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Thread: My roof is the strongest on the planet. Prove me wrong.

  1. #1
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    My roof is the strongest on the planet. Prove me wrong.

    As you have seen, I’m replacing the tin on my roof, and also upgrading it to bomb-proof status. The roof is timber framed with this unusual ring beam in the middle making a square- one beam on each hip a bit more than 1/2 way up the rafters. That is tied in to the timber framed joists below with upright posts. The rafters are dovetailed into foot-thick stone walls. The roof is skinned in 1” old-growth pine.

    New codes require all roofs to be skinned in 1/2” or better ply, regardless of how well the original wood is. I got a deal on some surplus 3/4” treated ply for $17.50 a sheet. That’s not a misprint! Seventeen dollars and fifty cents for 3/4” 4x8 treated ply! (Score!) That was laid on top of the original 1” pine and screwed with 3” stainless screws. On top of that are 2x4 purlins with 2x6 on eaves and ridges, screwed through everything into the beam rafters with 6” screws with wide heads. Ice and rain coating and flashing all wraps around the edges and the fascia boards nail over it to prevent wind from getting under and lifting the roof. Fascia boards are Cumaru, set in with stainless tapcons. Between purlins is a solid core foam and glass fiber insulation. Heavy gauge galvanized corrugated roofing on top of all that.

    So, I kind of like to overengineer stuff. For anyone worried about weight, I had an engineer look at my rafters and he literally blurted an expletive and said, “You could park a train on this roof.” He said he had never seen a roof built this sturdy. Walls have more than ample support as well.

    I upgraded the porch rafters to 3x6” (8’ span) and tightened up the spacing. Rafters tie into poured concrete beams with galvanized 1/8” thick L brackets. Also there is a ledger of treated 3x4 bolted into the concrete with stainless 3/4” all-thread set in epoxy. The rafters are notched into that and screwed with 5” lag bolts in addition to hurricane clips. L brackets are behind that notch so that it is not just tied in at the notch, but also at the full 6” portion. The leeward end of the rafters have similar, tied into a ledger bolted into stone walls and also with L brackets.

    My only concern in the next hurricane is should I buy red wine or white?

    :-D

    My title is a bit tongue-in-cheek. I think there are maybe a couple of concrete bunkers designed to withstand an atomic blast that would maybe at least be AS STRONG as my roof, but certainly not stronger. Should Armageddon come, any of you who survive are all invited over to my place for the after-party.

    By the way, also just kidding about the red or white wine. I will always respect the power of hurricanes and my concern would be for the many people affected by it. I’m sure you knew that.

  2. #2
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    Sounds pretty bullet proof to me. My only question would be to omit the purlins and keep the new roof dead tight to the score sheathing. No room for any air/wind to get in there an pick it up. But the 2x6s on the edge likely eliminate a lot of that potential.

    I like metal smacked down tight against sheathing and most mfg'rs screw spacing doesnt accommodate purlins well.
    Sometimes I just want to look at pretty pictures,... Thats when I go to the Turners Forum

  3. #3
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    Quote Originally Posted by Mark Bolton View Post
    Sounds pretty bullet proof to me. My only question would be to omit the purlins and keep the new roof dead tight to the score sheathing. No room for any air/wind to get in there an pick it up. But the 2x6s on the edge likely eliminate a lot of that potential.

    I like metal smacked down tight against sheathing and most mfg'rs screw spacing doesnt accommodate purlins well.
    I agree, but our code requires purlins for some reason- likely they never thought of other options.

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    Makes sense in that the logic would be fasteners into solid members but so many metal roofing mfr's are spec'ing for FLA they have way more screws than purlins can support as well as stitching seams and so on. Many of the fastening schedules ive seen for hurricane areas would pretty much require purlins on zero spacing to make them work.

    Youve been down the rabbit hole. Im sure you know what you need to be safe and have exceeded minimum standards.
    Sometimes I just want to look at pretty pictures,... Thats when I go to the Turners Forum

  5. #5
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    The load bearing structure of the roof certainly sounds bomb-proof, and from the sound of it you could certainly park a train on it - or 18 ft of snow (...you get snow, right?). But these are all 'down' loads.

    My concern would be lift. Aerodynamic forces from air flowing over the ridge generate low pressure on the down-wind side - - and so lift. It can literally suck the entire roof off the wall. What keeps the rafters attached to the wall? Any hurricane ties? Or the wall to the foundation?

    Something else to consider is this lift acting on the galvanized sheet. It's like the opposite of vacuum bagging - - if you have only 1 oz/sq-in of lift on a 2' x 10' sheet, it adds up quickly = 180lbs-ish. Can the screw heads resist this? Or do they just pull thru? Once the sheets lift off, it can be messy, if nothing else.

    Hate to be a downer, but its a sensitive topic: A EF-3 tornado just passed about 300-400 yds north of me (20 Oct '19). It was a bit hard on roofs, so I am still picking up shingles and pulling insulation out of the trees. Fortunately, for me at least, it is someone else's debris. Radar in Oklahoma City (200mi, so not line-of-sight by any means) picked up the debris cloud at better than 15,000 ft high.
    Molann an obair an saor.

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  6. #6
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    Quote Originally Posted by Mark Bolton View Post
    Makes sense in that the logic would be fasteners into solid members but so many metal roofing mfr's are spec'ing for FLA they have way more screws than purlins can support as well as stitching seams and so on. Many of the fastening schedules ive seen for hurricane areas would pretty much require purlins on zero spacing to make them work.

    Youve been down the rabbit hole. Im sure you know what you need to be safe and have exceeded minimum standards.
    The foam insulation is a glass reinforced and it does offer some support under the metal- nothing near wood, of course, but it at least backs it up. With all the other stuff on my roof, including solar panels to come, I decided not to have zero spaced purlins. Although the roof could probably handle the weight, the 3/4 ply added a lot. Even if I lose metal, the ice and rain barrier will keep me dry. (Obviously it won’t be for ice!)

  7. #7
    My only concern in the next hurricane is should I buy red wine or white?
    Malcolm, you need to be careful with this kind of talk.. (sound of me throwing salt over my shoulder)

  8. #8
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    Red. White has to stay chilled.
    Jason

    "Don't get stuck on stupid." --Lt. Gen. Russel Honore


  9. #9
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    If it blows away, everything else will be gone too.

    I don't put exposed fastener roofs on anything anymore, but when the Chinese screws need replacing, I use these. The #12, and #14's have much larger washers, and will usually work in stripped out holes of the regular, small ones.

    https://www.albanycountyfasteners.co...teel-s/709.htm

  10. #10
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    I think you need to build a shed as a sacrificial homage to the hurricane gods, just to be safe. And yes, red wine.

  11. #11
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    Maybe a lightning rod?
    Rick Potter

    DIY journeyman,
    FWW wannabe.
    AKA Village Idiot.

  12. #12
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    Malcolm, did you source the heavy duty corrugated metal locally, or did you have to bring it in? Curious to know your source, if stateside.

  13. #13
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    Quote Originally Posted by Ted Calver View Post
    Malcolm, did you source the heavy duty corrugated metal locally, or did you have to bring it in? Curious to know your source, if stateside.
    They make it locally with a die and sheet metal.

  14. #14
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    Quote Originally Posted by Rick Potter View Post
    Maybe a lightning rod?
    That is being discussed. I never had one and wondering if I need one, but now would be the time. I would really like to have one of these attached to it.
    220C81B4-5E5F-4781-8385-2C7CED32BD32.jpeg

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