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newflowers
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Posts:29
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| 04/27/2008 10:16 PM |
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I am still very much into my research phase as our build is another threeish years away. I do know we will build a small house with SIPs for the exterior walls and roof. The house plan I've selected is a one story, 1564 sq.ft., 1:12 roof pitch (which will be covered with metal) in Northern Idaho. Like most stock plans, this one is perfect except I will change the placement of a bathroom and add an attached garage.
My question is about vented versus unvented roofs. It seems to me that if one is going to build SIP, an unvented roof is a must. However, I have read some conflicting information about unvented roof in cold climates, yet it seems to me that with appropriate HVAC, this would be best. Even on the building science site, my understanding is unvented is better for hot/humid climates, but there was another article that indicated cold climate but...
So experts - do tell. Why vented? Why unvented? I am most interested as it applies to building in a cold climate. |
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trigem1
Registered Users
Posts:46
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| 04/28/2008 6:58 PM |
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I just happened to be over at the Building Dept here in Colorado, and I posed your question to the housing inspector. At least here in Grand County, if you have a SIP roof, there is no need for any venting. But if you're putting insulation right under the roof, you must have ridge venting, soffet venting, and a 1" gap between the bottom of the roof and the insulation. They like to see a plastic ridged spacer attached to the inside under the roof. Another tidbit he volunteered was that on the inside of your SIP walls, he said it would be OK to tape the OSB joints and just spread drywall mud onto the OSB, and that would satisfy the fire codes. No cutting or hanging drywall. I thought I’d try it on a piece of scrap OSB and see how well it would stick. If I wasn’t happy with it, I’d just screw some metal lathe to the OSB. How much would that save? SIP’s are looking better all the time.
Steve
GrandCountySIPs.com
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newflowers
Registered Users
Posts:29
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| 04/28/2008 8:36 PM |
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Steve - thanks so much for remembering my question while you were out. You're right - SIPs really are looking better and better all of the time. Even if one considers that it may be slightly more expensive, when one considers all of the advantages of using SIPs, those supposedly extra costs seem to melt if trying for the same quality in a stick built.
So... unvented roofs using SIPs may be specific to the county building requirements - I'll have to check with the Bonner County people and see what they have to say.
It seems to me that if the roof has the extra space here and there, the building cannot be airtight because between the inch gap and venting, there is definitely going to be air infiltration unless the roofing perfectionist is on duty. Wouldn't a thermal break cause ice damming and thus break/ruin the roof? This seems a primary reason for unvented roof assemblies. Or am I not reasoning clearly from lack of complete understanding? |
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trigem1
Registered Users
Posts:46
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| 04/28/2008 8:51 PM |
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I guess the idea is that a standard roof will leak warm air up throught the insulation, and the warm air will be vented out the 1" air gap to help prevent ice dams. I suggest to put ice and water shield all the way to the ridge, and almost garuntees no water damage. SIP's are almost air-tight, and won't leak air, so you don't need ventilation. The only way I know of venting a SIP roof is to build a cold roof over the existing SIP roof, which brings up another question as to the benifits, if any, of a cold roof with a SIP roof.
Steve
GrandCountySIPs.com |
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newflowers
Registered Users
Posts:29
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| 04/28/2008 10:47 PM |
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The more I learn about SIPs, the more excited I am about building this house - or having it built as the case may be.
Ultimately, with an SIP roof, I just need the panels, the roofing paper, and the metal? Can it possibly be that easy? Well, I also need gutters too.
If building a roof in a cold climate is this easy with SIPs, why then do contractors still use the more traditional build? This is faster, more secure, better, stronger - what's the down side I'm missing? |
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PanelCrafters
Registered Users
Posts:1237
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| 04/29/2008 6:59 AM |
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Posted By trigem1 on 04/28/2008 8:51 PM
I suggest to put ice and water shield all the way to the ridge, and almost garuntees no water damage.
I use to think that also, but more than 1 SIP manufacturer has stated that it's a bad idea. You need somewhere for the moisture to go if it ever gets in. |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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PanelCrafters
Registered Users
Posts:1237
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| 04/29/2008 7:02 AM |
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Posted By newflowers on 04/28/2008 10:47 PM
If building a roof in a cold climate is this easy with SIPs, why then do contractors still use the more traditional build? This is faster, more secure, better, stronger - what's the down side I'm missing?
Cost. That and the fact that many roofs are fairly complex, and better suited for trusses. |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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vtftravis
Registered Users
Posts:7
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| 04/29/2008 9:29 AM |
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| A cold roof is recomended. (reasons being panel telegraphing , shingle ridging ect.) If you are building your own house i would highly recomend you take a look at Joseph lstiburek's book "Builders guide to SIPS for all climates." |
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tmsu
Registered Users
Posts:39
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| 04/29/2008 12:38 PM |
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My roof is made from SIPs (8.5") EPS panels. I also used a standard truss to place the panels on. When I contacted the truss company to engineer the trusses, I told them to cut the "tail" off or have no over hang for the soffit as the panel itself would act as the 2' overhang. There was, as mentioned, a gap (2-3"??) that needed to be filled. I then cut OSB strips to panel the end of the trusses, which left a much smaller gap (1/2" - 3/4" gap). I then foamed the crap out of all of it to seal it up as best as possible. I then stuffed the pink stuff all around the perimeter.
I then made sure I had a supply and return in the attic to provide some air flow and heating/cooling. Obviously, there is no insulation above the ceiling but below the roof in a typical attic.
Anyway, my building inspector was slightly confused and asked about it. When I explained that the attic would be conditioned air, he was good with that. One thing to note, I am considering adding some insulation above the drywall ceiling (like a normal attic) to help hold in the heat/cool in the rooms on that level. |
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newflowers
Registered Users
Posts:29
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| 04/29/2008 10:15 PM |
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Posted By PanelCrafters on 04/29/2008 7:02 AM
Posted By newflowers on 04/28/2008 10:47 PM
If building a roof in a cold climate is this easy with SIPs, why then do contractors still use the more traditional build? This is faster, more secure, better, stronger - what's the down side I'm missing? Cost. That and the fact that many roofs are fairly complex, and better suited for trusses.
Maybe because my roof is very simple, the cost does nto seem that much more. And of course, I am adding to my cost by insisting upon a metal roof instead of asphalt shingles, but I'm going to live in this house until the bitter end - I do not want to have roofing issues.
Even if the initial cost of the SIP roof is more, when one factors the savings in energy, not buying insulation, vents, and other roof parts, is it really significantly more expensive? |
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PanelCrafters
Registered Users
Posts:1237
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| 04/30/2008 7:05 AM |
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Posted By newflowers on 04/29/2008 10:15 PM
Even if the initial cost of the SIP roof is more, when one factors the savings in energy, not buying insulation, vents, and other roof parts, is it really significantly more expensive?
No. But, many builders and people are looking for the least expensive scenario. And, a roof is not a racy item, like say, granite counter tops. People somehow find the $$$ for upgrades, but don't see the value in a dull item like a roof. |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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tmsu
Registered Users
Posts:39
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| 04/30/2008 2:45 PM |
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Posted By PanelCrafters on 04/30/2008 7:05 AM
Posted By newflowers on 04/29/2008 10:15 PM
Even if the initial cost of the SIP roof is more, when one factors the savings in energy, not buying insulation, vents, and other roof parts, is it really significantly more expensive? No. But, many builders and people are looking for the least expensive scenario. And, a roof is not a racy item, like say, granite counter tops. People somehow find the $$$ for upgrades, but don't see the value in a dull item like a roof.
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newflowers
Registered Users
Posts:29
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| 04/30/2008 5:08 PM |
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Well, a roof may not be a racy item, but even neophyte that I am, I can understand it is one of the more significant areas that must be done right the first time. A roof is not a fancy item - it's a basic item that must be as good as one can possibly afford. Who cares about granite when there are leaks or it's cold because the wind can blow inside of the house. It's not that I don't want the fancy things inside the house - I really do. I absolutely NEED a two-person Sanijet tub, and a Bain Ultra steam shower and soapstone counters, and wood floors, and Heartland Classic stove and matching refirgerator, and a myraid of fancy things. BUT... And maybe this is the point you're making and I'm finally getting it, the big but that people do not understand. I want and will have all of those things, but not at the expense of the building itself - the SIP walls and roof and floors, the foundation, the fiberglass windows - these things are not upgrades, they are the structure of the house that will keep the cold out and me warm and content within. I can live without some of my things - well, maybe not the tub - and can buy them later, but I intend to live in this house for my last twenty+ years without needing a new roof.
So back to my topic - talk to the Bonner County Building Inspector and ask about unvented as it applies to their code, but unvented with SIP roof is the better way to go. And the cold roof is what I should have. These are correct? I ordered the book - thanks for the recommendation.
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