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Covering up exposed foundation with siding/insulation

Ryan_Mount1 | Posted in General Questions on

Hi GBA, 

It’s been a little while since my last post.  Shortly I’ll be starting construction of a new home in zone 6 in Ottawa, Ontario.  2 storey home with garage in the basement.  I will definitely have a few more questions in the coming weeks/months. 

I’m contemplating insulation options for the basement.  One cost effective approach it would seem to be to use 3″ of recycled XPS on the exterior of the concrete.  This can be had for well under $1 sqft in our area.  I would then finish the interior with some more eps or polyiso, a VB if required by the inspector, and strapping/drywall.  

My top of foundation will be about 4.5 feet above grade with my sheathing hanging just proud of the concrete wall.  Self-adhered WRB/airbarrier on the sheathing, followed by 2″ of comfortboard, strapping and cement board plank siding as the main wall assembly.  My question is if I can run my WRB about 3′ down onto the concrete and continue with the comfortboard/cement board until I’m about 18″ above grade to cover up the exposed foundation.  I would then have my drip edge at the bottom of the siding with the recycled XPS below and finished in one of the accepted ways.  I haven’t been able to find much information on doing a transition like this from wood to concrete.  

Any thoughts would be much appreciated! 

GBA Prime

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  1. Expert Member


    You can certainly continue the siding over the concrete foundation. It will probably be a bit finicky to frame as the two never align exactly. Much more common though is to step down the concrete so it follows the grade. Is there a reason you don't want to do that?

  2. Ryan_Mount1 | | #2

    Thanks for the reply Malcolm. Glad my plan makes some sense. The reason for keeping the concrete higher is that it's fairly close to a river so if it were ever to flood (it has never been close to grade in the past but who knows what will happen with global warming) it gives me some extra breathing room before reaching wood framing.

    1. Expert Member
      MALCOLM TAYLOR | | #3


      Makes sense.

      One option you might consider is to end your rain-screen at the top of the foundation, and below that just frame out the wall to the thickness you need, and cover it with siding. That might be less involved than trying to secure the strapping through foam, and haring to detail the bottom of the wall close to grade with flashing. An addition benefit to having a line of flashing at the top of the foundation would be to hide any parts of the two assemblies that aren't exactly coplanar. Foundation walls rarely align perfectly with he framing above.

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