The role of subfloors in the tiny house

by andrewodom on February 28, 2012 · 22 comments


We have talked repeatedly about flooring for out tiny house and have even asked for your advice and experience on our Facebook page. But what I realized last night was that we have been grossly overlooking an even more important step; sub flooring.

It seems many of us take it for granted. I know I am not even sure of the real importance of subflooring or at least I didn’t until I started doing a little research. I sort of looked at it as a way to stabilize your true flooring choice. Turns out there is several choices to be made when considering subflooring and purpose for each one.

It is safe to say that one of the most important parts of a tiny house and its structural integrity is the flooring system. The floor system sustains the weight of the interior walls, roof, interior furniture, appliances, interior flooring, and its occupants. Other than the trailer the floor structure should be designed and built in order to determine the overall weight of the tiny house trailer as well as how much weight the floor can carry. Without proper research, instruction, and construction, it is plausible that a tiny house may have weak foundation footings (read: support jacks), improperly spaced or sized joists, improperly nailed sub flooring, etc. These sort of innocent errors can lead to structural failures including – but not limited to – excessive movement, sagging, unleveling, floor separation, and squeaking.

The Four Main Types of Sub Flooring

Plywood. Growing up in a 60 year old home our subfloor was little more than sheets of 1/2″ plywood. Nothing fancy and nothing manufactured, per se. However, for the last 30+ years the type of plywood has changed to a CDX tongue and groove style that is made from thin sheets of southern pine veneer that are then cross-laminated and glued together forming 4′ x 8′ sheets in either 5/8″ thickness or 3/4″ thickness. Because the edges are T&G they interlock nicely providing a strong base for the finish flooring. This type of plywood subflooring typically provides a freedom from squeaks and give a nice level surface for your finish flooring.

Plank. Having gone into several old barns looking for wood to be repurposes I have come across plank flooring quite often. Originally used in pioneer days as a finish (and only) flooring plank has become a type of sub flooring since the mid-century. Usually comprised of 3/4″ x 4″-8″ wide southern yellow pine boards, plank flooring is installed by nailing these boards directly to the floor joists. Because this type of sub flooring is usually found in substantially older homes and can loosen up over time from the expanding and contracting of the wood, it is important to fasten these boards down with a solid 2.5″ or 3″ deck screw.

OSB (oriented stran board). The simplest and most cost-effective sub flooring is OSB sub flooring. It looks like a sheet of glued together litter chips pulled from a hamster cage. In actuality, it is. OSB is nothing more than wood chips compressed and glued together to form a 4′ x 8′ sheet. Installation typically involves gluing and nailing the OSB sheets to the floor joists. This is probably the easiest and least time consuming of the sub flooring options as well.

Concrete. I do NOT recommend this to any tiny house builder. But I felt it needed to be included as it is an often used method of sub flooring. Perhaps if you are building a more traditional, sticks ‘n bricks, type of tiny house this is a reasonable option. But for mobility sake I would not even continue reading this paragraph if I were building a tiny house trailer. Concrete slabs usually consist of a 4″-6″ thick of at least 3,500 lb. strength concrete. The water used in the mixing of the concrete can take anywhere from 48 hours to 3 months to fully dry out and the concrete to set. This is not an easy process and takes more than one set of hands for even a small concrete pour. If you want to read more about our experience with pouring concrete you can do so here.

What kind of subfloor did you choose for your build? Did you have a positive or a negative experience with the selection and installation? Don’t forget, if you enjoyed this post and others like it please Share it, LIKE it, or Tweet it out there. We rely on voices like yours!

 

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Photo courtesy of Jeremy’s Tiny House

 

  • mizacy

    I will be using staggered sheets of 5/8″ thick plywood, doubled.  I am building on a goose-neck trailer and have a bit more ‘wobble’ in my floor and am banking on this making things a bit more ‘rigid’.  Just a hope though really…

    • anotherkindofdrew

      That is quite a bit of plywood. I think it will deal with the rigidity issue but it will certainly add the weight. Keep us posted Macy! 

      • mizacy

         It’s one of the reasons I added the triple axle :).

        • anotherkindofdrew

          If you finish that with a round off and a stuck landing I will be super impressed! ;)

          • http://www.facebook.com/people/Avril-Brown/100002663835705 Avril Brown

            I am impressed with your gymnastics allusion…. :)

        • Droid_ca

          Do you have a website where we can see pictures of your setup

          • anotherkindofdrew

            I am not sure if you are asking me or Macy. Macy can be found at minimotives.com

  • http://www.facebook.com/people/Avril-Brown/100002663835705 Avril Brown

    Hey Drew! I had a thought on this I would like to share. My own project is indefinitely delayed due to lack of funding. Dang. But if you read my blog much, (I hear it is great bird cage lining if you print it out, LOL), you will know that I am very concerned about the toxic load in the tiny house. I used to laugh at folks like me, but I have become extremely sensitive to toxic gasses and the like over the years. My concern is that in such a tiny area, if the subfloor is not allowed substantial off gassing, that it could be overwhelming. 

    Just a thought, as I said. All things considered, if my tiny ever gets going again, I plan to use as much recycled material, such as the barn planks, for the subfloor as possible. And one final note, Brad from Tiny Texas told me recently, that he knew of several people who were actually hospitalized from formaldehyde exposure. 

    • anotherkindofdrew

      I can certainly see as that would be a risk, sure. However, there is no more formaldehyde in OSB or plywood than there is in say the railroad ties many people choose to “recycle” for their “organic gardens.” We are surrounded by an artificial world and most people have no idea about formaldehyde content in building materials.

      Particle board (think cheap furniture from Wal-Mart and Target), plywood paneling (think pre-made cabinets from Home Depot), MDF (think drawer fronts and furniture tops) all contain levels of formaldehyde and most homes are filled with that. It is all about the resin-to-wood ratio and MDF has the highest ratio. 

      In fact though, OSB emits less formaldehyde than any other plywood containing UF resin. 

      • http://www.facebook.com/people/Avril-Brown/100002663835705 Avril Brown

        Absolutely about all of those things! Truth is, I am not much for buying any of it. On my blog, tinyhousewisdom, I mentioned telephone poles. I tried to burn one once in the mountain cabin I used to own. YIKES! You want to talk about TOXIC! Ickypoo! I bout keeled over from the fumes. YES these are toxic. 

      • JP

        Hi Drew – as someone who has the same issues as Avril (that is, heightened sensitivity to VOCs and formaldehyde), we’re also trying to figure out if we can build our tiny house without any formaldehyde containing materials i.e. plywood.  Just because we’re surrounded by an artificial world doesn’t mean we should throw up our hands and say “oh well”.  If you don’t have health issues, maybe you can afford to…but if living around VOCs and other toxins makes you so ill that you can’t be in your home….well, it becomes a lot more personal.  I know Tiny Texas Houses builds without plywood, but I’m unclear on whether or not they’re secure enough to put on a trailer and haul across country.  Anyone have thoughts on the structural safety of using wood planks as subfloor, etc., instead of plywood or OSB?

        • http://www.tinyrevolution.us/ anotherkindofdrew

          Thank you so much for joining the conversation JP. I always try to stay away from VOCs and other toxins. I don’t think anyone can afford the health issues associated with small spaces and toxin exposure. I am not sure I would be happy with just wood planks as a subfloor because with them you have two choices. The first being extremely long planks which would cause potential bowing and even cracking. The second is that you would have to scab a fair amount of pieces together which doesn’t displace weight well in this case. Personally we will be using LP ProStruct Flooring with SmartFinish.

  • droid_ca

    one of the Ideas I was considering for the tiny house that I’m trying to design is under floor storage I would like it to be deep enough that I can securely tie down 5 gallon buckets between the floor joists as well as have my water supply and battery storage the unfortunate  draw back is there would be no loft space…so I’m open to suggestions

    • mizacy

       Are you thinking to raise the floor up? which would inhibit being able to have a loft space?  Basically so you have a false floor?

      • droid_ca

        yes I’m thinking of brining the floor up about 2 feet so I can also include a under floor furnace as well as have storage from front to back I think the one thing that most small homes have is lack of storage space

        • mizacy

           It seems it may be possible to do that, maybe just in particular places even.  The height dimension is a pretty important one if you are on a trailer, you may have to choose between a loft and storage in your floors.  There are endless plans that would allow for a bed on the ground floor (no loft) and make that successful.  Personally, I am going with a vertical ‘wall’ of storage, like many other tiny houses, it just seems more efficient when you’re tied to the height limitations… Do you happen to have a website to keep track of your ideas/build?  I really like following other tiny houses’ progress and creative ideas!  Best luck!
          Macy

          • droid_ca

            Sorry no website or build journal l as of yet still working on my finalization of my plans and getting some of the small stuff sorted out and out of the way…all these fine details

    • Jay

      Why not have the holes cut in the floor, with flush trap doors to cover them, then sink the buckets into the holes when you’re stopped. Then you don’t have to raise the floor at all, you’re just using the space under the trailer. This space is only needed while you’re in motion.

      When it comes time to move, pull up the buckets, lash them down inside the house, and travel on.

      • droid_ca

        I’m not sure I understand what you mean but I sorta have an idea. What I’m thinking of would be for more of a long time situation so once you have all your supplies you would be good for a while I like  the idea of the holes through the floor it gives me an idea  but I would still need to have raised floors for it… Thanks anyways for your contributions 

  • Jay

    If one were to build on a trailer that already has a wooden deck, couldn’t the insulation be put under the floor, and the deck just finished? There seems to be a lot of unused space between the metal support beams that could be filled with EPS foam.

    • anotherkindofdrew

      For a tiny house you really want to have your metal framing on bottom. Then you need a barrier layer (radiant barrier, moisture barrier, rodent barrier, etc). A lot of people use metal flashing rolls but we are using EcoFoil radiant barrier. Then you want your joists. 2″ x 4″ framing is just fine. Then your 5/8″ subfloor. That is ideal, in my opinion. Oh, and of course the insulation in the cavities of the joists.

  • Bill

    The subflooring I recommend is 3/4″ tongue and groove “Advantech” , this has a “wax” coating and does not absorb water, like plywood, O.S.B. or planks hands down for a “Tiny House ” this is the best on the market….glue( construction adhesive) screws and ringed shank air nails at the recommended nailing pattern will last a long long time….

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