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-   -   Framing options for Attic floor (http://www.diychatroom.com/f19/framing-options-attic-floor-8484/)

jordan57 05-15-2007 10:02 PM

Framing options for Attic floor
 
Hello,

We have a story and half house. The upstairs was partly preped to be finished when the house was built. About 75% of the floor space was framed with 2x10's and decked. The rest was done with 2x8's and left open. We want to deck the remaining space and have the flooring match.

I was giving two options for completing this. First was to get 2x10's and sister them to the existing 2x8's and then deck.

The 2nd option was to use 2x4's to furr up the 2x8's to match the height of the 2x10's and then deck. If I use this options should the 2x4's run parrell to the 2x8s or cross them?

Thanks,
Jo

AtlanticWBConst. 05-16-2007 05:32 AM

Quote:

Originally Posted by jordan57 (Post 45168)
Hello,

We have a story and half house. The upstairs was partly preped to be finished when the house was built. About 75% of the floor space was framed with 2x10's and decked. The rest was done with 2x8's and left open. We want to deck the remaining space and have the flooring match.

I was giving two options for completing this. First was to get 2x10's and sister them to the existing 2x8's and then deck.

The 2nd option was to use 2x4's to furr up the 2x8's to match the height of the 2x10's and then deck. If I use this options should the 2x4's run parrell to the 2x8s or cross them?

Thanks,
Jo

Hi,

I don't see how the 2x4's would 'furr' up the difference in width.
2x4 = 1 1/2"
Difference of 2x10 over 2x8 = 2" (7 1/4" vs. 9 1/4")

It would seem that the less labor intensive option would be to install the 2x10's next to the existing 2x8's.

Ron6519 05-16-2007 05:34 PM

You don't mention the span these joists go over. The floor height evenness is not as relevant as the span.
Ron

jordan57 05-16-2007 10:38 PM

Its over a 3 stall garage. There is a beam running between the 2nd and 3rd stall. Currently there is a 20' length on one side and 14' on the other side.

I was leaning towards just sistering the 2x10's to the existing 2x8's. Thought it would be easier and stronger.

AtlanticWBConst. 05-17-2007 05:30 AM

Quote:

Originally Posted by jordan57 (Post 45313)
Its over a 3 stall garage. There is a beam running between the 2nd and 3rd stall. Currently there is a 20' length on one side and 14' on the other side.

I was leaning towards just sistering the 2x10's to the existing 2x8's. Thought it would be easier and stronger.

Make sure the ends will sit 'on top of' the outside wall top plates.

jordan57 05-21-2007 01:41 PM

I'm going with sistering the 2x10's to the existing 2x8's.

Is there any certain way to nail these or is screwing them together better.

Dont think I can get a nail gun inbetween the boards so I guess it will be done the old fashioned way.

Thanks,

Ron6519 05-21-2007 02:04 PM

I would nail them in at an angle, one pair every 12" or so with construction adhesive in between.
Ron

crecore 05-22-2007 05:54 AM

you would need to rip or plane them all to 2" as someone said. Do not put them opposite as your floor will be bouncy, sistering means putting them directly on top. The rest are all good tips, const adh, continue to the wall top plates, etc. Keep in mind that the reason they are 2x8's is that they werent designed for the attic in this area. Sisitering will not equal a 2x10 in strength. Definately check the span and look it up in the span charts (can be found online) or better yet talk to your local ceo.

AtlanticWBConst. 05-22-2007 06:06 AM

Quote:

Originally Posted by crecore (Post 45836)
you would need to rip or plane them all to 2" as someone said. Do not put them opposite as your floor will be bouncy, sistering means putting them directly on top. The rest are all good tips, const adh, continue to the wall top plates, etc. Keep in mind that the reason they are 2x8's is that they werent designed for the attic in this area. Sisitering will not equal a 2x10 in strength. Definately check the span and look it up in the span charts (can be found online) or better yet talk to your local ceo.

Actually, ''sistering'' means to place more material on the side of a joist in order to strengthen it.

After re-reading the original posters description of the area, I see that it is an unfinished upper floor. I was assuming the areas was simply attic storage.

To properly support the area as a living space above, the supporting floor joists up there should be sitting ''on top of'' the exterior wall studs, which sit under the top plates. To illustratate, see picture below:

http://i28.photobucket.com/albums/c2...T/IMG_0700.jpg

The existing 2x8 joists should be framed (built already) in this manner and in this arrangment.
So then, adding the 2" (with rip-down 2 by's) would be the structural method to ferr up the area to allow the floor heights to all be the same. You could still add the 2x10's, sistered to these, to add deflective strength, which I would suggest.


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