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Insulating Heavy-Duty 3/4" Tongue & Groove Plywood Flooring

Insulating Heavy-Duty 3/4" Tongue & Groove Plywood Flooring


Old 04-26-09, 04:31 AM
Thread Starter
Join Date: Feb 2007
Location: SouthEast Louisiana
Posts: 324
Question Insulating Heavy-Duty 3/4" Tongue & Groove Plywood Flooring

Heavy-Duty 3/4" Tongue & Groove Plywood Flooring

Specifically I have this in 12'x24':
TUFF SHED: Storage Buildings, Garages, and Custom Buildings are Built to Last

I have been agonizing (probably shouldn't be) for months over whether or not I should have the building lifted (after its settled on its leveled pressure treated wood wedges and concrete flat rectangular blocks) and sprayed with spray foam underneath to seal it from outside moisture.

I want this building to last well... a lifetime, but at a minimum 10 - 30 years. I am in a deep south Louisiana climate where humidity above 80% is a constant climate theme. The primary goal for this building is a small office/workshop which will have A/C running in it constantly during hot months.

Am I too worried about sealing UNDERNEATH the subfloor?

Should I leave airways to underneath the subflooring?

The only flooring there is, is the Heavy-Duty 3/4" Tongue & Groove Plywood Flooring which sits on stainless steel beams raise about 6-8 inches off the ground which was just grass till it was covered with this building. The warranty on this small building is 10 years and 30 years on the roof and I have the model which extends the roof edges outward from the walls so the dripping doesn't roll down the walls to the edges and base of the flooring.

I want to insulate with Spray Foam for sure (walls, ceiling, and under floor unless there is an easier better solution like interlocking styrofoam blocks??? anyone?), but do I need to worry about spraying underneath?

I have already decided I will weather seal the top of the floor on the inside of the building and then lay the thinnest of "office" style carpet using the double stick carpet tape. Will the weather seal on the top of the floor be enough?

Trying to avoid cost and having to raise the building or tilt it on its side to seal the bottom underside. I know I could probably do this myself if such a hydraulic system were for rent somewhere or if some other solution was out there, but I haven't seen any.
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Old 04-26-09, 05:01 AM
Join Date: Oct 2008
Location: New England
Posts: 9,999
Hi searcherrr, converting a building designed as a shed into conditioned space will take some planning, especially since you sound like you want to do it right.

First, you may have code issues, a shed is a shed, not living space. It may not have been built to the correct standard, as you know, you are in huricane country.

Lighting and electrical will be necessary and must be installed before the spray foam. That may have to be run underground.

Insulation and vapor barrier concerns need to be evaluated together. Here is a link for some reading: Energy Savers: Vapor Barriers or Vapor Diffusion Retarders

If you want your mfg warrenty to remain in effect, you may want them to approve all of your changes.

Verify that this is really what you want to do and that it is approved and we can continue with the list.

Old 04-26-09, 06:39 PM
Thread Starter
Join Date: Feb 2007
Location: SouthEast Louisiana
Posts: 324
Well, all I really need to know is the concern about the plywood subfloor. If you want to discuss the rest thats wonderful too and thank you, but I really need to figure this out regarding the floor because I have to get my grounding done before Hurricane season.

I bought the so-called 140 mph hurricane package. It "will" have 6 points grounded with auger spiral mounts into the ground from the base steel frame. I was thinking about buying extra lag bolts and screwing more of them from the inside 2x4's through to the base steel frame as the carpenters did, so the building will hold better to the base frame.

I say it "will have" the ground mounts because I'm holding off till I figure out what to do about insulating the floor, but I'm cutting it close. Hurricane season starts in June I believe.

Aware of needing to install electrical first before foam. I'm very thorough and interested in doing it right/safety etc.. and plan to wire it up myself. I've designed a diagram of how I want things to be and where.

Why would electrical need to be run underground? You mean the main electrical source? or all the other wiring to each outlet, switch, circuit breaker etc..?

I have also been mulling over the "code" stuff and I'm not sure what to do about it. I have a limited budget. I think I will be fine if I don't involve myself with code stuff. It has 1 door in front and 1 window in front also (same wall) and there are no other doors/windows except there will be 1 cutout for the A/C window unit on the west wall. I was planning on keeping an axe and fire extinguisher inside in case I'd ever need to evacuate another way other than the front.

Beyond that I'm just not sure what there is to worry about. I have been told by someone not to cut larger than 1/2" holes in the 2x4's to run wiring and since I want multiple circuits (8 to 10 of them) I will have to run a few cables. Tight outlet boxes, seal them up well, should i run wiring inside some protective piping???
Old 04-26-09, 06:47 PM
Thread Starter
Join Date: Feb 2007
Location: SouthEast Louisiana
Posts: 324

Would it help to install contractor weed stop/moisture barrier on the ground below the building? or for that matter what about 2 or 3 sheets of plastic or visqueen just underneath it and then tucked into the ground along the edges? Wouldn't this create a dry space that would constantly get air under there?

I know you are saying - its a shed - but it doesn't look like one. I had a regular door put on it and its sealed very well all the way around. In fact its sealed so well I've seen nails pushing themselves out on the outside and I've had to go and push knock them back in, but maybe thats just the plywood expansion.

I read this.
Energy Savers: Crawl Space Moisture Control

Moisture rises from the ground so if I can seal the ground seems to me I'd eliminate most of my problem right??????

I was thinking, I wonder if there is a painting system where I could lay a paint sprayer on a rail and have it pointing straight up at the under flooring and just drag it back and forth to cover the under flooring as best as possible... then I could use a spotlight to see what I've covered and push it back under there and paint again. I'd probably have to dig an access hole on the side of the building, but whatever.

Last edited by searcherrr; 04-26-09 at 07:12 PM.
Old 05-04-09, 11:04 PM
Thread Starter
Join Date: Feb 2007
Location: SouthEast Louisiana
Posts: 324

Can anyone comment here? Would it be worth it, if money is low, to put a layer of visqueen underneath the 8" high flooring?

I mean I read that link up above and it seems like it would help, but I wanted to hear from someone here. Sure I know visqueen isn't the only thing to do, but for right now if this would help it'd be good to apply.

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