Need help with insulation for cold climate

[Seigan]

Hi guys,

I need your help to straighten out my thoughts about

insulation

. I direct my question especially to them of you that lives in your Yurts in cold climates where it usually get down to -20c in the winters but on cold occasions can get down to -30c and in rare and extreme cases down below -40 (once or twice a century or so)... What

insulation

do you guys use? If wool felt then what density and thickness do you use?

I saw one company saying that their felt of 6 mm thickness could with stand down to -5c and their premium felt was 16mm thick. When I have read about u-value it said that if you double the material then you double the insulation value. With that logic then 60mm of the 6mm felt mentioned would withstand -50c - but it is really that simple?

In a research paper on sheep-wool I found they state that 40 mm felt with a density of 40 kg/m³ would have a thermal conductivity of 0.034 at +10c (which is the standard temperature of measurement). Mineral-wool with standard density of 25kg/m³ and 200mm have thermal conductivity of between 0.036-0.040 (the lower the better, still air has 0.019 if I remember correct). The research paper also stated that wool of 80 mm thickness but 20 kg/m³ held a thermal conductivity of 0.040.

We are building our Yurt in the north of Sweden (climate similar to Canada and Alaska but perhaps not as extreme and not as wet as the north west US or the UK... Temperatures seems to be a bit similar to southern/middle Minnesota during winter, not sure on snow load and damp etc though). Our plan is to put our wool felt insulation between two sheets of Bison Weatherproof Sheets (that let out the moister to a very high degree but keeps water and wind away), creating kind of a "pocket" or "duvet" closed by strong Velcro, keeping the wool dry but still let it breath but keeping the wind out. Outside of this we have a bubble wrap double coated with aluminium as a heat barrier. But we have a hard time figuring out the density and thickness of the wool felt... We are going with a boiler stove and a water floor

heating

system also so we will not only have a regular wooden stove, for a more "smooth" and continues

heating

.

The building standard here recommend 200mm mineral-wool in the walls and 400 mm in roof and floor. So that must manage the temperatures down to -50c (as i can be in the wind in the extreme cases). The question that pops in to mind is what density and thickness of sheep wool felt would give the same insulation value? And how do we calculate it?

If one only see to the mass of the material (25kg/m³ of 200mm thickness weight 5kg) then a wool felt that is 35,5 kg/m³ (that is the same as a 20 mm thick wool felt that weight 710 g/m²) must be 155 mm thick to have the same mass. If we check how much density we must have if the thickness is 60mm to get the same mass then it is 83kg/m³. If we use 100 mm thickness instead then we need to have a felt with density of 50kg/m³ to get the same mass. To give it a comparison; the insulation used before mineral wool hit the insulation market like a bombshell in the 1950s was saw dust, wooden chips and splinters/fibres, often mixed with strips of newspaper, textiles and other fibres such as hair/fur/wool. That mix often held a density between 45-60kg/m³ (the older the more dense it became).

The upside of a high density insulation is that it in prevent natural convection (airflow in the insulation) giving it much better insulation capacity. But what is the downside? The only thing I can think about is that it will not hold as much hot air and hence have lot less insulation capacity... But is that really the case?

Research paper mention above show a relationship that if you have have a high density insulation then you can maintain the same thermal conductivity with a thinner material. With both higher density and higher thickness then the thermal conductivity should decrease (which is what we want). With that relationship in mind it should be the mass of the insulation that matters, not the density and not the thickness. But in another place (information about mineral wool) they said that sure you could compress the insulation and put in more material (to increase the mass and density) to get a lower thermal conductivity in theory but in practice it is the thickness that is important... That got me second guessing everything I though I understood...

So what is you practical experience of this?

Any tip to straighten out those thoughts will be gratefully received.
Thanks.
Cheers.

[Bob Rowlands]

IME the whole key to keep insulation from rotting and molding is to make sure it breathes. It is my opinion yurts were developed in the dry climate of Mongolia. IME tents do very well in dry climates, like ours here in Colorado.

If I am not mistaken the traditional Mongolian yurt covering is a light colored breathable cotton liner over the wall and rafters, then the felt layers, and finally a cotton canvas cover.

Moisture

'does not' get trapped, it can escape as fast as possible and the layers stay as dry as possible. Of course cotton absorbs water like a sponge, but it dries fast in the sun. It is not hydrophobic like synthetic materials, so it can breathe. It is my opinion this is the way to go, in a dry climate, because that has worked for Mongolians forever. All natural materials.

I don't know about Sweden, so your weather might be significantly wetter. I really don't know anything about alternative insulations, wet climates (ours is dry like Mongolia) or more sophisticated up to date cover and insulation for such climates. FWIW there have several reports on this forum of problems with wet insulation and covering. I wish I had better advice yo give. Good luck to you.

[Jafo]

If you want my suggestion, perhaps keep the breathable insulation and instead go for a more powerful heat source. I have seen it over and over on this forum where people go crazy insulating their yurts only to be buried in black mold.

I'm not saying you can't insulate tighter, but you do need your yurt to breath. Concentrate on insulation under the foundation (if off the ground) and around doors and windows.

Just my two cents.

[Joe Chapman]

Yes, get that floor well insulated if raised. Cover gaps around the door, breathable material but most importantly, a good stove and lots of seasoned fuel.

[Seigan]

Hi guys.

Thanks for your advice.

Our intention is to use breathable materials. The Bision Weather Protection Sheet that we use is a very breathable material that act kind of Gortex but for buildings. The reason we want to use that as a cover around the sheep wool is to minimize exposure form outside (wet canvas, condense along the outer cover etc), keep the air inside more still (gives better insulation) and the last reason is to help keep bugs out (might not be fool proof but it will certainly help),

With this "breathable" approach we are a bit concerned though that the reflective coated bubble wrap might become a liability rather then a help as it might block the moister in the way out... But we do not know. So we are still a bit uncertain if we will use it or not.

I am not in the least worried about the floor insulation. We have 17cm of wooden fibre insulation and on top of that we have floor radiating heat system (pipes with hot water flowing in the floor). Also checked with local crafts men to see if they think the floor will be warm enough in our climate and all have given thumbs up.

We got all the gaps in and around the door covered (pun intended) and with both wind and water proof as well as breathable foil. And the parts of the door that will not be covered with the felt insulation is insulated with the same wooden fibre insulation we have in the floor. The door it self is also insulated, have three glass window and there is a rubber strip around the door opening to prevent cold air coming in. It meats all the building standards of an ordinary home here so that will not be a problem.

Neither are we worried about the size of our stove. We both have a 15-20kw stove boiler in the middle of the Yurt as well as heat solar panels (both water and air), a "dung heap heating system" and a heat recycling system on our out going air - all connected to a 500 L heat buffering tank that will heat up the floor heating system. I know people that heat 200m² houses with similar set-up with no problem at all and we have just 50m²- Therefore we are pretty confident that we will have more then enough heat generated - if we only can keep it inside.

Our biggest question mark regarding heat and insulation at the moment is the thickness and the density of the sheep wool felt insulation - hence my question above.

So to you that live in a cold climate (no matter if it is wet or dry) what kind of insulation do you use? If you use sheep wool felt what density and thickness do you use?

Thanks.

[hierony]

Hello Seigan,

Wow. I suspect you'd have enough power there between everything to keep even a simple tent hot! Of course, you didn't mention the size of your yurt...

One thing to keep in mind about condensation--it happens wherever the temp is low enough for the given amount of water vapor that is in the air (the dewpoint). In any wall there is a temperature gradient from hot to cold (inside to outside in winter). If water vapor is free to move all through the wall, it will condense where it meets it's dewpoint.

There are two ways to keep vapor from condensing in your wall--either keep the dewpoint of the inside air below the outside temperatures, or keep the water vapor out of the wall. Standard construction usually does the later (imperfectly but generally adequately). Yurts can't really do either easily or comfortably. If you can avoid accumulating too much

moisture

(showers, dishwashers, etc, avoided or vented directly outside) and vent the general air some (around 1-2 air changes per hour?), you should be able to avoid mold. I've also heard baking out the yurt once a week or so in cold/wet weather is advisable--and you have the power necessary to do that!

In terms of felt thickness & density, I can see scientific arguments going a few ways. To some degree, anything light & fluffy will compress some under the weight of your outermost layers. In terms of density of felt, think of it as many hairs/wires in a mesh--the path for heat to follow is very long & narrow and forked pathways are limited. The more you smash it together, the less air there is (best insulator aside from vacuum) and the more the fibers touch and have multiple heat pathways. But there could be some small details that become important at certain densities or with particular materials.

I might suggest contacting Groovey Yurts. They have been very informative, even when you aren't making a purchase. They use wool felt for insulation and could likely give you some numbers.

I haven't gone through winter living in my yurt yet (I'll let you know in a few months :P)--I have some wool blanket material as insulation that will get layered up. My yurt was however setup one winter and I can only second what's already been said--keep unintentional air leaks to a minimum.

Hope that helps some!

[Jafo]

Our temps get to the same as you describe. The bubble wrap foil is more than adequate in our case. Zero condensation inside, though I do get icicles outside.

[Seigan]

Originally Posted by hierony

Wow. I suspect you'd have enough power there between everything to keep even a simple tent hot! Of course, you didn't mention the size of your yurt...

Hehe yea that is the thought We have a 8 meter in diameter, 50 square meters and 5 meter high yurt. It is not a traditional one as you can see on the meassurments. We are trying to adjust it to the climate it is in. Better to be pragmatic the idealistic in this case

Originally Posted by hierony

One thing to keep in mind about condensation--it happens wherever the temp is low enough for the given amount of water vapor that is in the air (the dewpoint). In any wall there is a temperature gradient from hot to cold (inside to outside in winter). If water vapor is free to move all through the wall, it will condense where it meets it's dewpoint.

There are two ways to keep vapor from condensing in your wall--either keep the dewpoint of the inside air below the outside temperatures, or keep the water vapor out of the wall. Standard construction usually does the later (imperfectly but generally adequately). Yurts can't really do either easily or comfortably. If you can avoid accumulating too much moisture (showers, dishwashers, etc, avoided or vented directly outside) and vent the general air some (around 1-2 air changes per hour?), you should be able to avoid mold. I've also heard baking out the yurt once a week or so in cold/wet weather is advisable--and you have the power necessary to do that!

Thank you for that, that helps alot. There is one sheet used here called "vapor slower" that is used on the inside of the insulation to hold the vapor from the inside on the inside to be vented out as well as forcing any other possible vapor to go out instead of in. Also sheep wool can buffer up to 35% of its weight in moister without problem. So if we put the "vapor slower" on the side of the envelope facing inward and the weater protection sheet facing outward then the wool insulation will have very little exposure of vapor. At least in theory...

Had not thougt about using the vapor slower, just have it all "vapor open" from the inside to the outside (and not the other way around) to let it all out passing through the wool on the way out. But if it will condence in the middle any way then that is just a bad way of doing it. At least if there is a good ventilation system avaiable, which we hope to have.

We will have one outlet in the kitchen area and two in the bathroom and thoose two will be mechanic. We will also have a inlet high up on the wall (take in cold air the fall down mixing with already hot air and warm up, making no cold draft). We will also be able to, as so many others, open up the

dome

and vent that way. I am also wondering if we should have some sort of more permanent and weather proof outlet vent up there (other the open the

dome

up) or not.

Today We only have a outer cover of PVC tarp (do not breath at all) and a inner liner of the Weather Protection sheet and we let it stand unattended for 6 months over winter as a test. I had dark moldy nightmares and when we open up six moths later a smell hit our faces, of fresh wood a fresh air!! Even during damp weather it is very dry inside, and now we have no vent at all...

Any how Thanks for making me think in differrent ways!

Originally Posted by hierony

In terms of felt thickness & density, I can see scientific arguments going a few ways. To some degree, anything light & fluffy will compress some under the weight of your outermost layers. In terms of density of felt, think of it as many hairs/wires in a mesh--the path for heat to follow is very long & narrow and forked pathways are limited. The more you smash it together, the less air there is (best insulator aside from vacuum) and the more the fibers touch and have multiple heat pathways. But there could be some small details that become important at certain densities or with particular materials.

What you say seems very logical but that wouldhowever not explain why the higher density seems to demand less thickness to have the same thermal conductivity (as it is cunductivity you explain).

Originally Posted by hierony

I might suggest contacting Groovey Yurts. They have been very informative, even when you aren't making a purchase. They use wool felt for insulation and could likely give you some numbers.

thanks a million for that tip!

Originally Posted by hierony

I haven't gone through winter living in my yurt yet (I'll let you know in a few months :P)

Ohh please do!

[Seigan]

Originally Posted by Jafo

Our temps get to the same as you describe. The bubble wrap foil is more than adequate in our case. Zero condensation inside, though I do get icicles outside.

Ohh cool!

Do you have any membrane/liner on the inside to keep the condence outside?
How fast do it get cold after the fire has burnt out?

[Jafo]

Originally Posted by Seigan

Ohh cool!

Do you have any membrane/liner on the inside to keep the condence outside?
How fast do it get cold after the fire has burnt out?

There is a small liner on the inside, but it is mostly cosmetic.

Once the fire is out, it gets could within a few minutes. Probably a good idea to have a propate/NG backup.