Natural Cooling – Awnings and Eaves

by Erik North on August 31, 2012

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Hah! I haven’t dropped of the planet.

Wrapping up the natural cooling series, I’m covering awning and eaves. Granted, they’re radically different in utility as one can be added easily (awnings) and the other can be added even more easily by calling a contractor and dropping a couple grand (eaves).

Seriously, I thought I’d deal with both as they are providing the same conceptually benefit. They both physically extend the house’s edge and provide shade even if they are different in application.

Here Comes the Sun – I’ve touched on this previously, but that great ball of thermonuclear energy in the sky is dominant driven of cooling load and cooling costs. While that may seem forehead slappingly obvious, we’re talking more about solar radiation than just it being hot outside. Solar energy (that’d be sunlight) streams through open windows, beats against walls and roofs, roasting attic spaces and generally baking everything it touches like some Creature Double Feature heat ray. Using shade to minimize the heat ray is the easiest way to reduce your cooling needs.

The Premise – The Premise sounds like a bad mid-season replacement TV show, doesn’t it? Coming this summer on CBS! Actually, the cooling mechanic of both awning and extended eaves are approximately the same. During summer months, the sun travels at a much higher angle through the sky. The sun beats on the roof and streams through windows. An awning or eave shades windows from the more highly angled sun. In northern heating climates (well, OK all climates), the sun angles lower in the winter. The sun can their shine in helping to warm the house.

Awnings – Awnings work like cupping your hand on your forehead to shade your eyes. I mean if your hand was color matched and vinyl. Awnings are typically installed on the south side and can either cover individual windows or porches on the entire side. Awnings can either be a permanent fixture or retractable and matched to the aesthetic of the house. Retractable awnings are more suitable to northern or temperate climates where they can be taken down to allow sun in during the winter.

Eaves – If awnings are like cupping your hand to your forehead for shade, eaves would be like having your hand bolted to your forehead since birth. Eaves provide the same shade benefits as awnings with some drawbacks.

Eaves on a two story building will not shade first story windows. When snow piles up during the winter, extended eaves provide an excellent starting spot for ice dams. Lastly, east and west facing windows would derive less benefits since the sun would be streaming in from the south side.

All too often in warming and cooling climates, homeowners lean on their mechanical systems to do the heavy lifting of conditioning inside air. Minimizing the streaming sun can help reduce the load on those systems.

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