Attic insulation is easy to sell by the inch. Houses are less cooperative. A deep, fluffy attic can still leak heat through an unsealed hatch, wiring holes, open wall tops, or a bathroom fan duct that has wandered off course. Before buying more insulation, find out what the existing attic is doing.
How much attic insulation is enough?
Natural Resources Canada's insulation guidance lists recommended roof or ceiling values by heating degree-day zone. The table ranges from R-45 in Zone 4 to R-55 in Zone 5 and R-60 in Zone 6, with higher values in colder zones. Those are retrofit guidelines, not a substitute for the current Ontario Building Code, the local permit review, or an assessment of the actual assembly.
Insulation type matters too. Loose-fill cellulose, fibreglass, batts, and spray products deliver different R-values per unit of thickness and have different installation limits. Ask for the target R-value, product, installed density, bag count, and minimum settled depth in writing. Snowdrift-shaped insulation is charming only outdoors.
Inspect before adding anything
NRCan's roof and attic guide says to check roof framing, sheathing, soffits, fascia, leaks, stains, mould, flaking, and rot. It also warns that condensation can appear as frost during a cold snap. Fix roof or flashing leaks and identify the moisture source before covering the evidence with fresh insulation.
- Check for water marks, damp insulation, frost, mould, rot, and damaged framing.
- Confirm bathroom and kitchen exhaust ducts are sealed and terminate outdoors, not into the attic or soffit cavity.
- Look for gaps at the attic hatch, plumbing stacks, wiring, lights, chimneys, and wall tops.
- Keep soffit intake paths open with suitable baffles where the roof assembly needs them.
- Do not disturb unknown vermiculite or other suspect material. Health Canada says vermiculite insulation may contain asbestos. Stop and arrange appropriate assessment first.
Air sealing comes before the top-up
Warm indoor air carries heat and moisture through ceiling gaps. NRCan's air-leakage guide identifies the attic hatch, ceiling penetrations, ducts, chimneys, and partition tops as common leakage points. Seal compatible, safe locations first, then insulate without blocking ventilation. Otherwise the new insulation becomes a very nice blanket over the same old holes.
Before signing an attic quote
Ask how the contractor measured the existing R-value, which air leaks are included, how ventilation paths and heat-producing fixtures will be protected, and how the final depth will be verified. An EnerGuide home evaluation can document insulation and air leakage in the context of the whole house. If the complaint is one bedroom over the garage or one cold window, diagnose the room-over-garage assembly or window draft before buying a whole-attic answer. Also check the live Ontario Home Renovation Savings guide before work begins, because rebate timing enjoys rules more than surprises.
