Slab on grade foundation

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Posted by: from Brampton
10/12/2012 at 10:07:36 PM

Looking at building a new home and was looking at all the different foundations set-ups.

Has anyone done a slab to grade foundation? Are they permitted to be built in Ontario?

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Date/Time10/13/2012 at 12:35:32 AM

Hi Marko:

Not being familiar with your building codes, I cannot see why that type of construction is not permitted.

Slab on grade is the cheapest way to go. However, I have never built a home on slab. It proves to be very hard on the legs over time, and the slabs generally are cold.

I prefer to build on a 4 foot crawlspace. The crawl can be heated and if you use central heat ( as we do with heat pumps) the crawl stays warm and it can be used for your ducting/furnace and for extra storage.

We use one piece TJI's (premade engineered floor trusses) and they provide a good level solid base for your subflooring.

A house on a crawl or full basement will be worth more to a potential buyer than a slab home. Also, extra electrical drops can be left in the crawl for future expansion or needs.

What ever you do, the footings have to be taken to frost grade. With a slab on grade you then have to fill in the hole. You already have the footings and pony walls in place. Normally you pour a 2 inch slab of concrete for the floor in the crawl. The difference that you are talking about is the cost of the floor trusses and your sub floor vs 2 inches more cement. Not a lot of $$$ difference.

Good luck with your decision.


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Date/Time10/13/2012 at 3:33:14 PM

You can build slab on grade, but there are issues involved.

You must use a method of hard foam insulation or install an electric or water heating system through out the base of the concrete pour.

By the time you do this, I see no advantage of building this way. In addition, you pick up the square footage of the structure in a basement if you build the foundation and basement floor so you have a finished cieling hieght of 8'. If you are building 9' cielings in your new home I suggest you plan for 9' cielings in the basement as well. Also large windows.

This route is your best return on investment. And gives you more space to enjoy while you are in the home.

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Marko in Brampton
Date/Time10/13/2012 at 10:35:31 PM

Thanks for the reply.

I'm looking at building green thats why I was asking, minimizing my cost and waste of materials, I have a quote for full off grid system and they made a suggestion to build on a slab.

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Dave from 360renos in Navan
Date/Time10/14/2012 at 10:11:24 AM

Good Morning Marko

Yes they can be built in Ontario.

The minimum depth for the footings for an area containing no heated space is 1.2 meters BUT not less than the depth of the frost penetration which for the Toronto area is about 1.5 meters - taken from the latest Tarion Tables.

You just want to ensure the frost heave and adfreezing (soil can also adhere to the outer surface of the foundation walls and footings and exert an upward force directly on the wall) will not happen.

Preventing frost related problems with slab on grade should be followed with all of the latest in best practices such as free draining backfill, impermeable caps, foundation slip planes, exterior insualtion.

So you are going to be completing some digging and earth removal for your foundation one way or another and you would need to compare the costs to ensure your home requirements are met versus budget.

Hope this helps.



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