Expert: Bruce E. Johnson - 4/24/2011

Question
QUESTION: What I want: To get rid of the center post holding up my patio roof.

Why: We just added a beautiful water feature, and the center post ruins the view.

What I have: A 16 ft 4x8 horizontal beam mounted on three vertical 4x6 posts, one on each end and one in the center. The patio roof itself consists of asphalt shingles on plywood on 4x6 rafters on 16 inch centers. The beam is 13 feet from the house. The top of the beam (and the bottom of the rafters) is 90 inches above the concrete slab patio. The bottom of the rafters on the house end is 101 inches.
This is all located in suburban Phoenix, so snow is not an issue.

Some ideas for your comments if you would be so kind:

1- Just knock the center post out. Probably not a good idea.

2- Reinforce the 4x8 beam by bolting a 16 foot long 2x8 onto it. Reinforce the 4x6 posts by bolting a 2x6 onto each one for its entire height. Maybe even dig under the corners of the slab and pour a concrete footing. Then knock out the center post.

3- Add a 4x6 at a 45 degree angle starting 3 feet from each end of the beam to 3 feet below the top of each post. Maybe reinforce the posts and slab like in #2. Then knock out the center post.

4- Suspend the center from a (very) large helium ...never mind.

Any advice, ideas, or references to appropriate resources will be greatly appreciated.

ANSWER: Hi Bob, I opt for suspending it from a helium filled balloon..just kidding..it sounds like your present beam is sized properly for the spans involved. A proper beam size for a 16' span is suggested to be minimum 4x12 preferably a 4x16. This of course would hang down too far considering you are only 90" high on that side already.  Adding more 2x8's to your beam width would help followed up by your idea of adding "knee braces" at each end to reduce the span and beefing up your posts to handle the added lateral stress of the knee braces.  I am always cautious about removing structural elements without consulting a structural engineer locally to look at your particular situation. This would include any beefing up of your existing foundation pads.  I hope this info helps, please feel free to write again regarding this or other matters, sincerely, Bruce E Johnson ..bejohnsonconsulting.com

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

QUESTION: Thanks for your prompt and knowledgeable reply. Two more questions: Is there some other kind of reinforcement I could attach to the length of the wood beam to strengthen it (like steel or aluminum or carbon fiber)? How does one go about finding a local structural engineer? Do cities provide this kind of service? (OK, that's three. C'est la vie.)

Answer
Hi again Bob, yes there are alternate materials available, each with their own pros and cons but withou an actual visit to the site it's difficult to see what all is involved in your particular situation, thus the engineer suggestion.  Engineers are listed as PE "professional engineer". A trip to the yellow pages should unearth any number of them specializing in structural problems. You will probably need a permit to do this work anyhow so having an engineer come up with a working design, signed and sealed will be a step in the right direction..sincerely, Bruce E Johnson