SIP rot fix and... skylights!
Last Post 23 Aug 2019 05:09 PM by Dilettante. 3 Replies.
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daskcUser is Offline
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21 Aug 2019 08:26 PM
I bought a house a few years ago (on a budget) and have recently discovered that the roof structure is comprised of SIPs, as I've been slowly chipping away at renovations.

With each new project on the house, it becomes increasingly clear that the previous owner/builder was far more interested in cheap construction than quality/green/efficient building. The main house structure is comprised of steel C beams that form a gamble roof, with the top of the roof being nearly flat. The beams are around 6' on center, and then there are SIPs running perpendicular across them. And that's it. No other 2x framing that I'm aware of for this part of the house.

Initially, the "flat" roof was tar/gravel, which continued to leak, so the PO framed out a 5 degree pitch on top with ripped down 2x6's and 1x4 cross-members, screwing down corrugated metal on top of it. That leaked, too. Surprise! I've just recently added decking to this framing, ice/water shield, and hired out a contractor to install standing seam metal. No more leaks, thus far. I also cut a small channel into the ridge to allow for what I hope will be enough venting through the new ridge vent to allow for moisture to pass through and escape. There's no doubt in my mind that interior joints weren't taped.

At any rate, the good news is that there isn't any visible sagging on the interior (after nearly 40 years of leaks, etc.). I'm pretty confident, as such, that keeping the roof dry and allowing for some venting will extend the life of the house considerably. Perhaps the lack of attention to air tight construction has ironically staved off much more severe issues. On the other hand, it may be that the tar/gravel has hidden a fair amount of rot but kept the SIPs from experiencing sag.

Part of why I think it's partly the latter (other than the fact that you'd generally expect it to be the case, given what I've described), is because I've seen OSB rot on the steep sides of the gamble roof where there are asphalt shingles. I also think it's probably just as likely that it's the result of poorly installed flashing. At any rate, I'm having those shingles replaced next, but unsure how to address any OSB rot beforehand. It doesn't appear to be too extensive, but I won't know until removing the shingles. Again, since this home is a "budget" find, I'm looking for a relatively inexpensive fix. Any ideas are greatly appreciated.

Also, I'm going to be installing skylights -- which will essentially be windows since the 70 degree side roof line forms an angled interior wall. It's funky, but I actually like that it's a little different. That being said, the space desperately needs natural light. So I need to frame out for these sizable skylights (4'x4'), but not sure how to go about it. It doesn't seem like these SIPs are really carrying roof load up above -- with the steel frame handling that -- so I don't think there's a need for headers, etc. I've done quite a bit of remodeling work over the last decade, but this is new for me, so again... any ideas will be kindly received!

Thanks for taking the time to read and share your thoughts!

-David
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23 Aug 2019 07:00 AM
I'm sorry to say, that if you have face damage on a SIP, you NEED to get an engineer involved. You can't simply strip off rotted OSB and slap new OSB into place. Even with adhesives and screws/nails. The structure of the SIP has been compromised.

IF you are able to effect repairs, make sure you rebuild with an air gapped cold roof over the top of the SIP roof surface.

If you have to strip the rooftop, you may also see the spray-foam "fill" between panels has likely contracted away from neighboring structures and isn't actually filling the gaps anymore.
If you're able to repair, you can do something about it during the repair process.
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23 Aug 2019 02:31 PM
Thanks for the insights! Definitely was hoping that there'd be some potential for repair, and perhaps there will be with an engineer's insight. Are you aware of good regional or national associations/databases of engineers that have familiarity with SIPs?

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23 Aug 2019 05:09 PM
Unfortunately *I* am not (hence my moniker). =)
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