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Discussion Starter · #1 ·
Currently working on a summer cottage and the entire roof need replacing. When I looked in the attic, I saw the trusses are 2X4's that are mitered at the peak (no ridge beam). They are also spaced 24". Roof decking is 1X8 boards. Some have cross bracing, but most do not. I plan to cross brace those. Needless to say walking the roof is a little springy.

After tearing the current roof off, I'm considering overdecking the planks for more rigidity, but I'm concerned with the added weight.

How thick can I go (if at all) with the overdecking while remaining safe?

Any info or advice would be appreciated.
thanks
 

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Are they trusses or are they rafters? What do you mean by cross braced? A horizontal member running across the pairs of rafters? That would be a collar tie.

If the sheathing is 1x8, then another layer of sheathing is mostly just going to add more weight. You probably need to consider beefing up the framing.
 

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I found your post a little confusing, perhaps you can clarify. You said "the trusses are 2x4, mitered at the peak". Do you really have trusses, or do you have traditional rafters that are 2x4? Then you said there was no ridge beam. I am guessing you are referring to the lack of a ridge board, which is a non-structural element typically used to make it easier to nail the rafters (not tursses) together at the top. The lack of a ridge board is not a problem.

Then you noted that the spacing of the "trusses" (rafters?) was 24 inches oc. You did not list the span of the rafters, which would determine how much load they can carry.

The roof decking is apparently composed of 1x8's, which you are thinking of overdecking, apparently to correct the springy feel of the roof. Adding an additional layer of planking would add some stiffness to the roof, but the real issue is probably the use of 2x4's as rafters, 24 inch oc, and not the use of 1x8 roof decking. Also the lack of cross bracing between the rafters, although cross bracing for rafters is not common. What is common is the use of collar ties, but you did not state whether there are any collar ties present.

Before undertaking an overdecking project, you should probably measure the span of the rafters, tell us where you are located (wind load, snow load make a big difference in roof design). There may be more effective ways to stiffen the roof than adding another layer of decking.
 

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Discussion Starter · #5 ·
Thanks for the responses. Already learning things (terminology). OK. I have rafters, not trusses. I also have a couple of collar ties, not cross braces. Most of the rafters do not have collar ties. There is no ridge board. The location is southern Wisconsin and does get some snow. From memory, I think the pitch is 12/12. Thanks again.
 
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