Expert: Ted Barnhill (Principal, Design45 LLC) - 7/22/2010

Question
QUESTION: This is a ridge of a new higher pitched (6/12) roof that is built over old 2/12 one. Old ridge is 3.5 by 12 solid wood beam 19 ft long supported in 2 places in the middle (so span is about 6.5ft). New rafters (2x10, 12ft. long) will be placed over old ones, and we want to use two 2x12 as ridge beam (load bearing, midwest, snow). We would place 4x4 posts exactly over existing support points (so, also with 6.5 ft. span).

Any ideas ?

Thanks in advance.

ANSWER: Alex,

With the limited information that you have provided, I wouldn't see any problem with your proposal.  I base this on my reading of IRC 2006 table 502.5(2), which indicates that 2-2x12 will span 7'-6" as a header in an interior bearing wall supporting one floor only, with a house width of 24'.  This is a more demanding condition than I understand you ridge beam to be.  I don't fully understand your tie-in scheme (is the old roof to be completely removed?), but as long as your connection details are sound, the ridge beam itself should be sufficient.  Of course, you should consult a local engineer to be absolutely sure, as without seeing your situation I can't see any potentially complicating factors.

Ted Barnhill
Design 45 LLC

---------- FOLLOW-UP ----------

QUESTION: Existing roof's framing / decking remains in place and essentially serves as a floor of an attic (close to the attachment). You think one 2x12 could be enough then ?

Answer
Alex,

That sounds like a very unique attic!  If you are leaving an adequate ridge beam in your existing 2:12 roof, one option is to build a bearing wall beneath your new ridge, bearing on the old ridge.  If you instead want it to be open and choose to build a new ridge to span the existing 6'-7', your new ridge must be sized to support the loads involved.  A single 2x12 does not accomplish this.

As you have a unique situation with uncommon connection points, it may be wise to consult with an expert on site - be it an engineer, a building designer or architect, or a competent contractor.  Best of luck with your project.

Ted Barnhill
Design 45 LLC