Jay Casey
Registered Users
Posts:21
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| 03/19/2008 10:31 PM |
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The attic in my new ICF house will have a metal roof and icynene insulation blown onto the underside of the roofing material. That will make my house a complete envelop with icynene (or something like it) under the roof. I plan on having a standing seam metal roof affixed to the plywood on the roof deck with felt paper between the plywood and the metal. Is there anything wrong with this method of roofing a house?
Has anyone heard of a warranty issue if the metal roofing material is affixed directly to the plywood (with felt in between)? Does there have to be an air space underneath the metal roofing material?
Should I worry about the roofing material getting too hot since there will be no air space between the plywood and the insulation on the underside? If so, is there an easy fix to this problem?
Thanks for your comments.
Jay |
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wes
Registered Users
Posts:339
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| 03/20/2008 8:13 AM |
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Jay,
My only suggestion would be to use a product such as rooftopguard in lieu of the felt. Its stronger with less change of holes. Also, if you have a delay in installing the metal after the decking is in place, this product will weather much better than felt. Its very strong with less chance of wind or water damage.
Otherwise, I think you are on the right track.
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Wes Shelby
Design Systems Group
Murray KY
wandr@ainweb.net |
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Jay Casey
Registered Users
Posts:21
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| 03/20/2008 8:10 PM |
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Wes:
I found the Roof Top Guard II @ GuttersDirect.Com for $178 plus shipping for a 10 square rool (5' x 200'). That's quite a bit more expensive than felt! I like the fact that I can wait to install my metal roof but I don't know if I want to pay for that priviledge. And I don't think I would recieve a warranty since their installation instructions say it needs to be installed over a ventilated attic and I won't have that situation.
Have you seen anyone insulate the underside of their roof and then install metal roofing over the underlayment over the plywood? I just wonder whether or not the practice will cause any sweating, heat build-up (Roof Top Guard says it reduces heat load on roofs), etc, or any other unforseen problem. I just don't know if blowing icynene on the undersid eof the roof will cause a problem with the roof. Any suggestions?
I'll try to find Roof Top Guard at a cheaper price.
Thanks,
Jay |
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winfield
Registered Users
Posts:7
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| 03/20/2008 10:05 PM |
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Jay,
When we replaced our shingle roof with standing seam metal roof they put down 30# felt and then it was screwed into the plywood deck. There are no furing strips underneath. Has been on for 6 years and 3 hurricanes and not a drop of water has gotten in. We do not have it insulated the way you are doing it. It has held up great. we are 3 blocks from the ocean and have not had any problems with rust. Of course the screw schedual DDmight be different for your location
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wes
Registered Users
Posts:339
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| 03/21/2008 7:04 AM |
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Jay,
Rooftop Guard is somewhat more expensive than felt. I think we pay about $145 per roll. But I think it is worth the difference in costs. I've had to replace felt after just a couple days exposure because of wrinkling and tearing. Felt reacts to wind, water, and sunlite. There are other products similar to the rooftop guard that work the same. It just happens to be the one readily available here.
As to the insulation, my preference is to spray Icynene on the underside of the roof decking. It creates a conditioned attic space for ductwork, etc. And yes, I 've used this method with metal roofs, and it works just fine. |
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Wes Shelby
Design Systems Group
Murray KY
wandr@ainweb.net |
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FlaICF
Registered Users
Posts:166
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| 03/22/2008 2:05 PM |
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| It will take only a little research but I believe that the self adhereing roof underlayments are approved for the use when using metal. We built our home using Icynene under 5/8" ply and self adhesive membrane. It was to be metal but cost forced us to 40yr. dimensional shingles. Used Elk as GAF would not warranty their product with Icynene. |
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drogers
Registered Users
Posts:68
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| 03/22/2008 3:13 PM |
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| Most larger metal manufacturers will offer assistance in developing installation specs for your particular situation. I would contact them directly. |
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Vermonter
Registered Users
Posts:47
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| 04/01/2008 1:11 PM |
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| Rooftop Guard or similar is very much worth the little extra cost. Easier to apply, more durable surface while working, and superior long-term performance. |
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malibud
Registered Users
Posts:28
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| 04/01/2008 9:28 PM |
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A metal roof salesman told me to make sure that the installers use a 1"x4" furring strips to vent and keep the roof cool
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Vermonter
Registered Users
Posts:47
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| 04/02/2008 10:18 AM |
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| Here's some info http://www.buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates |
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Jay Casey
Registered Users
Posts:21
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| 04/02/2008 6:26 PM |
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Vermonter:
Thanks! This is an excellent website for those of us considering an unvented attic. This information sure makes me feel better about using an unvented attic. Now I just need to get comfortable that a metal roof affixed to the unventilated attic will still perform as expected. The site says that an unvented attic only sees temps within 10 degrees of a vented attic. If that is true, the metal roofing guys should still warrant their products when used with an unvented attic.
I just haven't found any good evidence that it would be a bad idea to use a metal roof over an unvented attic. So I plan to do it!
I wonder if it is okay to fix the metal roof panels directly to the plywood roof deck (with underlayment in between) or do I need to attach the panels to 1"x4" lath. I don't want the extra expense of the 1"x4"s if I don't have to use them.
Thanks,
Jay |
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James Eggert
Registered Users
Posts:994
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| 04/02/2008 7:59 PM |
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The installation should be reviewed with the metal roofing manufacturer.
Yes, metal roofs are placed directly to the plywood over Icynene insulated roof sheathing, thats how I always had it done and warranteed!
Also, there are numerous better underlayment products as mentioned above, including Grace Products and a host of others....all better than felt. Stop wasting your time trying to "save" a few hundred dollars and use a better product. You only get one chance to do it right! |
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Take Care
Jim
Design/Build/Consulting
"Not So Big" Design Proponent |
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cmkavala
Registered Users
Posts:762
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| 04/03/2008 10:31 AM |
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Jay;
we install steel roofing all the time directly to our steel skin panels, but still use a 30# slip sheet between steel skins |
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Chris Kavala
chris@southernsips.com
1-877-321-SIPS |
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malibud
Registered Users
Posts:28
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| 04/03/2008 11:13 AM |
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| the building science people seemed to lean toward useing closed cell as opposed to open. I have gotten different feed back from the insulation guys regarding leaks. Some say open cell so that you can see where the leak is coming from some say closed cell because by the time you find the leak the open cell foam soak up a huge amount of water. Any thoughts on the matter? |
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