Reinforce a wood shop floor- currently 3/4 ply over joists

Our small wood shop has an elevated floor due to being built on a hillside. About 1500 square ft.
6x6 posts with 6x12 beams, 2x10 x 10' fir joists 16" on center. All in good condition.

The floor is 3/4" T+G plywood, and over 30 years has gotten worn though a layer or two in certain areas. And we are starting to put heavier machinery on it.

What would you recommend to thicken the floor, and increase it's ability to handle point loads? Ideally, when I retire, it would be cool to be able to put a car in there. Or roll a pallet jack with a load on it.

So far,adding a new plywood deck over the old one, maybe 1 1/8" or 1 1/2" thick is the best idea I could come up with. About 50 sheets or so. Maybe use a bead of construction adhesive over each joist.

expanded metal sheet can take the load if it is tied off. metal plate (metal is always steel u.s.o), again tied off. Thin b-deck with concrete and add in radiant heat while you are at it.
If you stay with ply-wood: metal pads under your point loads spread the load out.

I would consider adding joists, decreasing the centers by half, then 1 1/8" tongue and groove plywood. It would be pretty cheap, and you could do it yourself. I cant see working on expanded metal- You would lose everything you dropped, you couldnt roll or drag anything, and it would hurt my tender tootsies.
I have 1 1/8" t&g in a few places and its pretty solid.
Not 20,000 lb machine solid, but for smaller machines its fine.

I would be cautious about taking a "DIY" approach to this if you're looking at heavier machinery or cars. It would be worth bringing in a structural/civil engineer to advise you, a grand or so up front could save you much more down the road (or down the hill...).

We used a product called "plytanium" sold at Lowes.

It is APA rated, learned stuff when we built our shop.

There is a span rating printed on the product, stuff at home depot did not have this

Been awhile so not certain on how it goes, Google it to check, but if I recall correctly the reference is say 3/4 material at 16 centers for loaded reference.

The span rating then is the centers distance for given material for same load.

Our steel joists were at 15 3/4 for even across the span spacing.

We used the 1.125 material which has span rating of 48 inches.

It is solid, jumping on floor mid span nothing moves...

It with 48 inch center floor support is same as 3/4 floor on 16.

Place this on your existing and weight spread real well

The glue and material are very stiff, the self tapping screws, thin drywall screws for steel, would sometimes have difficulty pulling in the area around the screw head for countersink, does well for not denting with chair feet.

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Your limit is going to be the 2 x 10 joists.

At that spacing, the floor load is 30 lb per square foot with 13' span and #1 lumber, independent of the flooring. You have 10', so it will be higher, but likely never anything similar to the weight of a car, or any seriously heavy machine.

Table saws, etc probably fine, but you can see that you may go well over the 30 PSF if there are multiples. And, then you have the weight of the operator as well.

Each joist is carrying a strip of floor that is about 16" x 10'. So about 12 square feet. Just adding it up at 30 PSF, that would be a maximum of about 360 lb carried on each (paying no attention to where the load is located along the joist).

Your shorter span could be rated higher if of better grade lumber, or the same 30 lb if only #2 lumber, at 10' And if you spread the loads then individual loads can be more. But likely not getting to the automobile level of load, where you may have 1500lb on the front wheels alone, both of which may end up on the same joist, if they run cross-wise.

Older post and beam warehouses and factories typically have 3 x 12 or 3 x 15 joists, and those are not finished lumber, but raw size. The depth makes a big difference, and the thicker wood alone already doubles vs what you have.

That building code rating is limited by allowable deflection, and normal factors of safety, but is a good limit to consider in figuring what you can put in there.

stoneaxe, when you say "heavier machinery", what kind of weight are we talking about. Big woodworking shaper, maybe a 1000 pounds, or something 10,000 lbs?

I'm no engineer or architect, probably half senile, but it seems to me you could get a lot of bang for your buck by reducing the span of your joists with additional posts and beams underneath. Then the additional plywood deck. You may still need some steel plate under the pallet jack, I use 1/8" x 4' x 4' sheets that I just place as needed. Moving those guys around is more effort than moving the machines!

Ries said:

I would consider adding joists, decreasing the centers by half, then 1 1/8" tongue and groove plywood. It would be pretty cheap, and you could do it yourself. I cant see working on expanded metal- You would lose everything you dropped, you couldnt roll or drag anything, and it would hurt my tender tootsies.
I have 1 1/8" t&g in a few places and its pretty solid.
Not 20,000 lb machine solid, but for smaller machines its fine.

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I just built a mezzanine to store paper files and was going to sheet it with 4x8 1 1/8 T&G ply...I would be interested in hearing what kind of numbers you guys get for this material.

out here?

145 dollars per sheet!

The OP is on a hillside, and we don't know the soil stability, the existing footings, area seismology, the annual rain/snowfall, the method of anchoring the the span to the hill, etc. Not to mention whatever the local jurisdiction requires for building permits and whatever.

I'd get an engineer involved.

The 6x6 posts are 3-5' deep, in a roughly 20" diameter hole filled with concrete, sitting on hardpan. If we get the big one, AKA Cascadia subduction quake it is going down hill. It has survived a couple quakes in the 7 area with no damage, the whole building shook and the ground outside was rolling like swells on the ocean.

The post's have 5x12 gluelam beams attached with bolts and shear plates, and the ones sitting on posts have 1/4" thick welded tee and shear plates- The beams have a 12' span.

The machinery I am putting on the deck will be woodworking equipment up to maybe 1500 lbs- the new shaper is about 1250.

Most of the many tools now are in the 500-1000 pound range, I have tried to place them over a beam or post.

The joists are very good quality fir- all that nice stuff that was cut after St.Helens knocked them down and they were cutting as fast as they could to get it off the ground before it rotted. Some of them were clear! They are solid blocked where they sit over the beams.

So my primary goal is to make the deck stronger -not too concerned about the framing right now-

BTW- the best option would be a larger shop to start with, with a concrete floor- this state, and in particular this area, does not like home based business so building a new shop would be a real hassle. Commercial locations could do but that is a lot of money -more than this old guy wants to take on.

That plytainium sounds interesting.

Phenolic ply ?
Mark

I helped a friend move a big lathe (5000lbs?)into his wood shop of similar construction, he pulled up floor first and blocked joists at mid point, replaced floor, and added another layer of 3/4" ply. It held the lathe, but it was sketchy, you could feel floor sagging as you walked up to lathe. I'm not sure what he ever did to reinforce things from there, my advice was build a form around perimeter of building, drill 6" holes throughout floor, and pump concrete.

How big of machines are you contemplating? What size cars?

I had a mezzanine with a 2x6's on 16" center 10' span sheeted with 1-1/4" marine plywood. I could roll a palletjack with a 4000 lb load on it across that floor. I had to build up speed to get through the droop in the 2x6's at mid span, but not terrible.

My current mezzanine has 2x10's on 12' span with 3/4 plywood on top. I have a few 2500 lb pallets up there and haven't broken the 3/4 with the pallet jack yet.

Like MemphisJD said above- Use B-deck and pour a real floor.

IMO, a job like this doesn't need an engineer. If you can add up the surface area of the footings you can calculate ground pressure. Make sure you're under an assumed minimum capability for your area's soil and then pour a nice floor in some pan decking.

I have a pile of 24' long 3" 18 gauge pan decking I bought leftover from a parking garage job. I paid $500 for it. It probably cost $30k new. It's going to eventually be the base for a second story concrete floor.

Cutting the span will have a YUUUGGGGE effect. Its not hard if you have good access underneath. I’d look at ways to add some footings and posts to cut the span in half.

I highly suggest some stout young men who can and will follow your directions. Get under there and dig some holes, pour some concrete and its done in a couple of days with enough help. This is mostly just fuckin’ gravity and how to resist it. Not rocket science.

If you want to maintain current floor height, you can add strips of plywood from underneath with 2x4 lumber sistered to the joists to hold the strips in place. Use plenty of adhesive, screws and nails to fasten the whole thing together.

This is standard procedure for reinforcing floors to take natural stone and tile. For that purpose the floor must have no more than certain specified deflection or the stone will crack. Doing what I outline I would absolutely put a 1000# machine on it. But you should ask a structural engineer to be sure. I think you will be surprised at his answer. In a good way.

henrya said:

Cutting the span will have a YUUUGGGGE effect. Its not hard if you have good access underneath. I’d look at ways to add some footings and posts to cut the span in half.

I highly suggest some stout young men who can and will follow your directions. Get under there and dig some holes, pour some concrete and its done in a couple of days with enough help. This is mostly just fuckin’ gravity and how to resist it. Not rocket science.

If you want to maintain current floor height, you can add strips of plywood from underneath with 2x4 lumber sistered to the joists to hold the strips in place. Use plenty of adhesive, screws and nails to fasten the whole thing together.

This is standard procedure for reinforcing floors to take natural stone and tile. For that purpose the floor must have no more than certain specified deflection or the stone will crack. Doing what I outline I would absolutely put a 1000# machine on it. But you should ask a structural engineer to be sure. I think you will be surprised at his answer. In a good way.

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Going to stay away from the underside if I can- the most would be to add some more beams- not going up into the joist bays as they are all insulated.

A thought just occurred to me- what do y'all suppose putting plywood on the underside of the joists would do? In essence, making the entire floor into a huge box beam or stressed skin panel?

If you use something like our 1.125 plytainium 48 inch span rated material on 16 inch centers it distributes the weight across multiple joists.

If the sheet is across the joists it improves this load sharing as the sheet being 8 feet rests on more joists.

Placing "X" bracing or just cutting out spacer blocks from the sheet and ancorig with long drywall screws these can limit to movement of the joists to reduce deflection further improving the load spreading ability of the sheet.

Do make some sketches with accurate dimensions and some here or your building inspector can provide an estimate of loading per Sq foot as well as point loads and maximum loads.

We built an 8 ft x 8 ft platform consisting of 2 sheets on bottom glued and screwed to a frame made of 2 x 10 lumber which was frame around perimeter with joists on 16 centers.

This was on second floor of office building where floor was not real flat so we screwed the bottom to the floor before internal glue set then glued and screwed top on.

Rock solid and the cell site we built on it weighed in at maybe 1500 to 2000 pounds.

This was spreading across 64 Square feet so floor loading was far less than rating, rated at 75 and we were less than 35.

Now that sprint is going away I would've to watch them try to remove it...we covered it with the same type of short nap carpet like stuff the room had and trimmed it well so it will need some work to see whatis there.

Will need to be cut apart to remove...

Back to point...

The better material can spread the 1500 pound weight over a greater surface area reducing the load per square foot.

Depending on where the weight is it may matter more due to framing.

X Bracing may improve the system performance so it needs to be discussed with engineer.

Our floor is 6 inch tall Z made of 12 GA rolled steel, 12 ft working length on 15 3/4 centers.

Floor rated 75 psf with 3/4 material, likely far more now if total load stays same.

Yours needs engineer to do some math...

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Just noticed above post, sheet on bottom limits twisting of beams and may help support but the screws are working harder and backwards.

Better to X brace or make squares that go between joists to limit twisting.

Adding sheet on top better as gravity works, but start with the thicker sheet and be done.

Adding another sheet increases psf rating maybe as it spreads the point loads on top to wider area.

However theists and rest of the support system has a maximum load rating so you may be able to get a 75 psf load rating it may be also limited to 3000 pounds total load due to supporting structure.

All parts of the system interact so you should get an engineer involved.

Building department folks often can give "general data" meaning generally a specified type and size beam can support x and if presented a drawing they could give general advise, to get red stamped usually requires $$$

I do not think you need reinforcing, just another later of plywood and sheet goods or block tile.
My shop is built similar to yours. My joists are engineered 12" and on 16" centers. Subfloor is 3/4" Advantec with 1/4" fir underlayment . I have 12x12" vinyl tile on top.
My heaviest machine is a 1200+ lb. mill and a bandsaw about 900 lbs. There is no deflection or bounce.
You should consult an architect or structural engineer.

Putting more material on top is the least effective method to get more load capacity. The idea of skinning the bottom is good but difficult to do under a building unless theres lots of room underneath. You’d ideally make a stress skin panel and it would be stiff. Possible downside is you might be making a rot box if it gets wet. You would want some ventilation.

Another method is to apply either wood or metal straps along the bottom of each floor joist. They would be most effective epoxied and screwed in place. Screws mainly to hold in position til epoxy sets. Look at an i-joist as an example of this configuration.

Still, the most bang for your buck is cutting the span. Very simple work, just need a little muscle.

Doubling the floor thickness and nailing it on close centers will reduce deflection by 4 times. Nailing a 2x6 along the bottom of each joist will create an I beam with the floor panel and make it way stiffer with little effort.