Choosing Floor Insulation

[conantum121]

I am installing a 24ft. Pacific Yurt, Winter

Insulation

package for walls and roof, 4*6 beams sitting on 4*4 posts, 1&1/8 ply floor. Im in Northern California: hot summer, cold and wet winter. Im looking for advice on the best

insulation

for the floor. I've heard a lot about the rigid foam. Im interested in non-toxcicity and insulation value. Is there an effective eco-friendly option that won't get moldy and attract critters? Vapor barrier recommended? Thank you.

[hierony]

I'm a fan of straw bale platforms--nice and thick insulation. It won't mold IF kept dry (ie, don't let water pool on it, make sure water drains away from your platform; potenially seal with stucco). I don't think you could easily use this for your framed platform though.

Sheep wool might be an option. Somewhat spendy but there are a couple places that market it as such. Often treated (w/ simple boron salts) to deter wool moths. Naturally flame-retardant. Available loose or in batt form. Some small local sheep farms might have a bit stashed away available (may not be washed or processed or treated)--contact your local sheep shearer for names.

I've also seen websites selling hemp insulation, cork insulation, shredded newspaper/cellulose insulation, cotton/denim insulation. I know cellulose is often used, denim sometimes used in normal construction.

There's one or two manufacturers that claim their glass wool or mineral wool is eco, for what that's worth. I count eco as something that *will* mold/attract critters, in the right circumstances. The trick is to prevent those circumstances (moisture accumulation, mouse access/population).

Moisture

barriers, keeping things off the ground away from water/mice, getting a good mouser cat, wormwood to deter moths, are all ways to prevent said circumstances

You might also consider a different platform style--a slab foundation under a raised platform would allow you to entirely enclose the slab (effectively preventing critter infiltration), place whatever type & quantity of insulation you want down there, plus give you storage space.

[Zelig]

Originally Posted by hierony

I'm a fan of straw bale platforms--nice and thick insulation. It won't mold IF kept dry (ie, don't let water pool on it, make sure water drains away from your platform; potenially seal with stucco).

I'm interested in your strawbale thoughts. I'm guessing from your picture that you are using this for your floor? Did you lay your bales right on the ground or build it up somehow? Did you use any vapour and/or

moisture

barrier(s)? Do you have any issues with surface water when it rains or snows? Any other tips or realizations would be appreciated as we are awaiting our GroovyYurt this spring and are debating the various floor options.

[hierony]

Hello Zelig,

It was actually from Yves of

Groovy Yurts

that I learned about the strawbale platforms--he's posted on the forums about his setup. I emailed him for more details--I'll share what I learned/he said (he's more verbose in french). I also have a few photos of my setup in my album. I started with a rectangularish platform which didn't work well, then rebuilt it circular to fit under the yurt (much better).

Yes, I am using the strawbales--I like them because it will be completely movable and I won't leave gravel or cement piers or holes behind, just a bare spot (the original meaning of 'yurt'). It also keeps the yurt above groundlevel, so no worries about water or snow getting inside. Of course, don't setup in a low spot with poor drainage where water will collect into the bales. Yves said he didn't have problems with moisture in the bales at all, that they looked new when taken up after two years.

Levelness: I was lucky to have an old asphalt pad already level for me--except for a tree root or two pushing up the asphalt in one corner. The bales did not smooth out the root bumps--I would recommend making your 'base' as level & smooth as possible/reasonable (<1" deviations). Yves suggested putting down a layer of gravel and then an 'earth sheet'/plastic layer to really do things right, but he didn't have the time during his setup. I didn't use anything under my bales (except asphalt pad).

Arrangement of bales is important--the yurt on top protects the bales underneath from weather. Anything sticking out will get water/snow on it and potentially mold. I made this mistake initially--I arranged my bales as a square inside the yurt circumference with the outermost bales sticking out (plus my OSB sheets stuck out initially, too). Then it rained, they got wet and the bales molded some Below is what I'd make from scratch--I think my setup actually has two or three circular layers instead of just one though.

Start by putting two bales in the middle with a rod/stick to define your center; use a rope/board to scratch the outer circumference. Tie a rope/cord the circumference length--paracord would be sufficient & cheap; ratchet straps are overkill. Knee/kick the outer ring of bales to fit the curvature & use the cord to hold your circumference. Then stack outwards from the center until you can't get anymore whole bales inside your outer ring--fill the gaps by stuffing with portions of bales. Make sure everything is level--adjust with bale flakes as need be.


Plastic sheeting--I originally had 8 mil plastic between the bales & OSB. I was planning on tucking it up inside the canvas under the lower rope once I cut the OSB circular, but it caught water before I got it setup that way. A couple spots on the OSB started to mold, plus a fair number of bales underneath got water through holes poked by straw/screws and started to mold, too Once I noticed this, I rebuilt circular and omitted the plastic sheeting.

Platform--Yves used 1/2" plywood sheets, I used 3/4" T&G OSB (11.5 sheets for my 20' ger). A little thicker would probably be good to reduce flex. Plywood is probably better than OSB (better water resistance/less edge swelling, less outgassing). I tried using screws though the T&G joint to hold everything together but it didn't work. Similar to Yves's setup, I ended up using 1x3 (furring strip) underneath all the joints to screw into to hold everything together. This picture shows one way to do this--perpindicular pieces would be required if not using T&G. Cutting the platform close to circular is essential (it'll catch water and cause problems otherwise).

Drip edge/border lip/skirt--with a traditional yurt like Groovy's, you'll want to have a drip edge/border lip/platform skirt. It'll keep the lattice on the platform in *very* strong winds; with the canvas & vapor barrier outside it/insulation & liner & lattice inside it'll help seal up the yurt; and also gives an exact diameter for setup purposes. I initially ignored this, but am going to install one shortly. I'm not sure what Yves used--maybe thin plywood? I'm thinking of using 1/4" tempered hardboard cut ~6" tall in ~2' long sections, screwed into the 3/4" thickness of the OSB.

As for critters (mice/insects), Yves didn't have any problems but he also had a cat. When I was rebuilding everything circular after the water problems, I did notice earthworms under the moldy bales. I'll probably be moving my yurt here come June, so I can report back on what's underneath :P I also have a design for a modular T&G board (pine or cedar) platform in place of the OSB, but need to test it first. If you really wanted to seal everything up, you could stucco the outermost side of the straw bales and glue/seal all the plywood joints. With just the canvas (no liner, no insulation, not a great seal between the canvas/platform edge but the crown ring covered) the yurt'll warm up with my 15-25 kbtu/hr propane heater in ~40 minutes.

Oh, each bale was $2.75 each, ~1'x3'x1.5' direct from farmer. I think I got wheat straw but there may have been some barley straw, too.

Let me know if you have anymore questions.

[Jafo]

My question about straw bales is, don't they eventually rot? How long do they last?

[hierony]

You know, some people have made entire houses out of strawbales Internet says/rumor has it there are strawbale houses over 100 years old. Mind you, these would be sealed with plaster/stucco--if you keep the moisture (and vermin) out, you keep the mold/rot out.

My yurt and the few other pictures that I've seen with strawbale platforms have covers that hang down below the platform at least a couple inches (up to a foot)--the yurt covers and helps protect the bales from rain. For plain bales, I'd guess anywhere from 2 to 5 years durability (unless they get wet during building). I think this is a great setup for temporary or short term yurt locations. Also almost dirt cheap (20' yurt: $200 straw, ~$200 plywood + screws + furring).

If you want something more permanent, you'd have to seal the outermost face of the straw with stucco/plaster, maybe put down sand and a moisture barrier underneath the bales. In that case, it'd probably last the life of the platform/yurt if sealed correctly.

[Zelig]

Thanks Hierony for your responses. Unfortunately for me, a bale costs about $6 CDN, but that is still within reason for the R-value, simplicity and non-toxicity value. Also, if the straw spoils it is still of value to us as mulch for gardens. My biggest concern is the water. We have a pretty level piece of land with heavy clay and in the spring and fall it gets quite wet, so I'd have to pick an elevated area and probably build it up a bit more with gravel.

[Jafo]

Well, toxicity aside, what about wrapping the bales in that plastic they wrap round bales in?

[Zelig]

Originally Posted by Jafo

Well, toxicity aside, what about wrapping the bales in that plastic they wrap round bales in?

I'd think tyvek or similar would be better in that it allows the bales to breath.

[hierony]

As long as you don't have any moisture sources inside/under/on top of your bales, you probably could just seal with any available plastic (UV stable). Tyvek would allow things to breath, but water vapor could get into the bales that way, too. [Tyvek is basically just a specially-made polyethylene tarp; it blocks convection/mass air flow & liquid water but not water vapor going either direction--not rec'd for humid environments].

Zelig, it sounds like you have a pretty tricky landscape. If you're Northern Ontario with a wet clay soil, do you get ground heaving during the winter? What's your biggest elevation difference? How deep is the frost line? Are you trying to go light, cheap, and simple? Or as insulated as possible for reasonable cost? DIY or professional construction?

SeverTheTether's setup for Northern Minnesota looks pretty nice, albeit spendy. They insulated the walls in the space between their slab & platform with spray foam I believe, and it sounds like they're pretty warm for it. You could probably replace the crawlspace siding/spray foam with straw bales if you sealed them with plastic/tyvek.

A two course (~11"/28 cm) circular retaining wall back-filled with gravel might do the trick raising you some. Est. cost for 6m/20' yurt is $300-600 for materials.

Somebody had the idea to combine earthbag foundations, scoria/lava rock, and yurts already. If you have lots of clay already, you might consider a cob foundation or such, too. Lots of options if you get creative!