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Community and Q&A

Pier and beam foundation in Climate zone 5

SouthGeorgianBay | Posted in General Questions on

I’m planning to build an efficient house in southern Ontario, and am looking at different foundation options. Any feedback would be greatly appreciated.

Here is one approach I’m considering: pier and beam, with deep open web floor trusses resting on the beams. The underside of the trusses would be sheathed in plywood. My preferred insulation, at this point, is dense packed cellulose insulation. I would use floor trusses at least 18″ deep. Airsealing would be a high priority.

A crucial detail to making this design work is freeze protection for the water supply line and drain pipe (plumbing is bunched together on the first floor). How have others handled this?

My thinking is to build a (very well) insulated box that would extend from the underside of the house to below the frost line (yes, like an insulated, unvented crawlspace), backed up with heat tape on the water supply line.


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  1. GBA Editor
    Martin Holladay | | #1

    Your suggested approach is the typical method of preventing pipes from freezing when you have a house on piers. I don't like the approach, because heat tape can fail, and electricity outages happen. For cold-climate homes, I prefer basements.

  2. Expert Member

    Graham, Whether the "box" is made of wood or concrete, the key to its success is to treat it as part of the heated building envelope, rather than something separate that relies on supplemental heat.
    My own preference is to build these service cores as mini basements with concrete walls, which can be insulated either internally or on the exterior. leave the top completely open so that it stays the same temperature as the rest of the house. That way the only time the services in the core can freeze is if the whole house loses heat - and in that situation you have more to worry about than just the core.

  3. SouthGeorgianBay | | #3

    Those are helpful suggestions Martin and Malcolm. Definitely worth doing this well. The street is known for wet basements, but a small conditioned space, maybe 6 feet by 6 feet (directly under the utility room) should be relatively easy to keep dry and warm, while avoiding using mountains of foam and concrete (part of the reason I'm thinking pier and beam in the first place).

  4. Expert Member

    The other benefit of incorporating a small square concrete core in a pier foundation is that you can use it as part of your shear bracing.

    The most common problem I see with pier foundations is that they get enclosed over time and then become a neither-nor space which is really a very poor crawlspace harbouring all sorts of pests with limited airflow. The trick is to make the piers architecturally interesting and provide a good ground cover so there is nothing to hide and no reason to enclose.

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