Thursday, August 14, 2014

How to build an energy-efficient home

There are just a few important things to know and to remember, when building an energy-efficient home. These are; insulation, air intrusion, thermal mass, and that windows and holes in the wall of the house lose about the same amount of energy.

Insulation is a means of capturing dead air and causing it to slow the exchange of hot energy toward a cold space. Most builders use fiberglass insulation. Personally, I prefer to use blown cellulose insulation. In America, we major the value of insulation, by giving it an R-factor. The R-factor of insulation is a reference for the ability of the insulation to slow heat transfer and to the R stands for resistance factor. The R-factor is only part of the story. Insulation can have a high R factor, but if air moves through it is almost useless. One of the things we do recently, in home construction, is to use Tyvek, a thin, breathable plastic membrane that stops the wind. In modern construction; we customarily have from the outside killing in; siding, Tyvek, insulation, and drywall. Customarily this results in what we call and R-30 wall.

In other countries they talk about a U-factor. The U stands for use factor. And this use factor is merely a combination of an R factor, and an ability to withstand air intrusion. Therefore, the use factor is actually more useful than strictly the R factor. For instance, a concrete wall, has a low R factor and a high U factor if the logs are made to fit tightly together. A concrete home has a low resistance factor, because concrete transmits thermal energy easily. To properly insulate a concrete wall, one should insulate the outside of the wall. And this brings us to thermal mass.Windows are a great energy waster. Each pane of glass has a resistance factor of less than one. A thermopane window has a resistance factor of about two or three including the airspace. The more windows a home has the more expensive it is to heat. Triple pane windows have a resistance factor of about five. A drapery fully covering a window will increase the resistance factor to about 20. Therefore drawn draperies will greatly increase the insulating ability of a home.

Thermal mass is simply the amount of weight that reaches a certain temperature and wants to stay at that temperature. For instance, I home with a brick floor, and lots of books and heavy furniture, has a lots of thermal mass. Once a home with lots of thermal mass reaches a comfortable temperature it tends to stay that temperature for a long time, even after they heat or air-conditioning stops. Offices tend to have high thermal mass. It takes a lot of energy to change the temperature of thermal mass. Thus, one should leave the thermostat at the same temperature and not move it up and down. Turning down the thermostat at night and turning it back up during the day wastes energy.