Weight limit of plywood floor?

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Forum topic by UKCat posted 12-15-2012 07:28 AM 6729 views 0 times favorited 7 replies Add to Favorites Watch
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82 posts in 1111 days

12-15-2012 07:28 AM

The floor in my shop is 3/4” plywood on treated 4×4 with 24” centers. I am trying to find out how much weight it can safely hold. I am hopefully going to pick up a G0490X tomorrow and this thing weighs 500lbs. I am concerned about putting it in my shop without doing something to strengthen the floor. I have a 250lb table saw and 300lb planer in my shop and the floor seems to support them without any problem, so maybe I’m worrying over nothing. Anyone have any advice on this?

7 replies so far

View sawdustbreath's profile


3 posts in 1033 days

#1 posted 12-15-2012 08:12 AM

It depends on how big the span of the room is to determine joist size and length

-- Use your hammer

View Finisher's profile


31 posts in 1182 days

#2 posted 12-15-2012 10:31 AM

You don’t mention what your 4×4’s are resting on? But, 24” center to center joist spacing is acceptable in construction that uses floor trusses and that type of floor I think is rated at 400 lbs. per square foot. The problem does exist of floors bowing a bit when you walk over them so I would think this would be a concern but if you are not experiencing that now you shouldn’t be concerned.

-- James, Michigan

View UKCat's profile


82 posts in 1111 days

#3 posted 12-15-2012 03:21 PM

The 4×4 are on 2”x4”x6”(?) concrete slabs every 2 foot.

View David Kirtley's profile

David Kirtley

1286 posts in 2041 days

#4 posted 12-15-2012 06:20 PM

Low tech diagnosis: Jump up and down on the floor where you want it. If it is bouncy, you may have a problem.

Simple solution if it is too bouncy is distribute the weight with something under it and make sure you place it on a support beam.

Bouncing will be the biggest problem. I can’t see a 500 lb static load being a risk of crashing through the floor.

-- Woodworking shouldn't cost a fortune:

View bondogaposis's profile


3382 posts in 1395 days

#5 posted 12-15-2012 06:26 PM

What is the span of the floor joists?

-- Bondo Gaposis

View Granddaddy1's profile


181 posts in 1245 days

#6 posted 12-15-2012 06:50 PM

If I understand correctly, you basically have a sheet of 3/4” plywood installed on 4×4 joists placed 24” on center. Then the 4×4 joists are bearing on concrete footers or blocks placed 24” on center. If that is the correct assembly, and your concrete footers are level and adequately placed, your floor system will hold much more than what you’re considering.

Good luck!

-- Ron Wilson - maker of fine firewood!

View a1Jim's profile


113738 posts in 2621 days

#7 posted 12-15-2012 09:06 PM

As a 25 year contractor I agree that you have more that enough support for a 500+ weight machine ,The other thing I would precaution others about is that 4×4s are not meant to be horizontle weight bearing members their only meant to bear weight for vertical loads . What should have been used is 2×6s pts or larger depending on spans.

-- Custom furniture

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