Several years ago when I started talking about my dream of building a ‘green house’ a friend said “oh I saw one of those … a kind of hobbit house…really ugly” So the first misconception to clear up is that green design has nothing to do with the aesthetics of the house! Whatever your taste (hobbit-like or otherwise) one can incorporate green design principles. Essentially it means building in harmony with the natural environment and cooperating instead of fighting with the regional climate. Green building takes a passive approach which requires less energy to run once the building is erected. It’s also know as bioclimatic design, eco-design, eco-friendly architecture, earth-friendly architecture, environmental architecture and natural architecture.
This post will focus on the design of the building itself, not the technology or specific materials to be used. I will cover those aspects separately.
My house is in Durban South Africa. We have an average of 320 days of sunshine a year. Temperatures range from 16 to 25º C in winter and 23 to 33º C in summer. However, before you consider relocating, the warm Mozambique current flowing along our coast and summer rainfall means we also experience high humidity which can be quite debilitating from December to March. So here is what we have briefed the architect to design into the house:
We want light (lots of) but not direct sunlight which would heat up the house and require us to put in energy guzzling air-conditioners so one of the easiest things to do is install tinted windows. Cross ventilation is also a vital consideration. Windows were planned so that each room would have opening windows on opposite sides of the room. The most challenging areas were the downstairs bedrooms which open onto the passage . Tricky to get cross ventilation as you can see from the drawing below.
We did three things; firstly designed opening windows above the doors and small high windows (second floor not in view) that open up into the passage. The passage windows slide sideways rather than level in our out so there are no unattractive or dangerous protrusions in to the passage.
Secondly we have put whirly birds into the roof of the passageway to draw the warm air up and out of the house. These are fantastic low tech gadgets that are used a lot in factories but surprisingly not in residential properties. The third thing we did was put opening windows at ground level next to the pond to draw in the cool air as it crosses the water. Thanks for this great tip Greg Seymour email@example.com
OVERHANGS, EYEBROWS, FIXED LOUVRES AND TREES
Sun pouring into a building is a costly thing to mitigate. Passive solar cooling eliminates the need for air conditioning. The image at the top of the page shows the house as it faces North. In Durban this is the hottest elevation. Fixed louvres will cut the sun’s strength considerably without blocking light. The verandahs are wide so that even in winter when the sun is lower it won’t penetrate into the house. Elsewhere on the building are ‘eyebrows’ to shade windows. Best of all (though not strictly a design feature) are trees and shrubs next to the building. Many are deciduous so in summer they are full of leaves when most shade is wanted and in winter the drop their leaves when a bit more warmth is welcome.
CONCRETE AND ROOF GARDEN
A study undertaken by Canadian researchers found that green roof habitats were very effective in reducing a building’s energy demands. The results show that a conventional roof absorbs solar radiation during the day, creating a high daily energy demand for cooling internal air spaces. In contrast, the growing medium and plants of a green roof habitat reduce the heat flow through the roof by providing shading, insulation, and evaporative cooling (shown in green below). It was found that the green roof habitat reduced the daily energy demand for cooling by a whopping 95%!! (If you’re interested in the tech stuff that’s from 19.3 kWh or 7,080 British Thermal Unit (BTU) per m2 for a building under a conventional roof to 0.9 kWh or 324 BTU per m2 for a building under a green roof habitat). Thermal mass is the term given to material (usually concrete or stone) which will absorb heat and prevent its entry into the home. Although there are eco-negatives associated with concrete because of it production processes judicious use can swing its rating into a green category. In our house concrete (a lot) has been required to build the base for the roof garden. Its payoff though is immense at many levels. More to follow on the wider range of green roof benefits and how to actually construct your own.
ROOF DESIGN FOR SOLAR PANELS
Ensure you plan carefully for the location of your solar panels. We were quite ignorant of how many we needed (24!) and initially made provision for only 8 on a section that also gets much shade from an ancient and huge Albizia adianthifolia. Our main roof was pitched – but the wrong way – which has led to delays with approval of plans as we’ve had to switch the pitch direction to accommodate the panels. In Durban one cannot make changes during the build without the risk of inspectors shutting down construction while you wade through approval bureaucracy so best to get it right up front. We’ve had expert help from Trevor Wheeler of http://www.solarsunsa.co.za/ and I strongly advise you get your solar needs properly specified from a specialist before you submit your plans. More posts to follow on the process of determining what your solar needs are.
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