Why Wood they?

Neil_K

I have a couple of ponderances that maybe you can tell me why:

1. Why are dimensional boards about an inch longer than they say? Example, my 2"x8"x16' joists were 16'1".

2. OSB for roof decking is staggered and perpendicular to the roof trusses. Why, then, does everyone put OSB on the outside parallel (the 8' side goes UP)?

Just curious. :confused:

Thanks.

Neil

Neil_K

I meant outside of the walls...

Hammertime

I'm not really sure but my guess would be that the boards are made and cut by machine. Most boards are cut to fit for it's installation. The same question would be why did they change all the measurements of would I.E. a 2x4 is actually 1-1/2x3-1/2. When in hte old days they were actually 2x4. I guess it's easier to say even numbers then 1/2" increments. But, again I think it would have something to do with the factory cuts they get.

as for the roof installs. I would also think it would be easier to make a 4'cut then an 8'cut and easier to stagger the joints to break the seems up for a better and more secure fit.

as for the walls I've always installed and seen them installed with the 4'side up. I would think it would be harder to install with the 8' side up especially working on the second story and up.

Neil_K

Funny, each time I read my second question, the more bass ackwards it read. I did mean the 8' side was vertical, no one around here (Charlotte, NC area) installs them sideways, either...

Teetorbilt

Back when a 2X4 was just that it was rough sawn as it still is today except today people expect finished lumber with tighter tolerences. Truing it commercially leaves todays specs. Plus you get more shavings for particle board.
The reason that you get a little extra on length is so that you can square the ends or get a better finish, commercial saws are not very good at this.
As for OSB, it's just giant particle boad to me, I have never bought a single sheet.

MinConst

Teetor is right on the money with why lumber is finished to 1 1/2" x 3 1/2". The length is determined by given sizes of floor joist. They run in 2' increments and the extra is to be able to trim to fit or square. If a 2x8x12 was 12' it would throw the whole world off. Or make us buy 2x8x14'. As for the OSB I also agree with Teetor. I know roofers that swear by it but it is still a questionable product in my mind. Even when plywood delaminates it is still there. OSB falls apart. It is more stable though. Built properly with plywood and your build will outlast OSB. One mans opinion.:D

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