Several Carport Framing Questions

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  #1  
Old 11-28-11, 02:37 PM
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Several Carport Framing Questions

Hi,

I'm building a 40' deep by 10' wide carport that will be attached to a detached garage. I already have a 2x8 ledger on the garage. The permits are approved for the 2x8 ledger, 2x6 rafters @ 16" OC. This will be resting on 5 6x6 posts 10'OC with double 2x12 headers between each posts. And for the record, it will have 2x4 purlins spaced 24" OC to support a metal roof. 3/12 roof slope.

I have a few questions before buying materials.

1. Should I use pressure-treated lumber for the 2x12 headers that are attaching to the 6x6 pressure treated posts? I know typically you don't frame with pressure-treated but I'd prefer not to cap or paint the wood for a natural look and at least the outer-most section will face the elements/roof run-off.

2. Related to the above, I don't think I need to use pressure-treated lumber for the rafters or purlins, right? They won't receive paint either but they will be covered by the roof so really shouldn't see much weather except for maybe severe wind driven rain.

3. What's the best way to attach the rafters to the 2x12's on the one side and the 2x8 ledger on the other? I'd really prefer to keep the rafters inward of the 2x12's for a clean look (as opposed to doing a birds mouth or something along those lines). I did see adjustable hangers online but they are ridiculously expensive and I would need 60 when you count both ends of the rafters! I was thinking maybe a hanger board of some sort like I did for stairs but with a 2x6, I'm worried about notching it out too much.

Thanks for your help!

Pete
 
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Old 11-28-11, 03:41 PM
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Pete Installing perlins across the structure is the least likely way to go. I would strap across the top of the rafters with 1x4's (PT)spaced every 24" for the metal to hit on. Pressure treated 2x12 may be called for, especially if it gets any rain. The rafters themselves don't necessarily have to be pressure treated since they will not be in the weather. Use common 2x6 joist hangers on both ledgers for your rafters, if you want them inboard. Do you plan on any type of overhang, or just allow the steel to overhang the edge for runoff? If you notch any lumber, you reduce the strength at that point to the size of the notch. If it is a 2x6 and you notch it 1 1/2", you now have the strength of a 2x4, which is not code compliant, and the inspector will get you on it.
 
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Old 11-28-11, 07:07 PM
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Chandler,

Thanks for the reply. I think we're talking about the same thing with the perlins except I was thinking 2x4's instead of 1x4's. That's what I did for the garage roof except that required much beefier material with the 9/12 slope! So maybe 1x's are fine for this.

2x6 hangers are perfect, I just didn't think they would work because the hangers are obviously at 90 degrees and the roof has a 14 degree slope. I guess you're saying that's ok?

And a new question (at least I forgot to specify earlier), how would you attach the 2x12 headers to the 6x6 posts? I guess I can use a double hanger but that won't look great and I'm not sure if the hanger would be too wide.

And yes, the steel roof would just overhang the edge for runoff. No overhang, as it's too close to the neighboring property anyway (yes, zoning signed off on that).

Thanks again!
 
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Old 11-29-11, 03:35 AM
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Yeah, a perlin will fit between the rafters, whereas strapping will sit above. 2x4 is better, but 1x4 is minimal, depending on what load you will be experiencing, too. Go here:LSU/LSSU Adjustable Light Slopeable/Skewable U Hangers to see a different joist hanger that will work with your sloped rafters. They are adjustable in the field to different slight variations in angle. As far as the 2x12's, I would let them in the 6x6 via a notch cut 1 1/2" x 11 1/2" and bolt them through the 6x6. That way you will be resting the 2x12 (one of them) on a vertical surface.
 
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Old 11-29-11, 12:33 PM
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Technically I'm in a 20PSF zone but we do get decent amounts of snow several times a year.

I like that idea with the 6x6's, as I think it would look good as well. I was a little concerned about the sistering board not sitting on anything but I guess it is just a sister board anyway. Why not just notch the entire 6x6 by 1 1/2 and butt the two 2x12's against eachother? You can still bolt them and they're resting on more surface.

I saw those hangers and they're the only I saw. They would be perfect except for the cost. I think I saw them at $125 for a 25 pack. I would need 60! So are you saying the 90 degree hangers you first mentioned wouldn't work? It is only a slight angle. Any other options that are normally done and approved?
 
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Old 11-30-11, 02:51 AM
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You may can get by using a standard joist hanger if you only have a slight angle. You can also notch the 6x6 3" to set both 2x12's on the solid vertical. You'll still need to bolt them to the remainder of the 6x6 to keep them stable.
 
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Old 12-01-11, 06:48 PM
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Chandler could he not cut shims to angle the hangers off the ledger to the proper angle? Just needing longer screws to go through the hanger and shim?
Also I would definitely install a board across the ends of the rafters at the outside to keep them from warping. 2x lumber would be best but 1x is better than nothing.
 
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Old 12-03-11, 04:38 AM
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Ben, it may be possible, but screws don't have shear strength that #10 joist hanger nails do. Using 2 1/2" joist hanger nails may be an option since they won't be going through anything like a single ledger anywhere. I am not sure, but he is indicating his angle is slight, so it would be a judgment call on site as to whether or not the shims or articulating hangers would be needed.
 
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Old 12-05-11, 01:20 PM
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The carport is only a 3/12 slope which comes out to 14 degrees, or 2.5' over 10'. So maybe regular joist hangers will end up working ok. I like the idea of the shim in the hanger too. At least I think that's what you're saying. Just a tiny bit of shim so that the entire weight of the 2x6 is resting on something.

Ben, the rafters will be inside of the headers and ledger on both ends. The only "overhang" will be a few inches of the metal roof. So I really shouldn't have to worry about the rafters warping.

So if you can picture this, the 6x6 posts will be notched towards the inside of the carport to hold the weight of the 2x12 pt headers. This will look a lot nicer as well, since the joints of the 2x12's will be "covered" by the 6x6's. This is why I need hangers on both sides for the rafters.

Can I get away with construction lags, 3 per board end (6 per post since 2 boards meet at each post). Maybe two lags screwed inward and one screwed outward?

This is all coming together in my head now thanks to your help! The only thing I'm second guessing is whether the inspector is going to make me add gutters to the carport. This would be hard because the 6x6 posts will actually extend beyond the header slightly with my plan above. But the garage will have gutters for the length and I show those in my approved plan. I never showed gutters on the carport. It is really close to the neighboring property though.

Thanks again!
 
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Old 12-05-11, 02:13 PM
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I would opt for carriage bolts instead of lags. More "through" holding ability. Pulls everything together nicely and evenly. Drilling a hole is a whole lot less labor intensive than running lags, unless you have an impact wrench available.
 
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