Floor Insulation Options: Sheep Wool, Cellulose?

by ziggy on October 23, 2011 -- 9 comments -- Follow

In pondering the floor insulation options for Strawtron, I’ve come to a bit of a question mark in the sheep’s wool department. Originally, I had planned on doing some light clay straw in the timber platform, between the floor joists, but I’ve come to acknowledge that the R-value of this method is lacking.

Light clay straw insulation values seem to clock in around R-1.5 per inch. For a 12 in. deep platform, that means about R-18 worth of insulation. However, recommended floor insulation in this climate is more like R-30! That causes me to do some reconsidering.

Other options include blown-in cellulose, or possibly sheep’s wool, which are pretty similar in their insulation values: about R-3.5 per inch.

I’m not crazy about blown-in cellulose, since it requires that a truck come in with a generator and do the work. Not my style. Also, not the most compelling of materials, even though it is recycled newspaper. But honestly, it could be worse.

I’m more intrigued by wool insulation, and apparently, in the UK and New Zealand, wool batting is manufactured for building insulation purposes. Now why doesn’t anyone in the US do that? It doesn’t seem practical to use loose wool to insulate a floor, between the cleaning, carding, and stuffing. There’s too much room for error. (Example: is the wool stuffed too lightly, or too heavily? All of that determines how effective it is.)

So I’m stuck. Is there some proven wool insulation methods used in floors? Is cellulose a better answer? Obviously, there’s rigid foam insulation, but that is the least appealing material, with its high embodied energy. Yeck.

Thoughts from readers appreciated!

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  • Rice-hulls. R-3/inch. If I am not mistaken, SE Missouri and Arkansas grow a lot of rice, so you could get some in-state, if not totally local. You could also grow your own rice and make hulls from that.

  • Kelly

    Hi Ziggy,

    I don’t have anything really useful to say, but I felt the need to commiserate. We just finished insulating the floor of our new house. It sounds like you’re going through pretty much the same thought process that I did. We started out wanting clay-straw, but the R-value wasn’t high enough. In my search for other materials I got really excited about the idea of wool. I have NO IDEA why wool insulation isn’t manufactured in the states! We finally ended up with a material I’m not really excited about. It’s a fiberglass batt made from recycled bottles that uses natural adhesives. It’s recycled, we didn’t need a generator to install it, it doesn’t off-gas anything nasty, and it’s actually manufactured locally. All of which is cool, I guess, but I still really don’t like it. I’m hoping we can find a better alternative for the walls.

  • Tim

    hey Ziggy:

    first off, I like to say I certainly appreciate what you are attempting to do and your building methods.

    As far as flooring installation goes, I have a couple comments. First, wool is a intriguing insulation. If it meets your R-value requirements, then your next consideration should include that wool has a unique features that it absorbs moisture (and still insulates) and then also gives back that moisture to the environment around it that is dryer than the wool. Hopefully what I just said made sense. This makes it uniquely wonderful for insulating certain parts of the interior of the house that are not exposed to cold walls. There are European’s that use this substance for the interior lining of cubicles and offices that are not air-conditioned– because of this property. In the summer — when it is more humid — the wool will absorb moisture, and whenever the interior air is drier — the wool gives back the moisture, and thus balancing the comfort level of the interior of the house. It is a wonderful natural substance to use — but she really had that gives close serrations to the moisture absorbing potentials of the substance.

    Secondly — if you are going to consider a floor insulation that is manufactured out of petrochemicals etc. — I would use spray foam on the floor insulation — it is much much more effective and faster than using rigid insulation for the floors. I have used both — and spray foam is just the way to go — and you can find on the Internet companies that will sell you spray foam kits if you want to do the job yourself. That certainly really lowers the cost of the spray foam — which can be kind of expensive to use — but much better in the long run. It does a much better job of sealing the air leaks — and also it provides some better sound insulation. another is at least one company that sells spray foam made from soy.

    by the way – I would love to see someone apply Wabi Sabi thinking to a whole house design.


  • The way I see it, you’re floor cavity will really just be a series of boxes, framed by your floor joists, with something on the bottom to hold it all up and your subfloor on top to close it in. While it may be something of a reversal of traditional construction, I fail to see why you can’t simply wait to put the sub floor on after it is insulated, allowing you to put in your “blown in” cellulose bag by bag manually. It means you’ll have insulated floors before you’re raising walls and roof timbers, but so what?

    In the same way, I believe you can get wool as loose fill for blow in methods that would work just as well. Remember to stuff those cavities tight. Air pockets between your floor and insulation are a bad thing, as is condensation with all of these.

  • Karen

    How about recycled jeans insulation? I don’t know much about how the cost (dollars and/or embedded energy) compares w/ other types you’re considering, but R-30 is available. I’ve had it filed in the back of my mind for years ever since I first heard of it — in case I’m ever in the position of being able to use it. Thanks so much for sharing your adventures!
    Available here…

  • Adam Atkinson

    Ziggy, check this out. Your readers may be interested as well. A stateside manufacturer of wool batt insulation. Several others out there too here and there.


    Adam Atkinson

  • Scott

    Make sure whatever you use for insulation isn’t bug food! That’s something I’ve always wondered about natural building-are insects/vermin more of a problem in that method of construction. Check local hospitals/colleges for *free* rigid foam! I work for a hospital, and could fill a boxcar with tombstone sized slabs of dense foam(easy to cut with a frozen food knife, filet knife or “hot wire”) in a year-it’s all thrown away-if you explain what you’re doing with the foam, they’d probably save it for you(transplant parts and some medicines come packed in it). Colleges and hospitals throw out amazing quantities of usable materials-it’s worth checking into if there’s a hospital/college nearby-even veterinary offices likely throw out a lot of foam. It already exists, why not reuse it?

  • Michael

    there is a substance that is all natural it is called rock wool insulaton and is made of minerals or molten rock and is a very good alternative to fiberglass or even some of the recycled paper type insulation Rock and slag wool insulation is tested to all applicable industry standards to ensure its R-value does not deteriorate over time.

    Loose-fill rock and slag wool resists settling, and batt products spring back after average compression so that the installed thermal performance is maintained over the life of the product.
    In fact, the higher density of rock and slag wool insulation allows it to achieve higher R-values than cellulose or open cell foam insulation when installed in wall cavities.Rock and slag wool insulation is naturally non-combustible (like fiber glass) and remains so for the life of the product without the addition of harsh or potentially dangerous chemical fire retardants.These products offer protection against damaging moisture infiltration that can reduce the R-value of insulation.

  • Adam: Fantastic! That’s what I’m looking for. I’m going to call this company and request more details.

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