Roof Pitch; 4/12 or 3/12?

[EddieWalker]

For metal roofs, you can go 2:12 without having to seal your seams. My supplier told me not to go any less then 2:12 because during a heavy rain, the water wont run off of the roof fast enough. 3:12 is good. I have 4:12 on my house and barn more for looks then any other reason. If it's dry, I can walk on it easily, but I won't go up there until the morning dew is gone. I also make sure that my shoes are clean because dust under them can cause me to slip.

 

[Diggin It]

My existing 24 x 30 two car garage has 2x6 rafters (2x6 base, 24' clear span with 2x4 cross members nailed on), stick built on site (not manufactured trusses) and it has held up fine for 20 years. It is 4/12 with shingles that have worn out and I'm in the process of putting metal over that. I can walk on it with no flex that would indicate weakness.

Truss makers have quoted theirs using 2x4s for all member which I'm not sure I'm comfortable with.

 

[Diggin It]

Since you said you are putting them on 24" centers I think you will be more than fine, your truss manufacturer will build them to spec for local snow, ice and wind loads. I'm assuming you will nail in 1x4's flat on top of that to screw to?

I've used 1x4s over the existing roof on the house and garage, but for this with no under decking, I'd plan on 2x4s.

 

[4570Man]

I just put up some 30 foot trusses all 2x4s. But for a simple lean shed stick built is probably cheaper.

 

[Diggin It]

I just put up some 30 foot trusses all 2x4s. But for a simple lean shed stick built is probably cheaper.

It seems close to a toss up. Truss quotes have been just under $100 each, delivered. But then I have handling issues, trying to get them in place and erected. Boards are a bit less expensive and a lot easier to handle, but then I have so much more cutting and fitting to do. While they could be simply nailed like the garage is, I'd want to add some steel structural plates (joist hangers, rafter angles, etc.) which will add some cost.

 

[4570Man]

2 guys could stick build it pretty easy. Setting trusses without a crane and only 2 guys would be a pretty rough job.

 

[Birdhunter1]

I've used 1x4s over the existing roof on the house and garage, but for this with no under decking, I'd plan on 2x4s.

2x4's would be stronger but I havne't found any issues using 1x4's flat on 24" center rafters with no decking and I weighed 260 lbs at one time.

On my horse barn, 4/12 pitch, I set trusses on 4' centers (28' wide) on a beam on top of posts and laid 2x4's flat and screwed the metal down. I'm very pleased with it.

 

[s219]

My existing 24 x 30 two car garage has 2x6 rafters (2x6 base, 24' clear span with 2x4 cross members nailed on), stick built on site (not manufactured trusses) and it has held up fine for 20 years. It is 4/12 with shingles that have worn out and I'm in the process of putting metal over that. I can walk on it with no flex that would indicate weakness.

Truss makers have quoted theirs using 2x4s for all member which I'm not sure I'm comfortable with.

2x4 on a truss is fine because of the truss structure -- take a look at it and it should be obvious why (it's the whole point of a truss). You could build trusses with toothpicks if it's done right (slight exaggeration but you get the point).

The max span I have seen with 2x6 in low snow load areas is about 16'. You mentioned walking on it which is one reason why you don't want to undersize rafters, especially if it's to be a metal roof. Undersized rafters deflect from the live loads of walking and will create problems with your roofing screws sealing. I happen to think those screws are the most vulnerable part of a metal roof since it doesn't take a whole lot of tweaking to cause leaks. Over-driving screws is probably the #1 problem, followed by live loads causing movement of the metal under the screw heads. I'd say under-driving screws is the least common problem.

So many people design for snow load only and ignore the live loads. Those can become a real issue.

 

[tcreeley]

If 2x6 are 24 oc. I would go with 4 : 12 pitch. Fewer problems from rain/snow/ice in the future.

 

[WM75Guy]

I prefer the 4:12 pitch for the look. Our shop has 4:12 pitch main roof with a 1:12 pitch for the 12' lean-to on each side. Have not had a leak in 12 years it has been up. Snow load is not an issue in East Texas.