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Old 11-05-2013, 09:38 PM   #1
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Help with Stiffening an Attic Floor for Finishing


I have a balloon framed two story colonial with an unfinished walk up attic. I'd like to floor the attic, possibly finish in the future as an office room, don't plan on adding a ton of live weight.

I'm looking for advice on the best way to stiffen and support this attic floor before laying a subfloor

The first and 2nd floors are 2x10 floor joists. The attic joists are 2x8. Everything 16 OC

The attic joists span 14' and 13' meeting in a middle beam.
The 2nd floor ceilings are plaster, in good shape
There is a good deal of electric and insulation between the joists and getting long 2xs up to the attic to sister beams is not possible.


1) Do I need further support or can I simply start laying 3/4 plywood (or OSB)

2) I looked into laying 2x4s on their face across the joists (where the knee walls would eventually go) and tying them to the gable end wall studs. (Ribbands right?) and I could further support by making stongbacks.

My concern with strongbacks is whether it really does any good without a top plate to distrubute the load.

3) Concerning laying the floor, 3/4 plywood is best? I'd rather use OSB for cost reasons but if plywood is lighter and stiffer thats probably a better way to go.

And the 4x8 boards will need to be cut to get them up the stairs, for stength/stiffness is 2x8 lengths or roughly 4x5 boards better?

Any advice is much appreciated. Thanks.

Last edited by TheEplumber; 11-07-2013 at 12:06 AM. Reason: advertising link removed
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Old 11-06-2013, 11:29 PM   #2
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The answers are on page 2 of your building permit papers/permit for the structural changes and liability for your HO Insurance carrier.

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