The short answer
Batt insulation costs $1.50 to $3 per square foot installed and needs a separate air barrier layer to perform as tested. Spray foam costs $4.50 to $8 per square foot but acts as insulation and air barrier in one step, sealing the gaps that let humid North Shore air reach cold framing. Closed-cell spray foam is the stronger choice for rim joists, crawl spaces, and any wall assembly with a history of moisture problems. Batt insulation, installed with a properly sealed poly or smart vapour barrier, is the more economical choice for a standard renovated wall where air sealing is handled separately and correctly.
Cost per square foot, and what you are actually paying for
Batt insulation, fiberglass or mineral wool cut into panels and friction-fit between studs, runs $1.50 to $3 per square foot installed for a standard wall cavity in 2026. It is the material most North Shore walls already have from original construction, and it is what most renovation quotes default to unless a client asks for something else.
Spray foam runs $4.50 to $8 per square foot installed, three to four times the material and labour cost of batt. Open-cell foam sits at the lower end of that range and closed-cell foam at the higher end, since closed-cell uses a denser, more expensive chemistry and typically needs a licensed applicator with specialized equipment on site.
The price gap looks larger than it is once you account for what each material actually does on its own. Batt insulation slows heat transfer through the cavity, full stop. It does nothing to stop air movement through the wall, because air passes through fiberglass and mineral wool almost as easily as it passes through open space. Spray foam expands to fill every gap it touches and, once cured, blocks air movement through that same cavity. So a batt quote and a spray foam quote are not pricing the same scope of work unless the batt quote also includes a properly detailed and sealed air barrier, which a surprising number of renovation quotes leave out or treat as an afterthought.
| Batt (fiberglass / mineral wool) | Closed-cell spray foam | |
|---|---|---|
| Cost per sq ft installed | $1.50 to $3 | $6 to $8 |
| R-value per inch | R-3.0 to R-4.3 | R-6.0 to R-7.0 |
| Acts as an air barrier | No, needs a separate sealed layer | Yes, seals as it cures |
| Vapour permeability | High, needs a separate vapour control layer | Low, closed-cell acts as its own vapour retarder |
| Best fit | Standard walls with air sealing done properly | Rim joists, crawl spaces, irregular framing, moisture-prone assemblies |
R-value and RSI: the number on the bag is not the number in the wall
R-value measures how well a material resists heat flow, with a higher number meaning better performance. RSI is the same measurement in metric units, the version that appears in the BC Building Code and in provincial energy guidance. Fiberglass batt runs roughly R-3.0 to R-3.8 per inch of thickness, and mineral wool batt runs R-3.7 to R-4.3 per inch. Closed-cell spray foam runs R-6.0 to R-7.0 per inch, roughly double the batt figures, and open-cell spray foam runs R-3.5 to R-3.6 per inch, close to batt performance but with the air sealing advantage foam carries regardless of cell type.
The number printed on a bag or a spec sheet describes the insulation material alone, in a lab, under ideal conditions. The effective R-value of a whole wall assembly, the number that actually matters, accounts for the wood studs that interrupt the insulation every 16 or 24 inches, since wood conducts heat faster than insulation does. A standard 2x6 wall filled with R-19 batt has an effective assembly R-value closer to R-15 to R-17 once the studs are factored in. Spray foam does not eliminate that framing effect, but its higher per-inch value and its air sealing performance close more of that gap than batt does at the same cavity depth.
Air sealing is the difference that actually shows up in a North Shore winter
This is the part that decides the argument on most renovation projects here. Insulation slows heat conduction through a material. Air sealing stops warm, moist indoor air from moving through gaps, around outlets, along top and bottom plates, through service penetrations, into a cold wall cavity. Those are two different jobs, and batt insulation only does the first one.
Spray foam does both because of how it installs. It expands into every gap in the cavity it is sprayed into, cures rigid, and bonds to the framing, so the same application that provides thermal resistance also closes the air paths a batt-and-poly assembly relies on a separate, carefully taped vapour barrier to close. On a wall being opened up during a renovation anyway, that combination is worth the premium in places where air leakage has been a known problem: rim joists at the top of a foundation wall, where the floor framing meets the concrete and gaps are almost guaranteed with batt alone; crawl space walls and headers; and any wall section with a documented history of drafts, ice damming, or condensation.
On a standard above-grade wall in good condition, the air sealing argument for foam weakens if the batt installation is paired with a correctly installed and taped air barrier, whether that is 6-mil poly sealed at every seam and penetration, or a smart vapour retarder membrane designed to vary its permeability with humidity. The material cost difference between the two options only matters once the air sealing scope is priced the same way on both sides of the comparison.
Moisture management in a climate that stays wet for months
The North Shore sits in one of the wettest parts of Metro Vancouver, with rain a near-constant condition from October through March. That matters for insulation choice because of how each material handles water vapour that finds its way into a wall cavity, whether from a small leak, from indoor humidity, or from the framing itself drying out after construction.
Fiberglass and mineral wool batt allow vapour to pass through relatively freely, which is workable as long as the wall assembly has a clear drying path, meaning vapour that gets into the cavity can eventually get back out rather than being trapped against cold sheathing. Mineral wool has an advantage here over fiberglass in a wet-prone assembly, since it does not lose R-value when it gets damp and dries out faster, while wet fiberglass compresses, loses loft, and holds water longer.
Closed-cell spray foam is close to impermeable to both air and vapour once cured, which means it acts as its own vapour retarder and blocks bulk water from moving through the cavity from either direction. That is a genuine advantage in a rim joist or a below-grade wall where moisture intrusion is a real risk. It is also the reason closed-cell foam needs to be specified carefully on an assembly with an exterior water source, like a wall behind failing cladding, because foam that seals the interior face of a wet cavity can trap moisture against the sheathing on the outside with nowhere to dry to. Open-cell foam is more vapour-permeable than closed-cell and allows some drying, but it also absorbs and holds bulk water if the wall gets wet, which makes it a poor choice below grade or in any assembly with an active leak risk.
Where BC Building Code requirements come in
Metro Vancouver, including the North Shore, sits in Climate Zone 4 under the energy efficiency requirements published for BC houses. Wall assemblies have a prescriptive minimum effective thermal resistance for that zone, and the specific number depends on whether the wall is part of a prescriptive compliance path or a BC Energy Step Code performance path, where the whole house is modelled and tested with a blower door rather than measured wall by wall. Confirm which path applies to your project with your building department or energy advisor before locking in an insulation type, since a Step Code path can change which material makes more sense for hitting an airtightness target.
The Code also requires a vapour barrier on the warm side of insulation in most wall assemblies in this climate, to control the direction vapour moves through the wall in winter. A batt-insulated wall needs that vapour barrier installed as a separate layer, sealed at every seam, outlet box, and penetration to actually function as designed. Closed-cell spray foam at a sufficient thickness satisfies the vapour barrier requirement on its own in many assemblies, since the cured foam itself is vapour-impermeable, which is one of the reasons it simplifies inspection on some projects even though it costs more upfront.
How we actually spec it on a project
On a whole-wall renovation where the cavity is already open, we default to mineral wool batt with a properly sealed smart vapour retarder for standard above-grade walls, because the cost difference funds other parts of the project without giving up meaningful performance when the air sealing is done right. We spec closed-cell spray foam specifically at rim joists, crawl space perimeters, and any wall section with a documented moisture or draft history, because those are the spots where foam's air sealing and vapour control earn the premium every time. Mixing the two materials by location, rather than picking one for the whole house, is usually the most cost-effective way to build the assembly.
Sources
Frequently asked questions
Is spray foam always better than batt insulation on the North Shore?
Not always, and the difference depends on where in the wall it goes. Spray foam earns its higher cost at rim joists, crawl space walls, and any assembly with a moisture or draft history, because it seals air leaks and controls vapour in one step. On a standard above-grade wall with properly sealed batt and a taped vapour barrier, the performance gap narrows significantly relative to the three to four times higher cost.
How much more does spray foam cost than batt insulation in 2026?
Batt insulation runs $1.50 to $3 per square foot installed. Spray foam runs $4.50 to $8 per square foot, with closed-cell foam at the higher end because of its denser chemistry and the need for a licensed applicator with specialized equipment.
Does batt insulation stop air from moving through a wall?
No. Fiberglass and mineral wool batt slow heat conduction through the cavity but let air pass through nearly as freely as open space. A batt-insulated wall needs a separate, properly sealed air barrier, usually 6-mil poly or a smart vapour retarder taped at every seam and penetration, to actually stop air movement.
What is the difference between open-cell and closed-cell spray foam?
Closed-cell foam is denser, runs R-6.0 to R-7.0 per inch, and is close to impermeable to both air and vapour once cured, which makes it suited to rim joists and below-grade walls. Open-cell foam runs R-3.5 to R-3.6 per inch, closer to batt performance, is more vapour-permeable so it allows some drying, but it also absorbs and holds bulk water if the wall gets wet, which rules it out below grade or anywhere with an active leak risk.
Why does mineral wool do better than fiberglass in a wet North Shore wall?
Mineral wool does not lose its R-value when it gets damp and dries out faster than fiberglass. Wet fiberglass compresses, loses loft, and holds water longer, which matters in a climate where rain is a near-constant condition from October through March and any small leak has months to do damage before the wall dries out.
Can spray foam trap moisture in a wall instead of stopping it?
Yes, if it is specified on the wrong assembly. Closed-cell foam applied on the interior face of a wall with an exterior water source, such as failing cladding behind a wall being resprayed from the inside, can seal moisture against the cold sheathing outside the foam with nowhere to dry to. This is why any wall with a suspected exterior water problem needs the cladding and rain screen addressed before the interior insulation choice is finalized.
What R-value does the BC Building Code require for walls in Metro Vancouver?
Metro Vancouver, including the North Shore, sits in Climate Zone 4, which has a prescriptive minimum effective thermal resistance for wall assemblies under BC's energy efficiency requirements. The exact number depends on whether the project follows the prescriptive path or a BC Energy Step Code performance path modelled and tested with a blower door. Confirm the current requirement with your building department before buying material.
Does spray foam satisfy the vapour barrier requirement on its own?
Closed-cell spray foam at sufficient thickness is vapour-impermeable and satisfies the Code's vapour barrier requirement in many wall assemblies without a separate poly layer. Batt insulation does not, and needs a distinct, properly sealed vapour barrier installed on the warm side of the wall to meet the same requirement.
Is spray foam worth it in a rim joist even if the rest of the house uses batt?
Yes, and mixing materials by location is standard practice on most of our projects. Rim joists, where floor framing meets the foundation, are one of the hardest spots to seal properly with batt because of the irregular framing, and they are a common source of drafts and condensation on older North Shore houses. Closed-cell foam at the rim joist alone, with batt everywhere else, is usually the most cost-effective way to close that specific gap.
Does insulation choice affect a BC Energy Step Code blower door test?
Yes. A Step Code path scores the whole house on measured airtightness with a blower door test, not on the R-value of individual materials alone. Spray foam's air sealing performance can make hitting a higher Step Code level easier, but a well-detailed batt and sealed vapour barrier assembly can also pass, so the right choice depends on the target Step Code level and how much air sealing labour the budget can absorb either way.
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