Attic Plywood Floor

[MrSnicks]

Hello all. Finally tackling my unfinished attic space.

The builder installed some 3/8 sheets of plywood for a small storage area. I'm 300 lbs and these have always felt "squishy" and worried me.

I've installed 3/4 OSB in the new areas. I've pulled up some of the 3/8 boards.

My question is, can I install another 3/8 board on top of the existing ones to increase rigidity and load bearing capacity?

Just pull out the nails in the existing board and use deck screws to screw down the 2 boards together?

 

[BillK]

If you are going to do that I wouldnt even bother pulling the nails. I would have used plywood. A lot stronger than OSB in my opinion.

 

[SteveCh]

I would leave the current 3/8 in place, set the additional sheets on top with edges offset from the original seams between sheets. No need to remove the fasteners in the original sheets.

 

[Arkive]

If you are going to do that I wouldnt even bother pulling the nails. I would have used plywood. A lot stronger than OSB in my opinion.

If he used Advantech he's probably fine. That stuff is beast.

 

[mike93lx]

What storage capacity is the roof and floor system designed for? Adding thicker decking won't increase that capacity

 

[Bottlecapdigger]

I would also use PL (panel adhesive) in between the 2 layers, screws and offset the joints like someone else said. This will stop the squeaking you'll create with the 2 layers, and make it stronger. Stuff is cheap and comes in a caulking tube. BCD.

 

[mike93lx]

I would also use PL (panel adhesive) in between the 2 layers, screws and offset the joints like someone else said. This will stop the squeaking you'll create with the 2 layers, and make it stronger. Stuff is cheap and comes in a caulking tube. BCD.

Making it nearly impossible to access the ceiling space if something ever needs to be done, like wiring.

Screws are plenty, IMO

 

[rsanter]

Yes the second layer will help but they will still flex together.

If you do it the best thing would be to use wood glue or liquid nails between the two layers. And ideally you would overlap the joints offset

 

[MrSnicks]

Thanks for all the replies. This is going to be temporary, just to walk on and store a few things. I have plans to get a structural engineer over to see if the area will support being converted to a finished living area.

 

[engineer2]

If you ever think you might need to get under the flooring sheets for future work, like electrical, I wouldn't glue the sheets together. I have 2 layers of 1/2" in my attic simply screwed down and don't have squeaks. If you have a squeak, just put a few short screws into the offending area.

 

[PelicanPines]

I'm of similar girth... I used 5/8" BC plywood...very strong...

 

[Innovate1]

Two layers of 3/8 is no where near as strong/stiff as one of 3/4 unless they are glued together but gluing has other drawbacks as mentioned. I used 7/16 osb for attic storage and am 185 lbs. It springs a little near the edges or on narrow pieces but otherwise ok for me.

 

[Garage Flooring]

I have plans to get a structural engineer over to see if the area will support being converted to a finished living area.

VERY GOOD IDEA!

1. Find out who the distributor for Lomanco attic ventilation is ASAP. To much plywood in an attic can interfere with proper ventilation and cause damage. Here to local Loamnco distributor has people trained in that area and they should be able to offer suggestions. THIS CAN BE A VERY VERY BIG DEAL

2. Check into running the second layer of plywood the opposite direction.