Getting ready to build a timberframe home. SIP panels are used for the walls and roof. Alot of the timberframe companies say that it’s fine to place the roofing material — felt and shingles — directly on the SIP panels w/o any kind of air circulation. Thus no soffet vents. That said, one vendor has a system that goes with their SIP panels that provides for the air space.
Thoughts? I know i need to buy more expensive shingles…thicker ones designed for hot roofs, but besides that is there much i should be concerned with and is it worth the extra cost of ferring up and installing a layer of sheathing above the SIP panels <– expensive and a pain. These panels have an R value of around 40 so i don’t think that the house will hot. BTW, there is no attic in these house…the ceiling is essentially the bottom of these SIP panels.
In case you’re not familiar with these SIP panels…essentially they are styrophome (EPS) between two layers of OSB.
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There has been some testing studies that indicate that composition shingles can have a reduced life in such an instance. That has led a few of the manufacturers to disclaim warantees for that kind of installation, so choose shingle brand accordingly.
In practice, most of us have found that the reduction in life expectancy is can be measured in months, a small portion of the overall lifespan projected. I think my memory is that the tests showed up to a 2-3% reduction in lifespan.
But the problem is that if the manufacturer has a bad batch, which lands on your roof, and you have them installed over an unvented space, you are "up a roof without a ladder" to paraphrase a popular cliche'.
Ano5ther concern you want to pay attention to is to be sure that all joints in your SIPs are well sealed with spray foam or whatever is recommended and that youhave a whole house ventilation and heat recovery system to control interior humidity that will otherwise collect at the ridge and feed the mold spores. Ask if the foam in your SIPs is teated with Borates which discourages both bugs and mold.
And I know you didn't ask, but by all means, use tarpaper underlayment. Some so-called roofers try to get by without it.
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Thanks...actually that's encouraging...months rather than years Most of these TF suppliers spec a 40 year shingle that's rated for a hot roof so hopefully that'll cover the warrenty/bad batch issue.
in this situation, is the surface of the roof noticably hotter to the touch and if so is there concerns w/walking on it when it's really hot?
Also thanks for reminding me about the borate treatment for the EPS. I guess i shouldn't assume that they are all treated.
There are ALWAYS problems walking on comp shingles in summer sun.
BTW, the color of the shingle and the part of the country your are in has more impact on life expectancy than the insulation/ventilation deal.
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