Redwood Load Bearing

[Brandon Weiss]

I'm looking to build a 4 posted porch extension. 4x6 posts. The top will be boxed in with 2x6 and then 2x4 boards running parallel to each other spaced about every 1.5ft or so. It will be an open top. I have heard that Redwood is not recommended for load bearing applications. Is this true?

Do we NEED the redwood, no. I'm thinking of using it because of its exterior durability. What other lumber would be good for this application? I don't mind staining/treating for water protection.

[Jamie Buxton]

Well, we've got whole cities built from redwood in northern California. In the late 1800's and early 1900's, redwood was the primary wood used to make houses. It was cheap, because it grew right here, and it came in giant-sized chunks.

Today, redwood is no longer cheap, and there are many alternatives for exterior structures. For instance, you might use pressure-treated lumber for your structure -- beams and joists and posts -- and use redwood only for the visible parts.

As for exactly what lumber to use for the dressing up, it depends on where you live. For instance, in some parts of the country, cypress is a good choice. You should fill in your profile so folks can help you better.

[Henry Ambrose]

The dimensions of your project would be very helpful. How far do you intend to span? Got a sketch or a picture?

Redwood is not the strongest but its plenty strong when used in appropriate dimensions.

Cedar might be nice.

Purewood - thermally modified yellow pine might be nice too if it comes in sizes that suit your project.
http://www.purewoodproducts.com/

[John Downey]

I have heard that Redwood is not recommended for load bearing applications. Is this true?

Some one somewhere might not "recommend" redwood for load bearing applications, but personally, I don't think much of such recommendations. Redwood is not as strong as some other woods that are more typically used for construction, but there is no reason it cannot be used when appropriately sized for the application.

This span calculator lists redwood as an option:
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

I've used a post and beam size calculator too, but I don't seem to have bookmarked it.

About the only reason I can see to not use redwood is your location. I didn't find that it lasted well outside in the sun when I lived in Tucson, not as well as douglas fir does. Unless its aesthetically desireable, I'd just use it for posts, elevated on footings to prevent rot, then use stronger wood for the horizontal members. Arizona is just not wet enough to really require woods like redwood when not in contact with concrete.

[Wayne Cannon]

I wouldn't get hung up on redwood. Unless you find old-growth redwood, the new rapidly grown stuff isn't very rot or insect resistant. Cedar would be better.

This USDA publication discusses both rot and insect resistance and mechanical strength of various American softwoods: http://www2.fpl.fs.fed.us/publications/fplgtr102.pdf