Expert: Paul S. Brown, AIA - 4/5/2006

Question
I want to build an outside Pavilion 16'long x 10'deep.I want to use 6 x 6 posts in each corner, do I "NEED" to use a middle post in the center of the 16' sides? and if not what size header should I use?(I would like to keep the center open).I appreciate any help thank you.

P.S. the roof pitch is 6/12 and I'm using 2 x 4 trusses on 2'centers.

Answer
Essentially what you are doing is building a post and beam frame structure to support your roof.
You can span the 16 feet with a large beam; a general rule of thumb is 1" of depth for every 12" of span; so this would be a 16" deep wood beam to span 16'.
You might be able to refine this rough rule-of-thumb further; particularly if you use laminated veneer lumber products.
If you don't want to hire a structural engineer to size the members for you (advised), visit your local library and take out a technical book on timber frame sizing.  Or, you can probably purchase a book like this at a good bookstore or your lumber yard.  You can also try typing in 'laminated veneer lumber' on Google, and see what you come up with; some of the manufacturers will actually offer to size your beam for you if you buy it from them.

I went on this website, the 'timber frame guild' :

http://www.tfguild.org/ubbcgibin/ultimatebb.cgi?ubb=get_topic;f=12;t=000088

and found this additional information:

You'll find some help in the Timber Frame Joinery & Design Workbook, a Guild publication. See the articles by Levin (pp. 20ff) and Chappel (pp. 32ff). Conventional span tables are included in Benson & Gruber's Building the Timber Frame House, Scribners, 1980. There are also a host of software products that do member sizing. These include Woodworks (see http://www.woodworks-software.com/ ) and Construction Calc. (see http://www.constructioncalc.com/ )

I hope this  helps.
PB