960s. Cheap fuel, smaller homes, and no national building code meant builders framed up two-by-four rough lumber walls, nailed lath strips to the inside, troweled on plaster, and called it done. The cavity behind that plaster was just air, and air is a poor insulator the moment any wind, stack effect, or temperature difference is involved.

In the Maritimes specifically, the housing stock skews old. Statistics Canada census data shows roughly one in three homes in New Brunswick, Nova Scotia, Prince Edward Island, and Newfoundland and Labrador was built before 1960. That means hundreds of thousands of houses are still operating with bare wall cavities behind original plaster and lath. If yours is one of them, you are likely losing 20 to 35 percent of your heating energy straight through the walls.

How Does the Drill and Fill Process Actually Work?

Here is the step-by-step we follow on a typical Greenfoot drill and fill job, the same one you can see Russell walking through in the video above.

1. Remove a single row of siding. Usually one course of clapboard or vinyl is carefully pried off and set aside. The rest of the cladding stays in place.
2. Map every stud bay. Crews use tape measures and stud finders to locate every cavity left, right, up, and down, including the partial bays around windows, doors, electrical boxes, and fire blocking.
3. Drill access holes. A small hole (typically 50 to 65 mm) is drilled into each cavity at the right height to let the insulation fill the entire bay.
4. Dense-pack the cavity with cellulose. A high-pressure blowing machine packs treated cellulose into the cavity at roughly 3.5 lb per cubic foot. That density is the magic number: it stops the insulation from settling years later, and it dramatically reduces air movement inside the wall.
5. Plug the holes with spray foam. Once the cavity is full, we plug the access hole with a small dab of spray foam insulation. Spray foam expands, seals the hole airtight, and bonds to the surrounding wood.
6. Trim flush, tape, and reinstall the siding. The cured spray foam plug is cut flush with the cladding, taped to keep everything tight, and the original siding row is reinstalled.

Most single-storey Maritime bungalows can be done in a single day. A typical 1.5- or 2-storey home takes one to two days depending on access and wall area.

Why Cellulose Instead of Spray Foam or Fibreglass?

For an exterior drill and fill on existing walls, dense-packed cellulose is almost always the right choice. Here is why:

• It actually fills the cavity. Cellulose blown at 3.5 lb/ft³ flows around old wiring, blocking, plumbing, and the irregularities of rough lumber framing. Batt insulation cannot do that without removing the wall.
• R-value that performs in the real world. Cellulose delivers about R-3.7 per inch, so a typical 3.5-inch 2x4 cavity hits roughly R-13. More importantly, the dense pack stops convective looping inside the wall, which is what makes empty walls feel so cold even when builders later staple in fibreglass.
• Made from 80%+ recycled paper and treated with borates for fire and pest resistance. Lower embodied carbon than mineral wool or spray foam, and one of the most environmentally friendly insulations sold in Canada.
• Manages moisture better than foam in old walls. Older homes need to dry to the inside or outside. Closed-cell spray foam in a wall cavity can trap moisture against the original sheathing and accelerate rot. Cellulose is hygroscopic, meaning it can buffer small amounts of moisture and release it harmlessly.
• Cost. Drill and fill cellulose is typically 30 to 50 percent cheaper per square foot than injection foam, with comparable real-world performance in a retrofit cavity.

For new construction, additions, or rim joists where you can access the cavity from one side, closed-cell spray foam is often the better tool. For attics, loose-fill blown-in is the standard. Drill and fill is a third, very specific tool for the job of insulating existing walls.

What Does Drill and Fill Actually Save You?

Going from no wall insulation (effectively R-2 to R-3 from the cladding and plaster alone) to a dense-packed R-13 cavity is one of the biggest single energy upgrades available to an older Canadian home. Real-world results we see across Atlantic Canada and BC:

• 15 to 25 percent reduction in annual heating costs, depending on fuel source and home size.
• Walls that no longer feel cold to the touch, eliminating the cold drafts that radiate off bare interior plaster all winter.
• Quieter rooms. Dense-pack cellulose is one of the most effective wall sound dampeners on the market, a real bonus in semi-detached homes or on busy streets.
• A right-sized heat pump. If you are planning a cold-climate heat pump install, insulating the walls first lets us spec a smaller, cheaper, more efficient unit that runs less and lasts longer.

Which Canadian Rebates Apply to Drill and Fill?

Most provincial energy programs treat dense-pack wall insulation as a top-tier eligible upgrade, often with the highest per-square-foot rebate of any retrofit. Current programs we work with:

• New Brunswick: The NB Power Total Home Energy Savings Program offers up to $1,750 in insulation rebates, with wall insulation among the eligible measures.
• Nova Scotia: Efficiency Nova Scotia's Home Energy Assessment rebates wall, attic, and basement insulation upgrades, typically up to $1,500.
• Prince Edward Island: The PEI Home Energy Assessment covers up to $1,500 in insulation upgrades for eligible homes.
• Newfoundland and Labrador: takeCHARGE programs rebate up to $3,000 in insulation work for eligible homes.
• British Columbia: CleanBC Better Homes and FortisBC together can deliver up to $5,500 toward a wall insulation upgrade.

Most of these programs require an EnerGuide pre- and post-evaluation by a registered Energy Advisor. Greenfoot can quarterback that process for you: booking the audit, doing the work, filing the paperwork, and getting the rebate cheque in your mailbox.

Is Drill and Fill Right for Your Home?

Drill and fill is almost always the right call when:

• Your house was built before about 1965 and has plaster-and-lath or original drywall interior walls.
• A pre-retrofit blower door or thermal scan confirms the wall cavities are empty or have only loose fibreglass that has settled.
• You have removable cladding (clapboard, vinyl, aluminum, or wood shingle) that we can pull a row of without damaging it.
• The exterior sheathing is in good shape (no widespread rot, no failed flashing).

It is usually not the right call for solid-brick homes without an air gap, log homes, or homes where the cavity is already filled with intact insulation. In those cases an exterior continuous insulation upgrade or a different approach makes more sense, and our Energy Advisors will tell you that up front instead of selling you something that will not perform.