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csaag 05-05-2009 02:24 PM

Wood strength question
I'm contemplating sistering in some 10 foot long 2x8's to my floor joists. An engineer hold told me to make sure the wood had could support a working stress of 850lb/inch

My question is how to identify the types of wood to satisfy that. When I go to the HD/Lowes they have a lot of Douglas Fir that seems pretty light. I don't know if the people that work there would know that info. I didn't see any type of info on the wood to tell em that info.

thanks for any help.

Willie T 05-05-2009 02:39 PM

Some reading for you..........

csaag 05-05-2009 02:55 PM

thanks , but there's a ref to 'Design value for joists and rafters' that sounds like it would have the necessary info, but there's only a link to purchase the book.

I'm just trying to find out how I find out about the wood the typical HD/Lowe's sells or if I'd have to go somewhere else.

*EDIT* my mistake - I click on the picture of the book and it actually brought it up.

QUES - is the wood at HD/Lowe's marked to show whether it's 'select structural' or 1/2/3 ?


Willie T 05-05-2009 03:16 PM

Sorry, I'm not even sure if L-H/D stores even consider grade. I order from a lumber yard for specifics.

Ron6519 05-06-2009 05:29 AM

What the big boxes sell depends on where they're located. This is also true of lumberyards. On Long Island, they sell both Doug Fir and the light weight Spruce. For structural work, Doug Fir is used to build houses. Spruce(s-p-f designation) commonly used to frame out basements where the walls are mostly partition walls.
In upstate NY, they use Spruce to build houses.
So just use what's commonly used in your area. If you can get a higher grade at the lumberyard, buy it there. The extra cost for a few joists isn't that much.

wildcat 05-07-2009 01:37 AM


Originally Posted by csaag (Post 269927)

QUES - is the wood at HD/Lowe's marked to show whether it's 'select structural' or 1/2/3 ?


It has to be, they can't take on the liability of selling lumber that does not have a stamp indicating its grade. Whether or not the employees there even know a enough about lumber stamps is another story.

I actually happened to check this out one day (I usually stay far away from the big box stores) and most of what I saw was "stud" grade. Yuck.

If you go to a lumber yard I bet they have someone that can look up the strength (in psi) for you and your application in the NDS (National Design Specification).

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