Thursday, July 2, 2009

Strategic Trees

The plan above is just to show how strategic plantings can reduce the house temperature by at least 10 degrees in the summer. This is an existing house built in 1937, no insulation except for heavy attic insulation recently blown-in to R30, and a light stucco exterior. Pretty typical pre-war construction (you can't get it built like this anymore). Also no shear walls, but that's a different issue.

This is a site plan showing how the trees have been planted over the years to block the summer sun and absorb the solar energy the sun provides. Because the house is relatively heavy construction and air-leaks like a sieve, not much point in trying to make it work like homes built in the last 20 years. It's a heat-of-mass system that works well because it resists warming up due to the deep foundations and large overhangs and porches. Has plenty of windows and fabulous cross-ventilation. Most homes of that era were built this way because there wasn't any air conditioning then, and you had to build homes in a way that used inherent material properties and site characteristics to balance the available light and temperature changes. New "green" concepts, right?

Also note the orientation of the house on the site. The east and north sides of the structure are situated so they have the most exposure. The south and west sides are surrounded by garden area. This is where the trees go.

The trees absorb energy and convert it to oxygen and H20, it's not just simple shade. So catching the sun on the south and west sides of the property are the most effective way to keep the entire structure from heating up as well as create a microclimate that's cool and shady. As a result, there's not much need to run the air conditioning except during those miserable August heat waves. So it's very low impact, which is a good strategy for single family residences, but it also contributes to the urban forest which counteracts the "heat island" effect from all the road paving, dark roofs and concrete work in urban areas.

This shows very clearly in my earlier post with the satellite and shuttle photos. The urban area is mostly gray, and the residential tree canopy immediately abutting the paved-over city is very visible. This is the mitigation that the tree canopy provides against the "urban heat island" that is being created across the landscape by development and contributing to the approximate 10-degree local temperature increase in these areas, as well as the lack of precipitation in urban centers.