Bales Over Wood Floors Instead of Concrete Slabs

Written by Andrew Morrison

Straw Bale house under constructionBuilding with bales over wood floors is an option that’s often overlooked in straw bale construction. Building a straw bale house on top of a concrete slab is certainly the most common system employed; however, it’s not the only way to go. If you have reason to build a raised floor system, you can. In the photo to the right, you’ll notice the change in grade from one side of the picture to the other. That’s a great reason not to build a slab as the amount of either back fill or concrete would be insane to make it work as a flat slab.

There are a lot of advantages and disadvantages to each type of construction, as with anything in life, so let’s take a look at some of those now to help you decide what is best for your build. (Remember, there are lots of other options too from earthen floors to pole structures. Don’t get stuck in the belief that you have limited choices. The largest limitation will likely be the building department, not the fact that you’re using bales for your walls.
Rather than focus on the negative and talk about disadvantages, I’ll simply discuss the advantages of each. Let’s lay it out here.

Concrete Slab Advantages: radiant floor tubing before concrete is poured
1. Large amounts of thermal mass. The ability to use that mass for passive heating and cooling is large.
2. Radiant heating. Again, the mass comes into play. Radiant tubing installed directly in the floors is an extremely efficient way to heat a house.
3. Durable. Nothing is more durable than hard concrete over time. It just gets harder with age.
4. Ease of installation. Built all over the world, concrete slabs are installed by many tradespeople. This brings down the cost as well.
5. Back to cost. Because the slab acts as the structural element of the floor AND the finished floor, it is a relatively low cost option.

Wood Floor Advantages:straw bale wall with round window
1. Perfect for working with uneven terrain. Like the photo at the top of the article, a raised floor can accommodate a sloping lot.
2. Deep excavations requiring basement walls lend themselves well to framed floors. Why not use a daylight basement or a full basement?
3. Applying wood, bamboo, cork, natural wool carpet, or any other finish flooring type is easy, and in many cases, easier than with concrete.
4. Comfort under foot. Wood floors have built-in, limited deflection which allows the floor to “give” under foot. This makes it very comfortable to walk on.
5. Access to utilities. Raised wood floors allow you to maintain access to things like plumbing waste lines which would be buried in a concrete slab. Should they ever fail, you have easy access for repairs.

There are some differences with the installation of bales over a wood floor as compared to a concrete slab. In most case, working over a wood floor is easier in terms of the bale installation; however, you need to decide what advantages are important to you and also what disadvantages come along with them. In my soon to be released, new production I show the details of working over a wood floor where as my old production focused on installations over slab construction.

You can learn even more about foundations and wood floors in our comprehensive How-To Instruction Video Series. It contains over 10.5 hours of top-notch, professional quality instruction on everything from foundations, to framing, to baling (post and beam and load bearing), to plaster. You even get a FREE set of the Mountain View Cabin construction plans with your purchase. All for only $40 and it’s delivered instantly to your inbox.

18 Responses

  1. I would like to say some words about wood floors lying on the wooden I-beams. If You need to build in areas with permafrost ground – You should ventilate underfloor space during all year. In this cases making basement walls is not good idea! Another way, your ground base will unfreeze and foundation will settle deeply. It will be better to build short columns, standing on the ground, (from 1.0 to 1.5 meters high), put on them main beams, then install wooden I-beams with floor system. Advantage of I-beams is the possibility to infill strawbales between them to make very good heat insulation.

  2. Andrew, I have had many questions when pondering raised floor installations of toe-ups as described in your other videos. For instance, is blocking needed (and if so, how often) under the toe-ups that run parallel to the floor joists? Should the floor joist layout be adjusted to give something for these toe-ups to attach to? I am a draftsman by trade and often try and detail or even model (in Sketchup) different scenarios to work these things out. I am anxiously awaiting your next video in hopes that it may answer some questions I’ve had for years!

    A heartfelt thanks for all of the information you have provided thus far and best wishes for continued success to you!

  3. Hi Brian. The questions you have are indeed covered in the new production. You can use either blocking or adjust the joist layout as necessary if you need to anchor the toe ups for a structural reason (i.e. shear design). If you don’t use the skins of the plaster or the overall wall assembly as the shear system, then you can simply attach the toe ups directly to the subfloor with long SIPs screws.

  4. Hey Andrew,

    It does seem most examples out there deal with slab construction, but I agree with you that building a bale house on a framed floor was really not difficult and seemed to work great, so I’m glad your new production deals with this method. One added advantage to a full-basement is it’s the least expensive way to gain square footage, which is good for things like mechanicals, storage, and the laundry which saves your prime floor space on the main floor for other uses.

  5. I have completed the shell of a straw bale load bearing structure. It is 1600 sq feet. It was build on a pier style foundation using concrete forms around the perimeter and suported with concrete piers that run in 2 rows under the structure and reach below the frost line. I live on the Canadian praries. The space is dirt with a vapour barrier that slopes down into a drain (rubble pit). The engineer recomended a scratch coat of cement to fascilitate water/ moisture drainage into the pit, which will also accomodate my grey water disposal. It will amount to a lot of moistur underneath, but am assured this system works. A red wriggler composting system is all that will be under the house, and it is not heated. My appliances are to include 2 small appropriately place hot water heaters that will fit in the upper floor middle portion of the design, and contribute to heating the bathrooms. The plumber will have to figure out how to get insulated pipes to my hook up from the well, and hope this can be done without going ‘under. We shall see next year what solutions are available. Anyhow, I have a raised wood floor and all is well.(Clearance beneath the house slopes into the center from the perimeter to a depth of about 7 feet at the drain. No vents were in the engneered design, so the slope, and vapour barrier, and drain are all integral to the function of this method to my understanding.

  6. Hope you’re new video/DVD will be out ASAP. I am ready to begin the foundation for a small home but don’t want to start until I can order, watch and follow your newest instructional video about building on wooden floor. Can you give us any idea when we can purchase this?

  7. Hi Andrew, In your article “Bailing over framed floors instead of concrete Slabs” you had put “Why not use a daylight basement or a full basement?” and did not answer that question in the article. I was thin king of doing a daylight basement, why would that not be wise?

  8. That’s terrible. I asked a question and never answered it?!?!? Whoops. Basements (daylight or full) are totally fine and there is no reason not to use one. You’ll need to consider the framing requirements of the added weight of the bales and plaster, but with that in mind, you are god to go.

  9. How do you finish the plaster of the interior walls that comes down to a wooden floor? As cement plaster and wood dries it contracts which could mean a gap forming between the floor and the wall. Is there a technique for this?

  10. You will need to provide baseboard trim to cover the expansion joint. In fact, most wood floors require that you leave a 1/4″ gap around all edges for the floor to move. The easiest way to do this is to use j-metal so the plaster stops above the floor and you can slide the flooring underneath the metal. This is most difficult where bales curve such as into doorways. It can be done with some care though.

  11. Hey there Andrew, thanks for the article. Very interesting; I honestly had never heard of straw bale construction until now!

    I’ve got a question for you: Is there a trend in the residential construction industry towards using a raised floor? I sell and install raised floors, but they’re for commercial buildings, and pretty much a completely different animal than what I believe you are referring to here. (my website for you to check out: so you can see what I’m talking about)

    Now, I actually have sold our commercial type of raised floor in a residential setting, a few times, but those were more of a high rise/condo type of building rather than a single family dwelling.

    Do you think the commercial/industrial type of access floor would ever be a good fit for residential dwellings? After reading over some of your posts about straw bale construction, I’m starting to believe anything is possible!


  12. Hi Ryan. I think this floor system may be more than what my clients and others building a straw bale house would be looking for. Looks like a cool product to be sure, but I think out of the picture for most in our field.

  13. Hi Andrew,

    I’m loving the information you provide but I have a question re: underfloor insulation. Is it possible to run a layer of straw bales underneath a wooden floor for extra insulation? If so, what would be the best base to prevent moisture inundation. Thanks Kiri

  14. Hey, I have some questions concerning the math for this where weight of the walls are floor loads are concerned.
    I’m no expert and it’s a lot of math, so I may be doing this all wrong. Skip to the conclusion at the end if you like.

    The stats i’ve got say:

    -Straw bale weight: ~7 lbs/ft3

    -“Adobe”/”Cob” weight: ~100 lbs/ft3

    -Average floor weight rating: 50 lbs/ft2

    Assuming 14″ x 18″ x 36″ bales, stacked at 14″ wide 18″ tall, 36″ long. Assuming 1″ cob plaster on each side of the bale.

    14 inches of straw and 2 inches of cob for every 16 x 12 section of floor.

    Every foot high you go would be roughly 24 lbs.
    ~8 lbs for each square foot of 1″ thick cob, 2 total, one on each side of the bale wall.
    ~8 lbs for a 12″ x 14″ section of straw bale.

    8+8+8 = 24lbs/1.33 sqft = ~18 lbs/sqft at 12″ high.


    Let’s make the wall 8 feet tall, standard living space.
    18lbs/sqft x 8 ft tall = 144 lbs of weight on 1 sqft of floor.

    Floors are rated at 50lbs/sqft. 144lbs is nearly triple the rating. Why don’t strawbale walls crush the floor?

  15. Hi Matthew. Thanks for your message. I am not an engineer, so I want to start by saying that you should contact an engineer to make sure that your math is correct and the information i provide below will work in your situation. Based on what my engineers have done over the years, I believe your numbers are off. One source of the mistake is that most walls are laid flat with the width of the wall being 18″. This spreads the load out a bit more in therms of the square footage of the weighted wall area.

    The engineers I have worked with typically consider the weight of a bale wall to be twice that of a conventional wall system. If you are using a lime plaster or an earthen plaster, it will be much lighter when it is dry, so you may need to reconsider the approach of using a cob weight. I’d suggest using a plaster weight from ASTM or the International Residential Code’s chart on building material weights.

    The floor systems of a framed house need to be strengthened to allow for straw bale walls to be placed on them. Typically that means increasing the floor joist size, reducing the joist spacing, or a combination thereof. Many bale house builders also use a concrete slab for their floor and so the load of the bales can be passed onto the concrete. What we know for sure is that you will definitely need someone qualified to create the weight rating for your wall system and to ensure that the framing is designed to carry that load with confidence.

  16. Hi Kiri. I am not a fan of using bales in this capacity as there is too much risk for moisture damage and infestation from rodents and bugs. I would stick with more conventional insulation materials like rock wool which can handle the moisture issues with no problem and provide excellent insulation.

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