Aluminum Wiring, Poly B and Ice Dams in 1970s and 1980s Markham Homes

Neeraj Moolchandani is a top real estate agent in Markham, Ontario. Published November 11, 2026 · By Neeraj Moolchandani, REALTOR®, Cofounder of the Kaizen Real Estate Team, eXp Realty, Brokerage

Move up buyers love the larger lots and solid construction in established Markham areas such as Bayview Fairway, Royal Orchard and German Mills on the Markham side of Thornhill, as well as Unionville and Milliken Mills. Our Kaizen Real Estate Team is one of the teams Markham families trust with these purchases, and these three issues come up often. Here is how to handle each one calmly.

Why These Homes Are Worth a Close Look

Many homes built in these areas in the 1970s and 1980s sit on generous lots with mature trees and established schools. Our post on neighbourhoods with larger lots shows where to look. The tradeoff is age. Systems that were standard then can concern insurers and buyers now.

Aluminum Wiring

The Electrical Safety Authority notes that many insurers will not provide or renew coverage for homes built from the mid 1960s to the late 1970s with aluminum wiring. ESA is also clear that aluminum wiring itself is safe when proper connections and terminations are made. The risk is overheating at connections.

• Warning signs include warm cover plates, discoloured switches or receptacles, flickering lights and the smell of hot plastic.
• Approved repairs use switches and receptacles marked CO/ALR, or copper pigtails joined with connectors approved for aluminum to copper.
• Push in terminals must not be used with aluminum wire.
• Hire a licensed electrical contractor who knows these methods, and have the work inspected by ESA.
• Keep the ESA certificate of inspection. Insurers often ask for it, and some may require full replacement with copper.

Poly B Plumbing

Polybutylene, often called Poly B, was common from the late 1970s to the mid 1990s. Westland Insurance notes it was most often installed between 1978 and 1997 and was removed from the Canadian plumbing code in 2005. Insurers may add a surcharge, set a deadline for replacement, or decline water damage coverage.

• Look under sinks, near the water heater and in unfinished basement ceilings.
• Poly B is usually grey, sometimes blue, with markings that include PB.
• Replacement is usually done by opening walls and ceilings in sections, then patching.
• Ask for a written quote that includes drywall repair and painting.

Ice Dams

Ice dams form when heat escapes into the attic or a cathedral ceiling, melts snow on the roof, and the water refreezes at the cold eaves. Water can back up under shingles and stain ceilings. Many older homes have less insulation and more air leaks than today's standards.

• Air sealing at the attic hatch, pot lights and wall tops stops warm air from reaching the roof.
• Added attic insulation keeps the roof deck cold.
• Good soffit and roof ventilation removes moisture and heat.
• Heating cables at the eaves can help as a short term measure, not a cure.
• When the roof is replaced, ask about ice and water protection at the eaves.

Ontario's Home Renovation Savings Program lists a $1,250 rebate for attic insulation on its own, and up to $250 for air sealing as part of a bundle that starts with a home energy assessment. See our guide to energy upgrades and resale value.

How to Buy One of These Homes Safely

1. Ask the listing agent early about wiring, plumbing and any insurance issues.
2. Make your offer conditional on a home inspection and on getting insurance; our conditional offers guide explains how.
3. Call your insurer before you firm up and ask exactly what they need.
4. Get written quotes from a licensed electrician and a plumber during the condition period.
5. Use the quotes to negotiate price or a credit, and keep every certificate after closing.

Our home inspection checklist covers the rest of the inspection.

Questions Markham Clients Ask

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