Building Homes or Extensions/Wood Span for 16x16 Pergola

Advertisement

Expert: - 11/12/2008


Question

16'x16' Pergola
I am builing a 16'x 16' pergola. I plan to have 8 4"x4" posts, one in each corner and also in the middle of each of the 4 sides. The posts will end up being no more than 7.5' apart. I plan to sandwich the 3 rows of posts with 2"x6"x16' boards (total of 6  boards). Then I plan to attach 2"x4"x16' perpendicular on top of that - on the 2" end of the board - approximately 18" apart.

To the top of all of this, I plan to add sheets of corruagted roofing - which is very lightweight itself - to keep out the rain and snow. I will have to have the 2"x6"x16" boards pitch slightly to allow the rain and snow to run/slide off the roofing material.

My concern is that whether the middle of this pergola will have enough support - because there will not be a 4"x4" post in the middle. Will the two 2"x6"x16" boards be enough considering the span?

I am attaching a layout to try and better explain what my plans are.

Answer
Hi Tammy, the middle support is a little puny considering there is no post.  You might try tripling up the joists over the middle where a center post would be and clipping the 2-2x6's to the bottom of that triple joist for added support. Also every board has a crown or high point on one edge, always put this high point up, this will help to counteract the gravitational forces that tend to make lumber sag over time. I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

Bruce E. Johnson

Expertise

I can answer any construction related question in regards to carpentry, concrete, drywall, masonry, structural elements of any type of building, residential or commercial. Interior or exterior.

Experience

Custom Commercial and residential buildings. Churches, theaters, schools and auditoriums. Most recently I am working with the Catholic Church on several design build committees. I have a website related to scheduling and project supervision. Although my expertise is more related to multimillion dollar commercial, educational and theatrical projects my generous credentials in residential and remodelling construction make me a viable source of information regarding all forms of building questions.

©2012 About.com, a part of The New York Times Company. All rights reserved.