Expert: Ted Barnhill (Principal, Design45 LLC) - 2/23/2009

Question
Hi Mr. Barnhill,

I am currently remodeling a 50's era cottage.  It originally had a rectangular footprint with hip roof.  At some point, an extension was added to the back and another hip end was added to the existing hip end about 1/4 of the way down from the ridge beam.  Both hip ends have dutch gables.  

I would like to remove the old exterior wall which now separates the kitchen and the extension and replace it with a beam.  The existing load bearing wall supports the old hip end rafters and the new hip end ridge beam / rafters which extend from the previous roof.  The load bearing wall is connected to an interior wall and the existing exterior wall with ceiling joists at 16” OC.

The span from the interior wall to the load bearing wall is approximately 10 feet and from the load bearing wall to the exterior wall is 8 ft.  I hope to span about 14 feet with the beam.  I asked a building inspector to evaluate my situation and he recommended a beam that could carry 550 – 600 lbs/linear foot.  This sounds like a lot to me, especially considering the condition of the current load bearing wall (water damage).  Does this sound reasonable or should I consult another expert?

Thanks!


Answer
Landon,

Your beam loading will depend on your roof load, and also on your framing geometry, especially whether the interior wall you mention is load bearing or not (I would guess not).  Your beam will bear half of the width of the span on each side; that is, 4' on the addition side, and somewhere between 5' and 12' or so on the "old" side.  Depending on your snow load, it is not unlikely that your beam would require (4+11 = 15)lf x 40psf = 600 lbs/lf capacity.

You mention a "ridge beam" in the new hip roof; this is not likely, but if you do have a beam rather than just a board, and it creates a point load on the new beam that you are designing, it is very important to account for this load as it may be quite large.

If the inspector has looked closely at your structure, he is probably correct; if he was working from your description, it may behoove you to have an engineer optimize your beam rather than trusting the (possibly conservative) inspector.  I hope this helps.  Good luck with your project, Ted.