Roof support info.

37chief

Well-known Member
Location
California
I have a shed with a corrugated tin roof. simple 2x4 construction to hold up the tin.
The ridge board is a 2x6 held up by 4x4 posts 8 ft on center to give me 16 ft. 4x4 each end, one in the middle. If I add one more 2x6 to the ridge board and bolt it together, can I remove the center 4x4 This will give me a 16 ft span. Will I have enough support to hold up the tin roof? Thanks for any engineering help.
Stan
 
I don"t think I would. You might get by bolting a 2x8 but not a 2x6. 16" is a pretty good distance to span if you are supporting any weight. Even with a 2x8 it may sag a little over time.
 
Make a lamanated beam with 2x6 with plywood nailed and glued 2x6 1/2 plywood 2x6 make it 16ft long and place under ridge.
 
You didnt say anything about a hill as that takes care of the wire being short. Made tons of fence but here we just dont have a field thats a full 1/4 as we usually have a road every mile thus with road rite of way always had the wire long enough.
 
Doubling the ridge board will make it twice as strong and twice as stiff. But removing the center post will require you to make your ridge board about four times heavier because you've doubled the span. Not only does each post have to support fifty percent more weight than before, you've doubled the average moment arm for the force. Think of it this way: Suppose you apply 10 pounds of force on a one foot long lever: that's 10 foot pounds of torque. Now put 15 pounds on a two foot long lever: you now have 30 foot-pounds. (Some structural engineer is going to come along and rip me apart, because this is nowhere close to an accurate analogy to your roof, but I'm just trying to show you why your ridge board needs to be much stiffer.)

If you double it with a pair of 2x8s, you might be getting close. I'd go with a pair of pressure-treated 2x10s. (Pressure-treated because I assume this will be exposed to the weather, and because pressure-treated lumber in most parts of the country is southern yellow pine, which is very strong). Alternately, you might want to support the ridge with an I-beam. 16 feet is a very long span.
 
Without seeing the building I don't know why it needs a ridge board. So for the time being I will agree with Gene. It don't take near as much material to hold up a roof as most folks think. But you do need an understanding as to where load forces lie.
 
The 4"x 4" poles seem a little light to me, should be using a lot bigger poles to start with and you say ridge pole is it sandwiched between the top ends of your 2"x4" or are your 2"x4"s sitting on top? 16' is a long reach. Hard to answer with out seeing it.
 
Another issue that would help support the ridge is ceiling joists in the shead. Collar ties would help if they were low enough, but the roof is trying to flatten with snow load and its own dead weight. This spreads out the walls and allows dropping of the center (sway backed) shape. Ceiling joists or cables used to prevent the spread should be placed as low as reasonable in the structure and glued/screwed to the rafters at or just above the perch at the wall plates to assure the control of that spreading action, and parallel to the direction of the rafters. Jim
 
2--2x6 on a 16 ft span is not strong enough--as stated below if there are rafters on each side of the ridge and cross ties or ceiling beams then a ridge beam is not needed
 
Stan, please clarify what your roof looks like. I envision a single-sloped shed roof, where the "ridge board" is actually a beam that supports the high side of the roof. But I think other folks assume you have a conventional peaked roof with the ridge in the middle and rafters on either side of the ridge board.

It matters because on a peaked roof, the ridge board doesn't carry significant weight; it's just a place to lean the rafters agains. On the other hand if you have a shed roof, the "ridge board" is supporting half the weight of the roof.
 
Doubtful, but a better description with some pictures or drawings are needed to tell for sure.

Look online to see how a new clear-span version of your building would be built today. You may find that nearly every 2X4 and 4X4 are replaced by 2X6 and 4X6.

If the center posts are removed, the extra span length will increase the loads on both the upper and lower parts of the rafters and also on the walls. 2X4's construction with 4X4 posts does not sound oversize for the building as it is now. How old is the building and what are your winds like?

Check the building over, if it is already starting to lean or sag anywhere I wouldn't start removing out any supports.
 
Mark B, your idea makes sense. I just couldn't figure out how a peaked roof would need more support unless there is nothing in the building to tie the walls together. It sounds like this a single sided roof and the center pole under the high open side is in the way of backing machinery that's wider than 8' inside. Jim
 
Stan, If I understand your question, you plan to have just 4 4x4 supporting the roof? If so, that sounds to me like is a strong burst of wind comes along, you will be posting pics of how a deck of cards came down.

Do you have any type of angle bracing on 4x4 and rafters?

IMHO, the ridge board has nothing to do with supporting the roof, it only holds the 2x4 rafters in place. If you want strength, try adding board and making your rafters look like trusses.

A pic will help us all. How big are is your header board.

Building inspector wanted two 2x12 header boards in my pole just for my 10 ft garage door, which wasn't supporting anything, it was on the end. My 30 ft trusses rested on the side walls of barn.
George

George
 
The header beam for the 16 foot door (48' trusses) on the side of my shop is made of 2X6s and plywood. Nine 2X6s total. Three high and three wide with plywood in between.
 

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