I was reading through a previous post and came across a concern about using SIP's on low slope roofs.

I am planning on a 3:12 (or 4:12 if I have to for other reasons) and wanted to use OSB SIPs. Are there any concerns with this?

Planning on metal roof (probably standing seam). I live in northern BC and not sure about sourcing metal SIP's (so let's assume that's out for the time being).

Does using snow stops impact this decision at all?

Thanks
North-cooke

I think flatter SIP roofs will require more intermediate support.  I think SIPS are the strongest when installed in a vertical position.

Alton, thanks for the reply.

You brought up something I had never thought of. And, I hope that the engineer would have a suitable calculation for the support roof SIPs require.

The concern I was actually raising -- but wasn't anywhere clear enough about -- is the idea of water penetration into the SIP from a low slope roof. In this earlier post, the guy's response was that you won't know you have a leak until the roof (and probably the wall) are rotten because the water has stayed inside the panel.

So, low slope SIP roof with standing seam metal roofing -- any concerns with leaking?

Yes, I have enough concerns with leaking on a low-pitched roof that I recommend using a ventilated nail base over the SIP.  I also prefer to use a continuous peel and stick membrane over the nail base right under the metal roof.

I think there is less chance for leaks if hidden clips are used instead of screws through the metal roof.  As you know long standing seam panels have a tendency to expand and contract during temperature changes so check into the possibility of using hidden clips that allow the metal to slip and slide.  In other words, install it like vinyl siding.  I think the expansion and contraction of long panels are also bad about making the screw holes larger than the neoprene washer thus leading to leaks in the future.  Keeping the standing roof panels under 27' in length when using screws or using hidden clips that do not bind tightly should help prevent leaks.

All of the above is just my opinion.  Please treat it as such.  People who specialize in installing metal roofs should have more quality answers.

North-cooke;

 I would consider 2/12 and less as low, regardless of pitch,  spans are measured in the horizontal. Urethane metal SIPs are probably available in your area , but typically they have less span capability than EPS/metal. The upside to metal  is they will not rot and are unaffectetd by water

Being built in Virginia...................This low slope roof with 1-3/4"/12 pitch roof   and 8 ft. cantilevered overhangs front and rear, roof panels are 12" x 53 ft. long

North-cooke,

Per most building codes a 3:12 is the minimum slope to use when installing roofing products like shingles or tile. Metal roofing can be installed on a 2:12 slope roof minimum. Like Chris said 2:12 and below is considered a low slope roof. Usually in climates that have a lot of snow roof slopes are usually much greater than 3:12 to prevent too much snow accumulating on the roof and causing structural damage to the roof system. If the 3:12 roof will be designed for worst case snow load, I do not see a problem structurally. However, the building code does not cover long term moisture degradation of OSB skinned SIPs used in a roof application. In my opinion at all costs one must allow the SIPs top surface to dry as quickly as possible if it gets wet. This means allowing air to pass over the top of the SIP by some means of ventilation. So the problem is not the snow or the SIP or the slope. The problem is the extreme cold temperature and what to do with the moisture when it is driven into your roof system from the outside. Moisture driven into your roof system from the inside is a whole other discussion.

Also FYI in my opinion when using a span chart to figure out panel spans, one should use the diagonal measurement between supports for roof slopes over 5:12 and not the horizontal distance between supports. A 10:12 roof slope is over 30% longer than the equal horizontal distance under it. This 30% increase in length is not addressed in some manufacturer's span charts and may cause the panel to fail in extreme circumstances.