Styrofoam insulation of a foundation.... 1

[CELinOttawa]

Has anyone seen a styrofoam lining used to separate a residential walk-out foundation from the poured slab on the inside? I couldn't think of any reason why this would be done... See attached photo (wall to slab interface shown). I'll post a sketch if anyone is unclear.

Pay no attention to the window on the left hand side - That's just waiting to be installed.

 

[Archie264]

I'm not entirely sure what I'm looking at but could it be part of a frost-protected shallow foundation? If you're in Ottawa I suspect you know far more about those than me, but in any case here's a relevant link:

http://www.nahb.org/assets/docs/pub...ected-shallow-foundations_1211200244041PM.pdf

 

[CELinOttawa]

Frost protected foundations keep the internal heat in the foundation.... This is the opposite; The insulation is on the INSIDE. I'm starting to think someone misread the plans... *sigh*

 

[CELinOttawa]

Well Archie, it looks like you're right.... This is shown as one of the types of frost protected foundations; I've just never seen this one. They are almost always the "traditional" (the reference's term) type around here.

First time for everything... Thanks for the link, not a bar reference. A star for your trouble.

 

[Archie264]

Could be. The possibilities for misinterpretation are nearly endless. I once saw a picture of a section call built into the pavement. The builder thought it was supposed to be part of the building! That's one example of why I believe that good, clean drafting still matters.

 

[Archie264]

Hey, thanks, no trouble. Our posts crossed in the mail, by the way.

 

[dik]

Used them lots of times... Type 4, Extruded polystyrene... works well and have used it to protect footings for walk out type basements as well as stairwells...

Dik

 

[CELinOttawa]

I've actually designed them as well, but I haven't see the type that captures the heat in the slab as well as at the foundation wall's outside surface. Seems a bit counter-intuitive; I would think you want the heat from the slab to get to the foundation wall and to the keep it there, but there are some of these FPSF details which seem to first try to keep the heat from leaving the slab, and then have the outter wall insulation I used to...

 

[jayrod12]

I've seen it installed on the inside face like that to prevent the cold outside from travelling through the grade beam to the slab. It's for comfort in an attempt to keep the slab slightly warmer. I believe the architects used the term cold strike.

 

[dik]

CEL... insulation usually placed on outside of foundation, too, to try to minimise any heat loss. Our neighbourhood can be cool in the winter.

Dik

 

[CELinOttawa]

I've seen, and specified, the insulation on the outside of the foundation... My hesitation about placing the styrofoam on the inside is that this is a shallow foundation. Should the heat fail (which has happened, and in fact happened for some people for more than three weeks in the dead of winter in 1998), the insulation between the slab and the inside face of the foundation wall could deny the foundation heat needed to prevent frost heave.

I really dislike this particular type of FPSF. I don't think it is a wise detail for the serious cold of come Canadian climes, including Ottawa. Why not simply double the insulation on the outside? I looked at the amount of insulation involved, and the total is MORE for the installation all under the slab and to the edges versus a second layer of insulation on the outside.