What is a party wall?

A party wall is a wall that forms the boundary between two separate properties and belongs jointly to both property owners. In Ontario, party walls are common in semi-detached homes, townhouses, and connected residential buildings where the wall serves as the physical divider between neighbouring units.

Before demolishing or significantly altering a party wall, property owners must notify their neighbours and typically secure written agreement. This requirement exists because damage to a party wall can affect the structural integrity, support, and safety of the adjacent property. The wall may carry the roof load of both buildings or provide lateral bracing, so careless removal can cause the neighbour's structure to shift, settle, or fail.

When demolition contractors are brought in to work on a property with a party wall, they need to confirm whether the wall will be removed, retained, or modified. If removal or significant work is planned, contractors should verify that the property owner has obtained neighbour consent and understands local building code requirements. Failure to follow proper procedures can result in liability, stop-work orders, or costly repairs to an adjacent home.

Party wall agreements also clarify who bears the cost of any damage, how work will be sequenced, and what temporary bracing or support is needed during construction to protect both properties.