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Roof Framing for Almost Flat Roof

cakins's Avatar

Join Date: Jan 2005
Posts: 144

09-05-05, 10:43 AM   #1  
Roof Framing for Almost Flat Roof

I'm replacing the rotted roof on a workshop area slightly smaller than 12 x 16. The roof barely has a slant to it, maybe 4 inches in the 12' width.

Currently the roof framing is 2x4's - some of which show evidence of bowing a little - on 18" centers more or less. Several of these are rotted to the point I'll have to replace, but I'm wondering if the framing is correct to begin with.

The span from the ledger board on the house to the outside wall of this room is 9' 6" so a doubled 2x4 beam (and post to support it) is present, about 2-3 feet from the ledger board, but I think this still leaves too much span for 2x4 rafters - thus the bowing from that beam to the outside wall.

I certainly didn't want to get into a huge construction project, but I don't want to just put new 2x4 rafters back in either if it's not proper.

Can anyone help me with info on what normal rafter sizes are for something like this?

If I go with larger rafters can I increase the spacing between rafters?

What size rafter would I need to use in order to eliminate that 2x4 beam and post? Would the cost of such a rafter size be huge? Or would it be more economical to get a couple engineered beams that would span the entire length (almost 16') without posts, use them and then keep the 2x4 rafters?

As you can tell I need help :-)

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IBM5081's Avatar

Join Date: Oct 2004
Posts: 655

09-05-05, 10:58 AM   #2  
Span tables

Google for "span tables"

Here is one hit:

I think that you will get the idea.

There are different ratings for live loads (like a habitable room) and dead loads (like storage).

Snoonyb's Avatar

Join Date: Aug 2004
Posts: 1,150

09-11-05, 06:09 AM   #3  
Here is another link;

And as a for instance, here on the truely left coast a 2x6DF used as a combination RR/CJ with a slope less than 3&12 has an allowable span of 13'11". However, because insulation requirements, a minimum joist depth of 2x10 would be used.

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