Gin
New Member
Posts:9
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| 26 Dec 2010 02:10 AM |
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If anyone has some actual experience with using either steel or OSB sips related to the construction of a Butterfly roof design; then please reply with your comments or suggestions as it pertains to the construction of such a roof. I am interested in this particular roof design and would like some input as to the methods in the roof design as mentioned. The roof pitch would be 1.5:12 to 2:12 with a overall span of approximately 38-40 ft, thus each 1/2 gable would be either 18-20 ft in width.
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cmkavala
Veteran Member
Posts:4327
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| 26 Dec 2010 08:09 AM |
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Posted By Gin on 26 Dec 2010 02:10 AM
If anyone has some actual experience with using either steel or OSB sips related to the construction of a Butterfly roof design; then please reply with your comments or suggestions as it pertains to the construction of such a roof. I am interested in this particular roof design and would like some input as to the methods in the roof design as mentioned. The roof pitch would be 1.5:12 to 2:12 with a overall span of approximately 38-40 ft, thus each 1/2 gable would be either 18-20 ft in width.
Thanks Gin; regardless of OSB or Steel SIPs, you will need to pay particular attention to the roofing for the invert, I see more and more plans going "Retro" must be a growing trend. We just shipped a 2/12 pitch in Roanoke |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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ecoarchitect
New Member
Posts:29
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| 26 Dec 2010 02:42 PM |
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really the main consideration is the integrity of the roofing membrane
be sure that supporting beams for the SIPS have very very low deflection
as well as great SIPS anchorage and reduce the SIPS deflection as much as possible. |
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SimonD
Basic Member
Posts:167
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| 26 Dec 2010 03:09 PM |
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Make sure you have a place to put all the water that concentrates and sheds off the low end of the valley. If that water isn't managed and directed away from your foundation, you will have problems. |
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| Building Designer PANELfusion, LLC Tampa, FL [email protected] "Metal SIP Advocate" |
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SimonD
Basic Member
Posts:167
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| 26 Dec 2010 03:14 PM |
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You should mention where this roof is going to be built. It matters. Different climate regions have different design issues. |
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| Building Designer PANELfusion, LLC Tampa, FL [email protected] "Metal SIP Advocate" |
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Gin
New Member
Posts:9
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| 27 Dec 2010 04:20 AM |
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Steel SIP Man; your roof for the Roanoke project is a shed roof. I am questioning about a Butterfly roof, otherwise two gable roof lines opposing each other that adjoin in the center on a horizontal rake both roof pitches approximately 2:12 or less. So what I am interested in is the best construction method to encompass a butterfly roof design. Geographical area is the south east absent of any snow fall. Rain water cistern would be utilized in order to collect the water for its practical use, i.e., irrigation and grey water use. Thanks again.
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cmkavala
Veteran Member
Posts:4327
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| 27 Dec 2010 06:33 AM |
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Posted By Gin on 27 Dec 2010 04:20 AM
Steel SIP Man; your roof for the Roanoke project is a shed roof. I am questioning about a Butterfly roof, otherwise two gable roof lines opposing each other that adjoin in the center on a horizontal rake both roof pitches approximately 2:12 or less. So what I am interested in is the best construction method to encompass a butterfly roof design. Geographical area is the south east absent of any snow fall. Rain water cistern would be utilized in order to collect the water for its practical use, i.e., irrigation and grey water use. Thanks again.
Gin; you are correct, I only mentioned it because it was also a little less than 2/12 and it was what I consider a "retro" design and I have seen several of the "mono" sloped and "butterfly" designs come accross my desk in the past few months. I am familiar with the "butterfly" design and I think SimonD, echoarch and myself all pointed to the center valley as the point of concern, glad you are not attempting this in a snow climate. You will need to consider the benifits of each system, if termites or rot are a concern in your area your choice should be easy. |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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SimonD
Basic Member
Posts:167
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| 27 Dec 2010 02:16 PM |
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There's nothing about the shape of an "inverted-gable" roof that specifically lends itself to any one type of panel or other roof system for that matter. Superior water proofing measures come into play because your located in the south east, your roof is low slope and you are collecting water with your roof valley. A clearspan of 18'-0" for metal SIPs is right at the upper limit of their structural performance. Wood SIPs would need reinforcement to achieve that span. Knowing the wind design criteria for your location will determine the thickness of your roof panel and whether you may need intermediate support. |
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| Building Designer PANELfusion, LLC Tampa, FL [email protected] "Metal SIP Advocate" |
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cmkavala
Veteran Member
Posts:4327
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| 27 Dec 2010 02:47 PM |
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Posted By SimonD on 27 Dec 2010 02:16 PM
A clearspan of 18'-0" for metal SIPs is right at the upper limit of their structural performance. Wood SIPs would need reinforcement to achieve that span. Simon; depending on thickness and loads 30'+ is easily attainable |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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ICFHybrid
Veteran Member
Posts:3039
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| 27 Dec 2010 02:49 PM |
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My new project has butterfly roofs. What's interesting is, I've noticed that if you are 50 years old or over, you refer to it as "cool", "modern" or "contemporary" while the under-50 crowd tends to call it "Retro". Ha ha.
This style became popular after WWII when the idea was to be efficient and simplify, although I think Frank Lloyd Wright used elements of it even before that. The butterfly roof is ideal for collecting rainwater and it also allows for larger windows for more light or passive solar. Probably resists wind well, too.
It's not the first thing you think of if snow loads are an issue, because the roof pitch tends to be quite low, like 2:12, and you do want to keep an eye on the runoff in the valley between the pitches. Here in the PNW we aren't known for getting a lot of snow, but occasionally it does happen, so I think we will have some sort of electric resistance heating to help clear the valley on occasion, just to be sure.
Instead of running long rafters, you can run glu lam beams the long way and then cross with roof joists. That's pretty simple. We considered SIPS, but rejected them pretty early because of the pitch. I'm sure there are people who can better tell you how to make SIPS work for you with that kind of a roof, but neither engineer, architect, builder or homeowner felt too comfortable sticking with them on this low pitch. It's 2 X 12 roof joists (purlins) @24" OC spanning up to 14' between the GLBs with foam sprayed in the cavity. Pretty simple. It also solves the problem of roof over hang as either the GLBs or the joists can be cantilevered out to shade any windows below.
As we have proceeded with this, a number of people have remarked that they are seeing more of these types of roofs right now, probably because of the simplicity, rainwater and light collecting features already noted. |
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Gin
New Member
Posts:9
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| 27 Dec 2010 11:37 PM |
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Question. Steel SIPS Man mentions, "depending on thickness and loads 30'+ is easily attainable" Are you implying a 30' clear span, but with what kind of reinforcement are you using? My question really is related to the use of an 8" SSIP and what length of clear span could be acquired when considering its use in the construction of either a Butterfly roof or a Skillion roof design both with a 2/12 or < pitch. Also since it is a SSIPS that I am inquiring about then as I have read a roof would be required as it is already skined in metal, but I do realize the one valley would need to be addressed; but what is the best possible method in resolving the issue? |
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Gin
New Member
Posts:9
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| 27 Dec 2010 11:41 PM |
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Correction regarding the use of a SSIPS for the roof. I have read that a roof membrane would not be required as it is already skinned with metal, but my concern was about the one (center) valley as to maintaining a leak free seal. So what would be the best possible resolution to this issue? |
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Dick Mills
Basic Member
Posts:217
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| 28 Dec 2010 03:27 AM |
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With this kind of roof design, one would think that it would be prudent to build up the valley at the center to ensure that rain water will drain to the roof edge and ensure that it doesn't pool anywhere along the valley. Probably would need at least a 1/4 inch per foot for proper drainage?? |
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cmkavala
Veteran Member
Posts:4327
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| 28 Dec 2010 08:05 AM |
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Posted By Gin on 27 Dec 2010 11:37 PM
Question. Steel SIPS Man mentions, "depending on thickness and loads 30'+ is easily attainable" Are you implying a 30' clear span, but with what kind of reinforcement are you using? My question really is related to the use of an 8" SSIP and what length of clear span could be acquired when considering its use in the construction of either a Butterfly roof or a Skillion roof design both with a 2/12 or < pitch. Also since it is a SSIPS that I am inquiring about then as I have read a roof would be required as it is already skined in metal, but I do realize the one valley would need to be addressed; but what is the best possible method in resolving the issue? Gin; yes a 12" SSIP could span 30 ft. depending on what area of the country you are looking to use it, There is no additional reinforcement needed. I need to know the specific area of the country you would be using the 8" in order to give a specific span. The cost difference between 8" and 12" is only about 80 cent per sq. foot, plus the cost of freight (less panels per truck) but depending on the size of the house freight may not be a factor . Any comments about leaving SSIPs bare have been about "simple gables" however, I would need to see a specific plan before I could determine if it could be accomplished on a butterfly design |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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ICFHybrid
Veteran Member
Posts:3039
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| 28 Dec 2010 11:10 AM |
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Probably would need at least a 1/4 inch per foot for proper drainage?? 1/4" per foot minimum. We set the high point at 1/4" (per foot), then looked at how much higher we could make it without it harming the appearance. On a low slope roof, the "cricket" gets pretty broad pretty fast. It ended up a little less than 1/2" per foot. We built up between the rafters to support roof sheathing and a big metal cricket pan over that. You can make the build-up "diamond" shaped so it drains an equal amount to each side, but we are collecting rainwater and in our case that necessitated collecting where we hadn't planned on it, so we drained only one way, making the crickets "triangle" shaped. |
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SimonD
Basic Member
Posts:167
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| 28 Dec 2010 02:21 PM |
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My experience with metal SIPs has only focused on panels up to a thickness of 8". Yes, Chris is right metal SIPs can achieve longer spans, but the structural efficiency goes down and cost goes up. You can use a heavier gauge metal skin, increase the density of foam core, embed structural members in the core and of course increase the panel thickness. In my experience panels over 8" thick are a very custom kind of thing.
Theoretically, you could use metal SIPs without a membrane, but your configuration of roof increases the risk of leaks. If I was forced to design a roof like yours using metal SIPs without a membrane, I would space the two roof planes apart and create a recessed gutter trough/scupper system at the valley to ensure the water left the roof. With a standard valley, you couldn't make me engineer it using metal SIPs without a membrane. |
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| Building Designer PANELfusion, LLC Tampa, FL [email protected] "Metal SIP Advocate" |
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SimonD
Basic Member
Posts:167
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| 28 Dec 2010 02:37 PM |
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ICF Hybrid is right, If your valley is going to be level and your roof is not going to be pitched to one side, you will have to build up the valley with a cricket to make the water shed to the sides of the roof. If the roof is visible from above, that can spoil the 'clean lines' of the roof. With metal SIPs, as soon as you build up the roof at the valley (overlay one roof with another) and not provide a gutter system as mentioned above, a membrane for the entire roof would be necessary. |
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| Building Designer PANELfusion, LLC Tampa, FL [email protected] "Metal SIP Advocate" |
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SimonD
Basic Member
Posts:167
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| 28 Dec 2010 03:48 PM |
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Here are some diagrams. A fourth choice and 'cleanest look' in my opinion is to slightly pitch the whole roof to the front or back to create positive water flow for your valley, but that will mean you will need a slight angle to the top of the side walls.
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| Building Designer PANELfusion, LLC Tampa, FL [email protected] "Metal SIP Advocate" |
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cmkavala
Veteran Member
Posts:4327
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| 28 Dec 2010 07:30 PM |
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Posted By SimonD on 28 Dec 2010 02:21 PM
My experience with metal SIPs has only focused on panels up to a thickness of 8". Yes, Chris is right metal SIPs can achieve longer spans, but the structural efficiency goes down and cost goes up. You can use a heavier gauge metal skin, increase the density of foam core, embed structural members in the core and of course increase the panel thickness. In my experience panels over 8" thick are a very custom kind of thing.
Theoretically, you could use metal SIPs without a membrane, but your configuration of roof increases the risk of leaks. If I was forced to design a roof like yours using metal SIPs without a membrane, I would space the two roof planes apart and create a recessed gutter trough/scupper system at the valley to ensure the water left the roof. With a standard valley, you couldn't make me engineer it using metal SIPs without a membrane. Simon; the difference in panel cost to go from an 8" to 12" in thickness is about .80 cents per sq. foot and not custom at all, we shipped 3 tractor trailer loads of 12" x 53 ft./ 18ft. to Callaway, Va. and some 12" x 22ft. (floor) to Brunswick, GA. this past year We never embed structural members in the core , the panels will go the distance on their own. |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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SimonD
Basic Member
Posts:167
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| 30 Dec 2010 04:38 PM |
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An 8" thick 26ga. steel skinned SIP with 1lb. density EPS foam core can clearspan 18'-0" up to a wind speed of 123 mph. This is a readily available non custom panel specification that several companies supply. The specifics of your project will determine if this panel is suitable for your project. |
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| Building Designer PANELfusion, LLC Tampa, FL [email protected] "Metal SIP Advocate" |
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