Is the most energy efficient home one without windows?

May 30th, 2009 by Matthew Leonard

That’s a saying that has been around the building community for many years. It finds its roots in the fact that the most available windows are roughly R-2 to R-3.5 and a 2×6 stud wall is R-21, well actually it’s about R-13.7 after you look at whole wall R-Value and subtract the negative effect of the studs. So windows have always been a weak point in the exterior wall and if you eliminated them, you’re whole wall R-Value of 13.7 doesn’t get subtracted by the inferior windows and you have a more energy efficient shell or do you.

One major area this idea neglects is a technology that’s been around for thousands of years, even though it is simple, the majority of builders don’t include this in their homes. The technology is called “Passive Solar Design” and it uses the basic geometry of the angle of the sunlight at different times of the year. In the northern hemisphere, the sun is high in the sky in the summer months and low in the sky in winter. By simply orienting the structure on the site so there’s plenty of windows on the southern exposure, you let the warming rays of the sun enter the home to heat the materials and thermal mass, dense objects that absorb heat energy and store it for later use, to minimize the need for additional heat. In the summer, roof lines and other appendages shade the windows from excess heat entering the home requiring less energy to cool it.

So by not having windows, you would loose the benefit of the free energy the sun provides through passive solar heating. Granted the lower R-Values of the windows don’t hold the heat as well but there are new windows available through, SIP Systems and Serious Materials, that have R-Values up to 11.1 or very close to that whole 2×6 wall and granted it’s still nowhere near the performance of Structural Insulated Panels (SIPs) but these higher R-Values combined with High Solar Heat Gain (HSHG) glass, allows the maximum heat into the home and maximizes how much it holds in at night.

To further maximize the effectiveness of Passive Solar Design, reduce the number and size of windows on the east and west sides of the home and use Low Solar Heat Gain (LSHG) glass as in the summer months the sun is low and will add extra unwanted heat that increases the load on the air conditioning system. To even further improve the performance of Passive Solar Design, reduce the northern exposure windows as much as possible as there is no benefit for solar heat gain on that side of the home. Passive Solar Design also needs high performance exterior wall systems like SIPs to maximize heat retention when there is no sun.

So there you have it. The most energy efficient homes have windows, that’s good because there’s so much to see outside!

To see an example of maximized passive solar design go to the New Berlin Passive House page.

This entry was posted on Saturday, May 30th, 2009 at 2:45 am and is filed under Energy Efficiency, Green, Save Money, Structure, Uncategorized, Windows.