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Old 10-18-2010, 03:27 PM   #1
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Attic flooring - OSB or Plywood


Hello,

The attic in my 2 story house is built using 2x8 joists and fibreglass insulation. I'm having an additional 6" of blown-in cellulose insulation installed to improve the energy efficiency.

I would like to use the attic space for additional storage. I'm planning to install 2x6 rafters on top of the existing 2x8's (24" apart) and then planning to install 1/2" plywood or OSB. Even though I don't need the entire 40'x40' space in the attic, I'm planning to install flooring on all of it - except for the boiler and ductwork.

I would appreciate any comments on the approach. Would the additional weight of 2x6's and plywood/OSB impact the structural integrity of the house?

Thanks for your help/comments.

Best.


Last edited by tariqk; 10-18-2010 at 04:06 PM. Reason: more appropriate subject
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Old 10-19-2010, 06:58 PM   #2
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Attic flooring - OSB or Plywood


1/2" plywood?

Two feet on center?

The boilers in the attic?

Flooring?

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Old 10-19-2010, 07:03 PM   #3
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Attic flooring - OSB or Plywood


You would need at least 3/4 inch material to avoid it being springy.
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Old 10-19-2010, 07:52 PM   #4
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Attic flooring - OSB or Plywood


The additional weight of wood is not a concern, the real problem is the storage in the attic for which the existing and new added joists may not be sufficient. There isn't enough information to go by as to how the joists are supported and their span.

2' spacings, 1/2" plywood or OSB, all these are OK for light storage.
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Old 10-20-2010, 08:15 AM   #5
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Attic flooring - OSB or Plywood


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Originally Posted by II Weeks View Post
1/2" plywood?
- Yes, I was planning to use 1/2" (or maybe 3/4" based on feedback) plywood or OSB.

Two feet on center?
- The existing joists are 16" apart. The new ones that I put are 24" apart since I only plan on storing light stuff like Christmas decorations and kid toys.

The boilers in the attic?
- My bad, its the air handler for the AC.

Flooring?
- just some planks.
Hope this clarifies.

Thanks
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Old 10-20-2010, 08:17 AM   #6
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Attic flooring - OSB or Plywood


Thanks for your response(s). I'll plan to use 3/4" OSB or plywood and leave the spacing between 2x6" as 2'.

Thanks again.
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Old 10-20-2010, 11:25 AM   #7
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Attic flooring - OSB or Plywood


For light storage in the attic, I would use 1/2" plywood, cut into 12" rips spaced 1/2" apart. This will let any heat/moisture from the conditioned space below to vent without condensing on the bottom side of the plywood. The framing would sit on 1x4 secured perpendicular to the joists over the bearing points to keep the new joists free-spanning over the bearing wall below. Use a 1x4 on the ends of the new as a rim joist to prevent lateral displacement (tipping over) held flush with the top edge. No OSB as it cannot handle moisture well and mold loves it. Figure the 2x6's at 24"o.c., to check your spans by entering them under "ceiling joists w. 20# load" here: http://www.awc.org/calculators/span/...orizontal+Span

Gary

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