Now that I have sorted the toilets out I have gone back to thinking about the pros and cons of laying insulation under the floor of the building.
The Fundamental Conflict
I have been struggling with this issue since starting my house design. In a standard house floor insulation would be a no-brainer. Insulation is placed under the floor to prevent the warmth built up in the interior of the house from being leached away into the somewhat colder surrounding earth during the winter months.
Earthship purists argue that floor insulation cuts your building off from the massive thermal battery also known as the Earth. Consequently, although your bermed building has substantial thermal advantages over a typical stick framed house, it is not taking advantage of the earth’s constant temperature and is consequently missing the boat (or ship so to speak).
To me this insulation issue has two practical realities; physical comfort, and the energy consumption required to maintain the house’s environment at a livable level.
Typical house construction achieves physical comfort by using energy (fossil fuel, electric, wood) to maintain the inside of the building at a comfortable temperature. Take away the energy and the building quickly matches the surrounding temperature (frozen in the winter, and really hot in the middle of summer).
Our current house (two 1970′s era 10′x30′ office trailers placed side by side) adequately demonstrates using lots of energy to maintain a comfortable inside temperature in the winter. The walls and roof are very poorly insulated. Last year when it started warming up in the spring our ceiling developed ‘leaks’, despite having been re-roofed recently. In spots the roof insulation and vapour barrier is so thin or non-existent that the warm moist air rising through the ceiling condenses and forms ice between the ceiling and the roof. Presumably when the ice gets thick enough the formation of ice drops off because it is now insulating the ceiling! In the spring this ice melts and leaks back into our living space. We heat with electricity and due to our poor insulation we spend a lot to maintain a comfortable temperature in our 600 sqft.
A typical house built today has better insulation but the problem is the same. If the energy is shut off the house rapidly becomes a really well insulated (by current standards) ice box. So, we achieve a comfortable living space at a high energy cost.
The approach taken in earthship design is to passively heat the house with solar power stored in thermal mass. The idea is to achieve a comfortable living space at no or minimal cost. The issue becomes one of defining comfort. By today’s standards comfort means a constant inside temperature in the neighborhood of 20 degrees celcius.
I think comfort may need to be redefined when high energy cost heating is limited. The reality is that the inside temperature will fluctuate somewhat (say in a range from 15 degrees celsius to 22 degrees celsius). This implies a willingness to use sweaters as required or supplementing the passive heat actively when the solar gain is not enough due to cloudy periods or cold snaps.
In many parts of the world a home that guaranteed a livable space with minimal energy might be considered a slice of heaven on earth. As little as 60 to 70 years ago many people in North America would have whole heartidly agreed. We have been spoiled by cheap energy to the point that acceptable comfort is quite rigidly defined!
This comfort versus energy usage trade off is highlighted in cold climates by the issue of floor insulation. Without floor insulation the building taps directly into the constant heat sink provided by the Earth, thus making the building easy to heat. In fact, you could probably lock the door on your building for the entire winter without taking any precautions with regard to frozen pipes or frost/water damage. The constant earth temperature and passive solar gain will guarantee that the living space maintains an above freezing temperature. The trade off for this low maintainance living is an inside space with fluctuating temperatures and a cold floor.
What Other Thoughts Exist on this ?
Still not feeling comfortable with this insulation issue, I read fairly extensively over the last couple of weeks to get a better handle on it.
Turns out a bermed earth house builder named Rob Roy has built earth bermed housing both with and without floor insulation and lived in both buildings. His buildings are both close to the Canadian border in New England so the winter temperatures he is dealing with are similar to ours. He documented his experiences in two of his books that I listed in the references. His first building had no floor insulation and his second one did.
His take on insulating a bermed building is very pragmatic and dependent on your climate (he differentiates between the northern and southern states). In a warm southern climate your primary goal is to maintain a cool inside climate during hot weather. Using no insulation under the floor of the building makes sense as the earth’s temperature acts as a passive air conditioner.
In northern climates your goal is geared more towards maintaining a warm inside climate during cold weather. Quoting from Earth Sheltered Houses, “Without insulation … the fabric of the building becomes one and the same with the earth’s mass … In order to control the mass fabric of the home itself, we must place the insulation between the home’s mass and the earth.” He is re-stating basic thermodynamics and his argument makes a lot of sense.
I suspect the earthship design has been successful without floor insulation because most earthships are being built in New Mexico and are more concerned with summer cooling than winter heating.
We will provide alternate heating in our home with the two wood stoves shown in our plans. These stoves are more aesthetic for us than practical. We have had wood heat in the past, enjoyed it, and miss it now that we rely on electric baseboard haters. We hope to construct these stoves ourselves as detailed in the Earthship Volumes as opposed to purchasing.
We are also debating putting radiant heat in the floors to provide an active means of heating the thermal mass of our home. We have some concerns about our solar gain in December and January. We live in a fairly narrow river valley and get minimal sunlight due to clouds and fog during these months. We have access to significant quantities of waste wood due to our location so a radiant heat system fueled with wood seems practical to us. The decision to install radiant heat will be governed ultimately by cost.
In a typically Canadian manner I have chosen to straddle the fence on the issue of floor insulation. My intention is to insulate under the footings with 1″ of rigid EPS (R5). I also plan to insulate under the floor spaces (again R5). I will NOT insulate under the planters or cistern. I also am thinking of leaving a percentage of the central floor space uninsulated.This practice of leaving some of the floor uninsulated is used sometimes in conjunction with radiant heat floors to guarantee that if the building is left unheated for periods of time over the winter the facilities sensitive to freezing will not be damaged because the building is coupled to the Earth’s constant temperature. I think this decision will have minimal impact on my ability to control the temperature of the mass fabric of the home, and keep it hooked up to the Earth’s thermal battery.