What is the difference between R-20 and R-28 wall insulation performance in a NB garage?

In a New Brunswick garage, the difference between R-20 and R-28 wall insulation is meaningful but not dramatic for heat retention — the bigger impact is on condensation control, heating costs over a six-month winter, and whether your wall assembly handles NB's moisture conditions without problems.

What the R-Values Actually Mean

R-value measures thermal resistance — how hard a material works to slow heat transfer. R-20 resists heat flow at a rate of 20 (in imperial units), and R-28 resists it at 28. That's a 40% improvement in the insulation layer itself, but because heat also escapes through framing, windows, doors, and the ceiling, the real-world improvement to your overall garage envelope is closer to 15-25% better heat retention when upgrading from R-20 to R-28 walls.

To put that in practical terms: if your R-20 garage loses enough heat on a -25°C Moncton night that your propane unit heater runs for 6 hours, an R-28 wall might reduce that to roughly 4.5-5 hours under the same conditions. Over a full NB heating season of 4,800-5,200 heating degree days, that difference adds up — but it's not transformational on its own, because walls are only one part of the thermal envelope.

How You Actually Achieve R-20 vs R-28 in NB

This is where the choice gets practical. R-20 fits neatly into a standard 2x6 wall cavity (5.5 inches of space) using high-density fibreglass or mineral wool batts. It's the most common wall assembly for insulated garages in NB — straightforward to install, widely available at any NB building supply store, and code-compliant for heated garages.

R-28 requires either a thicker wall or a hybrid assembly. Your main options are a 2x8 wall framed at 24 inches on centre (which gives you roughly 7.25 inches of cavity for R-24 batts plus a bit of sheathing contribution), or a 2x6 wall with continuous rigid foam insulation on the exterior or interior face. Two inches of exterior rigid foam (approximately R-10) added to a 2x6 R-20 batt wall gets you close to R-28 effective, and this hybrid approach has an important advantage beyond the raw R-value.

The Condensation and Vapour Control Difference

In NB's climate, the location of the condensation plane within your wall assembly matters enormously. When warm, moist garage air meets a cold surface inside the wall, moisture condenses — and if that happens within the batt insulation or against the sheathing, you get mould, rot, and structural deterioration over time.

A 2x6 wall with R-20 batts and a standard 6-mil poly vapour barrier on the warm side works adequately, but the sheathing still gets quite cold in a -25°C NB winter, which creates some risk of condensation at the sheathing layer. Adding exterior rigid foam to reach R-28 keeps the sheathing warmer by moving the thermal break outward — this is called keeping the dew point outside the structural assembly, and it's one of the best things you can do for long-term wall durability in a Maritime climate garage.

If you're building a heated workshop or a garage that will see regular use through NB's winter, the hybrid R-28 assembly with exterior foam is genuinely worth the extra cost. If you're building a garage primarily for vehicle storage that you'll heat occasionally, R-20 in a 2x6 wall is entirely reasonable and what most NB contractors will quote as standard.

Practical Cost Difference

Upgrading from R-20 to R-28 on a typical 24x24 two-car garage adds roughly $800-$2,000 in material and labour costs depending on the method chosen. Exterior rigid foam adds more because it also requires longer fasteners, adjusted window and door bucks, and additional labour. The payback period in heating cost savings depends on your fuel type and how heavily you use the garage — for a frequently heated workshop, payback is often 5-8 years. For a garage heated only when you're working in it occasionally, payback stretches to 15+ years.

The ceiling is where your insulation dollars work hardest in NB. Heat rises, and a garage ceiling with R-20 while your walls have R-28 is leaving significant money on the table. Prioritize R-40 to R-50 in the ceiling before worrying about the wall upgrade from R-20 to R-28.

If you're planning an insulated garage build and want to compare options with a local contractor, New Brunswick Garages can match you with garage builders in your area through the New Brunswick Construction Network — free, no obligation, and they'll know exactly what wall assemblies work in your part of the province.