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  1. #1
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    Default Attaching 16' shed rafters to old tobacco barn.

    I have a sturdy old 32x40 tobacco barn that I need more space. Have decided to add a 15' add-on enclosed shed for tractor and or travel trailer storage. A 40' long driveway. I already have and so will be using 18'x6"x6" posts for the wall to be covered with metal and a bunch of 16' 2x10s for rafters, header boards and such. I am running the new roof under the barn 10"overhang snug under the existing 2x4 fascia. The barn rafters are on 2' centers and the shed roof needs to be 16" on center.

    My first thought was to run a double 2x10 header board and butt the rafters against it with joist hangers which I have boxes full but I got to looking at that and thinking there could be pull forces. I could lower the header and run the rafters on top but haven't thought of a good way to attach. It would have been nice to just lap the rafters to the barn rafters but the spacing is wrong, The barn rafters are 2.5x2.5' oak with 10' span to next row of posts, not much to lap to) and just doesn't work out with the new roofing slipping under the old corrugated metal roof.

    There are millions of barns with add on sheds. How did they attach the rafters? How would you do it. BTW the barn outside wall being attached to, has cedar posts on 7'6" centers (has to do with the desired spacing of the hanging rails for tobacco) with an odd one at the end.

    I already have dug my holes for the concrete set of the posts but I can move the wall in or out a few inches to accommodate a different hanging strategy.

  2. #2
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    Default Re: Attaching 16' shed rafters to old tobacco barn.

    Got confused on this one. I think it should have been in the Projects category. How do I move it.

  3. #3
    Gold Member Scrambler82's Avatar
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    Default Re: Attaching 16' shed rafters to old tobacco barn.

    First not a carpenter but I have built a house and a barn and two sheds.

    The main problem at the barn attaching point is what the siding will support and are the studding on the barn wall going to support a ridge board. I like to cut small flats in the rafter on both ends and let them set on a support header and the top plate of the wall.

    So thinking along those lines... I would attach a ridge board on the barn at the top of the roof line and secured to the rafter and siding of the barn, then add a double just under that to support the rafters.

    Also, if this addition is 15' wide, I think the rafters are going to be longer than 16'.
    Also, also... what kind of loading does the roof have to stand up to ?
    I would check with l coal codes but I am thinking the rafters need to be 2x14" and depending on pitch of the roof the length will be longer than 16' but I do not have a calculator with me to figure it out.

    Again, this is the way I would do it, do it right the first i me is the most important thing to me so I would slightly over-build to be on the safe side.
    “Do It Right The First Time"
    Purchased Mahindra Max28XL (43 hrs), HST, TLB


  4. #4
    Elite Member s219's Avatar
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    Default Re: Attaching 16' shed rafters to old tobacco barn.

    I have lagged a "ledger" board into the wall of the main building and then sat or bracketed rafters onto it. That assumes the wall framing is beefy enough for lags and can support the additional live/dead/snow load (in most cases it can, but be sure). You can buy "ledger-lock" timber screws that will make short work of it, using a battery powered impact driver.

    Unlike a gable roof with a ridge (where you'd use rafter ties or collar ties across the ridge) there shouldn't be a whole lot of sideways outward force. But if you had concerns about that, Simpson makes a deck tension tie (DTT2Z-R2) that could be used to snug and secure every 2nd or 3rd rafter using threaded rod through the wall.

  5. #5
    Super Star Member EddieWalker's Avatar
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    Default Re: Attaching 16' shed rafters to old tobacco barn.

    Not positive on exactly what you are having to deal with concerning the tobacco barn or your need for 16 inch spacing for your rafters.

    Pics would really help.

    Not knowing what the roof is like, Ideally I would want to remove part of the existing roof and get my rafters on top of the top plates and anchored to the sides of the existing rafters. Since you said you want the new roof to be under the existing roof, I would then try to remove part of the siding of the wall and attach the rafters to the existing studs. If none of that is possible, then you need a ledger board. As s219 mentioned, attach a ledger board to the existing building. Lag bolts should only be used if you cannot get bolts through the wall and you're unable to tighten them from the inside. Bolts would be best, then lag bolts.

    Sometimes the best options is just building a wall next to the existing building to support the new roof.

    Read up on building a deck and how you attach it to a house, the roof is basically the same principle, just at an angle.

    Eddie

  6. #6
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    Default Re: Attaching 16' shed rafters to old tobacco barn.

    Thanks for the replys. Each of you confirmd or added something to get me going. Sorry about no pictures, barn is in KY and I live in Alabama. I am just seeking to be ready to hit the ground running next time I go up there next week. The barn is pole barn, no studs, just 10" to 12" diameter posts in a row 3'8" on center down each side of main driveway 12' wide. Outside walls parallel to this driveway have cedar poles 7'6" oc with stringers spanning them with 1" poplar planking nailed on as siding. This forms another 10' driveway

    The rafters at the outside wall rest on a 2"x6" oak board laying flat on top of posts with a 3"x5" notched into the pole on the outside under the 2"x8" to stiffen and strengthen it. This forms a sort of fat L beam. The 2.5" rafters are notched slightly for nailing into the L beam construction.

    When I slip the new rafter under the fascia it buts into the 3"x5" with about 1" overlap. it would be more if I was not changing the roof pitch to less steep. My plan was to notch the posts and place a double 2"x10" belt under the 3"x5" as a header board and use joist hangers because that is what I had but it just seemed that I need to deal a little more with the pulling forces. Deck construction is plenty strong in most regards but decks typically are not being pulled away from the structure with the header where as this roof is sitting on an outside wall of post with no bracing and tied into the barn.

    So Scrambler82 idea of the double to support the load doing it the way I am thinking would butt into the double as a to a ridge board and use the joist hangers to support the load, then run some Ledger lock screws in from the back side of the double into the end of the rafter to pull it tight. I am thinking 3 8" screws. And come to think of it s219 I want to bolt the double to the top of the barn post, not just lag it.

    My thinking was originally as EddieWalker described but once I got up there 20 feet in the air looking things over it just was not going to work out that way. So the idea of dropping under the existing fascia came into focus. Once you realize that the siding is coming off, and that in a tobacco barn you have complete access to the post construction inside and out once the siding is removed I think you can see where I am going. The nice thing about a tobacco barn is that basically you have scaffolding built in. You don't need ladders, just climb the rails, 3'8"OC Those rails are what make the building so sturdy. Everything is tied together and braced. I will be weakening things a bit by removing the bottom row of rails to make the drive way taller but not by much since there are more levels of rails on up to the roof. And it is built out of sawmill oak about 100 years ago.

    Not the way I would build a building today so as to have lots of open space but for vehicle parking four 40 foot drives ways in the dry ain't too shabby for such a small expense.

    All these bolts and lags add up expense. The barn is built with nothing but big nails and it holds together like a tank. Would be nice to have that kind of lumber as affordable as it was back then.

  7. #7
    Elite Member s219's Avatar
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    Default Re: Attaching 16' shed rafters to old tobacco barn.

    Quote Originally Posted by Raised on a Deere View Post
    Deck construction is plenty strong in most regards but decks typically are not being pulled away from the structure with the header where as this roof is sitting on an outside wall of post with no bracing and tied into the barn.
    There should be no significant lateral loads on a lean-to roof from dead weight or snow. Gravity acts down! The only time lateral roof loads come into play are when you have a non-structural ridge line with opposing rafters that want to push outward (in which case rafter ties or collar ties handle it). If you had a structural ridge that supported the tops of the rafters, it's no issue. What you're building is really just like 1/2 of a regular roof with a structural ridge.

    Or think of it this way -- what if you were building a carport with a flat roof, or a carport with a slanted "shed" roof. In both cases, gravity loads go straight down. There's no reason to think the shed roof is going to want to pull to the side versus the flat roof, just because it's on an angle.

    What you do need to deal with are wind loads, which will create lateral loads as well as uplift. And then live loads, if they are a factor. That's a good reason to tie it in sideways with some sort of anchoring, regardless if it's flat, sloped, etc....

    In the case of a deck, the concern would be live loads from people traffic, which is why newer deck construction uses those Simpson anchors and threaded rods to connect every 2nd or 3rd or 4th joist through the ledger board into the structure (in the case of my house, they tie the deck joists to the interior floor joists). There have been many deck failures over the years where the joists pull away from the ledger and the deck collapses. Doesn't matter how many lags or bolts you attach the ledger with if the joists tear away!

  8. #8
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    Default Re: Attaching 16' shed rafters to old tobacco barn.

    s219 your comments fit exactly what I want to address. I to have seen the decks pull away and I know how wind plays with barn structures. I sat out a few thunderstorm down draft situation while unloading hay into barns as a lad and it was awesome and scary to see one wall or the other tugging at its moorings as the wind did its uplift, lateral and down all in a minute before the steady rain storm took over. I don't want to create a weak spot in the old structure. The old siding is coming down so the wind load will now be transmitted through the new shed wall. I see that I want to bolt the header to the posts, lag the rafters and may not do the bolt thing you described but at opportune places lap some timbers from the barn structure to the new roof system, as you say every few rafters. I did not know about those bolt things until after reading here I walked through Lowes fasteners and there they were. Nice stuff for doing it stout.

    Thanks for all the brain power exercised here in sharing your thoughts.

  9. #9
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    Default Re: Attaching 16' shed rafters to old tobacco barn.

    Buy your bolts at Tractor Supply Company if you want to save some money. I'd take a few bolts over several lag screws any day. You're going to need a long drill bit which you can order from Harbor Freight if you don't have a store close to you.

  10. #10
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    Default Re: Attaching 16' shed rafters to old tobacco barn.

    Quote Originally Posted by 2manyrocks View Post
    Buy your bolts at Tractor Supply Company if you want to save some money. I'd take a few bolts over several lag screws any day. You're going to need a long drill bit which you can order from Harbor Freight if you don't have a store close to you.
    Thanks for the tip on screws and bolts. I discovered recently that they sell their bolts by the pound.Just toss what you want t in your basket. They weigh it nuts bolts washers large and small in one bunch and out the door you go. Wasnt thinking of them about the barn bolts. Duh.

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