I’m thinking of putting some plywood in my attic to add a bit of storage space and for the kids to use from time to time, I was wondering if I could get your input on the best way to do this. I live in the SF bay area, the house was built in 1940 and has plaster ceilings. The space I’m thinking of is on top of their current bedroom and looks like this:
https://drive.google.com/file/d/1aNHWkm8no80NHlN-gTNMtPMFLKdw1WZj/view?usp=sharing
The space is about 16′ by 13′. The joists are 2×4″ with 16″ centers, and there is a 2×4″ sistered to a 1×8″ running perpendicular to the joists for support. The edges of this space are roughly aligned with the walls of the bedroom. The insulation is about 10-12″ thick. There is a pull down ladder in the hallway just to the left of this picture. I was thinking of screwing down some 2x8s perpendicular to the joists on 16″ centers and then laying 1/2″ plywood on top of that. Though getting 16′ long 2x8s into the attic would be a challenge… What do you think?
Replies
Pic didn't come though.
"Screwing down 2x8s perpendicular to the joists..." - you mean on top of the joists, so they run the length of the attic? ABSOLUTELY NOT !!!!! (assuming existing 2x4 joists run the width).
Do the 2x4s run full width of the attic or do they butt/ overlap at a center supporting wall below? Is that where the 1xx8 is?
If just for light storage, sister existing 2x4s using 2x6s or 2x8s, face to face of the 2x4s. Use lots of Simpson screws/ nails and construction adhesive. Nails/ screws need to be protrude opposite side of joists by 1/2" minimum so use min 3 1/2" screws.
https://www.strongtie.com/strongdrive_exteriorwoodscrews/sds_screw/p/strong-drive-sds-heavy-duty-connector-screw
Sistering may have to alternate sides of each 2x4 joist, depending on existing framing conditions.
Glue and screw sheathing also.
http://www.grabberman.com/Media/TechnicalData/Product282.pdf
Frankie
Thanks for the info. Here's a link to the photo:
https://drive.google.com/file/d/1aNHWkm8no80NHlN-gTNMtPMFLKdw1WZj/view?usp=sharing
The 2x4s run from one wall to the other. The supporting 2x4 & 1x8 is in the middle of the supporting walls, lying on top and perpendicular to the 2x4s with no supporting wall underneath it. Sistering the existing 2x4s is tricky because of the 2x4 and 1x8 lying across the middle of the joists.
The 2x4 ceiling joists are not sized to support lots of load.
but if you want to put in a floor, and keep the insulation below, I would make up some open top plywood boxes, and sit them upside down on the joists. You can make each one a couple feet on a side, and a foot deep. glue and screw or nail them together.
you can cut half inch deep slots in the box sides where they sit on the joists to keep the orientation and then tack a 1x around the perimeter to keep it all together.
Will have to cut a slot in the insulation to let the sides of the boxes reach the top of the existing joists.
these will be fairly easy to take up that folding stairway.
but you do have to think about what this will do in the next earthquake.
If it was me, I would leave this space as it is and get a shed for the back yard.
Are you sure those are 2x4’s? I am not understanding how the insulation could be “10-12 inches thick” if it is only a single 2x4? Could they have added the 2x4 on top of the joist in order to increase the thickness of the insulation? If in fact there is more structure - joists large enough to accommodate 10 to 12” of insulation, then I think you could do the attic easily. As far as plywood, I would steer clear of it. I would recommend 1x 6’s or 8’s and space them apart 3/16 to 1/4 inch. You can precut them and assemble with screws in the attic- wrestling plywood up to the second floor and then up to the attic via a drop down ladder will wear you out. If you use spruce 1x6’s you will have a nice splinter free floor. Be sure to identify any NM wire run and make sure that you mark it’s location so you do not injure it, but also if you ever need to come back and access it.