How do I know if my Ottawa home's foundation can handle a second-storey addition?

Whether your foundation can carry a second storey is the question that shapes the whole project: the budget, the timeline and sometimes whether it is feasible at all. The way to find out is a structural assessment by a Professional Engineer. A second storey adds a lot of weight, and the City lists structural alterations among permit projects, so expect your designer to need engineering for the permit drawings.

The engineer looks at several things. The first is the foundation walls themselves: what they are made of, how thick they are, and their condition. Poured concrete, concrete block and older stone foundations behave differently, and older foundations may need reinforcement or underpinning before they can carry more load. Cracks, bowing or water damage all need to be understood before anything is added above.

The second is the footings. Foundation walls sit on footings that spread the building's weight into the soil, and those footings were sized for the house as it was built. Adding a storey increases the load on them. The engineer compares the new load with what the soil can support. Soil varies a lot across the Ottawa area, and on sensitive clay, including Leda clay, the Ontario Building Code requires footing sizes to be engineered.

That is why a geotechnical investigation is often recommended alongside the structural assessment, especially on clay. Test holes near the foundation tell the engineer what the soil is and how much it can carry. Without that information the engineer may have to make conservative assumptions, which can lead to a more expensive design than needed.

The third is the first-floor framing. Joists, beams, columns and their connections have to carry the new loads down to the foundation. Undersized members may need new beams or posts in the basement. The engineer will also look for sagging, deflection or earlier renovations that complicate the load path.

Frost matters too. Under the Building Code, footings in clay or soils that are not clearly defined must be at least 1.2 m deep and not less than the depth of frost penetration. Extra weight on footings in marginal soil can cause uneven settlement, and any existing deterioration should be repaired before adding load.

Do the assessment before you commit to a design. The engineering fee is small compared with the project, and it tells you what reinforcement, if any, will be needed so you can price the whole job. Then ask for itemized quotes from addition contractors in the Ottawa Construction Network directory.

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• 613Bins
• JC Carpentry
• Custom By Arie
• Speedy Pete's Inc
• Steven Labelle - Your Complete Home Renovator