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Insulating Older Homes in Ontario: Pre-1970 Houses With Empty Walls, Balloon Framing, No Vapour Barrier and Plaster, Where the Money Goes First and What Each Step Costs
Insulation & Air Sealing
Insulating an Older House: The Walls Are Empty, the Attic Leaks Like a Colander, and the First $7,000 Should Not Go Where You Think
A house built in Ontario before about 1970 was built to be heated, not to hold heat. The walls are 2×4, often with nothing in them at all, or a few inches of rock wool or sawdust that settled to the bottom of the bay in 1962. The attic has 3 in. of something. There is no vapour barrier anywhere, because nobody had thought of one, and the house has stayed dry for seventy years for exactly that reason. The basement is stone or block with the floor joists sitting on it in open air. It is a drafty, honest house, and it can be made to hold heat for about the price of a used car if the money goes in the right order. Here is the order.
What you are dealing with
Balloon framing, common to about 1940, runs the wall studs in one piece from the sill plate in the basement to the top plate under the attic. Every stud bay is a chimney from the basement to the attic, open at both ends, and that is where the heat goes: basement air rises up the wall cavity and out into the attic all winter, carrying moisture with it. Platform framing, from the 1940s on, breaks the bays at each floor, but the top plates still leak into the attic the way they do in any frame house. The pre-1970 house adds no air barrier of any kind, plaster and lath inside, board sheathing with gaps outside, and windows that rattle.
Inside the walls, in Simcoe County, I find in roughly this order: nothing; a settled slump of rock wool in the bottom third of the bay; sawdust; and once, newspapers from 1931. The walls were never designed to be insulated and they have dried in both directions for their whole life. That is the fact behind the vapour barrier question below.
The stops, before anything is bought
An older attic has three things that stop the job before it starts, and they are checked from the hatch with a flashlight before the first quote. Vermiculite, the grey-gold pebbles, is left alone until a lab test says what it is, and nobody blows anything over it. Knob-and-tube wiring, the single wires on porcelain knobs, cannot have insulation placed over or against it; the electrician comes first. And wet or mouldy insulation, common on a house with a fan venting into the attic or a roof that leaked in 1998, comes out and is not buried under new insulation. The fourth stop is in the basement: a wet wall, efflorescence or standing water at the floor is fixed before anything is put against it.
Where the money goes, in order
- Attic air sealing, first and alone if that is all you can do this year. On a balloon-framed house the tops of the wall bays are open to the attic and have to be blocked with cut foam board before the top plates can be sealed. Then the stacks, the wires, the chimney dam at 3 in., the bathroom fan run out through the roof, the hatch. $0.75 to $1.50 a square foot, $600 minimum, the top of the range on a balloon frame. The highest-return thing on the page, and the one most contractors skip.
- Attic to R-60. Over dry clean old fill, a top-up at $0.065 per R-point added; from R-10 to R-60 is 50 points, $3.25 a square foot. From bare joists after a removal, $3.75. Baffles in every bay first, $3.50 each, and on a house with no soffit vents at all the ventilation has to be made before the attic is filled or the roof deck sweats.
- The basement rim joist and sill. On a stone or early block wall the sill plate sits on an uneven top with daylight in places, and the rim is the leakiest part of the house. 2 in. of closed cell foam in each bay, including the top of the wall, at $5.50 a linear foot, with backing where the bays are open to the floor above. This is the one place in an old house where foam is plainly the right answer.
- The basement walls, if the basement is dry. Rigid foam against the concrete, taped, 2 in. R-10 at $3.50, or closed cell at 3 in. for about $4.25, then a stud wall if the basement is to be finished. Batts alone against a stone wall fill with water by March. The basement wall page has the assemblies.
- The walls, last, by drill-and-fill. Dense-pack cellulose blown through 2 in. holes from outside under the siding or inside through the plaster, one hole per bay per storey, $2.50 to $4.00 a square foot of wall, default $3.25, plus patching. It packs to about 3.5 lb per cubic foot, which slows air as well as heat, and it is the one wall insulation that works in a closed cavity. The empty 2×4 wall goes from about R-4 to about R-11 effective, and you feel the difference the first night.
The vapour barrier you do not have, and probably should not add
Every pre-1970 wall in Ontario has dried inward in summer and outward in winter for its whole life with no poly in it, and it is still standing. Dense-packing it with cellulose does not change that; cellulose is vapour-open and holds and releases a little moisture without harm, which is why it is the right product for a wall you cannot put a vapour barrier in. What you do instead is make the inside surface vapour-slow with two coats of good primer and paint on the plaster, keep the house humidity sane, and seal the air leaks at the baseboards and outlets, because air carries far more moisture into a wall than diffusion does.
Where people go wrong is gutting a room, putting R-14 batts and poly in a 2×4 wall with board sheathing and no house wrap, and sealing a wall that used to dry both ways so it now dries neither. If a room is gutted, the better move is 2 in. of closed cell on the back of the sheathing and a batt in front, the flash-and-batt wall at about $3.60 a square foot, which puts the air and vapour control at the sheathing and lets the inside dry inward; the flash and batt page has the condensation arithmetic. Bare foam in a living space gets its drywall before anyone moves back in.
A 1950s bungalow priced in order
1,200 sq ft bungalow, 1954, platform frame, 3 in. of settled rock wool in the attic at about R-10, empty 2×4 walls, block basement, dry, unfinished, 140 lf of perimeter, 1,100 sq ft of net wall above grade. Attic air sealing with the chimney dam, fan rerouted and hatch gasket, 1,200 at $1.25 is $1,500; baffles $300; insulated hatch $200; cellulose top-up from R-10 to R-60, 1,200 at $3.25 is $3,900. Attic $5,900. Rim joist and sill, 140 lf at $5.50 is $770, with the foam minimum covered because the basement walls are done the same day: 2 in. rigid foam on 1,120 sq ft of block, taped, at $3.50 is $3,920. Basement $4,690. Walls, drill-and-fill through the siding, 1,100 at $3.25 is $3,575, plus the patching. Total $14,165 before HST, $16,006 with, with the walls last and skippable if the money runs out, because the attic and the rim did most of the work.
A blower door on a house like this reads 8 to 15 ACH50 before and typically a third less after the attic and rim, with the walls taking it further. On propane or oil the payback on the attic alone is a few winters; on gas it is longer; on either the cold bedroom stops being cold. The EnerGuide evaluation is worth having first on a house like this, because the assessment path of the rebate program is the only way the walls and basement see any rebate at all; check the program site before you sign.
A tightened old house needs its ventilation looked at after the work: the bathroom fans that were venting into the attic now go outside, the kitchen needs a real exhaust, and an oil furnace or a natural-draft water heater in a basement that is suddenly tight can backdraft. An HRV is the usual answer and the sizing comes from a stamped heat-loss design, which is what OntarioHeatLoss.ca does; the too-airtight page covers what to check.
Questions people ask
What is the best way to insulate an old house in Ontario?
In order: air seal the attic, including blocking the open wall bays on a balloon frame; take the attic to R-60; foam the rim joist and sill; insulate the basement walls with foam against the concrete if the basement is dry; and last, dense-pack the walls with cellulose by drill-and-fill. The attic and rim do most of the work for the least money.
Should I add a vapour barrier to an old house?
Usually not in a closed wall. A pre-1970 wall has dried both ways its whole life; dense-pack cellulose keeps that and a good paint on the plaster slows vapour enough. If a room is gutted, closed cell foam on the sheathing with a batt in front is the better wall. Poly over batts in a 2×4 wall with no house wrap outside is the assembly that rots.
How much does it cost to insulate the walls of an old house?
Dense-pack cellulose by drill-and-fill, $2.50 to $4.00 per sq ft of wall plus patching, about $3,575 for the 1,100 sq ft of wall on a 1950s bungalow. It takes an empty 2×4 wall from about R-4 to about R-11 effective and slows the air through it. Gutting with foam and batts costs several times that and is only worth it if the room is open anyway.
What is balloon framing and why does it matter for insulation?
Framing to about 1940 where the studs run from the basement sill to the attic plate in one piece, so every wall bay is an open chimney from the basement to the attic. The tops of the bays have to be blocked and sealed before the attic can be air sealed, and the bays themselves are what drill-and-fill cellulose is for.
Is there a rebate for insulating an older home in Ontario?
The standalone attic rebate, up to $1,250 for an attic at R-12 or less taken to R-50 or more by a contractor on the participating list, if the house qualifies. The walls and basement only see a rebate through the assessment path with an EnerGuide evaluation before and after. Nothing is deducted from the price; it comes afterward, and the program site is checked before signing.
Start with the attic number
The attic insulation cost calculator prices the first and biggest step, with the air sealing, baffles, hatch, removal, HST and the rebate check as their own lines, so you can see what the attic costs before the rest of the house is on the table. If you have quotes for the whole house and they start with the walls, the $99 review will say why the order is wrong and what to do first.
Sources and further reading
- Keeping the Heat In: Natural Resources Canada: the plain-language Canadian guide to air sealing, insulation materials, basements, walls and ventilation.
- Canada Mortgage and Housing Corporation: the Canadian research on basement moisture, wall assemblies and ventilation that these pages lean on.
- Building Science Corporation: the cold-climate basement, wall and roof assembly guidance that explains where the condensation goes and why foam goes against the concrete.
