Making my mainstream building issues rounds yesterday I ran across SIPS over Timbers from these guys, two failures within 8-12 years and they can not figure out why or what to do: We are in the middle of such a build and I know it will have the same issues when I first seen the plans but, it is not my design.
"You may want to read this thread below, your design is the same. I follow alot of the debates, issues, and what other building scientist are saying and there is alot of controversy around SIPS drying directions"
We live in a high relative humidity (RH) climate zone, winter and summer, this build is in 3), so FYI. Vapor drive is from high to low RH and has little to do with air sealing, air direction, or temperature. Some are installing "whole building dehumidifiers" that choose the "dry inward" design theory. Cooling can help but you really need a humid-stat or phychrometer tied to the seams and inside building since it may not be enough around here. Since the tongue and groove is not a vapor barrier it will allow drying inward if the RH is kept low (45-50) in theory (again not temperature dependent). I prefer drying outward but, too late for that.
Since the Architects design does not dry to ventilation channels (furring strips between the metal cladding and SIPs) outward and the water and ICE is zero perm not allowing it, the only direction for drying is inward. Moisture will get between the seams/cavities (roof, walls, etc) in all buildings that is proven. That means that the relative humidity (dry bulb vs wet) indoor has to stay within 45-50 percent which is normal (for eyes, skins, etc) and never get above 70 since that is when mold spores start to germinate if there is not drying within 48 hours based on spore testing.
Hope this helps. Just would be ashamed for this roof to rot out in 8-12 years like these below with Timbers, or cause lots of indoor health or indoor air quality issues. "
The manufacture (Thermocore, MO) in my case try and make clients believe there is alot of "30+ sustaining testing" on SIPs which is a far stretch of the imagination. The test I believe being referred to is below. It is VERY limited and does not use the polyurethane or OSB we use today, manufacturing methods, or installation...the test has more natural material SIPS.
I find it interesting the Timber companies and SIP manufactures are in bed with one another, you can usually find cross-links on their sites. No mention of post and beam with a Strawbale wrap that actually does have alot of Emperical evidence starting with NE in the late 19th century. But heck, no manufacturing to make money on $ since it is done at the job site by owners or contractors, farmers! Huge hygroscopic interior mass in the form of earth and lime plasters helped keep the roof dry and free from rot.
Interesting too all the attempts to fill the seams with foam and rubber that won't work since it is too skill based at the job site. A better solution would be a continuous, no seam design. By the time you add all the cost to make this design work outside the factory you've lost the benefit and time and speed the factory provides. Thermocore seams are a joke, a open cell neoprene seal between T&G to stop capillary uptake, that is stapled to OSB, gets crushed, does very little, but yet they tell clients how great it is. The sealants/foams, seals will lose their memory over time due to fatigue. The lifetime warranty is worthless,
"This warranty does NOT include expansion and contraction of panels due to weather, or temperature or humidity differentials, ..."
I have my theories and that is what they are, theories. If the manufacture wanted to they would provide computational fluid dynamic test (lab/model, feild) and drying speeds based on drying different directions.
It would not be perfect but better than nothing. We know PU can not manage moisture since it's moisture contents is low, other than act as a barrier, nor does OSB have much holding/releasing capability. They also claim a whole r-value of 40 (6.5 thick) and the panel was never tested in the installation. They also drill holes (two per panel) to hoist them into position by crane that gets filled with open cell foam. We know in most cases it is food for fungi and rot just like water and ice. Little heat and moisture is all it needs.
So a design that is monolithic, transfers heat slowly that dries out walls without a significant heat loss, that is hygroscopic, this design cannot provide through the seams over long cycle lives. Hempcrete w/mag sheathing would be a good example that can.
I'll also recommend more wood vs drywall as interior finishes since it has better hygroscopic properties. The slab drying will probably cause seam drying issues over at least the next 6 months-year. It also needs lower RH to dry which is hard to find around here.
I'd like to see a lot more information with this level of detail on this forum. SIP's were never a major consideration in my own project but if they were I would have wanted do research well beyond what manufacturers and installers have to say about it. At first glance they do seem like an attractive option for roof panels.
I have only built with SIP's once about 10 years ago on a kit log home build. We haven't had any issues, but like you said; it's all in the details. I don't like foam in any of it's iterations, so it's not something that I will be doing again.
I was however contacted about 3 months ago to diagnose a weird wet area on a timber frame/sip home. It sounded like a lot of other problematic homes, but when I told him what I thought the problem was, he didn't want to hear it, so I was not called back.
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