Carpentry question...

BJordan

Eight Pointer
I have a 20'x20' storage building and am wanting to attach a 20'x12' leantoo to the back of it. Whats the best way to attach the joists to the existing building? The existing building is T111 siding and the leantoo will be mounting to the side with the "A" part of the roof. The building is built on pillars and the rear of the building is 30" off the ground so there is plenty of room to mount it and still have headroom under the leantoo. This is what I have in mind so far.

4 5"x5" poles spaced eveny across the 20' direction and using 12' 2x6" spaced 16" on center. The poles will be in the ground 11' from the building giving me 1' of overhang. Is 11' to far for a span for 2"x6"? Not sure what pitch I'm going with on the roof either. Roofing material will be tin with firring strips. I was thinking of attaching a 2"x6" to the builing and attaching a 2x4 to the bottom of it to make a shelf for the joists to sit on and then just attach them with nails toenailing them. I'm also not sure the best way to set the joists on the poles, notch the poles and set a 2X6 on them, then set the joists on the 2x6 thats attached to the poles?

Any tips or advice will be greatly appreciated.
 

Soilman

Old Mossy Horns
Contributor
You can usually get away with 2 foot spacing rather than 16" on a roof. 16" is way overkill, expecially for a tin roof.
Next suggestion is, place a furring strip no more than 3-4" from the end of the overhang. This will keep it stiff enough to not flap and loosen the tin during wind.
USE metal roofing SCREWS to secure the tin down rather than nails.
2 x 6's should span 11 feet fine.

The "shelf" idea will probably work, but you can also buy joist hanger from any building supply store fairly cheap, and attach them to the 2 x 6 you mentioned attaching to the garage.
 
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brownisdown

Twelve Pointer
Contributor
^ Pretty good advice there. I would screw your 2x6 to the existing building at every stud location and then use the metal joist hangers. I personally wouldn't use the shelf idea you explained since your supporting fasteners would be in tension which I always try and avoid. Instead of the hangers you could double up the 2x6 fastened to the existing building wall and then cut a birds mouth in your rafters and set them on top of the 2x6 "plate". I'd use a 2x6 joist plate between your poles also. 2x6 rafters at 24" O.C will work fine for a shed roof like that.
 

Longrifle

Old Mossy Horns
Contributor
I'd double the 2x6s at the eave sill plate and use 1x4 purlings of #2 pine across your rafters on 2' or 3' centers to screw the metal to. Double screw the panels between the high ribs at eave and wall, it'll stay there.
 

Southside

Ten Pointer
For the following pitches here are your rafter lengths.
3/12-11'4" + 1' overhang
4/12-11'7 1/8" +1' overhang
5/12-11'11" + 1' overhang
So 12 footers will be to short. I would not go under a 3/12 pitch even if using metal roofing. These lengths are figured for setting posts and beams 11' to the outside. Therefore your inside clear deminsion would be 10'7".
2' rafter spacing is sufficient (16" is better though). Use a 2x8 against bldg and butt a 2x2 under rafters once nailed in place or use the hangers. I personally don't like hangers.
Unless your matching something existing regular metal roofing may be cheaper than 5v tin? I would attach a drawing of my description but i have no idea how to attach a pic.
 

mekanizm

Old Mossy Horns
Contributor
I used 16' 2x6's for my shed roof (15' span). That is a long span so I put them on 16" centers. I used 2x4 purlings (overkill but what I had on hand) and 36" wide ribbed metal roofing panels screwed down (appx. $1/ft^2). I saw a little bowing when 5" of snow sat on top of it but it has stayed flat for 7 years now. I used hangers screwed to a 2x6 lagged to the existing wall studs on the high side and birds-mouthed the low end to sit on an oak 2x8 rough-sawn that was notched into the posts (as in doubling a 2x6).
 

mudflap

Ten Pointer
I would rather overkill than cut corners, last snow we got you could tell who "overkilled" and who didn't!
 

Triggermortis

Twelve Pointer
Contributor
For the following pitches here are your rafter lengths.
3/12-11'4" + 1' overhang
4/12-11'7 1/8" +1' overhang
5/12-11'11" + 1' overhang
So 12 footers will be to short. I would not go under a 3/12 pitch even if using metal roofing. These lengths are figured for setting posts and beams 11' to the outside. Therefore your inside clear deminsion would be 10'7".
2' rafter spacing is sufficient (16" is better though). Use a 2x8 against bldg and butt a 2x2 under rafters once nailed in place or use the hangers. I personally don't like hangers.
Unless your matching something existing regular metal roofing may be cheaper than 5v tin? I would attach a drawing of my description but i have no idea how to attach a pic.

Best answer.
 

Longrifle

Old Mossy Horns
Contributor
If you have a BDC nearby 3' wide Galvalume Master Rib panels are $1.65 a linear foot right now....
 

BJordan

Eight Pointer
Thanks for all the replies so far, I already have the poles, (4 5"x5"x14' cedar) the tin, (lots of commercial R-Panel tin), and lots of metal furring strips. I mentioned earlier the poles would be 11' from the building but I dug them 10' from the building and 6'8" apart and two feet deep. I think I'm going to screw a 2x8 across the back of the building and use hangers for the rafters. I'm still undecided and usnure of how to sit the rafters on the poles and what pitch to go with. Is there anything better or easier than notching the poles and sitting a 2x6 on/nailed to them? Is a 2x6 big enough to support the rafters spanning 6'8" between poles.
 

mekanizm

Old Mossy Horns
Contributor
I'm still undecided and usnure of how to sit the rafters on the poles and what pitch to go with. Is there anything better or easier than notching the poles and sitting a 2x6 on/nailed to them? Is a 2x6 big enough to support the rafters spanning 6'8" between poles.

a 2x6 spanning 7' as a load bearing beam is borderline at best IMO. I would probably step up to a 2x8 yellow pine for that one. You are not talking a lot of weight so I would think you could thru-bolt it to the post or possibly lag but chainsawing a notch is what I do since i already had the chainsaw out to cut the posts to height. I went with a pitch that gave me the clearance on the low side I needed and that also looked pleasing. I suspect it's slightly less than 3/12.
 

dc bigdaddy

Old Mossy Horns
Contributor
Leave the chainsaw in the shop.

Notch the post by cutting it from both sides with a regular circular saw. Screw the 2x8 to the studs and use joist hangers. Space the rafters at 3' on center then run your purlins based on Longrifle's recommendation. Through bolt the 2x8 to the post in the notch.
 

Southside

Ten Pointer
Thanks for all the replies so far, I already have the poles, (4 5"x5"x14' cedar) the tin, (lots of commercial R-Panel tin), and lots of metal furring strips. I mentioned earlier the poles would be 11' from the building but I dug them 10' from the building and 6'8" apart and two feet deep. I think I'm going to screw a 2x8 across the back of the building and use hangers for the rafters. I'm still undecided and usnure of how to sit the rafters on the poles and what pitch to go with. Is there anything better or easier than notching the poles and sitting a 2x6 on/nailed to them? Is a 2x6 big enough to support the rafters spanning 6'8" between poles.

Notching the columns at top to accept the beams would be best. Should step up to 2x8 do beam material.
 
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