What an older building might be hiding.

About each hazard

1. Underground oil tank

   Before natural gas reached a neighbourhood, many homes were heated with oil stored in a steel tank, often buried in the yard. When owners switched to gas or electric heat, the tank was usually left in the ground, sometimes filled with sand.

   Steel tanks rust. Leftover oil can leak into the soil and groundwater and spread to neighbouring lots. Under BC law the current owner can be responsible for the cleanup, even if a previous owner installed the tank. Some insurers and lenders will not cover or finance a property with a tank.

   Rough costs: a scan is about $150 to $350. Removing a tank that has not leaked is about $2,000 to $10,000. Cleaning up contaminated soil can pass $50,000 and, in serious cases, cost far more.

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2. Asbestos

   A natural mineral fibre that was cheap, durable and fire resistant, so it went into many building products: drywall joint compound, textured ceilings, vermiculite attic insulation, vinyl flooring, pipe and duct wrap, and siding.

   It is not a hazard while it is sealed and left alone. When it is cut, sanded or broken during renovation, fibres get into the air and can cause serious lung disease, including mesothelioma and lung cancer.

   Rough costs: testing a few samples is inexpensive. Removal must be done by a licensed abatement contractor and often costs $10,000 to $50,000 for larger jobs.

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3. Aluminum wiring

   When copper prices rose, aluminum was used for the small branch circuits that feed outlets, switches and lights. The heavy 240-volt circuits for stoves and dryers are often aluminum too, but they are not the same concern.

   Aluminum expands and contracts more than copper and oxidizes at connections. Connections can loosen and overheat, which is a fire risk. Warning signs include warm cover plates, flickering lights, a burning smell and breakers that keep tripping.

   Rough costs: an electrician can pigtail each connection with copper, usually $1,500 to $3,000 for a house in about a day. Some insurers ask for the electrician's certificate.

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4. Knob and tube wiring

   An early wiring system with separate wires held on ceramic knobs and passed through ceramic tubes in the framing. It has no ground wire and usually came with a small fuse panel.

   The insulation becomes brittle with age, and the system was never designed for modern loads. Over-sized fuses and later add-ons can make it overheat. Many insurers will not cover a home with live knob and tube.

   Rough costs: full replacement is often $6,000 to $12,000, and more if walls must be opened.

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5. Poly-B piping

   Polybutylene, a grey plastic water supply pipe used as a cheaper alternative to copper. It is usually marked "PB" and is easiest to spot at the water heater and under sinks.

   Over time the pipe and especially the plastic fittings can crack and leak, and damage is more likely with heat, sunlight, chlorine and high water pressure. Insurers may charge more or exclude water damage.

   Rough costs: replacing it, usually with PEX, is often $6,000 to $20,000 depending on the size of the home and how much finished wall must be opened.

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6. Poor drainage

   Perimeter drains are pipes laid around the footings to carry groundwater away from the foundation. The pipe material changed over the decades: clay tile, then concrete tile, then corrugated plastic, then rigid PVC.

   Old clay and concrete tile cracks and fills with roots and silt. Corrugated plastic can be crushed. When drains fail, or the ground slopes toward the house, water gets into the basement and can lead to rot and mould.

   Signs: stains or white mineral deposits on basement walls, a musty smell, lifting flooring, peeling wall finishes, and pooling water in the yard. Repair costs vary with access, landscaping and depth.

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7. Building envelope (leaky condo)

   The envelope is the walls, windows and roof that keep rain out. In coastal BC, many wood-frame condos and townhouses built in the 1980s and 1990s had no drainage gap behind the cladding, so water that got in could not get out.

   Trapped water rots the framing inside the walls, often without visible signs. Repairs usually mean rebuilding the walls of the whole building as a rainscreen, paid for by owners through special levies.

   What to read: the depreciation report, recent strata minutes and any building envelope report. Look for past or planned special levies.

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8. Radon

   A natural radioactive gas from uranium in soil and rock. It has no colour, smell or taste, enters through cracks and gaps in the foundation, and collects in the lowest levels of a home.

   Long-term exposure raises the risk of lung cancer. Radon is the second leading cause of lung cancer in Canada. Levels depend on the ground under the home, not its age.

   Rough costs: a long-term test kit is about $30 to $50. If a test is above the Health Canada guideline of 200 Bq/m³, a certified radon mitigation professional can install a system that vents it from under the slab.

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