SIPs best practices: roof, siding, wallb
I’ve been reading all I can here and all over the net trying to find a “best practices” guide for building with SIPs. The manufacturers are often coy about key issues and I’m… confused.
FYI, I’ll be building in the California mountains – moderate temps (lows around 20F in the winter, highs around 90F in the summer, usually between 30F and 80F), with lots of snow (a few storms already this year, 120 psf snow loads, up the six feet in a single storm).
ROOF
More so than even with a normal roof, I find a lot of conflicting information regarding the hot/cold SIP roof issue. Current code in Juneau following the problems with SIPs roofs there is to require a cold roof with 1.5″ gap between the SIP OSB and the actual roof decking. So the roof is
– SIP
– 2×2 strapping
– roof decking
– felt
– roofing
This seems like an expensive, laborious and wasteful way to build a roof. It makes me think that if it’s going to involve that much labor, I may as well do something like 12″ TJI, blown-in cellulose and baffles. That’s two whole layers of OSB saved.
SIDING
Do I need furring? Some sources seem to say that you can put felt/housewrap right over the SIPs, but others say that if you aren’t using clapboards, you need to provide a space for airflow. We will like put up something like Hardipanel (fiber cement) because of the fire hazard. So am I back to SIP + felt + furring + siding?
WALL COVERING (wallboard, T&G, etc</b>
Can I put the wallboard/tongue-and-groove, whatever right over the SIPs?
Confused,
Tom
Replies
Do I need furring? Some sources seem to say that you can put felt/housewrap right over the SIPs, but others say that if you aren't using clapboards, you need to provide a space for airflow. We will like put up something like Hardipanel (fiber cement) because of the fire hazard. So am I back to SIP + felt + furring + siding?
I don't know about hardipanel, but if you use hardi lap siding, you can avoid the furring if you use SS fibercement screws instead of nails. That is what I did on my house. On the other hand, furring it out for a rainscreen design is a very safe way to go.
Can I put the wallboard/tongue-and-groove, whatever right over the SIPs?
My panel installers screwed drywall to the wall panels before putting them up. Because I built a timberframe, this saved me from having to cut sheetrock to fit tight to the posts and braces, etc. On my ceiling, I applied t&G cedar to the frame, then tar paper, then had the panels set on top of the exposed ceiling. This prevented me from having to cut the cedar to fit between the timber frame rafters. In doing my research before building, I found many different opinions and no consensus on many issues.
I don't know about hardipanel,
Same stuff as hardiplank (the lap siding you're talking about), but since it doesn't lap, the whole thing is in contact with what's behind it and therefore less able to allow airflow (though I hardiplank has a fair bit of contact area as well).
I applied t&G cedar to the frame, then tar paper, then had the panels set on top of the exposed ceiling.
I actually have some cedar on the lot that I'm thinking of having milled and putting on the ceiling, so that sounds fairly appealing. I don't quite follow, though. It sounds like you have this system:
- t&g cedar concealing the frame
- empty space except for frame members
- paper on top of the frame
- panels on top of the paper
- presumably more paper and whatever roof you have.
Is that right?
problems associated with snow shedding make it better to keep it all up there IMHO
Well, one part of a certain couple wants to go with a metal roof partly because it sheds snow, though mostly for the fire resistance. The other part of said couple would rather have something that would keep the snow up there, rather than sliding and destroying everything on its way down. However, I have yet to see a recent park service building at our altitude with anything but a metal roof, so I'm thinking they might know something I don't.
Ultimately, whether it sheds the snow or not, local code requires it to be built to handle the load, so that's a constant. But it seems to me that if I'm going to have a thick roof no matter what, I can put lots of insulation up there with many systems, SIPs or otherwise, and I'm having trouble seeing how doing a cold roof with SIPs is worth the trouble.
Thanks for the info guys
Tom
I actually have some cedar on the lot that I'm thinking of having milled and putting on the ceiling, so that sounds fairly appealing. I don't quite follow, though. It sounds like you have this system: - t&g cedar concealing the frame - empty space except for frame members - paper on top of the frame - panels on top of the paper - presumably more paper and whatever roof you have.
Actually what I did was to sheathe the outside of the frame (rafters) with the cedar, good side facing in. This allows the entire frame to be visible from within the house. I then tar papered the cedar (from the outside) as a safeguard against any knotholes or cracks which might develop and expose the panels. Then I had the panels placed over the tar paper, and then another layer of tar paper over the outside of the panels. On this I installed hiden fastener metal roof, which sort of mimicks the standing seam roofs but without the need for special seam forming tools. It doesn't look quite as authentic as a true standing seam, but it was a lot cheaper as I could do it myself. The roof manufacturer permits installing the roof without an air space or "cold roof" design. The nice thing about the panels in my case was the ability to expose the rafter timber framing, as well as simplifying the insulation process.
My pitch is 12/12, so I don't get any real snow buildup before it slides off. Last winter, I never saw any more than 2" on the roof, and yes, we got a lot more snow than that last winter! While it still accumulates on the ground, it does not seem to come off in huge, potentially dangerous avalanches. If the roof pitch is steep, even with your snowfall, you probably won't have the sliding problems. You will have a huge pile of snow next to your house.....
Wally and Mike,somehow I missed these followups when they came up. Belated thanks.Mike, I really like that system and have been thinking along those lines more and more.BTW I have a huge pile of snow next to my house now. You mean I'll have a huger pile ;-)
I haven't worked with SIPs, but in a high snowfall area like yours, you'd be well advised to go with a cold, snow-retaining roof and engineer it for the load. The problems associated with snow shedding make it better to keep it all up there IMHO. So that means strapping the roof out for airflow as you described. You didn't say what type of roof material you were going with. If it is to be some kind of metal or masonry tile, then your strapping will do double duty: cold roof separation and roofing material anchorage. That might even affect your choice of roof altogether - saving the material cost and labour cost of installing OSB might make other roofing materials worth considering. Lot easier to haul bundles of 2x2 around up there than 4x8 sheet stock.
Wally
Lot easier to haul bundles of 2x2 around up there than 4x8 sheet stock.
Okay, I hadn't thought of that. In other words, a thrid option is to choose a roofing option that can go on 2x2 @ 16" OC or something like that? That brings me back to metal or something quite expensive doesn't it?
There are quite a few options that come to mind, and I'm sure a visit to a few roofing suppliers would briung many more to light. Obviously cedar shakes are not an option because of fire, and they are getting expensive anyway.
Terra cotta and other ceramic tiles make a distinctive architectural statement that may or may not work for you. They reflect a lot of solar energy and therefore make for a cooler roof in the summer. But also heavy and require some special tools to cut.
Metal roof can be expensive, and if you go with standing seam, you won't be able to do it yourself unless you have access to some pretty serious equipment. Simple corrugated steel is inexpensive and easy to handle and work, but it has a distinctive look that may or may not please your eye.
There are some nice stone-coated metal tile systems on the market that are attractive, light, D-I-Y-friendly and bombproof. Buy-in cost is higher than ashphalt but you won't be up there shingling again in 20 years either. http://www.decra.com/ for a look at one of the systems. Worth checking out because there are so many different looks and colours available.
Common to all of these is the possibility that the extra cost compared to ashphalt will be reduced or possibly neutralised by the savings gained from not having to pay for purchase and installation of OSB sheathing.
Wally
wallyLignum est bonum.
tlambert
I'd be curious to know how bomber screwing 2x2 straps to 1/2" osb is. Could be it doesn't matter.
Can't go wrong with a rain screen for any siding imho, although the attachment of the strapping presents itself again.
I've also seen drywall put on before installing the panels, could do the same with any interior finish I think.
I'd be curious to know how bomber screwing 2x2 straps to 1/2" osb is. Could be it doesn't matter.
I think it does matter. My (extremely limited) understanding is that if it needs strength, you back the furring with adhesive and get a a nice strong bond between the OSB and the furring pretty much regardless of what the screws do.
Tom