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Calculating plywood weight holding ability

pete6032

pete6032

Diamond Member
I have a sump pit in my basement with a 2x2 wooden frame around the pit. The frame is made out of 1x6s. The frame cover is a 2x2 piece of 3/4 inch thick plywood. I want to put the backup battery on top of the frame cover but I worry about the frame cover warping over the long term since the battery weighs about 50 lbs. Is there any way to calculate whether or not a 50 lb battery on 3/4 inch plywood would eventually cause warping?
 
if you put the battery there, you will have to move it if there is any issue with the pump? seems like not a great idea.

you could put a couple 1xs or 2xs across the ply and screw them into the frame and plywood for reinforcement. is the 1x6 vertical around the edge or laid flat?
 
herm0016 said:
if you put the battery there, you will have to move it if there is any issue with the pump? seems like not a great idea.

you could put a couple 1xs or 2xs across the ply and screw them into the frame and plywood for reinforcement. is the 1x6 vertical around the edge or laid flat?
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The 1x6's are placed vertical around the edge. 3 of the four frame pieces are screwed into studs in drywall since this is in a closet. Putting the battery on top of the pump wouldn't be a problem. There are cords that go from the battery to the pump and to the outlet but there is more than enough cord for me to pick the battery up and move it a few feet if I need to get into the sump pit for any reason. The only thing I can really find online about weight bearing is a maximum weight bearing calculation. That's a lot different than whether or not something will warp over time if a heavy weight is put on it.
 
3/4 plywood can easily handle a 50 pound battery.
Look at it this way, Pete. It is standard subfloor and loads are calculated at 40 PSF live load.
That means the typical construction, 1.2 SF of that 4 SF plywood can handle the weight.
24" span is also common.
Don't sweat it.
Will it warp over the long run? Probably some. Will it matter?
Not at all, unless it bothers your sensibilites.
If you are concerned, put a vertical strongback of anything under the battery. a 1x4 glued and screwed at right angles to the bottom of the plywood, for example.
 
Is this a lead acid battery? I can't think of a worse place to store it than over the sump. Two issues: 1) the sump is likely the most humid spot in your house, leading to corrosion, 2) if the battery leaks, the acid goes exactly where you don't want it and it's really hard to clean up.
 
A cheap polyethylene drain pan would alleviate leakage concerns. Not sure about excess humidity being localized in the area of the sump, could be a concern if the air in the space is stagnant. Sometimes space is at a premium and sacrifices have to be made, a small fan might alleviate concerns about humidity buildup in the area.
 
It's a 2x2 chunk of CDX, does it really matter if it warps? A far greater concern is moisture damage and rot. Plywood doesn't like to be wet all the time.
 
Greenman said:
It's a 2x2 chunk of CDX, does it really matter if it warps? A far greater concern is moisture damage and rot. Plywood doesn't like to be wet all the time.
Click to expand...
I would like a reasonable seal over the top of the pit box. There is quite a bit of cold winter air that escapes out of the box.
 
I build battery boxes out of marine ply and coat them with epoxy. They are everything-proof.
If you want to "brick shithouse" this, get some epoxy and coat it both sides, and add a stiffening rib and a little 4 oz glass across that rib.
Position the rib(s) under the battery across the middle of the cover, and done.
It won't sag, rot, discolor ( as long as it is not in direct sunlight).
 
Fair enough. How much area does the battery cover? If it's a distributed load that's only 12.5 pounds per square foot.
I'd try a piece of 3/4" CDX, and check it every couple of months. If it fails step up to 1 1/8 CDX, or laminate two pieces of 3/4" together.
 
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