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by • March 14, 2011 • RoofingComments (16)9879

Venting a Metal Roof with Rigid Foam Underneith

In our hot Texas climate nothing beats a metal roof for longevity and energy efficiency.  I’m a huge fan of the silvery Galvalume color because it has a radiant barrier built in and that silver color helps keeps our houses cool.  In this video I’ll show you the best practice method for installing a metal roof on a vented lath system.  Plus, we used a layer of 3/4″ rigid foam on the roof deck to help keep the heat out of our sealed/foamed attic underneath.  Architecture by Heimsath Architects, construction by Risinger Homes.  -Matt Risinger

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  • Its good to read this informative post ,Metal roofing is a good deal provide safety and durability for our house.Gulf Coast Supply is a leader in manufacturing metal roofing and components, serving all of Florida and Southern Georgia.

  • Hi Matt, I enjoy your blog quite a bit. 2 questions on this post: 1) do you think this open vented space will cause the roof to be more noisey in the rain? 2) why do you lay the 1x strips diagonally instead of straight up to the peak? Thanks

  • Hi Matt, I realy enjoy your blog quite a bit. I have 2 questions about this post: 1) Do you think leaving this vented open space will cause the metal roof to be noisier than laying it directly on the roof deck? 2) Why do you lay the 1x strips diagonally across the roof instead of straight up to the peak? Thanks.

  • @jwcates3: I have not heard any complaints about noise from doing this in the past. It probably helps that there is several inches of spray foam under the roof deck however. The furring strips are diagonal so that the panels can be screwed down easily compared to needing precision placement if they ran vertically. Appreciate your comments. Matt

  • Foam Roof insulation comes with so many advantages. One of them is the prevention from leakage and help you achieve three times the economic, environmental and social performance. Thanks for sharing such a nice post.

  • Sheryl Thornton

    Matt,
    Thanks for your awesome videos. I have learned a ton by watching your videos over the last year. I am building my families house with this same exact roof system except mine is on a metal structure. My house- Metal 8″ purlin filled between purlins with spray foam/7/16 osb/waterproofing/iso foam/standing seam roof.
    A couple questions if you dont mind.
    If I don’t have enough in my budget for the Carlisle Wip product is there a good product that is cheaper?
    Which ISO foam board did you use?
    If my roof is a 2/12 does it need to be vented with the 1×4 lath strips?
    Blessings,
    Josh

    • Josh, Sounds like a well built house! Couple suggestions. This video shows my preferred method. http://youtu.be/DpxLi_Rm30s I would definitely suggest 2″ or more of rigid foam on the roof top because of the metal rafters and their need for a thermal break. Regarding the Carlisle WIP 300HT, if you aren’t in the hot South you can use a non-High-Temp version that’ll be less expensive. Look for a 40 mil peel & stick product. Several manufacturers make a version of this product. Use the expensive peel & stick on top of the OSB, then on top of the foam you could use a less expensive product for underlayment.
      Yes on the 1×4 venting. Very important especially because of your low slope.
      On the ISO I’m not brand specific. PolyIso is the best value for your dollar, but Dow XPS is the best choice because water won’t affect the R-value if it gets wet. EPS is the cheapest foam for the money but also the most prone to shrinkage and lower R-value. Any foam up there is fantastic so don’t get too hung up over the brand/type. Hope this helps. Matt

  • Robert Fordham

    Hey Matt, thanks for the great blog! I am remodeling a small 50 + year old house, it has a cathedral ceiling (2×6 rafters). I will be refooing with metal, but because of the lay out I can fur down on the inside but the cathedral ceiling has to stay. I have a insulation contractor friend that will sell me all insulation at cost (cheap) but doesn’t do sprayfoam. I live in south GA and it is hard to find good info related to cathedral ceiling insulating in the south that won’t cause moisture problems later on. Any advice?

    • Robert, Could you use Rigid Foam on the roof deck? You could do 4-6″ of insulation up top and not have to any (or little) inside. Just be careful to not do more than one vapor barrier. Use a WIP 300HT on top of the deck and be sure that that’s the only barrier to moisture drying to the inside. Hope this helps. Matt

      • Robert Fordham

        To clarify, 1/2 osb on rafters, 4 to 6 inch of foam board, 1/2 osb, WIP 300HT, 1×4 on 45 degrees, and then metal roof? Last question, on the roof stripping, do you think that putting 3/4 osb vertical stripping (3 inch strip set on 16 to 24 inch centers) and then 2×4 horizontal stripping would be better to have metal roofing screws to hold better and vent roof? I seen some studies on this and I know a roofing contractor that does some government buildings and he says use a 2×4 because the screws will hold and not back out over the years, and I have personally seen several houses with 1×4 slats that the screw backed out on part of the house between 10 and 15 years later.
        Thanks

  • Guy Tech

    Hi Matt,
    I like the concept of leaving an air gap between the metal roof panels and the roof using 1×4 stats. I noticed that wood you used appeared to be untreated, which I think could lead to rot or perhaps insect damage over time. I’ve read that using pressure treated wood is not recommended because the pressure treated wood can lead to corrosion since wood contains copper or other metals. Could a wood primer be used to add some protection? My concern would be outgasing during high temperatures during the summer, or that the prime might retain water. Is there an alternate to using wood for the slats?

    You do a lot of really great video presentations! Thank you!

    • Matt Risinger

      In my 13 years of doing rainscreens I’ve found that the untreated wood battens last just fine. They have no UV exposure to degrade them, and if they get wet they dry no problem. Insects could be a problem, but you’ll know pretty easily if you have a termite infestation. I’d stay with the untreated 1x battens. Matt

  • Colin D Brown

    Thank you for the great videos! I am in Florida, My questions are:
    1 – Why does the Carlisle product go over and not under the foam?
    2 – Would a product such as a solar radiant barrierbe of much benefit? http://www.atticfoil.com/index.php/products/perforated-single-sided-radiant-barrier-foil-60-wide/

    • Thanks for commenting. On the first question, yes I would run a layer of Carlisle WIP 300 HT on the roof deck the foam over it. I generally add another layer on top as a belt & suspenders approach. On the second question. I’m not sure where the foil would go? A radiant barrier needs an air gap in front of it to work. It won’t provide benefits if its sandwiched inside. Maybe you can clarify where you are thinking of putting that?
      Best, Matt

      • Colin D Brown

        Thank you for taking the time to reply! I was concerned about foam fasteners working loose under the membrane (thinking something would have to hold it until furring strips are added). I was thinking the radiant barrier would go over the furring, leaving 3/4″ air gap? Keep up the great videos!