Do I need to remove old insulation before installing new drywall on exterior walls in a GTA home built in the 1970s?

In most cases, yes — you should remove and replace the old insulation before installing new drywall on exterior walls in a 1970s GTA home. While it may be tempting to leave existing insulation in place and simply board over it, there are several critical reasons why removal and replacement is the better approach, both for building performance and code compliance.

The primary concern with 1970s insulation in GTA homes — particularly the bungalows, split-levels, and two-storeys across Scarborough, North York, Etobicoke, Mississauga, and Brampton — is what type of insulation was originally installed. Common insulation materials from that era include fibreglass batts (often R-8 to R-12, well below current code requirements), mineral wool batts, and in some cases, urea-formaldehyde foam insulation (UFFI). UFFI was widely used in Ontario homes during the 1970s energy crisis and was banned in Canada in 1980 due to off-gassing concerns. While aged UFFI is generally considered safe by Health Canada, its presence can affect home resale value and should be disclosed. If you open up your walls and find yellow or tan crumbly foam, have it tested before proceeding.

The Ontario Building Code requires a minimum of R-24 for above-grade exterior walls in renovations where the wall cavity is opened up. If you are removing drywall and exposing the wall cavity, this triggers the requirement to bring the insulation up to current code standards. The original R-8 to R-12 fibreglass batts from the 1970s do not meet this requirement. Simply boarding over them without upgrading means your renovation will not pass inspection if permits are pulled — and exterior wall renovations that involve changes to insulation or vapour barriers do require permits in Toronto.

Even if the existing insulation appears to be in good condition, 50-year-old fibreglass batts have typically settled, compressed, and lost a significant portion of their insulating value. They may also be harbouring moisture, mould, or pest contamination that is not visible from the front face. Removing the old insulation allows you to inspect the wall cavity, framing, and sheathing for hidden damage — a critical step in older GTA homes where decades of freeze-thaw cycles, ice damming, and wind-driven rain may have caused deterioration that is invisible from inside the room.

The vapour barrier situation is equally important. Many 1970s GTA homes either have no vapour barrier, an inadequate vapour barrier (thin poly that has been punctured and torn over decades), or the vapour barrier was installed on the wrong side of the insulation. The Ontario Building Code requires a 6-mil polyethylene vapour barrier on the warm side (interior side) of insulated exterior walls. When you remove the old drywall, you have one opportunity to install a proper, continuous vapour barrier before the new drywall goes up. If you leave the old insulation in place, you cannot inspect or replace the vapour barrier behind it — and a compromised vapour barrier in Ontario's Climate Zone 6 leads to condensation inside the wall cavity, which leads to mould and structural damage.

Before disturbing any materials in a pre-1990 GTA home, you must test for asbestos. Joint compound, drywall sheets, and insulation materials from the 1970s may contain asbestos fibres. Ontario Regulation 278/05 requires that suspected asbestos-containing materials be tested by an accredited laboratory before any disturbance. If asbestos is found, certified abatement professionals must handle the removal — this is not optional and not something a homeowner or general drywall contractor should attempt. Asbestos abatement in a GTA home typically adds $3,000–$8,000 to the project cost.

The recommended approach for a 1970s exterior wall renovation is: remove old drywall, test for asbestos and UFFI, remove old insulation, inspect framing and sheathing for damage, repair as needed, install new R-24 fibreglass batt or mineral wool insulation, install a continuous 6-mil polyethylene vapour barrier with all seams taped and sealed, then install new 1/2-inch drywall. The cost for this complete scope on a typical room (12x12 with two exterior walls) runs $3,000–$6,000 including insulation, vapour barrier, drywall, taping, and finishing.

This is firmly in professional territory — the combination of potential hazardous materials, building code requirements, vapour barrier installation, and drywall finishing makes it a job for an experienced contractor. Get matched with a drywall professional through Toronto Drywall Installers for a free estimate on your exterior wall renovation.