Roof construction for a shed….Please explain

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Old 02-27-13, 02:56 PM
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Roof construction for a shed….Please explain

​I am currently planning to build a shed this summer and have run into a bit of confusion when it comes to the roof. I have a decent knowledge base when it comes to construction, framing, etc but I have never done a roof before.

After some research I have found that a typical roof should consist of one of these two designs. 1. A ridge board supported by posts going either to the floor or the supporting walls. All rafters would then be running off the ridge board. 2. Rafters connected to each other with collar ties and rafter ties. Another option would be to use Trusses, which from all the ones I have found seem to have some sort of horizontal support that forms a triangle.

My confusion came up when I started looking at shed designs. I went to a few places around town and they all seem to use the same design. I also found similar designs on the internet. From what I have seen none of these designs incorporate rafter or collar ties. They all have an open design to provide more head room. So what keeps the roof from collapsing or pushing out the walls?

I have attached a pic of what I am talking about. Here are a few links also:
How to build a shed roof, Shed roof construction, Shed roof design.
Weaver Barns - Standard Features

Thanks in advance,

Matt
 
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Old 02-27-13, 03:03 PM
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Welcome to the forums!

Personally I'd install collar ties.... even with a ridge board. They probably figure they can get away without it because the roof is small. The carpenters should be along shortly with better advice for you
 
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Old 02-27-13, 05:01 PM
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I agree with Marksr, that they probably decided to omit the joists/collar ties for headroom and figured they could do it since the shed and roof are small. Not a lot of weight to cause the walls to bow.

If you follow one of your links to a similar one, you will notice that most of the "homemade trusses" have gusset plates which are often used in shed construction. Not the sort of thing you'd see in residential construction.
 
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Old 02-27-13, 05:48 PM
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Thank guys! So in your opinion is it OK to use gusset plates without some sort of horizontal support, like a collar tie or rafter tie? The shed I plan to build will be 12x20, with the trusses spanning the 12' distance. I also plan on using shingles for the roof so it will have myself and another guy on top of it for that work. It just seams like it wouldn't be able to hold much weight.
 
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Old 02-27-13, 05:59 PM
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Downward pressure on a roof turns into outward pressure on the walls when there are no collar ties. So on a shed that is say, 12' wide and 12' long, the greatest pressure will be on the middle of the wall... 6' from each end. In theory, if they used a 2x4x12' for the top plate, that wall isn't going to bend very much if there is any outward thrust on it. The lack of weight on a small roof and the short span of the wall (only 12' long) would make it pretty improbable that the wall would bow much.

Now if that wall is 20' long, (as you are planning) it becomes MORE likely that the wall will bow without collar ties... so it would probably be advisable to install either some collar ties or ceiling joists- at least in the middle of the shed where that outward force on the walls will be the greatest.

Have you looked into gambrel roof styles?
 
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Old 02-27-13, 06:29 PM
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Look at the lower picture, that is some mighty honkin' laterals holding the side walls from spreading.
 
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Old 02-27-13, 06:36 PM
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Lower picture looks like a 10" wide shelf to me, with a 1/2" plywood top.

The side walls won't spread on the ends. The greatest outward force is in the middle of the longest walls, and it decreases toward the end walls which are strongest at the corners.
 
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Old 02-27-13, 07:36 PM
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If you are going for a high enough ceiling, then ceiling joists (completing the triangle) would be best and it would provide storage space above. Build an access opening in one of the gable ends and have a 20' storage loft.

Lumber can be purchased in 20' lengths, so a possibility to reduce the spreading effect would be a 2x10 x 20' ridge beam. Followed by the top plate of each 20' wall being a similar 2x10 laid flat. Adding a collar tie every 4' is just a good practice.

There is a hotel not far from me that had a long narrow storage shed build and they obviously weren't thinking about the long problem. It's a sway back now.

Bud
 
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Old 02-28-13, 06:22 AM
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Shed

If you want to maintain an open design without a ceiling, install ceiling joists spaced four feet apart. This will prevent the side walls from spreading and still allow space to store long items on top of the joists.
 
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Old 02-28-13, 07:45 AM
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If you go with rafters, I would definitely incorporate ceiling joists, probably every 4', just as Wirepuller suggested. The absence of them may not be noticed immediately, but you would definitely have "I should've" moments down the road. As for trusses, in addition to the more conventional ones that you mentioned, there are scissor trusses, which would provide the most open ceiling, attic trusses, which could provide better storage space above, although the same could be accomplished with rafters and ceiling joists, and gambrel trusses, which could provide storage above, as well as that traditional barn look from the outside. Plenty of options, depending on what your needs and wants are. And don't base your options simply on what your local big boxes carry; local lumer yards are a great source for quality materials and advice.
 
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