Roof insulation and bringing up to standards in Montreal

In a poorly insulated Montreal home, heat passes through the ceiling, warms the attic space, melts the snow on the roof covering, and that water refreezes at the cold edge. The result: icicles, ice dams, spring leaks, and higher heating costs all winter long. Attic insulation that does its job solves both problems at once: indoor comfort and how the roof behaves outside.

It’s the most common mistake: adding insulation and blocking attic ventilation. In that case, moisture stays trapped, the insulation loses its value, and the attic wood eventually suffers. Ventilation is part of quality workmanship, not an add-on. The roof deck wood turns black, moisture spreads to the attic walls, and the repair ends up costing more than the insulation itself.

Icicles that come back every year in the same spot. An upstairs room that’s impossible to heat. Condensation or black marks on the underside of the roof deck. Insulation that’s compressed, shifted by vent airflow, or soaked from an old water leak. Mold in the attic, too: in that case, wood decontamination and removal of the old insulation must come before any new installation. Cut corners on decontamination, and the mold comes back under the new insulation. Removal is done by vacuum extraction, without spreading spores through the house. An inspection helps decide between simply adding insulation and a full renovation, including the vapor barrier.

In an accessible attic, blown-in insulation—fiberglass or cellulose—remains the most common solution: it fills the nooks and installs quickly. Spray polyurethane is better suited to difficult areas, low slopes, and junctions, because it insulates and air-seals in one step. On a flat roof, insulation is installed above the decking, within the roof assembly: the work is then planned along with the membrane replacement. The same principles apply in residential and commercial, with different insulation types and thicknesses.

Bringing up to standard isn’t limited to insulation thickness. We check ventilation and vent distribution, the condition of the vapor barrier, baffles at the roof-to-wall junction, airtightness around penetrations, and the absence of residual moisture in the attic. Note: insulation work may be eligible for the Quebec government’s Rénoclimat program; conditions and amounts are detailed on the official website. Spray polyurethane is better suited to difficult areas, low slopes, and junctions, because it insulates and air-seals in one step. On a flat roof, insulation is installed above the decking, within the roof assembly: the work is then planned along with the membrane replacement. The same principles apply in residential and commercial, with different insulation types and thicknesses.