There are many possibilities for the flooring in the cooler, as long as you follow the basic rule of making sure it is waterproof.
- Concrete slab (no sealing necessary)
- Plywood or OSB painted with exterior paint
- Horse Matting, waterproof and great for high traffic coolers
Insulating your floor is even more important than insulating your walls.
Coolers built on a deck need at least as much (preferably more) insulation in the floor as in the walls. If you build on a deck instead of a slab, you need to insulate the floor to at least R25 (and R30 would be even better).
If you have an untreated wood floor under your cooler, you will need to put in a vapor barrier. This is how we did ours on the farm:
- We put three layers of carpenter plastic between the styrofoam and our top layer of plywood. Some people happily report using single pond liners instead.
- We stretched the plastic out into a “bathtub floor” that goes up the walls a couple inches
- There it is gathered under “Roof Edge”* that is screwed about 3 inches up from the floor all the way around the wall like metal baseboard trim.
- We caulked the entire top of the Roof Edge so the water dripping off the walls won't slip between the plastic and the wall, and pool up under the floor.
*Roof Edge is cheap and available in the flashing and roofing sections of all the big box hardware stores.
Concrete Slab & Dirt Floors:
Since cold air falls, insulating the floor of your cooler traps the cold air - keeping your electricity bill lower and reducing the load on your A/C. Whether or not it makes sense to insulate the floor depends on your targeted cooler temperature:
- Above 45°F / 7.2°C -- insulating the floor is not worth the investment except in a very hot climate.
- Down to 38°F / 3.3°C -- customers in hotter regions will need to insulate the floor, but in northern climates you may still reach 38°F / 3.3°C without it.
- Below 38°F / 3.3°C -- floor insulation is required. Even just 2 inches of insulation makes a big difference. R-25 to R-30 is best.
If the concrete pad extends beyond the cooler, the pad can absorb radiant heat. In this case, you'll need to insulate the floor.
Haven't poured the concrete yet?
- Use gravel for the first layer.
- Second, put down a plastic vapor barrier.
- Then place a layer of below-grade rigid foam insulation; 2 inches is fine, and 4 inches is fantastic.
- Rebar or mesh comes next.
- Lastly, pour! We mix in fibers to make it stronger.
How To Insulate the Floor:
Whether you're building up on an existing trailer deck, above a basement or on a slab, you do not need to frame out a floor.
- Place rigid foam directly on the floor. Try to use more than one layer of insulation and place each layer with the seams in the opposite direction of the one before so the stress points are not all in the same place.
- Lay 3/4" plywood painted with exterior paint directly on top of the rigid foam. If you measure carefully and cut carefully gravity will hold it all in place.
The plywood spreads the load out enough over the rigid foam; even after 10 years, our foam still looks fine.
In fact, if you were to stud out your floor, you actually risk decreasing the effectiveness of the insulation, because the studs can create thermal bridges where the cool air flows out through the less-insulated studs, between small gaps in your insulation.
In outdoor free standing coolers you may tilt the floor towards the door so that any water that gathers if you are taking a hose in your cooler to clean it can naturally drain out. Don't forget to site your structure so the water has someplace to go once it leaves the front door. (If your cooler isn't seeing heavy action you can just clean it with a mop and a bucket and don't need a tilt.)
If you’re building on a trailer or a deck-type floor, this is easy to do. If you're pouring a new slab, just build it above grade a bit and put your form-work a barely noticeable “off-level” towards the door.
The only people maybe needing drains are folks who do meat processing (see our specific recommendations on the Hunting & Meat page) and regularly spray down the cooler. Otherwise, it's more trouble than it's worth. If using a drain, make an airtight plug for it, so you won't lose cool air when you are not draining fluids.
There isn't enough water accumulating to necessitate a drain, and putting one in would just compromise the integrity of the cooler. The only thing the drain will really be letting leak out is cold air.