A few fun facts you should know before embarking on your rigid insulation adventure:

1). It’s a sticky, disgusting, toxic mess that never ends.

2). I can’t even donate my clothes to Goodwill after using spray foam. They’re destroyed.

3). There’s always another gap or crack that needs foam. Have I mentioned it never ends?

4). If you screw it up, you’ll be shivering in your bed for years to come in between unpleasant nightmares about cracks and holes…

5). You WILL get it in your hair, face, eyes, nails, mouth, hair, feet, wrists, neck, and hair.

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Still want to insulate your tiny house?

Of course you do! I mean, you kinda have to do it. I’ll explain our process and you can either mimic us (but hopefully with a better attitude), or you can spend more money, buy wool, or get your insulation blown in and save yourself the headache. The choice is yours.

We used rigid foam insulation. This is readily available at Home Depot or Lowes and is sold in a bunch of different varieties. We purchased 1″ and 2″ R-Tech boards to fill our 3-1/2″ framing.

GOAL: To have insulation flush with the house’s framing without any holes or cracks. If your insulation is not flush, or protruding out, your interior paneling will become warped. THIS IS NO BEUNO.*

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Make it flush!


STEP 1). Measure and cut both a 1″ and 2″ board to fill your framing. We chose to sandwich the boards against each other with the radiant barrier (or reflective side) of both boards facing outward.

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Mom was definitely the champion foam slicer. Thanks Mom!

Build Tip:

Leave yourself a 1/2″ gap between your boards and framing. Also cut around any wires and plumbing. Secure wires to your framing when possible.  

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Make sure to cut around wires and add nail guards to protect them

STEP 2). Spray “Great Stuff” (expanding foam) into the gaps.

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Use spare wood to hold your foam boards in place

Build Tip:

Always wear protection gear. This “Great Stuff” can be nasty stuff if you get it on your skin. Remove any debris you don’t want to forever be incased in your walls. Spray along the gaps of your boards. Spray slowly! Great Stuff can expand over the next 10 minutes, so less is more. Use spare wood to secure your foam boards in place if necessary. Spray foam can get behind the board or wire and expand more than expected and, once it’s dry, your insulation will be frozen and protruding past your framing. THAT’S REALLY BAD!!* 

*So the worst has happened: your foam boards have pushed themselves out beyond your framing and frozen in place. Well, don’t panic. I’ve been there. Your next step is to dig out your wires (carefully) and to shave your boards down to become flush with your framing. Meaning you will lose time, patience with yourself, and your board’s radiant barrier. Shave a spare board’s radiant barrier off and glue it to the naked board fused in your wall. It’ll do.

STEP 3). Trim the excess dry spray foam.

Build Tip: Once your spray foam is dry, use a sharp knife or saw to trim the slack. We actually sharpened a putty knife and that seemed to work pretty well. Now that your insulation is flush with your framing, without any holes, you can attach your interior siding.

**Did you get it in your hair? Try soaking your scalp in olive oil… not that we learned the hard way or anything.

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He maybe needed a haircut anyway… 🙂



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  1. January 24, 2018 / 3:12 pm

    Could you avoid spray foam all together if you tightly fit boards in the cavity and tape all seams?

    • January 29, 2018 / 11:39 am

      The idea with foam is to create a sealed house. If you don’t use the spray foam, you won’t have a seal a your R-value will go down.

  2. Maureen C. Allen
    August 31, 2017 / 9:17 am

    Never a more persuasive argument for hiring a pro–yuck! And thanks. What’s your position on SIPS (structural insulated panels)? Do they require supplemental insulation? (I’m in the north GA mountains: 90+ degrees summer, 10 degrees winter)

    • September 5, 2017 / 5:10 pm

      SIPs are great! But you will have to have your design all figured out and have the panels made. They do not require extra insulation, but extra is always nice is extremely cold climates. SIPs can also be pretty expensive, so keep that in mind.

  3. December 16, 2016 / 11:44 am

    How is the insulation during the winter? Warm enough?

    • December 16, 2016 / 2:49 pm

      I wish I had done spray foam. It’s fine, but more is always better.

      • Mochi
        December 31, 2016 / 3:12 pm

        Because it’s not warm enough? Or to save all the work of using rigid?
        I got a quote for closed cell spray foam and it’s $$$$… But I run cold and it’s important that I’m comfortable! Do you think rigid is enough to stay toasty in a mild(ish) climate, or is just worth the splurge?
        Also, I had been planning on using 2″ + 1.5″ rigid to fill the entire 3.5″ cavity… Why leave a half inch of space?

      • January 3, 2017 / 12:09 pm

        Rigid is fine for mild temperatures. Even cold temperatures if done right. I just don’t like mine because it was a pain to install and it’s not as much of a vapor barrier as spray foam. The 1/2″ recommended was for the sides (cutting within the studs). You will use great stuff to fill the gaps and cracks and it expands.

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