Expert: Bruce E. Johnson - 6/20/2011

Question
Hi,

We have a patio on the rear of the house that has a wood framed cover.  The cover is 16' x 24'.  The long side is attached to the building, the opposite long side is supported by 4x4 posts, 8' apart OC, with a header beam.  The problem is whoever built the thing used stacked 2x4's as the header beam, but not on edge (really crappy construction).  Of course, the beam is now sagging between the support posts.  I would like to replace the header beam, but not sure if I need to use 4x4 or 4x6 lumber.  Basically, my question would be what is the maximum span for 4x4 beam and/or 4x6 beam?

I can give more details and/or provide pics if you would like.

Thanks,

Henry

Answer
Hi Henry, a good rule of thumb for beams is one inch of depth per foot of span so an 8' span would require a 4x8 beam.  However since your beam is supporting a minimal roof load and doesn't have the weight of a drywall ceiling bearing on it..you can probably get by with a 4x6 southern yellow pine or douglas fir beam..I hope this information helps, please feel free to write again regarding this or other matters, sincerely bruce johnson..bejohnsonconsulting.com