Building Homes or Extensions/rafters for a pergola

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Expert: - 2/23/2009


Question
I am building a 14'x20' pergola using trated pine with four 6"x6" posts.The beams that I will be using are 2"x8". Can my rafters be 22' long between the beams? Thank you for taking the time to answer my question!

Dan

Answer
Dear Dan,

Depending on the loads, the maximum span for a 2x8 beam supporting a roof would be about 8 feet.

The 6x6 posts can support tremendous loads bearing straight down, but should not be much taller than 8 feet for stability.

So using the sizes of lumber you mentioned, you should really have at least 3 posts per side, and any rafters 22 feet long would need to be at least 2x12s on 12" centers, again more or less, based on your climate and projected roof loads.

Assessing a design for any building takes some calculations by someone who knows engineering principles. The best way to build if you don't have someone to look at your plans and you are unfamiliar with how much lumber can do is to find something that has stood the test of time in your area and copy it.

Good luck.

Daniel

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Daniel Humphrey

Expertise

I can answer questions about designing and building homes and outbuildings, especially for colder climates. I am expert in timber framing, but of course I also know about other kinds of residential construction techniques and materials. Because of my emphasis on using local materials and organic alternatives, I know quite about about Green Building and am willing to do the research to find out more.

Experience

I've been a timber framer for 20 years, working as a general contractor who designs and builds custom timberframe homes, working as much as possible with local organic materials, from foundation to finish. I also have expertise in designing, building, and setting up pre-fab remote camp facilities on terra firma or temperate glaciers for research and expeditions, using helicopters for support.

Education/Credentials
B.A., M.F.A.

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