How long have we been building houses? A lot longer than we have been air conditioning houses.
Well we have certainly done things to keep warmer and dryer for thousands if not 100’s of thousands of years–but we have also done things to keep them cooler as well.
As a designer/builder for most of my adult working life, I have marveled at how ignorant we are of how to accomplish keeping warm, dry and cool.
We now have air conditioning systems that allow us to live in places where not too long ago it would have been considered uninhabitable–or at least inhospitable.
We have long had the knowledge to mitigate the use of air conditioning to some degree and yet we simply choose to turn down the knob on the thermostat.
Today I just want to talk about a few “passive” things that can be done to greatly decrease the use of actual mechanical air conditioners.
First and most important is house design and orientation. Obviously if we build a house and make all the south facing walls floor-to-ceiling glass, with no roof overhangs, we can expect to find ourselves inside a solar heated oven. Just providing a roof overhang to prevent the sun from hitting the windows directly can go a long way to turn the oven down a bit. By eliminating ground and other surfaces that might reflect the sun’s rays into the home can also be an improvement.
Of course reducing the amount of glass itself will make the most difference because then the walls themselves can be better insulated. This brings us to the huge topic of insulation in general. There is nothing like highly effective insulation in the walls and ceilings to keep the heat out of the house. This is not as simple as it may seem because heat is always attempting to move to cold and make balance. When it is 95 degrees outside, all that hot air is just hungry to gobble up our pathetic little bubble of coolness. So our air conditioners have to work their butts off to maintain that bubble of coolness.
While today I do not want to go into how I think houses should be built to eliminate the need for air conditioners altogether in many areas, I want to talk about ways we can deal with adverse conditions in our older homes in passive ways. While these things will not reduce your need for air conditioning in some areas it may greatly reduce the amount they may have to run. It may mean in some hot humid areas you might have to add a dehumidifier to make up for what the AC used to do.
The short story in all of this is to insulate your house as much as practical and use good air sealing type insulation–anything longer and we are into the full fledged novel.
One of the most important things you can do, if you live in an area where the nighttime temperature drops even 20 degrees between daytime and nighttime, is to change the air in the home and lower the thermal loading that has built up in the home during the day. The house is then closed up during the day to keep the nighttime cooling in and then the process simply repeats itself. In an average size house, even a simple window fan in a window on one side of the house and a window open on the opposite side of the house can accomplish this goal.
I cannot stress the importance of roof overhangs to keep the sun out, but in older homes that is not likely going to be possible.
In my own house, built in the early 30’s, the overhangs are insufficient to keep the south facing windows from overheating the house in the summer. So a simple thing I have done is to shade the windows with a grape arbor–the one plant now creates shading of most of my south facing windows and makes an amazing difference, and of course provides grapes in the fall.
While we certainly do not get as hot as lots of areas of the country, my house certainly never needs any mechanical air conditioning. The attic has a ton of cellulose fiber insulation, the walls have minimal insulation limited by the 2×4 wall thickness, and we put a fan in an east window at night and open up a west window–on those occasional really hot days.
Before the days of the grape arbor, we use to have to do the fan approach a lot more.
If you have a house with a basement, you can open up a basement window (as the path to the upper fan in the window) and get the benefit of the cooler basement to improve the cooling of the interior space during the nighttime. Accessing the constant ground temperature is another thing that can have a huge impact on minimizing the mechanical cooling needs of the home.
A huge number of homes across America could benefit from this passive approach to improving house comfort and energy efficiency.
Charles Buell, Real Estate Inspections in Seattle
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WA State, Home Inspector Advisory Licensing Board