What's the required foundation depth for building a new home?

The existing 24-inch foundation is too shallow for today’s standards and doesn’t meet Ontario Building Code requirements for a new two-storey home. Modern homes must sit on foundations that reach the frost line, which is about 48 inches deep, and the old foundation likely cannot support the added weight of a second storey. In most cases, the foundation would need to be replaced or significantly upgraded before building. If you’d like more information or want help reviewing your options, feel free to contact us anytime. We can guide you through every step of the process.

You have to reach the frost line based on OBC (Ontario Building Code), and it's at least 4ft (120 cm) for the GTA new built houses.

Ultimately I think the best person too answer this question would be an engineer. But there are variables too your question. Since you would be adding a two storey home on top of the existing foundation that was meant for the weight of a bunglow as previously mentioned, I woukd think that it is not sufficient for a two storey home build onto it. When was the foundation originally poured? if you are going too be removing the old house anyway why not just get the foundation redone also and maybe have a basement incorporated too your new two storey home. All things point too not reusing the foundation too me. Again its just an opinion and the engineer would have too tell you based on load calculations and how brittle or not the current foundation is and if it survives the demo process as well. Thx

In Ontario, standard depth for a structure such as your describing requires foundations to be built to 48” depth (frost line). It’s most cost effective to remove the existing foundation, excavate to the appropriate depth, and build a new footing and foundation. Good luck!

OBC requirements differ from area to area. The 24" does not meet current standards.

You will need a minimum of 48" as it must be below the frost line. If you are not needing the basement, you can save a lot of money and build on helical piles. Of course you will need an architect, engineer and a building permit before you can start construction.

The short answer is probably not without a proper engineer’s review. Modern foundations are usually deeper than older ones because of frost depth, soil conditions, and the added weight of a two-storey structure. A 24-inch foundation with 10 inches of concrete might have been fine for your bungalow, but a two-storey home usually requires at least 36 inches and sometimes more depending on your soil. Before building, you’ll need a structural engineer to inspect the existing foundation. They can tell you if it can be reinforced or if it needs to be replaced entirely. Building without meeting current standards is risky and could lead to serious structural issues later.

It might be possible to build a two-storey house on the existing foundation, but it cannot be assumed. Older bungalow foundations at about 24" deep are often too shallow by today’s standards. Foundation depth is mainly to protect against frost, which is usually done by going below frost level (often around 4 ft) or by using rigid insulation to create a frost-protected shallow foundation. If the property is in a flood zone, deeper foundations may not be allowed, and insulated shallow designs are often used instead. A two-storey house is also much heavier than a bungalow, so the existing foundation must be checked to see if it can handle the extra weight. Based on our several experiences in building new homes, we can offer a free meeting session to review your foundation and explain the best options before you move forward.