Building Wood Shed - Need Help Calculating Beam Size That Holds Roof Up

[BoylermanCT]

I started building a wood shed lean to that will be attached on one side to my garage. I dug the holes for the posts today, and plan to get order the lumber on Monday. I need help in calculating the size of the beam that will support the rafters.



I am having 3 6x6 posts spaced 10' apart. On top of the posts is a 23' beam of unknown width and height. The beam will go past the end posts by 18" on each side. The posts are 11' from the garage wall. Based on an 11' span and 24" centers, the charts say to use 2x8 rafters. Rafters will go past the beam by 1'. I will use 1/2" plywood or OSB for decking and then tar paper and metal roofing.

I can't find a chart showing what size the beam on top of the post should be. I know I can do triple 2x12's and have it covered. But that will be a heavy beam to lift into place. Can I do triple 2x10's or 2x8's? I was planning on attaching the beam to the post using a Simpson bracket made for attaching 3 2x's to a 6x6.

I live in CT, and code calls for roof loads of 30 psf. Thanks!

 

[polkwrangler]

2x 10 should be plenty good,i built a firewood storage building with 2 x 10 ,has roof and walls It can hold four truckloads of split oak with all that weight never had a problem.

 

[RNeumann]

Triple 2x12s looks like the ticket. You lift one 2x12 up at a time- build in place.....one person job!!!

Typically the Simpson tie going from the post to the beam is made for dimensional lumber. Since you are sandwiching 3 2x12s you will need to add some plywood to fur out to the post and Simpson width.

 

[Barnbuilder]

How about a double 9-1/4" LVL? Should be more than enough and it would be full length. You can notch the 6x6 so LVL can sit on it. Throw a couple 5/8" galvanized. Carriage bolts through it.

 

[mikester]

I started building a wood shed lean to that will be attached on one side to my garage. I dug the holes for the posts today, and plan to get order the lumber on Monday. I need help in calculating the size of the beam that will support the rafters.

View attachment 625349

I am having 3 6x6 posts spaced 10' apart. On top of the posts is a 23' beam of unknown width and height. The beam will go past the end posts by 18" on each side. The posts are 11' from the garage wall. Based on an 11' span and 24" centers, the charts say to use 2x8 rafters. Rafters will go past the beam by 1'. I will use 1/2" plywood or OSB for decking and then tar paper and metal roofing.

I can't find a chart showing what size the beam on top of the post should be. I know I can do triple 2x12's and have it covered. But that will be a heavy beam to lift into place. Can I do triple 2x10's or 2x8's? I was planning on attaching the beam to the post using a Simpson bracket made for attaching 3 2x's to a 6x6.

I live in CT, and code calls for roof loads of 30 psf. Thanks!

This is a good question for your building inspector NOT the internet full of eager people unfamiliar with your area, climate and codes. The required beam size is based on a calculation of roof pitch, applied loads and allowed deflections...thats why you cant find a chart.

 

[sailfast]

This is a good question for your building inspector NOT the internet full of eager people unfamiliar with your area, climate and codes. The required beam size is based on a calculation of roof pitch, applied loads and allowed deflections...thats why you cant find a chart.

This was an excellent example of one of those eager people offering incomplete half correct recommendations.
The calculations for this can be found on the internet. And, you might want to get the help of an engineer or architect. However, under the circumstances is something you can figure out yourself.

 

[radioman]

With building experience in central nys with similar snow loads, since you have 6x6 posts, nothing wrong with overbuilding. I would just use 2x12s and put them up one by one. I have done it this way. However since you have 10ft spacing of posts and 18 inch overhang you really don't want a slice in the middle completely. I would find a lumber yard that carries 20 footers 2x12. Use 12ft on the outside and one 20 ft inside. Use scrap of 12ft to fill in the 18 inch spacing overhang. Be sure to add metal splice plates in the middle and brackets to hold beam to posts. Follow the beam load carrying screw pattern and spacing. Should be in your local permit office. Can use the decking guidelines. These are the things a local building inspectors look for regardless if you have a permit or not.

 

[EddieWalker]

Your ten foot span isn't very much. For my porch here in East Texas, where snow is not a factor, I went with three 24 foot long 2x8's for my beam on posts 12 feet apart for a total width of 24 feet. What I liked most about that is the 2x8's where one continuous board. I had to go to a store that sells more to contractors and home builders, because Lowes and Home Depot only sell lumber 16 feet long.

First thing that I would figure out is what did people use for the garage doors when building houses in your area? Granted, most garage doors are either 9 feet wide or 16 feet, but once you see what was used there, then it should be easy to determine what will work for your project.

While the size of the beams are important, how you attach your ledger board to the existing building is even more important. Code is changing on this almost every year because of catastrophic failure that has resulting in how the ledger board was attached. Usually it's because nails where used, but the lack of proper flashing that leads to rot is also very common. The ledger board is your lynch pin and keystone to what will keep it in place. Fasteners absolutely have to be structural. Nails and screws are just fasteners, and NOT structural. They can NEVER be used to support a load of any kind. This is also why joist hangers have specific nails and screws that can be used, and only they can be used.

If you decide to go with 12 foot long boards for your beam, be sure to use plywood between the boards to join them together over your center post. 4 feet of plywood on each beam with liquid nails or something similar so that there is no way that the boards can pull apart. Also be sure to nail or screw the boards together top and bottom, ever 12 inches. Be sure to either use metal fasteners to attach the beam to the posts, or notch the post so the beam rests in a L shape cut out of the post. I prefer to do both with 6x6 posts. I set the post so it's a little taller then I need it to be, then I determine my beam height and draw a line across each post to where I want the beam to rest. Then I cut it out and install the first post to the tall L part that I've cut out. Then the plywood, and then the other board. It makes it easy to get a very strong beam without lifting all of it at once.

 

[goeduck]

With building experience in central nys with similar snow loads, since you have 6x6 posts, nothing wrong with overbuilding. I would just use 2x12s and put them up one by one. I have done it this way. However since you have 10ft spacing of posts and 18 inch overhang you really don't want a slice in the middle completely. I would find a lumber yard that carries 20 footers 2x12. Use 12ft on the outside and one 20 ft inside. Use scrap of 12ft to fill in the 18 inch spacing overhang. Be sure to add metal splice plates in the middle and brackets to hold beam to posts. Follow the beam load carrying screw pattern and spacing. Should be in your local permit office. Can use the decking guidelines. These are the things a local building inspectors look for regardless if you have a permit or not.

^^^ good advice. I like the 12/20 length of 2x12s concept. Around here without plumbing and electrical this might not require a building permit unless due to being a lean to. But no reason not to look up local code and keep your nose clean.

 

[goeduck]

First thing that I would figure out is what did people use for the garage doors when building houses in your area? Granted, most garage doors are either 9 feet wide or 16 feet, but once you see what was used there, then it should be easy to determine what will work for your project.

I thought this was a wood shed.