Strip the stucco off a 1960s Burnaby bungalow and you can often see daylight through the wall. Not through one hole. Through the gaps between old board sheathing, along the sill plate, and around a dryer vent someone cut in decades ago. That is the case for air sealing during a renovation in BC: once the cladding is off, the leaks an older house has carried for sixty years sit right in front of the crew for about three weeks. Then they get covered again for another forty.
Most homeowners plan an exterior renovation around what they can see: cracked stucco, soft trim, tired siding. Air leakage never makes that list, yet in a typical pre-1980 house it accounts for a quarter to a third of the heat you pay for. It also carries indoor moisture into the wall, which on the coast matters more than the heating bill.
Is air sealing worth doing during an exterior renovation in BC?
Yes, when the cladding is already coming off. Sealing the sheathing, sill plate, rim joists, and wall penetrations from the outside typically adds $3,000 to $7,500 to a single-family envelope project in Metro Vancouver. It usually takes an older home from 8 to 12 air changes per hour at 50 pascals (ACH50) down to 3 or 4, and cuts space-heating energy by roughly 15 to 25 percent. Doing it later means removing the new cladding.
Where older BC homes actually leak
Every era of BC housing leaks in its own way. Knowing which one you own tells you where the money goes.
Pre-1950 character homes in East Vancouver, Kitsilano, New Westminster, and Victoria's Fernwood and James Bay were sheathed with 1x6 or 1x8 boards, often laid diagonally, with building paper or nothing at all behind the siding. Every board joint is a crack. A 2,000 sq ft character house can carry well over half a kilometre of them.
1960s and 1970s houses, including the Vancouver Special, brought plywood sheathing, which helped. Many split-levels and bi-levels from this era also have a cantilevered floor section, and the underside of that cantilever is one of the leakiest spots we open up in Burnaby, Coquitlam, and Richmond. Single-glazed aluminum windows from the period often sit in openings with no air seal at all, just stucco packed tight to the frame.
1980s and 1990s homes usually have better sheathing and polyethylene on the inside. They leak at penetrations: gas lines, exhaust ducts, hose bibs, exterior lights, cable runs, and heat pump line sets added later. Each one is small. Thirty of them add up.
Across all three eras, the same spots come up again and again:
- The sill plate, where wood framing sits on the concrete foundation
- Rim joists at each floor level
- Window and door rough openings
- Service penetrations through the wall
- Sheathing seams and board joints
- Junctions where a wall meets a deck, a bay window, a chimney chase, or a lower roof
What an exterior renovation can't reach
Here is the part most energy articles skip. The biggest single leak in many older houses is not in the walls. It is at the ceiling: top plates of interior walls, pot lights, plumbing stacks, and the attic hatch, all opening straight into a vented attic. Warm air rises, and stack effect pushes it out hardest at the top of the house.
Working from the outside, we can't touch that. We can seal the walls, the rim joists, and the sill, and close the wall-to-roof junction at the top plate where the eave allows it. A realistic exterior-only result on an older house is 3 to 4 ACH50. Getting below 2 usually means pairing the exterior job with attic work, either at the same time or the following summer.
That is not a reason to skip the exterior sealing. It is a reason to know what number to expect, and to be wary of anyone promising Passive House airtightness from a re-clad alone.
Picking the layer that does the air sealing
An air barrier has to be continuous. Think of it as a line you could trace around the whole house with a pen without lifting it. On an exterior renovation, that line usually moves to the outside face of the sheathing, and there are three ways to build it.
Taped sheathing. On plywood or OSB in good condition, every seam gets a high-performance tape and every penetration gets a gasket or boot. It works well, costs the least, and is easy to inspect.
Fully adhered membrane. A self-adhered weather barrier bonded to the sheathing acts as both rain and air barrier. This is our usual pick over board sheathing, where taping hundreds of joints is unreliable. On boards in poor shape, we sometimes overlay new plywood first.
Fluid-applied membrane. Rolled or sprayed on, it handles complex geometry like bay windows and curved walls well. It needs a dry, clean substrate and a crew that checks film thickness, so it is weather-dependent in a BC fall.
Whatever the system, it has to stay vapour-open in our climate. Many older BC homes have polyethylene on the inside, or will get it during a later interior project. A vapour-closed membrane on the outside traps moisture between two impermeable layers, and the sheathing in between pays for it. We specify vapour-permeable products on the exterior of almost every wall we retrofit.
The mistake we see most often is sealant on the wrong layer. Someone runs a bead of caulk around the outside of the stucco or siding, at the trim, the window heads, and the base of the wall, and calls it air sealing. Cladding is designed to drain and dry behind itself. Caulking it shut traps water against the wall and does almost nothing for air leakage, which happens one layer deeper.
The sequence on site, and the three tests
Air sealing is not a separate trade on an exterior renovation. It is a set of steps built into the envelope work, and the order matters. On a typical older single-family house, our building envelope contractor crew works like this:
- Baseline blower door test before demolition, so there is a real starting number. An energy advisor runs it to the CAN/CGSB-149.10 method in about two hours.
- Strip the cladding and inspect. Older walls often hide rot at the sill and under windows. Repairs come first, because sealing over soft wood solves nothing.
- Seal the sill plate and rim joists with gaskets, sealant, or spray foam where the gaps are irregular.
- Build the air barrier across the sheathing: tape, membrane, or fluid-applied, depending on the substrate.
- Detail every penetration with a boot or collar tied into the barrier, and connect window and door frames to it with transition membrane.
- Mid-construction blower door test with the barrier still exposed. This is the one that matters. A smoke pencil or thermal camera finds the leaks while they can still be fixed for the cost of a roll of tape.
- Exterior insulation, rainscreen strapping, and cladding go on over a barrier that has been proven.
- Final test for the record and for any rebate paperwork.
Each test runs $400 to $700 in Metro Vancouver. The mid-construction test adds a day or two to the schedule. Skipping it is the most common reason a retrofit lands at 5 ACH50 instead of 3.
Windows deserve a separate note. If you keep your existing windows, we can seal the frames to the new barrier, but an old aluminum slider leaks through its own sashes and no perimeter detail fixes that. If window replacement is anywhere in your next ten years, the exterior renovation is the right moment for it, because the rough openings are exposed and the flashing is being rebuilt anyway.
What the numbers look like
Take a 1970s two-storey house in Burnaby, about 2,200 sq ft, tested at 9 ACH50 before work. After exterior air sealing as part of a full re-clad, a result around 3.5 ACH50 is typical.
Space-heating demand on that house drops by roughly 20 percent, which works out to about 4,000 to 5,000 kWh a year of heat that no longer escapes through the walls. What that means in dollars depends on the fuel:
- Electric baseboard: roughly $550 to $700 a year saved at current BC Hydro rates
- Natural gas furnace: roughly $150 to $300 a year
- Heat pump: roughly $200 to $250 a year, because the heat pump already delivers more heat per unit of electricity
On $3,000 to $7,500 of added scope, payback on baseboard heat runs about 5 to 12 years. On gas, energy savings alone stretch it past 15. We tell clients that plainly. The stronger case is everything else: no drafts at floor level, rooms that hold their temperature, less moisture driven into the wall, and a smaller heat pump if you convert from gas later. Cutting heat loss by a fifth can drop the required heat pump size by half a ton, which is $1,000 to $2,000 off the equipment price alone.
For scale, the BC Energy Step Code, which governs new homes rather than renovations, sets airtightness targets from about 2.5 ACH50 at Step 3 down to 1.0 at Step 5. EnerPHit, the Passive House standard for retrofits, asks for 1.0. An older home at 3 or 4 after an exterior renovation sits well within what a careful retrofit should reach, and it is two to three times tighter than when it started.
Rebates change often, so check current CleanBC Better Homes and utility offers before demolition. Several Canadian programs have required a pre-retrofit EnerGuide evaluation, which includes the baseline blower door test, and there is no way to get a valid baseline once the walls are open.
A tighter house needs planned ventilation
An older house at 10 ACH50 ventilates itself, badly and unevenly, through its leaks. Seal it to 3 and most of that accidental fresh air is gone. Without a plan, you get condensation on windows in January, cooking smells that linger, and higher indoor humidity that the walls then have to manage.
Two things need to happen alongside air sealing an older home.
Mechanical ventilation. At minimum, bathroom and kitchen exhaust fans that actually move air, plus a controlled supply. Below about 3 ACH50, a heat recovery ventilator (HRV) is the right answer for most families. Retrofitting an HRV into an existing house costs $8,000 to $15,000, depending on how hard the duct runs are. We coordinate this with licensed mechanical trades so the ventilation and the envelope work are scheduled together.
Combustion safety. If the house has an atmospheric-vented gas water heater, an older furnace, or a wood-burning fireplace, a tighter envelope combined with a strong range hood can pull exhaust gases back indoors. The energy advisor runs a depressurization check at the final test. Sometimes the answer is a sealed-combustion appliance or a make-up air damper. Either way, it gets decided before the house is closed up, not after.
Townhouses and low-rise strata buildings
The same approach works on townhouses and three- and four-storey wood-frame strata buildings, with two differences.
First, air sealing has to be written into the tender. If the specification only says "replace WRB," the bids you compare will not include sealing details or testing, and the lowest bid will leave them out. Specify a target and a test method so every contractor prices the same work.
Second, leaks between units matter as much as leaks to the outside. Smoke, cooking odours, and noise travel through the same gaps. Exterior sealing helps with stack-effect drafts in stairwells and upper suites, but sealing between suites is interior work and should be scoped on its own line.
How we approach it
MV Construction has completed 200+ renovations across Greater Vancouver and Vancouver Island over more than 10 years, including envelope retrofits on character homes, Vancouver Specials, and 1980s strata buildings. Our crews are fully licensed and WCB-insured, and our workmanship is warranty-backed. We are also Passive House Certified, which shapes how we detail every exterior job: airtightness, insulation, and moisture control get treated as one connected problem rather than three line items. If you are also weighing added insulation, our guide to an exterior insulation retrofit covers R-values and costs in more detail.
Where to start
If your siding, stucco, or windows are due for replacement in the next few years, plan the air sealing now, before anyone prices the job. Book a baseline blower door test, ask every contractor how they will build the air barrier and who runs the mid-construction test, and get the target number in writing.
When you are ready, our team will walk the house, review the wall assembly and any test results, and put the air sealing scope, target, and timeline into a written estimate before work starts. Call (778) 375-5672 or request a fixed-scope estimate for your exterior renovation.
