Cheap floor insulation options include an air gap using empty glass or plastic bottles, straw and hay bales or loose and mixed with the earthen floor, closed-cell underground foam insulation at R-5 per inch and waste materials such as cotton and jean clothing and carpet.
What’s the Best Floor Insulation
What’s the best floor insulation depends on your situation, budget, and available materials. For earthen floors, insulation air insulation works pretty well and is free if you can find enough bottles or drink enough beer.
Another cheap option is straw or hay bale as they trap a lot of air, are structurally stable and strong, and available in most areas of the USA and Canada.
1. Glass and Plastic Bottles
Glass and plastic bottles create an air gap, and the air is an effective insulator. This is a very cheap, well… free except for the super expensive beer that was in the bottles.
I used my empty 620ml beer bottles under the concrete slab for the adobe building and I may do the same under the earthen floor for my earthbag house.

Check out my article on how to use free bottles for insulation here.
Scott Boyd
The Steps To Add Glass Bottle Insulation Under Floor
- Dig down to the depth of your bottles, plus an inch for sand and a few inches for the earth.
- Level the base.
- Spread out the sand base layer and level.
- Lay the bottles on the sand with the fat (bottom) ends or sides facing the exterior walls (not the narrow necks).
- Place the bottles to fill in the remaining area. You can walk on the bottles when necessary.
- Cover the bottles with sand and make sure to fill any cavities.
- Add at least three inches of earth to bring the floor to the desired height.
- Level and compact and repeat until you have a solid floor.
- Finish the floor with linseed oil, tile, or epoxy (I would only use this method if you created a design or added color to the earth floor that you want to see without damaging. This will not be as comfortable or cool on the feet).
You can read my article here about 7 free or cheap flooring options and build a cheap garage here, and find cheap land in USA here.
2. Straw and Hay Insulation
Straw and hay have an R-value range of about R0.91 to R3.05 per inch. Bales are usually 18” wide and 14” high (source). You will have to dig the floor down a long way, but it may be worth it. The earth that you are digging up can be used to cover adobe or earthbag walls and you can read more about how with my article here.
If you have the depth it is better to stand the bales on their edge as they have higher compression strength than from top to bottom. But you also have to dig four inches deeper, but it produces a stronger and more insulated earthen floor.
If you don’t want to dig out 14 or 18 inches of earth to make enough room for the straw you can lay the straw in loose to any depth that you require. However, it is not going to be a solid floor unless you mix the straw with the earth and add water.
Straw and hay bales cost between $3 and $5 dollars in Nova Scotia and I am sure that is close to the range throughout the USA and Canada.
You can trowel this adobe mud mix level and when it will dry to a hard surface that you can finish with a number of options.

3. Foam Insulation
Closed-cell foam insulation, XPS Extruded Polystyrene is very efficient insulation at R-5 per inch and there are several manufacturers that produce versions designed for above and underground installation. These models of foam resist compression and are a good option for under an earthen floor if your budget can handle the substantial cost.
In Nova Scotia, we have to install 4” under-engineered slabs to meet the R-20 requirement and this really adds to the overall cost. For an earthen floor, a person can install between one and four inches depending on your budget.
Additional cheaper materials can be added on top of the foam insulation to bring the R-value up to the desired amount.
Now you might be asking “where can I get this for free?”.
- Check with freecycle.org.
- Check with local home builders as they always have smaller pieces left over that ends up in the garbage. They will be happy to have you do a cleanup as it saves them labor and tipping fees at the local landfill.
- Check with local hardware stores as many full pieces of foam get damaged by forklifts and careless employees. Some foam because weathered from being exposed to sun and dirt and becomes un-sellable. Offer to help clean up the yard for them!
TIP: To greatly improve the effectiveness of the home’s ability to resist temperature changes then simply add four feet of XPS closed cell underground foam insulation out from the foundation of the house.
The slows the heat or cold from entering the earth at the foundation or footing, where it can enter under the floor. This is required by the building code in some municipalities in Nova Scotia.
Table 1. Cost of Foam Insulation Under Earthen and Concrete Floors
Floor Sqft | Thickness | R-Value | Cost $ |
500 | 1 | 5 | 305 |
2 | 10 | 590 | |
3 | 15 | 895 | |
4 | 20 | 1180 | |
1000 | 1 | 5 | 610 |
2 | 10 | 1080 | |
3 | 15 | 1790 | |
4 | 20 | 2360 | |
1500 | 1 | 5 | 915 |
2 | 10 | 1670 | |
3 | 15 | 2685 | |
4 | 20 | 3540 | |
2000 | 1 | 5 | 1220 |
2 | 10 | 2160 | |
3 | 15 | 3580 | |
4 | 20 | 4740 |
4. Old Clothes and Carpet
If you have a lot of cotton shirts and jeans that are not worth donating to charity then toss them into there the floor will be located. It won’t help much, but any amount helps, it is free, and it avoids more garage in the local landfill.
Old used carpet is a big contributor to landfill waste so be on the lookout on garbage days for free insulation!
Bookmark this page as I will update it once I finish my floor in the earthbag house.