Photo: Monstera

How do I protect the underside of my shed floor?

Excavate out the ground between each of the floor joists (and underneath most of them), leaving columns of dirt/soil underneath the corners and center, and then put bricks, concrete/cinder blocks, or pour concrete forms around those dirt/soil "columns".

diy.stackexchange.com - How can I protect a shed floor from ground moisture?

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I needed some sort of workshop/storage/playhouse, so I thought I’d build a shed with three sections:

Workshop - 2.4m x2.4m

Storage - 1.2m x 2.4m

Playhouse - 2.4m x 2.4m

Now I intend on turning the playhouse section into a gym, but I have a problem. After four years the OSB3 floor has gone spongy and needs replacing for something stronger to take the weight of the equipment and the duress of what it is to be used for. I think I know a couple of contributing factors that may have led to the floor deteriorating. The end of the garden has always been soggy. Even in the summer, it takes a good bit of nice weather to dry it out and even then it’s normally only the surface that's dry. I dug up and filled the area (7m(L) x 3m(W) x 0.3m(D) with 40mm gravel and used that for the shed base to sit on. Also, when building the shed it started to rain, so I covered it in some sticky backed plastic we had lying around (the stuff you use to protect laminate flooring when painting etc) to protect it. As this covering was on the floor, any treatment to it was overlooked and I think the plastic covering didn’t allow the OSB3 to breathe and as such it retained any natural moisture it absorbed over the years, so it went spongy.

The Issue

Now that I’ve pulled the OSB3 floor up, I intend on replacing it with some Spruce floorboards. Obviously, I’d like to not have to do this again in a few years so I’d like to take this time to do everything I’ve thought of in hindsight to protect the base, BUT, I’m not sure what to do.

After the long story, this is where you come in!

These are some of the approaches I’ve thought of, but I’m not sure what’s best: 1... Lift up the shed and lay some DPM on top of the gravel to stop moisture from rising up through the base. As much as I’d like to do this, the shed weight is well in excess of a ton so it’s not an option

2... Lay some DPM OVER the base’s bearers and lay the floorboard on top of it to protect the floorboards, but what about the base under it?

3... Paint all the base’s bearers and the underside of the floorboards in some kind of wood protection (not sure which type)

Wood preserver?

Bitumen?

This is pretty much all the info I can think of, so any help with what to do to help protect and preserve the base and floor would be VERY much appreciated.

I look forward to your responses if you have time.

Thanks!

UPDATE: I've added some photos for reference.

4x2 frame waiting to be covered in 18mm OSB3

Mostly complete bar additional trimmings and sorting the garden

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Should the underside of the floor be insulated?

Floors above cold spaces—like vented crawl spaces and unheated garages—should be insulated, but don't forget about under the flooring. This will help ensure maximum energy efficiency for your home. According to the U.S. Department of Energy, it's ideal to insulate: Slab floors built directly on the ground.

accurateinsulation.com - Underfloor Insulation Options | Should I Insulate Under My Floor | MD & DC

As a homeowner, you may know a little bit about insulation and what it does. You probably even know that your attic and walls should be insulated. But what about the floors? Keep reading to learn more about installing insulation under your flooring!

Should I Insulate Under My Floor?

It’s a good question, one we often hear. Floors above cold spaces—like vented crawl spaces and unheated garages—should be insulated, but don’t forget about under the flooring. This will help ensure maximum energy efficiency for your home.

According to the U.S. Department of Energy, it’s ideal to insulate:

Slab floors built directly on the ground

Foundation walls of unvented crawl spaces (as an alternative to floor insulation)

An insulated slab is easy to heat, and placing the mass of the slab in your house’s thermal envelope helps keep interior temperatures comfortable. Most slab insulation is done during home construction. While insulating a slab in an existing home can be more expensive and a bit more invasive, it is possible to dig around the perimeter of the house and install insulation, typically foam board. Insulating the exterior edge of a slab can reduce heating bills by 10 to 20 percent in many homes! Foam-in-place insulation can also be blown under floors to help insulate and reduce air leakage. It’s a good idea to install an air barrier—caulk, foam sealant, etc.—to help prevent cold air in the garage from “short circuiting” the insulation under the subfloor as well.

Underfloor Insulation in Maryland & DC

If you’re located in the Washington, DC metropolitan area, call the team at Accurate Insulation. We install floor and underfloor insulation and have experience with new construction and retrofit projects of all kinds. Contact us today to learn more!

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