House profile 1999 climate by surly

In mid-summer the path of the sun is quite different. It rises in the east-south-east and sets in the west-south-west. At noon the sun is almost overhead, only 8º from the vertical. North-facing windows will get hardly any sun, and none if the roof has eaves. South-facing windows will get some early morning and late evening sun. East-facing windows get sun all morning, and west-facing windows get sun all afternoon.

To have comfort in a Manilla house, we should let in the winter sun and keep out the summer sun. We can do this simply by facing most windows to the north, and sheltering them by eaves. We should not have windows facing east or west, as they admit so much summer sun. West-facing windows are worst, because they let the sun in during the hottest part of the day.


A few south-facing windows may be needed for light or for views. They let in no useful winter sun, although they don’t let in much unwanted summer sun either. Orientation of the windows of the house

To allow for many north-facing windows, I wanted the house to be long from east to west. The shape of the block of land was not very favourable. In the end, I faced the house 8° west of true north, and stepped back the axis of the house towards the south-west. In the north walls I put a large window in each room. North-facing clear-story windows carry sunshine further in to the house. The total area of north-facing windows is 20 square metres. This is 70% of the window area, and 13% of the floor area of the house. Although there are some trees to the north, they shade the house only slightly in winter.

Eaves shade all north-facing windows. The line from the edge of the eaves to the bottom of the window has a slope of 2:1. Sunshine begins to come in below the eaves in mid-March, and is again shut out seven months later, in mid-October. For the five hotter months no sun enters the north-facing windows. In summer the eaves shade the whole of the north wall to ground level.

I have protected the east and west walls of the house from the heat of the summer sun. A double garage shields the east wall to the full height of the house. The west wall has an upstairs veranda (a talar) almost 3 metres wide, fitted with canvas awnings. Under the veranda there are two 10,000 litre water tanks. When full, they will contain 20 tonnes of water. This large mass of water will tend to keep a steady temperature.

Heat can be stored inside a house in heavy materials that have a high specific heat. These include rocks, soil, concrete, bricks and water. The greater the mass of these materials, the greater is the thermal mass of the house. Such materials are slow to heat up, but hold their heat for a long time. A concrete floor, or a brick wall, heated by the sun will keep the house warm at night. If the following day is overcast, the house will still be warm.

I include the volume of earth, gravel, bricks and concrete extending 500 mm below the floor slab as part of the thermal mass of the house, because I have insulated around the edge (see below). This makes a total of about 200 tonnes of thermal mass. The temperature of this mass will not change much over periods of days or even weeks. Manilla’s average temperature is 16º. I hope the floor of the house will stay a few degrees warmer than this all year round.

A low-energy house must be protected from heat and cold by a shell of insulation. Any kind of wall or roof insulates to some extent. The insulating effect is expressed as an “R-value” (for thermal Resistance). Ordinary walls, whether wood-framed with weather-board, or brick veneer, or double brick, are about R = 0.50. Unlined roofs with ceilings are about R = 0.70 in summer and R = 0.35 in winter. If one adds bulk insulation or reflective foil insulation, one can add the R-value of the insulation to that of the wall or roof. In our climate it pays to increase the total R-value to about R = 2.50 in the walls and R = 3.50 in the roof.

To protect the soil and footings under the main concrete slab from heat gains and losses, this mass has also been insulated. Sheets of 50 mm polystyrene foam are placed vertically inside the strip footings to a depth of 300 mm to 900 mm. The edge of the floor slab, unfortunately, could not be insulated without risking termite entry to the house.

Fans placed high up in the clear-story spaces serve two functions according to the season. On summer nights they are angled outwards to assist the stack effect by ejecting warm air through the clear-story windows. On sunny winter days they are angled inwards to blow hot air down from the top of the internal brick walls. This allows the heat to be absorbed in other parts of the house, rather than being radiated away from the warm bricks at night.

I use a heat-pump hot-water service (Quantum). This operates like a refrigerator except that it heats rather than cools. It has a compressor, which pumps fluid to evaporator panels mounted on the roof. If this system is run in the daytime, it uses about one-third of the electric power of a hot water service that has a heating element. Unfortunately, it will not save power if it is run in the cool of the night, when cheap “Off-peak 1” power is available. I have been authorised to use “Off-peak 2” power, but the cost saving, compared to a heating-element system using “Off-peak 1” is very small. Appliances

I use motors on the curtains of north-facing windows. These are very expensive. The reason for having them is that these curtains, in five different rooms, should all be opened and closed at the same time each day of summer and winter. In winter they should be opened each morning to let the sun in, and closed each evening to keep the warmth in. In summer, they should be closed each morning to keep the heat out. Then they should be opened each evening, along with the windows, to allow the house to cool. A clock controls the motors. In future I may use a radiation sensor. NatHERS Rating