Tiny House Construction: Insulation

We’ve been busy installing our insulation in the Tiny House we are building.  We went with a closed cell foam board insulation product that will have a high R-value and will also offer some extra structural reinforcing.

We wanted to have the house spray-foamed with 2 lb. foam, but alas, the price came in way too high ($1,600).  We found this insulation on craigslist for $400 for the whole lot.  A great deal, but we’ve spent three days installing it, which is a long time.  It’s a very tedious process!  First, we measure the wall cavity it needs to fit into… 

Then we cut a piece from the 4′ x 8′ foam sheet using a special utility knife blade and a straight edge, then we insert the perfectly cut piece into the wall cavity.  Each piece fits tightly between studs so we’re hammering them into place.  This tight fit is where the structural support comes from.

After the foam insulation pieces are installed we seal up any gaps or cracks with a spray foam product…

Here are some photos of the interior with the foam board insulation installed…

I really wish I would have taken a picture before we cleaned up, the floor was covered with tiny bits of foam.  The mess was driving us crazy so I was more focused on finding a broom than a camera when we finished yesterday.

Here’s a wall that is still waiting for a few pieces of insulation:

We have to cut each piece of foam to fit around the electrical wiring (visible in the photo above), which seems to be in most every wall cavity!  I understand why soft, flexible fiberglass batt insulation is the conventional choice in the construction industry today.  It’s light, flexible and pre-cut!  But we are getting more insulation with the foam in the same wall thickness.

We’ve got an R-19 in the walls and an R-30 in the ceiling, which meets the current energy code, in Flagstaff anyway.

Next, we’ll finish installing the metal roofing and start on the interior drywall.  which will feel so nice to get a finished material on the walls.

We have a deadline of mid-May because we gave our landlord notice that we’ll be moving out (of our 1400 sf rental house).  So, we need to keep busy!  And we need to try an off-load some of our stuff.  It’s amazing how easy it is to acquire stuff…  We have less than the average [american] person, but it’s still more than we’d like to have, and more than will fit into the new tiny house!

I’m excited to downsize and lighten the load.  Me and my stuff have traveled almost 3,000 miles in the last ten years.  Kind of ridiculous!  From Fort Collins to Los Angeles, then Los Angeles to Denver, then Denver to Loveland, then Loveland to Prescott (via Santa Fe).

Phew.  (thanks to my family and friends who have moved my stuff with me – multiple times… haha.)  I just remembered one cross-town  move in LA where I left food in the fridge… hey, why not?  Well, the milk spilled and was leaking out the door into the U-haul.  Haha!  Gross.

Okay, hope all is well!

– Carrie

Categories: Tiny House Construction | Tags: , , , | 24 Comments

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24 thoughts on “Tiny House Construction: Insulation

  1. heath cole

    wow, it’s *really* coming along!…:D…& the insulation looks great…i like what you did with it…and you’ll be glad you did down the road…enjoying watching your progress…can’t believe your transition is like a month away!…:O…sending good energy your way!…:)

    • hi Heath, thanks for the good energy! it’s so encouraging all the support we’re getting via the internet and our blog. it’s so fun to have a project, but it really helps us keep going to hear comments and support and to share our progress with the world.
      One month away!!
      take care,

  2. katie

    yeah yeah! It’s coming along beautifully!

  3. Steve

    Its all looking GREAT, BUT a MASSIVE MASSIVE thing you MUST MUST MUST do is insulate the floor! I live in a self converted bus and my BIGGEST mistake was not to properly insulate the floor… a vehicle this is where all the COLD air comes in from….under the vehicle. It sounds crazy but it is TRUE! I live in the UK and our temperatures in a mild winter still make floor cold, and you’ll burn heat to keep the cold out! If I was you put 100mm of insulation under the floor whether inside OR outside between the chassis members. DEFINITELY DEFINITELY insulate the floor you will REGRET it massively if you don’t, trust me, I do! Keep up great work. Steve.

    • hi Steve! yes, totally agree – very important to insulate the floor in an elevated building. And we did! The floor is a wood framed platform over the trailer bed / framing members, so we put full depth foam board in the floor too – so we have R-24.5 in the floor.

      Have you thought about adding insulation to your bus? I wonder if you could get it spray foamed from below and then spray bed-liner “Line-x” over that for durability? Or put sleepers on the floor on the inside and get a couple inches thick of foam board inside?
      thanks for your comment and for following along!

      – Carrie

  4. Matt


    I have a small, un-insulated cabin in the Northeast (cold, snowy winters). And I wanted to do what you did and place foam insulation against the inner roof. But I was told that I could not place the foam insulation directly against the inner plywood, as this would trap moisture in the plywood, between the foam insulation and the roof shingles. What are you doing to insure that moisture does not get trapped?

    • hi Matt! phew, moisture is a tricky issue. except that we live in Arizona where there is about 3% relative humidity? so not a problem for us! haha.

      No seriously though, causing mold would be very bad, and you definitely want to avoid it. There are a lot of opinions on insulation and vapor barrier details, so make sure you ask a contractor / builder who has worked for a long time in your area.

      the foam board we used (polyiso) has a foil layer on both sides and acts as a vapor barrier, to prevent moisture from inside getting into the insulation / wall cavity. the dew point will happen on the outside, above our waterproofing roof membrane, where warm insulated roof cavity meets cold air, so that’s fine. we don’t want to install a visqueen vapor barrier on the inside of the ceiling as that just seems like creating a trapped moisture problem.

      I worked for a general contractor in L.A. on some big jobs and my superintendent was of the school of thought that walls need to breathe, because water can always get in, the question for mold prevention is can it get out? if it can’t get out, mold will grow inside the wall cavity. that being said, foam board is not permeable and does not allow air to move through the walls. so Tyvek is a must as it allows moisture to get out on the exterior.

      so, that was a long answer! and probably not very helpful, sorry… good luck finding the solution for your building. maybe get a few opinions, and foam board manufacturer’s installation instructions can be helpful because they are so worried about liability (and mold growth is a big one) that they are very particular about install methods.

      take care,

      • Matt

        Carrie, I will talk to some contractors and see what the insulation manufacturers recommend. I’ll be back with my findings, but with 3% RH you should be fine.

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  6. Victoria

    I live in Oregon….lotsa rain, cold in the winter and super hot (above 95) about a month a year…I’m looking to build my tiny house where it can breathe….have you thought about wool? I’m waffling between the stuff like you used and wool….any thoughts?

    • Well all homes should breath, that is part of what make a healthy home. So I guess I can not say which one is better, the only thing that I would say is that which one way more? and are you going to be moving it much?

      Hope that helps,

  7. Angela

    In a video I believe I saw that Dee Williams used wool in a tiny house in the Pacific NW, and the amount used in that house was insufficient for winter. You’d have to hunt the reference down yourself.

  8. Good tiny article. I enjoy the pictures and how you show how you did it.

  9. G’Day! Carrie,
    Thanks for your thoughts, building house in north karnataka, very tight budget. want to cut the cost in construction. some body suggested me to buy tiles with little damage (for floor) wholesale.. instead of contracter buy the tiles. while fixing … can cut the tiny damaged part of each. can i rely on this?

    • I’m sure you could use damaged tiles, just check in with the installer prior to purchasing, they might have an opinion on the overall material to labor costs…

  10. Van

    Total old school thinking…houses do not need to breath…people need to breath …tight homes are energy saving homes…VENTALATION…controled and proper VENTALATION will take care of health and moisture (mold) issues..

    • well, you’re right – using modern materials (stick framing, spray foam, OSB sheathing, house wrap, building paper, ) houses don’t need to breathe – but they are so tight that they do need to be ventilated. (HRV or ERV)

      however, any natural building materials do need to breathe… straw bale, cotton or wool, earth plaster, adobe… these will hold moisture and grow mold if air (containing water) cannot travel in and out of them.

      and where it gets tricky is that wood (framing & sheathing) is a natural material… so there are still schools of thought advising ventilation in wall cavities.

  11. susan

    wondering how long your tiny home has been finished? I live in Arizona (Tucson) and hope to build a tiny house someday to retire in and hope to park it in an rv park. I am guessing insulation is less of a factor in our climate than colder ones but I know it is still important and apparetnly pretty tircky to deicde on the bes toption. did you use an hrv or erv option?

    • we did not do an hrv / erv… we did have to use a window AC unit in Arizona and Santa Fe, FYI. tiny houses get very hot! unless you can park in the shade, they heat up like a car.

  12. Kalem

    I’m in flagstaff as well. Where did you get r19 and r30 foam board? All I can find is r13.1 from home depot. Any direction would be greatly appreciated.

  13. Rick Roberson

    How do you get R19 in wall when the foam value is R5 per inch and you framed in 2×4.

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