Frost protected shallow foundations

[Bill Houghton]

Bill,

I used sfpf in northern Wisconsin on a off and on heated weekend cabin, the inspector had no problems and did not balk at this method at all, I myself was worried but this method is adopted in the UDC code. It has been 3 years now and no heaving at all. Make sure you use the high density foam.

jr1318,

Thanks for your input.  How deep did you go with your frost walls + footing?  Was it a monolithic slab with thickened periphery or footing and block wall?  Is the high density foam the blue board from the Big Box or do I have to special order something?

Also Glenn, thanks for the pic and info on the truss above.  There was a lot of good stuff on that site.


Bill in the U.P.

[tc-vt]

Bill,

Here is a picture (and the direct link to it) of a truss that closely resembles my trusses.  On mine the section of the truss where the top chord for the roof is parallel to the interior bottom chord is longer.

Tom

http://www.djjackson.ca/tray.html

[Bill Houghton]

Tom,

Dont you have an attic truss or are your trusses a combination of the two?

Bill

[jr1318]

Bill,

I went down 12 inches brought in 6 inches of sand for good drainage ( I built on a heavy soil almost like clay) laid my foam, set forms for concrete brought in 12 more inches of sand. It is a monolythick slab with 16 inch deep by 16 inch wide edges, and poured slab. The foam you need is blue but there is a high density, I know the big box in St Paul area of Minnesota and Western Wisconsin do carry it.

Jim

[tc-vt]

Bill, 

I found a few pictures.  You can't see the top chord because it is buried in the sprayed foam insulation.  That section of the trusses, the part below the level of the ceiling, is only about8 inches deep.  I might have better ones at home that show the trusses before the foam insulation was done.







I'm almost sure the foam you want is extruded polystyrene (EPS) and not expanded polystyrene (XPS).  The two most common brands of extruded polystyrene are Dow Blueboard and Owens-Corning 'pinkboard'.  They come in 2x8 foot sheets with tongue and groove in thicknesses of 1/2, 1 and 2 inches - maybe others.  There is also 1/4 inch available.

Tom

[Bill Houghton]

Jim,

Thanks for the information.  Any links here to your project?  I'd like to see it.


Tom,

Thanks for the truss (and all the other) information.  Is that Icynene foam that you had sprayed into your wall and ceiling cavities? 

Just checked with Menards, 14" deep, 24' long I joists about $56 each, so between $1175 to $1344 for my second floor if the attic trusses don't work out.



Bill

[tc-vt]

Bill,

That's closed cell foam.  I went for about 2-1/2 to 3 inches in the walls and about 4-5 inches under the roof.  It has an R-value of around 7 per inch.  As I understand, as it ages the R-value decreases a bit as the blowing gas is replaced by air.  I think it cost around $5200 for my 20x30 with 3 foot high knee walls and 12/12 pitch roof.


Tom

[Bill Houghton]

Hi Tom,

Did you spray that foam in yourself?  Was it like the tiger foam kits or one of those?  Did you finish your second floor with an open ceiling to the peak?

This week I am looking into the availablity of the denser foam for my FPSF design.  I think I am going to cover the whole bottom of my excavaton with 4" of foam (over gravel), then put the treated wood footings right on top, per the FPSF unheated structure design.  That way I can insulate below my floor to avoid heat loss and not worry about having to heat under the footing for frost projection.  It will be about 50 4x8 sheets of 4", so I hope the price isn't way up there. 

Well, just got the quote for the 4" of foam, $2200!  Maybe I will end up with a poured footing and 42" block frost wall yet.

The truss quote should be here in the next hour.

Thanks again for everyones help.

Bill in the U.P.

[tc-vt]

Bill,

I contracted the fam job.  The kits I have seen are only for small jobs.

Tom