Thoughts for lightweight 12” raised attic floor


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Old 11-28-09, 11:13 AM
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Thoughts for lightweight 12” raised attic floor

Hello!

Looking for some ideas to build an attic floor for storage purposes only.

I have a standard bi-level house, attic is approx 28’x40’, the roof peak is just about 6’ high and the attic is accessible by pull-down ladder. Ceiling/floor joists are 2x7.

The attic has only 3.5” insulation; I’d like to fill the existing space with 3”more and overlay the top with approx 12” of fiberglass insulation. The left ½ of the house attic is never used. The right ½ (where the latter is) is currently covered with scraps of subfloor to form a storage area.

So anyway, I would like to build a raised floor on the right ½ of the house so that I can get insulation there, but still have a convenient space to store seasonal items. I would also like to box out the attic latter so that I can insulate it and seal it up from air leaks. I would also like some ability to pull up this floor in the future if I need to run new wire/lights/etc; but this won’t be very often.

I thought about laying a bunch of 2x12s perpendicular to the ceiling joists and then laying on top inexpensive ½” sub floor to form my floor. But, I’m thinking this will be costly, very heavy, and probably overkill. I figure (not including the attic door hole) I’m probably covering approx 12’x12’ square for the storage space.

So, I’m wondering if anyone has ideas on how I can make something cheaper but sturdy enough crawl around on for storage. Maybe a framework of cut 2x4’s and subfloor? Anyway, any thoughts appreciated.

Thanks!
 
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Old 11-28-09, 11:36 AM
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Attic

Is the roof framed with trusses or rafters?
 
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Old 11-28-09, 11:45 AM
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I believe it is all rafters. The whole house is a rectangle. Looking across the house from the attic, I have sloped boards from the front and back of house forming a single peak down the center line of the house. Hope that makes sense
 
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Old 11-28-09, 01:22 PM
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What is the span, from bearing to bearing , of the 2x8's?

Are they 16" or 24" on center?

Be safe, Gary
 
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Old 11-28-09, 03:56 PM
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I am pretty sure they are 2x7's (I know 2-by usually measures less, but these boards definitely measure 7" or slightly less) .... and everything is 16" on center

Thanks!
 
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Old 11-28-09, 06:05 PM
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I need to know the span --- 1. how far between supports below. One center wall with the ceiling joists lapping each other from side to side? 2x8 joists will span 18'6" with a 20# live load and 10# dead load. Length of each joist across house at storage area.

2. Do you have plaster and lath ceilings or drywall?Makes a big difference for load.

I would use the proper lumber (after span stated) on tops of existing with a notch for the conduit running across the joists for future wiring. Insulate with un-faced glass (high density) batts and plywood deck. The lightest, strongest way would be I-joists and structural rim, OSB the ends for turn-over. Attic access: Energy Savers: Attic Access Insulation and Air Sealing

Be safe, Gary
 
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Old 11-29-09, 07:29 PM
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Ok, sorry if I misunderstood.....

The house front-to-back is 28ft. My upstairs floor has a hallway directly down the center side-to-side (and the attic hatch is in this hallway). So the joist span in the attic is something around 12' from the exterior wall to a load bearing wall in the hallway.

The ceilings are all 1/2" drywall.

Thanks, I didn't think about those engineered lumber products like the I-beams. For such a floor, can I go 24" on center to cut down on materials and weight?
 
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Old 12-01-09, 07:11 PM
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So you are spanning 12-1/2' with 2x8's, 16"o.c. If the ends near the house are not angle cut too much, there wouldn't be a problem stacking another joist on top. Troubleshooting Guide to Residential ... - Google Books If you wanted another joist for attic storage 24"o.c., you could put 2x6 sleepers (perpendicular) on the old joists at each end only and then install new ones (2x6's) after insulating. These span 12'3" and carry 25# per square foot. A rim joist or blocking required against rotation.

Be safe, Gary
 
 

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