Unless the home is a cave (and probably even if it is!), insulation is essential to making a home truly passive solar.
Walls: Really thick walls such as used in rammed earth and "earthships" depend on what I call "thermal lag" -- the time it takes for temperature to pass between inside/outside of the exterior walls. Since the earth used in such construction has a terrible R-value, their walls need to be super-thick - 3 feet is common - and therefore consume huge amounts of floorspace. That become a serious consideration thru-out the design process.
For example, a 30' x 50' home with conventional 6" frame contains a net living area of 1421 SqFt. Using 3' thick walls, the same-sized home contains a net living area of only 1056 SqFt. In this instance, if the construction costs are $60/SqFt, that's $21,900 additional cost to accomplish the same unusable space, increasing a monthly payment by nearly $200 each and every month!
The designer is well-advised to first juggle the NET floorplan, and then ADD the exterior walls!
Therefore, the wall construction becomes the primary consideration in accomplishing the necessary thermal mass. The thickness of thermal-mass exterior walls and their integral insulation (if any) must be determined by consideration of all the climatic factors of the building site - those include temperature extremes, humidity, wind, days of autonomy (the number of consecutive days or time-period where unusual temperature extremes might occur).
It was all these considerations of wall thickness, thermal lag, integral insulation and climate which evolved into the SolarSense. Building with poured concrete walls with embedded insulation cuts the necessary wall thickness to about 1/2 that required of earthships and rammed earth, etc. The use of soil cement (or perhaps other materials??) rather than redi-mix concrete is simply an option for those with impossible budgets and plenty of energy!
Roofs & Ceilings: Roof structures need to be thick enough to contain many inches of insulation thickness, regardless of the type of insulation used. The roofs of a solar home need not be greatly different than in today's super-insulated tract housing. However, there's NO exterior component of any home, solar or not, that should not be considered in the design process.
Floors: Because sun angles are such that the largest amount of solar isolation thru glass doors and windows is directed to the floor, the floors are a critical component of the thermal mass. That demands that the floors be concrete, not wood, and that serious consideration be given to thermal loss thru the floors. Further, the thicker the structure of floor and of the thermal mass beneath it, the better the performance of the entire solar home.
Dealing with the weight and nature of concrete, and additionally the weight of a thick layer of rock or other mass beneath the concrete, throws the matter of insulating such floors into the experimental category. I plan considerable experimentation and testing of high-density foam insulation beneath such loads. The problem, of course, is compression of the foam beneath all that weight, and appropriate methods of installing and floating such a floor so-as not to result in undue breaking of the concrete or undue settling of the floor over time.
One approach to this dilemma might be under-floor concrete piers extending to solid bearing beneath the floor and fill. Reinforcement of such floors are not an overly-complex engineering problem, but other considerations are the cost of engineering and construction, and the thermal loss which will result from conduction thru the piers.
This is really an engineering issue. I'm a designer with only very basic knowledge of engineering, and NOT a structural engineer. If you as the reader have input or ideas, or would be willing to assist in refinement of this approach, know that you would be SO welcome!
Openings: So, now we're left with what is always the biggest problem in preserving that precious good conditioned indoor temperature, whether provided by the sun or by the wasteful ways of conventional heating and cooling systems. Because solar heating requires a goodly area of south-facing glass, and because the typical double-glazed window is only R-2, there's really only one answer to this dilemma, and requires another page -- see Windows/Shutters.
To some extent, one might take advantage of the moderate temperatures deep underground. It takes much less solar (or furnace) input to offset 56 degrees.f than 10 degrees.f!
Backing a house into a hillside, or berming exterior walls, is a great help in reducing the demands for insulation and thermal mass. Most frame homes would be unable to accommodate such an approach, which virtually demands reinforced masonry or concrete.
Burying all but the southerly exposure of a home under 5 feet of earth would be even better, but demands major consideration regarding structural strength, waterproofing and ventilation. There could be considerable extra expense in trucking and placing that much cover.
For myself, being a "view guy", a buried house gives me a claustrophobic shudder, but that's not everyone, of course.
The characteristics of concrete/soil-cement walls in the SolarSense approach can accommodate partial burying with little additional cost, such being mostly the inclusion of additional rebar within the walls.
Updated by RonKZ Sunday, August 15, 2004
copyright 1998 - 07 July 2006 by Ron Klotz-Zellhoefer, SolarSense Designs, Arizona & New Mexico
Permission is granted and welcomed for personal application only.
