Cellulose vs Spray Foam vs Fiberglass: An Honest Look at Shop Insulation

Once you’ve decided your shop will be heated, the next decision is what goes in the walls. Ask three builders and you’ll get three different answers, and usually the answer is whatever that builder happens to install. We install cellulose, so you know where we stand. Here’s the honest comparison anyway, because the right choice depends on the building, and pretending otherwise doesn’t help anybody.

Fiberglass batts

Fiberglass is the pink stuff most people picture when they hear the word insulation. It comes in batts sized to fit between studs or girts, and it’s the cheapest option on the shelf.

The catch is that the R-value printed on the package assumes a perfect installation. Batts that are cut short, stuffed around wiring, compressed behind blocking, or slumped over time leave gaps, and air moves through and around fiberglass more easily than most people think. In a house wall with careful workmanship it does the job. In a big shop wall with long spans, penetrations, and metal cladding, the difference between rated performance and installed performance is where fiberglass falls down.

Verdict: fine on paper, hard to install well in a shop, and the weakest of the three at stopping air movement.

Spray foam

Spray foam is applied as a liquid that expands and hardens in the cavity. Closed-cell foam runs about R-6 to R-7 per inch, which is the highest of the three, and it air-seals as it insulates. For odd cavities, rim joists, and buildings where every inch of wall depth counts, it’s a genuinely strong product.

The tradeoffs are real, though. It’s the most expensive option by a wide margin. Install quality is everything, since foam that’s mixed or applied wrong doesn’t cure right and there’s no easy fix. And it’s permanent. If you ever want to rewire a wall or add a circuit, you’re cutting through hardened foam to do it.

Verdict: the premium option. Right for some builds, more than most shops need.

Cellulose

Cellulose is dense-packed fiber blown into the wall cavity under pressure. It runs about R-3.5 per inch, so it doesn’t match closed-cell foam inch for inch. What it does do is fill the cavity completely. It packs around wiring, blocking, and every irregularity in the wall, with no cut-and-fit gaps, and at proper density it slows air movement through the wall instead of letting it wander. It’s also made from more than 80 percent recycled paper and cardboard, which matters to some of our customers.

The honest limitations: because the R per inch is lower, the wall needs enough depth to hit the target, which is why insulation should be part of the wall design from the start rather than a decision made after framing. And like foam, the install matters. Dense-pack done loose is just fluffy paper.

Verdict: for most heated shops on the Prairies, a properly designed wall with dense-packed cellulose hits the performance target at a cost that makes sense.

Why we build with cellulose

We use our own cellulose system, SOPRA-CELLULOSE (formerly known as Weathershield), with WallBAR for wall cavities, installed by our own crews. That last part is the point. We design the wall depth with the insulation target in mind, then the crew that knows how the wall went together is the crew that fills it. No handoff, no third-party installer discovering surprises, no gap between what was quoted and what’s behind the cladding. It’s a big part of why our shops stay warm in February.

If a project genuinely calls for foam, we’ll say so. That happens. But for the everyday heated shop, the working farm shop, and the storage building that needs to stay above freezing, cellulose in a wall built for it is the answer we’d give a neighbour.

Planning a heated build and not sure what the walls should be? That’s exactly the conversation a quote starts.

Submit your request for quote online: sandstormalberta.com/get-a-quote/

Built honest and true.