What is the typical cost overrun percentage for home additions in Ottawa?

Additions often cost more than the first quote, and it is smart to plan for that from the start. There isn't a reliable published figure for the typical overrun on Ottawa additions, though, so be wary of anyone who quotes one as fact. What you can do is understand where overruns come from and set up your contract and budget to absorb them.

Foundation and soil surprises. Additions involve new foundations, and what is underground isn't fully known until excavation starts. On sensitive clay, including Leda clay, the Building Code requires footing sizes to be engineered, and conditions can turn out different from what was expected. A geotechnical investigation before pricing reduces this risk.

Conditions in the existing house. When the wall where the addition connects is opened, contractors may find undersized framing, old water damage, outdated wiring or insulation that needs replacing. Older homes are more prone to this. Asking your contractor to do some exploratory opening at the connection point before the price is final can turn unknowns into known line items.

Schedule extensions. Permit reviews, inspections and changes requested during the build stretch the timeline, and a longer job carries more overhead. Ask the City for current review timelines, and ask your contractor how delays are handled in the contract.

Changes you make mid-project. Upgrading windows, moving walls, adding a bathroom or choosing different finishes after signing is the most preventable source of extra cost. Each change order means re-ordering, rescheduling and sometimes redoing finished work. Choose finishes before you sign whenever you can.

How to protect your budget:

• Get a detailed written scope that says what is included and what is excluded.


• Ask for allowances to be listed with dollar amounts so you can see where costs might move.


• Keep a contingency on top of the contract price, and ask your contractor what they would suggest for your house.


• Put every change in writing with its price before the work is done.

Know your rights too. Under Ontario's Consumer Protection Act, a supplier can't charge more than 10 per cent over an estimate in the agreement, and a contract over $50 negotiated in your home must be in writing. Under the Construction Act, the owner holds back 10 per cent of the price as work and materials are supplied.

When you compare contractors, ask how they handle unforeseen conditions and whether they have WSIB coverage or are exempt. Browsing addition contractors in the Ottawa Construction Network directory at justynrookcontracting.com and comparing itemized quotes helps you see who prices thoroughly.

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• Callandgone
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