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This is a "derived" question from What is the most sustainable heating strategy for a home? .
When talking about a home that has to withstand cold winters (-20 C), insulation is a big part of keeping this home sustainable. So if I am looking for a new place to live, or if building a new one, what is relevant "insulation wise"? Does the material used to build the walls have a big impact? Brick vs Wood for example?
Short answer: The average R-value of the building shell is the most important thing to consider whenever the outside temperature is going to be very different from the inside temperature.
Long answer: In new construction, you can build your walls thick and fill them with insulation, or even use structural insulated panels instead of traditional materials. You can just pick your favorite insulation and make sure the walls are designed to use it effectively. From a heating standpoint, it doesn't really matter if you use fiberglass, foam, insulated concrete forms, or blown-in cellulose as long as the wall assemblies have the R-value your looking for and everything is built and installed correctly. In a cold climate, reducing heating fuel consumption will have a far greater impact over the useful life of the insulation than choosing "green" materials. That said, some materials are clearly more sustainable than others. Refer to Zach's answer for more information on that.
If you're buying an existing but under-insulated home you might want blown-in cellulose because it can be installed in uninsulated cavities without tearing apart the wall. It's also very simple to add a layer in the attic. If/when you need to replace the siding, you might want to install foam boards between the wall and the new siding. Foam boards are also a good option for masonry or concrete walls. Wood-framed structures will probably give you more options for adding insulation than masonry or concrete walls will because wood-framed walls have cavities that can be filled with just about any type of insulation.
Also keep in mind that insulation only prevents heat transfer through itself. Studs between insulated cavities will conduct heat better than you'd like no matter what. Ideally, your home will have a continuous "shell" of insulation that is broken only by windows, doors, plumbing penetrations, and exhaust outlets/air intakes. That said, some insulation is better than none, and at some point the cost just isn't worth it unless you have a whole lot of money to throw around.
This is a deceptively simple question. Most of the complications come from your interpretation of sustainable. Let me give you a quick summary and explain why it isn't enough:
Fiberglass insulation is the most common these days. It is easy to install. However, it is not healthy to breath, so the installer must wear protection to avoid contact with skin and inhalation. It has higher embodied energy than cellulose (970 MJ/m^3)
Blown Cellulose (dry) insulation is not as common these days since it settles. This causes the top of the wall over time to become not insulated at all. For a diligent home owner, and depending on how the wall was constructed, this can be fixed by periodically adding insulation from the top of the wall. However, this problem is harder to deal with when there is compaction under windows and other places where it is hard to access later. It has lower embodied energy than fiberglass (112 MJ/m^3). This can easily be used in attics where settling isn't much of a concern.
Wet Cellulose (wet) insulation is very similar to blown cellulose except that it is blown in wet so that it binds to whatever it hits and doesn't settle over time. This is fairly standard, but can only be around 4" thick before you have to start embedding some plastic or other support to help hold up the insulation. It is string enough to not sag, but not when spanning large gaps.
Styrofoam insulation is often used under foundations, but also in walls. It is strong and easy to install, but the manufacture still creates many harmful chemicals, to both those manufacturing it and the general air quality.
Rice Hulls can be used in a similar was as blown cellulose and has similar problems. It can settle, though I haven't been able to find anyone saying how much they settle. It is also an agricultural waste product.
Spray Foam is often used to fill in lots of gaps and is great for sealing your walls. A lot of heat is lost through tiny cracks in walls, around windows, etc. Spray foam in these places can be especially helpful. There are many spray foams available, some claiming to be 'green,' which one is most sustainable could be its own question. Most spray foam is toxic enough that there are warnings on the label saying you shouldn't let it touch your skin.
Sawdust was used a long time ago, but has since been replaced by blown cellulose.
Trade Offs Do you consider small amounts of ozone 'unsustainable?' What are the trade-offs between ozone depletion and embodied energy (styrofoam vs fiberglass)? What are local labor costs? If one insulation takes twice as long to install, perhaps you'd have been better off installing the easy/cheap one, and putting the rest of the money in solar panels, organic food or any number of other places. Extra thick walls to support extra insulation will (depending on your wall construction method) require extra wall material (wider studs in a framed wall). That could also be factored in.
Thermal Mass Another thing to consider is thermal mass. It is helpful to have things like concrete, earth, brick and water inside (or a part of your inside wall). This is most helpful in places which have large temperature swings. In these places if it is 70 during the day and 20 at night, your thermal mass can hold your house at daytime temperatures all night, without having to turn on the heat (and visa-versa in the summer with cool nights). In places where the swings are less, thermal mass is less important, though still helpful.
Air Tight Even if you have highly insulated walls, small gaps which let outside air inside and visa-versa can have a huge impact on heating/cooling bills. Some insulation types are better at preventing these kinds of gaps than others.
Strawbale is one of the most sustainable methods. A bale wall runs somewhere between R20 and R40 depending on whose lies you believe. (Building With Bales)
Straw is a byproduct of grain production. (Wheat, oats, barley, rice,...) and bales can often be had for little more than the price of running a baler and buying the string. Typical costs when I have bought bales is about $2/bale. Each bale is about 3 square feet of wall.
There are bale houses in Nebraska that are over a hundred years old.
There is a lot of detail work to a bale house. The net effect is that commercial houses built this way cost 10-20% more than conventional construction, but use a small fraction of the heating energy. In many climates the waste heat of human activity will keep the house warm down to below zero temperatures. (CREST Strawbale mailing list, yahoo group http://groups.yahoo.com/groups/SB-r-us/
However a large fraction of shell of the house is DIYable after attending a couple of workshops or wall raisings.
Note that bale roofs do not work well. At this point blown cellulose is the common practice for attic spaces, and styrofoam, PU foam is used to decouple foundation from ground.
Some people who are building straw-bale houses here in Denmark uses mussel shells (http://upload.wikimedia.org/wikipedia/commons/thumb/4/45/CornishMussels.JPG/1280px-CornishMussels.JPG) for insulation between the ground and the floor.
I believe wool is one of the best insulation materials available. It does not affect your indoor air quality, it is available in batts and can be installed as easily as fiberglass insulation (without compromising the health of the installer!). Wool will not settle like cellulose, it will continue to insulate even if it gets damp, and it has a natural resistance to fire, mold and pests (many insulation types contain chemical additives for these purposes).
Many areas have a source of local wool, however there are currently few companies producing wool insulation. Currently, transportation may add to the embodied energy of using wool insulation in your home.
One of the most efficient insulation materials I know is foamed polyethylene with aluminum foil on one of the sides. It provides good heat insulation while providing sound insulation. In any case you need to calculate actual heat transfer ratio of the insulation, cost of insulation upgrade, how much you will save taking into account cost of the insulation upgrade and risk of breaking your neck while upgrading insulation. Anyway, if there is any kind of risk that you'll break your neck while upgrading insulation, you need to hire someone to risk their lives, so allow for additional insurance costs :-)
The neighbours. The first insulator you must struggle for are the neighbours. I know that what I say is the a socialist (i.e. antihuman and anti-natural) terror but you must live compactly in one house with many many people must live in your house and you must consume the leaks of each other through the walls. It is a common misconception that you do greener if you take some territory in suburbs or wild forest where you build a house, stick American flag there, and start polishing the grass lawn. It must be better since you use better materials than the multifloor block of flats does. Right? Though this trick is typical, let's be fair and assume that we use the same good insulation everywhere. So, instead of using a lot insulation materials (it is greener to use more materials, right?), you should start by minimizing the perimeter of contact surface between temperatures.
I know that bees do not freeze in their hive without any heater and poor insulation when there is -20 around. Furthermore, insulation-by-neighbours reduces all other factors of your ecological footprint and allows for additional efficiency of heaters: densely populated city can be supplied with efficient public transport in place of private cars, which is 10x more efficient alone when there is a lot of people to use it. Furthermore, cars will not fit there because city has shrunk 10-100 times and thus, distance has shrunk correspondingly. This means that you need to maintain orders less communications: roads, water, electricity, other cables, and nullify the light pollution accordingly. Shorter distances also make heat electropower stations practical, which further increases efficiency by 30%.
You can downvote now. I understand that what you actually looking for is something different, the isolation from the neigbhours.
We used wool. Waterproof, fireproof and very warm
