Thread: Structural Insulated Panel ??

Hopefully somebody here is more familiar with SIP construction than I am.

I did my second SIP home in 9 years. The first one had no visible structural problems. This one, however, had many.

The house had signficant foundation settling that has caused what I think is extreme deflection in 2 SIP roof panels. Both had about 1 inch of deflection, or more appropriately creased, over a span of about 1.5 feet. OSB cladding on both sides is intact without cracks or visible de-lamination, but I'm wondering how much deflection is acceptable without significantly weakening the panels' structural integrity. I did recommend a structural engineer look at the roof along with the foundation.

There was also absolutely no attic ventilation and no insulation above ceilings. Is this common? Most information I've researched indicates that the average R Value of SIP panels is about 15. Wrote both up as defective.

Thanks in advance for any info or input.

Jeff

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Jeff,

A true SIPs house (panels as roof) would not require attic ventilation as the attic would be unventilated (i.e. conditioned space). The SIPs is the insulation and the air barrier. The ceiling would not be insulated.

Originally Posted by Bob Spermo

A true SIPs house (panels as roof) would not require attic ventilation as the attic would be unventilated (i.e. conditioned space). The SIPs is the insulation and the air barrier. The ceiling would not be insulated.

I agree. The SIP panels are both the thermal and pressure boundary of the house which would make the attic within the conditioned space (so the attic floor does not need to be insulated).

If enough movement has occured to open gaps between the SIP panels the integrity of the pressure boundary and the thermal boundary have likely been compromised. I would recommend a blower door test along with an IR camera to verify the integrity of the SIP panel joints.

The R value is dependant on 2 things, the type of foam used and the thickness. It could easily be an R 48 roof.

Originally Posted by Jeff Spencer

Hopefully somebody here is more familiar with SIP construction than I am.

I did my second SIP home in 9 years. The first one had no visible structural problems. This one, however, had many.

The house had signficant foundation settling that has caused what I think is extreme deflection in 2 SIP roof panels. Both had about 1 inch of deflection, or more appropriately creased, over a span of about 1.5 feet. OSB cladding on both sides is intact without cracks or visible de-lamination, but I'm wondering how much deflection is acceptable without significantly weakening the panels' structural integrity. I did recommend a structural engineer look at the roof along with the foundation.

There was also absolutely no attic ventilation and no insulation above ceilings. Is this common? Most information I've researched indicates that the average R Value of SIP panels is about 15. Wrote both up as defective.

Thanks in advance for any info or input.

Jeff

A little link for examples.

4-1/2" SIPs

There is of course poly foam panels that are about an R6.5 or so per inch so a 3 1/2 inch foam core would give about , I believe, into the low to mid R20s. The standard panel gives about an R17 for a 3 1/2 core. In reality, and I get dispute all the time, the R value as far as I am concerned is much greater than a standard stic frame and bat insulation do to how tight it is. No drafts, consistent or more uniform insulation, air leaks around boxes is zilch etc etc.

I think sips are fantastic for building and the next home will probably be a sip home. Heat and AC are extremely cheap in a sip home. Of course if you bump the core up to
6 1/2 inches then you are an R25 with standard foam and the roof could be an R50. Now kick that up a notch with poly and cool the home with a few ice cubes and a fan and heat it with a few candles. Of course nice windows as well.

Great for a retirement home.