How much does it cost to re-insulate interior basement walls with mineral wool batts versus fibreglass batts in a Moncton NB semi-detached home?

For a typical Moncton semi-detached home, expect to pay $2,500–$4,500 for fibreglass batt basement wall insulation installed, or $3,200–$5,500 for mineral wool batts — with mineral wool costing roughly 25–40% more but delivering meaningfully better performance in a basement environment.

Both options require framing a new stud wall against the foundation, installing the batts, adding a vapour barrier, and typically finishing with drywall if you're creating livable space. The framing and finishing work is the same regardless of which batt you choose — the cost difference is almost entirely in the insulation material itself.

What You're Actually Paying For

A semi-detached in Moncton typically has a basement perimeter of roughly 100–140 linear feet on the two exposed sides (the shared party wall doesn't need exterior insulation treatment). At 8-foot ceiling height, you're looking at 800–1,100 square feet of wall area to insulate. Framing a 2x4 stud wall 1.5 inches off the foundation face, insulating with R-14 or R-20 batts, installing 6-mil poly vapour barrier, and drywalling runs approximately $18–$28 per square foot all-in for fibreglass and $22–$35 per square foot for mineral wool, including labour.

If you're not finishing the basement — just insulating and vapour-barriering without drywall — costs drop to roughly $8–$14 per square foot for fibreglass and $11–$18 for mineral wool. Many Moncton homeowners insulate the basement walls without finishing them, which is a perfectly valid approach that captures most of the energy savings at a fraction of the full renovation cost.

Why Mineral Wool Is Worth Considering in a Moncton Basement

Basements in Moncton sit in some of the wettest soil conditions in NB, and the city's older housing stock — a lot of it built in the 1960s through 1980s — has foundation walls that see seasonal moisture movement even when there's no active leak. Mineral wool (Rockwool/Roxul) is hydrophobic, meaning water beads off it rather than absorbing into the fibres. If your foundation wall ever weeps moisture or a minor flood occurs, mineral wool batts dry out and retain their R-value. Fibreglass batts absorb moisture, lose R-value when wet, and can harbour mould growth in the fibres — a real concern in a basement environment.

Mineral wool also provides R-3.3 to R-4.2 per inch compared to fibreglass at R-3.0 to R-3.7 per inch, so you get slightly more thermal resistance in the same stud cavity. In a 2x4 wall cavity (3.5 inches deep), mineral wool delivers approximately R-15 versus R-12 to R-14 for standard fibreglass. That difference matters in Moncton's climate — the city accumulates roughly 4,900 heating degree days per year, and your basement walls are in contact with soil that sits at or below freezing for five to six months annually.

The Vapour Barrier Is Non-Negotiable

Regardless of which batt you choose, 6-mil polyethylene vapour barrier must go on the warm (interior) side of the insulation — between the batts and the drywall, never between the batts and the foundation wall. This is the most common installation mistake in basement retrofits. Placing the poly against the cold foundation traps moisture inside the wall cavity and guarantees mould growth within a few years. Every seam should be lapped 12 inches and taped, and every penetration (electrical boxes, pipes) sealed with acoustical sealant.

One Important Caveat Before You Insulate

If your foundation wall shows any signs of moisture intrusion — efflorescence (white mineral deposits), staining, dampness, or past flooding — address that first. Insulating over an active moisture problem hides the evidence and accelerates the damage. A waterproofing assessment before insulating is money well spent.

Also worth knowing: this type of project is typically eligible for NB Power's Total Home Energy Savings Program (rebates up to $5,000) and the Canada Greener Homes Grant. You'll need a pre-retrofit EnerGuide evaluation before work begins — don't skip this step or you lose the rebate eligibility entirely.

For a free quote from local Moncton insulation contractors, New Brunswick Insulation can match you through the New Brunswick Construction Network. Browse contractors in your area at newbrunswickconstructionnetwork.com/directory?category=insulation.