Fibreglass Batts.
Batt insulation is cheaper per unit of R-value, better on sound transmission than spray foam, and reversible. What it does not do is act as an air barrier — and in Zone 7A that is a separate, mandatory requirement.
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A batt fills a cavity. It does not seal one. Once that distinction is clear, most of the foam versus fibreglass argument resolves into a straightforward question about which problem you actually have.
The airtightness obligation is separate from the insulation obligation, with its own clause and its own test — which is worth reading before assuming a batt job is finished when the cavities are full.
Where Batts Are the Right Answer.
This is a real product line rather than a fallback, and there are assemblies where recommending it over foam is simply correct.
- Open, regular cavities with full depth available — the case where cost per unit of R-value is the deciding factor and there is nothing complicated about the geometry.
- Interior partitions where sound transmission is the objective: published testing puts 2x6 R-19 batts at STC 45 against five inches of closed-cell foam at STC 37, and Canadian NRC research measured a 4 to 6 point STC loss when foam replaced glass fibre.
- Steel-framed partitions in particular, where the Gypsum Association reports fibre insulation beating both spray foams by 8 to 10 STC points because foam stiffens the resilient framing.
- Hybrid assemblies — closed-cell foam at the sheathing for air and vapour control, batts in front of it for the remaining R-value at lower cost.
- Assemblies where reversibility matters, since closed-cell foam bonded to sheathing is effectively permanent and batts are not.
- Embodied carbon, where fibre products generally sit below foam per unit of R-value even after the move to HFO blowing agents.
- Careful installation, because a batt only delivers its rating when it fills the cavity without gaps, compression or slumping — friction fit, split around wiring rather than compressed behind it, and in contact with the air barrier plane.
- The same Zone 7A effective RSI targets apply regardless of material: RSI 10.43 ceilings below attics, RSI 3.08 walls, RSI 5.02 floors over unheated space.
Deciding Between Batt and Foam.
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Ask what the problem is
If the answer is not enough R-value in an accessible cavity, batts are usually the efficient answer. If the answer is air moving through the assembly, or moisture reaching a cold surface, batts on their own will not fix it.
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Check the geometry
Regular bays with square ends suit batts. Joist ends, cantilevers, curved surfaces, steel purlins and irregular cavities do not, and a poorly fitted batt performs well below its label.
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Decide who provides the air barrier
Something has to. Sheathing membrane, sealed polyethylene, a taped panel system or a layer of closed-cell foam — but not the batt itself, whatever the cavity is full of.
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Consider a hybrid
Foam for continuity where continuity is the problem, batt for volume where volume is the problem. On a lot of Central Alberta assemblies that is the answer that actually optimises the budget.
Frequently Asked Questions About Fibreglass (Batt) Insulation
Is fibreglass worse than spray foam?
For different jobs, in different directions. Foam is dramatically better at stopping air movement — it clears the code's air barrier material threshold at around 25 mm where a batt never will — and it delivers more R-value per inch of depth. Fibreglass is better on cost per unit of R-value, better on sound transmission through a partition, better on embodied carbon, and it can be removed. Neither is universally correct, and a contractor who says otherwise is describing a price list rather than a building.Do batts meet the Alberta code?
The insulation requirement, yes — the code sets effective RSI targets and does not specify a material. What batts do not do is satisfy the separate airtightness obligation. Sentence 9.36.2.9.(1) requires a continuous air barrier system, Sentence 9.36.2.10.(1) requires the material providing the principal resistance to air leakage to conform to CAN/ULC-S741, and Sentence 9.36.2.9.(2) requires continuity across joints, junctions and penetrations. A batt assembly needs something else to do that job.How much insulation do I need in an attic if I use batts?
The same as with any other material: effective RSI 10.43, about R-59.2, for a ceiling below an attic in Climate Zone 7A with no heat recovery ventilator, or effective RSI 8.67, about R-49.2, with one. The word effective is doing work there — the figure is for the finished assembly including heat flow through framing, so a batt job with gaps at the ends, compressed sections or slumping will not deliver its nominal rating.Can batts and spray foam be used together?
Frequently, and it is often the best use of a budget. A layer of closed-cell foam at the sheathing provides the air barrier and, at 50 mm, the vapour barrier, and fibre in front of it makes up the rest of the required resistance at a lower cost per unit of R. On roofs the same idea carries a condition: the guidance the Alberta-adopted RDH report reproduces is that at least 60 percent of the total R-value in Zone 7A should be air- and vapour-impermeable, and that ratio comes from a US code table cited as building physics guidance rather than from a Canadian code.Which fibreglass products do you install?
Batt insulation including Johns Manville Fiberglass. Product selection on a given job follows the assembly, the required effective RSI and the framing dimensions rather than a house preference, and we will tell you what is going in before it goes in.