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Goldengreg
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Posts:5
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| 12/15/2006 8:59 PM |
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I'm designing a house using r-control sips and wondering if anyone might have some input for me regarding roof sips. The house is 24' wide simple gable design but there is a 119 psf snow load. I'm trying to figure if I can do a simple span from the top plate to the ridge beam without an intermediate purlin. I'm going to have the plans reviewed by an engineer before I submit them, but before I get any further with these drawings I'm trying to figure out if it will work. I was thinking of using the 7.25" core panels, but could up that if necessary. Thanks for any input. Greg
Here is the load design chart that I was looking at for r-control
http://www.r-control.com/downloads/literature/Load_Design_Chart.pdf |
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PanelCrafters
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Posts:1329
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| 12/15/2006 10:25 PM |
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Posted By Goldengreg on 12/15/2006 8:59 PM
I'm designing a house using r-control sips and wondering if anyone might have some input for me regarding roof sips. The house is 24' wide simple gable design but there is a 119 psf snow load. I'm trying to figure if I can do a simple span from the top plate to the ridge beam without an intermediate purlin...I was thinking of using the 7.25" core panels.. By any chance is this in Golden, CO.? Doesn't matter, forget the 8.25" panels. Why are you building with SIPS? Think minimum 10.25".
Even with 10.25" panels, and that load, my guess is that you'll need a purlin or structural splines(or maybe even embedded structural lumber). Now, there are certain locales(such as Leadville, CO) that reduce the load depending on the roof slope. But that is fairly rare.
Greg, this is not a simple hand off for a sig project. Your roof needs to be engineered. And, even a liberal engineer would be using questionable ethics by allowing raw panels, without some additional structural considerations. |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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mmacgowa
Registered Users
Posts:542
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| 12/16/2006 6:54 AM |
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Goldengreg,
You need to provide more information regarding slope and distances for the panel spans to determine the math. You are not going to get very far where the snow load is 119 psf. The table in the link won't even work for you. @ L/360 with a 12" panel you can only span 4' with a load of 104 psf. Since 104 is less then 109 you will have to start with an engineer. It sounds like you are building a small house with a lot of snow---maybe housing for elves? Are your initials SC?
I would have to go with JC on this one because your snow load is so great. But for your early design phases, consider that you will be usings purlin and structural members in the panels. And if you are building in Golden, you had better check your figures on the snow load requirements as they should be in the 40--50 psf range. |
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Goldengreg
Registered Users
Posts:5
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| 12/16/2006 11:01 AM |
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| Thanks for the input, the house is in Alma, CO at almost 11k ft elev. but I do live in Golden. I'll definitely be using either the double 2x spline or one of the i-beam splines. The roof is 12/12 pitch with metal roofing and no dormers so hopefully I can make it work. I'm open to using the thicker panels if needed for structural purposes. The other setup that I had thought of was 2 beams running 8' in from the exterior walls with no ridge beam. Is this acceptable? Thanks again for your input. Greg |
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PanelCrafters
Registered Users
Posts:1329
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| 12/16/2006 1:52 PM |
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Posted By Goldengreg on 12/16/2006 11:01 AM
I'll definitely be using either the double 2x spline or one of the i-beam splines. The roof is 12/12 pitch with metal roofing and no dormers so hopefully I can make it work. If you are trying to save energy, I'd try to skip the 2x splines and use the Std Super Spline. Of course, you would need to support from below with beams/purlins.
I'm open to using the thicker panels if needed for structural purposes. What about saving energy? 8.25" R-30 panels would barely meet code in most parts of Colorado, but they are energy wasters.
The other setup that I had thought of was 2 beams running 8' in from the exterior walls with no ridge beam. Is this acceptable? Ask an engineer. But I would use a ridge beam, if for no other reason than to ease the assembly.
In that location, if the house(cabin) is going to be occupied for any amount of time, I would specify 8.25" walls and 12.25" roof. But, if energy savings and indoor comfort are not concerns, you could just stick frame it! |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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Goldengreg
Registered Users
Posts:5
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| 12/16/2006 8:48 PM |
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| Thanks again, I've done quite a bit of research about efficiency, r-values etc., though I'm by no means an expert and the conclusion that I've come to is that although r-values are a decent way to gauge efficency of insulating materials they really don't do a good job at all telling the whole story about efficiency of a structure. The other thing is that it seems that the theory that you need a significantly better insulated roof than walls is less significant when using radiant heat, which doesn't have warm air accumulating at the ceiling to the extent that forced air would. Sure it would be great to have 12" thick sip roof, but is it really worth it? Seems like air infiltration/thermal bridging are much bigger culprits. Thanks for your input. Greg |
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PanelCrafters
Registered Users
Posts:1329
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| 12/16/2006 10:27 PM |
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Posted By Goldengreg on 12/16/2006 8:48 PM
Thanks again, I've done quite a bit of research about efficiency, r-values etc., though I'm by no means an expert and the conclusion that I've come to is that although r-values are a decent way to gauge efficency of insulating materials they really don't do a good job at all telling the whole story about efficiency of a structure. True. Having an R-30(for instance) wall, and a high air infiltration rate, pretty much neutralizes the high R-Value wall.
The other thing is that it seems that the theory that you need a significantly better insulated roof than walls is less significant when using radiant heat, which doesn't have warm air accumulating at the ceiling to the extent that forced air would. One would think so. Yes, a radiant floor is warmest at the floor, but I think that the air is being warmed by the surfaces that have absorbed radiation. Hot air rises, and heat moves to cold.
Sure it would be great to have 12" thick sip roof, but is it really worth it? Seems like air infiltration/thermal bridging are much bigger culprits. They are. Is it worth it? That would depend on your goals. My next house will be Super Insulated. Not necessarily to lower my heating bills, but to reduce the heat loss, so that a larger portion of my heating needs can be met with active solar. Can you imagine a 3,500 sqft house with a Total Heat Loss of around 20k BTU/hr(at the lowest temperature expected[-10°F in my situation])?
It all depends on your needs and goals.
However, energy costs will continue to outpace inflation for the foreseeable future, so it makes sense(to me) to build the most efficient structure possible. |
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....jc
If you're not building with OSB SIPS(or ICF's), why are you building? |
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mmacgowa
Registered Users
Posts:542
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| 12/17/2006 6:40 AM |
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Greg,
If I am looking at the table correctly, you will have to have a beam of some sort less then 4' in every direction. And while you might not need a ridge beam, there would have to be beams less then 2' down on each side as the ridge would then be cantilevered. And I was looking at the 12" panels. Perhaps you can get by with less if you can specify thicker OSB. I would guess that there are some tight beams in the area and that most of the homes have 1" or better plywood on the roof.
Another concern I would have when accumulating 100lbs./ft is creating a case for an accelerated lifetime on the panels. There is an article by John Paige on the web somewhere. He is an engineer that has done a lot of SIPs but warns that deflexion is natural and that roof SIPs over time will show deflextion. Your time could be sooner then later with those loads.
There is truly a tradeoff between comfort and design. I think you are on the right track, but I would send the drawings to a SIP company for bid. And once you have committed to the project, the engineer can tell you how many beams you will need, the size of the panels, and how much it is going to hurt your pocket book. But you will be warm and cozy as you are right about the thermal breaking and R values. |
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sipdesigns
Registered Users
Posts:3
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| 12/27/2006 3:49 PM |
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| Any real good panel company should provide you with Engineering solutions.
Jeremiah
sipdesigns@cox.net |
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