The Solar Slot

Recently I dipped my toe into the controversial pond containing the often competing imperatives of Canberra’s garden city character and people’s right to do as they see fit on their aspirational quarter acre … or in modern parlance 0.6177 hectares. I mentioned the difficulties in dealing with regulated trees, wild cards or potential black holes the normal punter should watch out for when imagining their own Grand Designs. I recently designed a house for a senior public servant who had bought a plot of land with seven regulated trees on it. It took many, many months to battle through the system and arrive at a workable solution. So caveat emptor where garden bit of the city is concerned!

Other than the issue of regulated trees what are the other ‘tricks for new players’ one should be conscious of when ‘eeny minny mo’…ing blocks for potential development?  Other than the normal ‘location, location, location’ thing probably the first cab off the rank would be an awareness of the block’s basic orientation? To ensure a sustainable outcome the most suitable blocks to redevelop are ones in landscape format, those with a long axis facing north. Look for a shape akin to that of a single bed in plan form and facing a specific directiion. It is not vital to have the long side of the block facing precisely true North, anything in the ‘solar slot’ is acceptable. The ‘slot’ is an angle between 20° west of North and 30° east. A rectangular house facing following the geometry of this block can be simple in plan form, cheaper to build and design and will naturally be able to take advantage of all of the available winter sun.

Canberra is a heating rather that a cooling dominated climate by a factor of about 8. By this I mean that if you were to heat and cool house to normal temperatures throughout the year one would use eight times more energy on heating compared to cooling. If you’re going to utilise the free energy from the sun getting the simple orientation equation right is a vital first step. Selecting the correct block makes all the subsequent design decisions click into place like lids on a pen. This is 101 in the school of passive solar design for our climate. Perhaps ignoring this simple principle was excusable in a previous less energy conscious age.  It seems unforgivable however to see how blind Freddie continues to the drop the precious ball.

With a good block selected the next thing is to get the most important parts of the house in the right spot.  This sounds obvious and it should be; it means locating the key living areas (probably the family meals kitchen zone) facing north. These too should have their long axis facing the sun and relate well to private outdoor spaces. A long rectangular house on a rectangular block also has the added bonus in that it is also less likely to overshadow itself. In thinking about these key living areas one trick is try to achieve a one-room thick  space with the benefit of allowing one to have alternative outdoor spaces both winter and summer on either side of the house. As long as the net energy balance works out this is a good way of avoiding glare.  The passively designed houses of the 70’s often had windows on the north only side and combined them with dark floor and wall finishes resulting in uncomfortable glare. Small double glazed openings on the south have the advantage of promoting good cross ventilation and that lovely indoor-outdoor feeling to key outdoor areas that most of us crave.

Combine these simple principles with high-performance windows, good levels of insulation for walls floors, ceilings, and you have a simple base recipe for good sustainable design. It is important to remember that a house is more than a machine for collecting heat it needs to be home too. I haven’t touched on the mysterious matter of thermal mass in this short piece but will return to it at some other time. The subject is definitely less complicated than cosmic dark matter or mysterious dark energy but often equally misunderstood