Shed Building Advice

[jadefox]

Hi, All.

We're adding a 32'x10' shed to the side of the barn. Part of it will be for implement storage and part will be wood storage. We have a basic plan, and I was hoping to float it here for some feedback:

We will be using four pre-cast piers with 6x6 pt posts. The header and ledger boards will be 2x12s, and the rafters will be 2x8s. We'll double up two headers on either side of the 6x6 posts. We'll add 2x6 Y-bracing at each post.

The roof will be metal and I'm thinking steeper than 12:4 (we're in Maine).

Half of the shed will have a deck for wood storage.

We'll probably sheath the other half of the shed for more weather protection.

The big questions are: 1) Can I get away with just three piers? 2) If I use four piers, can I still use 16' 2x12s for the header even though they won't meet at a post? Otherwise I'd have to use three 12' board trimmed and meeting at each of the center two posts. Other thoughts?

Thanks in advance.

 

[s219]

Your headers should meet (or overlap depending on the arrangement) at the posts.

The real answer to your questions is determined by the snow load on the roof. Starting with that, you can figure out what size rafters you need, what size header, the number of posts, and the size of the footings.

I think it's easy enough to eyeball things or look at a similar shed that has already been built and has survived a couple decades to get sizing, but if you want specifics for a paper design, you really need to compute the roof loads and propagate them down through the structure, each step of the way. If any one part of the structure is sized wrong, you'll have problems when the roof is loaded up with weight.

 

[jadefox]

Your headers should meet (or overlap depending on the arrangement) at the posts.

The real answer to your questions is determined by the snow load on the roof. Starting with that, you can figure out what size rafters you need, what size header, the number of posts, and the size of the footings.

I think it's easy enough to eyeball things or look at a similar shed that has already been built and has survived a couple decades to get sizing, but if you want specifics for a paper design, you really need to compute the roof loads and propagate them down through the structure, each step of the way. If any one part of the structure is sized wrong, you'll have problems when the roof is loaded up with weight.

Thanks for the quick reply. So I should go with 2x12x12' (the span between posts is actually 10.7' with four piers) for the headers bolted at each post?

Regarding eyeballing, I've been doing that, and I think I'm happily overbuilt at 4 piers with the header, ledger and rafter sizes speced out above...especially with a steeper metal roof and southern exposure.

Thanks again!

 

[s219]

I'd have to pull out my design tables and run the calculations to say for sure. If just concerned about the headers, figure out the snow load in psf for your area, multiply by the area of the roof, and then divide by the length of the header. That will give you the lb/ft distributed load on the header, and you can use wood design tables to figure out what size header is needed for the spans you want to use between posts. Can also take snow load x area and then divide by the number of posts to determine the loads that the posts and footings need to carry. Divide each post load by the area of the footing to determine the needed soil bearing pressure.

I can tell you that for a Virginia snow load (30 psf if I remember right) a double 2x10 header supported on posts every 10 feet was enough for a roof I built that carried about 8' span to the center and was 24' long. In that case the header beam would have seen 30*8*24/24 = 240 lbs per foot loading.

 

[jadefox]

I'd have to pull out my design tables and run the calculations to say for sure. If just concerned about the headers, figure out the snow load in psf for your area, multiply by the area of the roof, and then divide by the length of the header. That will give you the lb/ft distributed load on the header, and you can use wood design tables to figure out what size header is needed for the spans you want to use between posts. Can also take snow load x area and then divide by the number of posts to determine the loads that the posts and footings need to carry. Divide each post load by the area of the footing to determine the needed soil bearing pressure.

I can tell you that for a Virginia snow load (30 psf if I remember right) a double 2x10 header supported on posts every 10 feet was enough for a roof I built that carried about 8' span to the center and was 24' long. In that case the header beam would have seen 30*8*24/24 = 240 lbs per foot loading.

GSL for our town is 50. I'm down to around 36 psf with a metal roof depending on slope. For the header to post connection, which is preferable?

 

[HCJtractor]

I use the "eyeball" method rather than the Mathematical. I would use 4 piers, and have the headers meet in the middle of the posts and bolt or lag screw them. I built one almost identical in design. I don't have the snow load, but I think that would be plenty strong for a shed. I understand that computing the exact requirements would be superior, but for a shed, (and me not having the engineering skills and being cheap), I think your design is sufficient.

Sent from my iPad using TractorByNet

 

[HCJtractor]

I would vote method A. But B would be adequate. But I like the ledges better. And I would use 5/8 " galvanized bolts.

 

[dadster4]

I would vote "A" also, with the 5/8" bolts. As for the deck, I would recommend setting the joists on top of the headers and not rely on metal joist hangers. Blocking between joists and a header will keep them square.

 

[s219]

GSL for our town is 50. I'm down to around 36 psf with a metal roof depending on slope. For the header to post connection, which is preferable?

I am OK with method B for simplicity, but it wouldn't pass code here. When we had a barn built, the normal way to do it was method B, but it got rejected by the county (unfortunately I had to get permitted for that). So what we did was notch the post enough to support one header directly, and then bolted the second header through the face of the first one. Kind of like your bottom sketch, but only notched for one header. Everybody was happy with that.

There wouldn't have been enough meat in a 6x6 to do method A, at least not according to code. Would have been OK with me though.

How are you changing a 50 psf snow load to 36?? It's 50 psf over the projected area of the roof, since gravity acts straight down. Roof slope shouldn't change that at all, nor material. And the span calculation for a rafter also is based on the horizontal span (or half span if there is a ridge), so slope won't affect that either.

I did asphalt roof on my barn with a 8:12 roof pitch. My boat house is a metal roof with a 4:12 pitch. But both have to handle the same exact snow load rating over the projected area of each roof.

 

[Zerk]

I am just a hack, but have started building shed style roofs, with bird mouth rafters. I put my headers on top of the posts. I live in an area with 300" of snow.

So I would do the bottom design and cut out the post and the header on it.