Is Roxul mineral wool worth the extra cost over fibreglass batts in Campbellton NB? | Insulation IQ?

For homeowners in Campbellton — one of New Brunswick's colder subregions, with a climate that regularly sees heavy snowfall and extended periods well below -20°C — the question of mineral wool versus fibreglass is a genuinely important one. The short answer is that Roxul (now marketed as Rockwool) mineral wool batts offer a meaningful set of advantages over standard fibreglass, and for many Campbellton applications, the extra cost is justified. But it depends on where you're installing it and what you need most.

The cost premium is the starting point of the comparison. Mineral wool batts typically cost 40 to 70 percent more than equivalent fibreglass batts at building supply stores in the Campbellton and Bathurst area. An R-24 mineral wool batt for a 2x6 wall cavity might run $90 to $110 per bag compared to $55 to $75 for a comparable fibreglass product. Over an entire house, that difference can add up to $500 to $2,000 or more in material costs depending on the project size.

So what do you get for that premium? Fire resistance is one of mineral wool's strongest advantages. Rockwool batts are non-combustible — they're made from basalt rock and steel slag, and they can withstand temperatures above 1,000°C without melting or contributing to flame spread. Fibreglass, while not highly flammable, does melt and can soften at lower temperatures. For Campbellton homes using wood stoves or pellet stoves as supplementary heat — common in this region — or for fire-separation assemblies in garages and between units in multi-family construction, mineral wool provides genuine added safety margin.

Sound attenuation is another standout benefit. Mineral wool has a much higher Sound Transmission Class (STC) rating than fibreglass at equivalent thicknesses. If you're insulating interior walls between bedrooms, a home office, or a garage-to-living space wall in a Campbellton home, mineral wool batts reduce sound transmission noticeably better than fibreglass. For exterior walls, the difference in acoustic performance matters less, but in a busy household or a duplex conversion, it's a real quality-of-life improvement.

Water resistance is a meaningful difference for Campbellton's climate specifically. Mineral wool does not absorb water — it repels moisture and dries readily if it gets wet during construction or from a roof leak. Fibreglass batts, while also not fully hydrophilic, can absorb moisture into their facing and binders, losing R-value when wet and potentially supporting mould growth if they remain damp. In a climate like Campbellton's, where snow and freeze-thaw cycles are intense and construction sequencing sometimes leaves walls open to the elements, mineral wool's moisture resilience is a practical advantage.

Dimensional stability also favours mineral wool. The dense, stiff nature of Rockwool batts means they hold their shape and fit snugly in stud cavities without sagging or shifting over time. Fibreglass batts can settle slightly, particularly in sloped or irregular cavities. Mineral wool friction-fits tightly and stays put, reducing the risk of settling-related gaps developing over the decades of the building's life.

R-value per inch is approximately equivalent between the two products — both achieve roughly R-3.7 to R-4 per inch — so mineral wool doesn't offer a thermal density advantage in standard wall cavities. The thermal performance difference between properly installed mineral wool and properly installed fibreglass in the same 2x6 cavity is marginal.

For Campbellton applications where mineral wool pays for itself most clearly: exterior walls exposed to wind-driven rain (the Restigouche River area sees significant precipitation), garage walls and ceilings with fire-separation requirements, party walls in semi-detached homes, home theatre or music rooms, and any assembly where moisture risk during construction is high. For interior partition walls with no fire or acoustic requirements and limited budget, standard fibreglass remains serviceable.

NB Power's efficiency rebates and the Canada Greener Homes Grant do not differentiate between fibreglass and mineral wool — both qualify for the same rebate amounts on eligible retrofit projects.

For a project-specific recommendation on whether mineral wool's premium is worth it for your Campbellton home, the insulation professionals listed at New Brunswick Insulation can provide an honest assessment based on your wall assemblies and budget.

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• 3Tone Construction Ltd
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• Brunswick insulation & roofing