What makes a house hard or expensive to insure?
Knob-and-tube or aluminum wiring, galvanized or polybutylene plumbing, a sixty amp service, a roof past its life, an oil tank, and a history of water claims. Any of these can mean a surcharge, a condition to fix within thirty days, or a refusal.
Insurers price the things that cause fires and floods, which are the same things buyers ignore at a showing.
Electrical: knob-and-tube and aluminum branch wiring often require replacement or a specific inspection. A sixty amp service is usually a decline or a condition to upgrade.
Plumbing: galvanized supply lines corrode and polybutylene fails, and both drive water claims. Some insurers refuse outright.
Roof: past its expected life means a claim waiting to happen, so expect a condition requiring replacement within a set period.
Oil: a current or former underground tank is the most serious of these. Contaminated soil is a remediation bill that can pass six figures, and it becomes yours on closing.
Get a quote during your condition period, not after. If a property is uninsurable your lender will not advance funds, so this is a financing problem as much as an insurance one.
Next questions
What is knob-and-tube wiring and does it matter?
Pre-1950s wiring with no ground, insulated with cloth and rubber that becomes brittle. It matters mainly because insurers surcharge, condition or decline on it, and a full replacement is a five figure job.
Ontario
How old is too old for a roof, furnace or water heater?
Asphalt shingles last fifteen to twenty-five years, a furnace fifteen to twenty, an air conditioner twelve to fifteen, a water heater eight to twelve, and windows twenty to thirty. Anything within five years of the end of that range is a cost you are buying.
Market practice