Monday, July 16, 2012


How does using certain construction materials save you money on heating and cooling costs in your home? What are some of the classic blunders that people make with layout or design?

Considering design materials for homes to save companies (or the owner-builder) money or contribute to greater profits (or money saved in-pocket!), think INDIGENOUSLY. If there is an abundance of a particular type of material in your area, then it will be easily accessible and cheap. If one lives in a rocky area, build a rock house. If one lives in the forest, build a log house. I once lived in the plains area (Nebraska) among great acreages of farmland, so we built a plastered straw-bale house. Our walls had an R-factor of about 50. There are of course many other types of alternative building methods for construction. Adobe, rammed earth, cob, and cordwood are but a few of them.

Saving money on heating and cooling costs runs right in there with layout/design. This goes back to the passive solar design of houses where the house actually becomes the solar collector. The thing to remember is that EVERY HOUSE IS A SOLAR HOUSE. South windows are what one needs for an efficient passive solar house here in the northern hemisphere. North windows are almost a total loss as they gain zero sunlight and they lose a great amount of heat. Also having the glaring sun beating in a west window on an already hot summer evening just overworks the air conditioner and runs up the utility bill. East windows tend to be a bit nicer to have because they are the first to gain those welcomed sun rays while drinking the morning coffee at the kitchen table.

The keys to an energy efficient passive solar home are these: thermal mass, window area and placement, and proper overhangs.

THERMAL MASS: Thermal mass is the heat sink for storing and maintaining temperatures in the home--these *conduct* heat/cold rather than insulate. The ideal thickness for mass materials is 4-5 inches. Thermal mass is made up of the combination of WALLS (plaster, brick, adobe, rammed earth, stone, masonry fireplace or other mass products are far superior to gypsum board), FLOORS (brick, tile, etc. are far superior than carpeting or linoleum, which actually insulate and isolate the thermal mass from the interior of the rooms instead of conducting it), and FURNISHINGS (which are minimal unless they have a lot of thermal mass in them).

WINDOW AREA AND PLACEMENT: There is a specific glass-to-mass ratio that makes for an efficient design. The amount of glass on the south wall should equal 7% of the homes total square footage. (Example: 2,000 Sq. Ft.= 140 Sq. Ft. of glass). This 7% amount of glass should not be exceeded or overheating will occur. Note that this 7% applies to a conventional home with wall to wall carpeting. If more glass area is desired, additional thermal mass must be added to compensate. The 7% is NET Sq. Ft.; the total window area less the trim. Multiplying the entire window by .8 will get the net glass area. (Example: A 3’x5’ window is 15 Sq. Ft.- 15x.8=12 Sq. Ft.)

East and north glass should not exceed 4% of the total Sq. Ft. West glass should not exceed 2% of total Sq. Ft. Each design starts with the 7% of south glazing (NET). To increase beyond this we must add thermal mass usually starting with the floor and then the walls. An additional 1 sq. ft. of south glass may be added for every: 5.5 sq. ft. of sunlit thermal mass floor (the max. amount of sunlit floor is 1 .5x the south window area) 40 sq. ft. of floor that’s not in direct sunshine 8.3 sq. ft. of thermal mass wall. The recommended maximum amount of glass on the south side for direct gain is 12-15%.

PROPER OVERHANGS: Keeping the sun out in the summertime is as important as letting it all in in the wintertime. Overhangs at the proper length will allow this to work at all times of the year. Although there is a formula that exists if you google it, but some excellent tools for calculating overhangs (among other solar tools) can be found here: The idea is to keep the sun out of the windows when the sun is at it’s highest (summer solstice) and to let it all in when it’s at its lowest (winter solstice).

Usually it is considered best to put the living areas on the warmer south half of the house, and the bedrooms and storage areas on the cooler north half (people generally sleep better in a cool room than a hot one). The kitchen usually generates its own heat from all the major appliances so it is best suited for the northeast corner (the coldest corner of the house) with the dining room next to it on the southeast corner (remember the early morning coffee I mentioned earlier?).

Enjoy the heating and cooling savings of up to 60% with your passive solar design!

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