Monday, May 9, 2011

Insulation investigation

Incredible sunset outside the shop last night

Today is one of the nicest days of the year. It is sunny, clear and warm out but somehow I find myself stuck inside on the computer researching insulation. I should have done this on one of those cold sloppy winter days. Oh well. They say you are not supposed to go grocery shopping when you're hungry, right?

Basically, I am ready to put my roof together. The 2x4 framing is finished, the paneling is back-primed and the sheathing is neatly stacked. All I need now is to pack the framing with some sort of insulation before I nail everything together. Last night I calculated the amount of insulation I will need. I have not done a good though comparison of different types of insulation yet, but my original thoughts were to use blown in cellulose. I want to avoid fiberglass for health/sustainability reasons. Cellulose is recycled, will fit all of my odd sized cavities and has a good R value. For the roof however, I need something lighter so that the panels will be a manageable weight. My first thought is to use EPS insulation (rigid boards of polystyrene, like foam cups). It is light, air tight an has an excellent R-value.  It may not be the most sustainable option, but it might be a reasonable compromise. The last one I am considering, which might work for the walls and roof, is spray on expanding polyurethane foam. It can be made with soy oil rather than petroleum and supposedly has no VOCs when it is cured. This is important for me, especially in a space as small as mine. There is no Formaldehyde in my house yet! Spray foam does have the best performance characteristics but with that comes the price.

That is what I am considering, but I would love to hear of other options that you might know of. It is far too nice out for me to be inside any longer, so the research will have to wait for another day! I'm off to caulk the siding joints finally.


  1. Ever thought of a free option? like wattel and dub ( which breaths and keeps warm) or straw bale ish Idea? Thached roofs are the best the house is cool in the summer no matter how hot it is outdoor and super insulated in the winter...Ive built with both methods and they work wonderfully, the singled roof just doesn't do the same thing I feel like plus those roofs last at least 50 years and wattel and dub is cheep easy and very quick plus it gives texture and would fit ur beams well...just my thought

  2. Thanks for the ideas. I definitely need to stick with something light in the roof since the panels are going to be removable. I am also set on the idea of a standing seam copper roof for the durability and because I love the look. You have me thinking on the walls though...

  3. I also really like wattle and daub or light-clay-straw. The moisture regulating benefits would be great in a tiny house. However, I suspect that given the low R-value it might not make as much sense in walls that are not massive. There is a company called Econest that has used light clay straw to great effect, but this is with a monolithic wall (enveloping a timber frame) roughly a foot thick. But then, maybe it would be OK with such a small space to heat.
    Aside from the weight being a hindrance to mobility, wouldn't cracking under road stress also be an issue?
    When I looked into spray on expanding foam, I found that it wasn't all it was hyped up to be. Even with the soy-based foam, the same nasty petrochemicals are required. The industry claim is that the toxic substances used become harmless once they react with each other. But what happens when the mix is not just so and you therefore have that unbound portion of said toxic chemical left in your wall? While researching I came across a few cases of people with chemical sensitivities who had to move after having spray foam installed.
    I also agree that blown-in cellulose is an all around great choice, but there may be one option that trumps it. Have you considered sheep's wool insulation? It will be more expensive, but the benefits are many:
    This couple has used wool insulation in their tiny house and talk in depth about their choice here:
    As for thermal mass, what about surrounding your wood stove with adobe bricks or something along those lines? I had envisioned a small rocket-mass-heater in my plans for a tiny house on wheels, but I think I will have to do a lot of experimenting before that would be doable. There is still a significant weight issue, but there is always the option of using less mass or making the mass removable for transport. This may give you some ideas:
    Since you already have a great wood stove, check out what this person did to get more out of their wood stove:

  4. I've heard of a cotton insulation-I think made from recycled clothes/cloth

  5. I second the sheep's wool option. Check out, who even have an organic fire-retardant.

  6. Sheep's wool is definitely a good idea and I agree with what the other fellows suggested. How did it go, Ian? And what did you use for your roofs insulation? Having a good insulation gives you a lot of benefits, such as lowering your heating and cooling bills and being confident that snow build-ups won't be a problem for you. One last thing, be sure to have routine checkups on your roof and insulation, so that you could see if some places need repairs.

    Lino Kosters