Cool temperate climate houses

Tasmania's climate of cold winters and mild summers creates opportunities as well as hazards for
designers who are considering passive solar principles. In Tasmania, summer snow has
been reported at elevations as low as 300 m. Therefore, in this climate, the
aim of a house design is to maximise building heat gain in winter.

Access to sunshine throughout autumn, winter and spring is the top priority - avoid blocks which
will be over-shadowed by obstructions to the north, east or west. You'll need information
on solar elevation. Shelter from cold winter winds is also a consideration. Sites on
hilltops are windier than those in valleys. Check the prevailing wind direction in
winter, sites on the lee side of hills will offer some protection.

In a cool temperate climate such as Tasmania, more north-facing glass is required and the area
of north-facing windows should be 20 - 35% of the floor area of the room they are in. Use 20% in
buildings of low heat storage capacity and 35% in structures with high heat storage capacity.
East-facing windows (with external shading to restrict summer sun) should be used to
provide morning sunlight during the cooler months and you should concentrate seriously
on blocking heat loss via drafts. All outer doors should open on to a small entry hall which acts
as an air-lock between inside and outside and concrete slabs should be edge insulated.

Insulation should be used to its maximum effect - especially under timber floors and thicker
insulation should be applied in external walls and very thick ceiling insulation should be adopted.

Sun-porches, glasshouses or conservatories are all effective in trapping the sun's heat.
Double-glazed windows also help to reduce heat loss. Condensation will be a problem in
uninsulated houses in this climate. It occurs when moist air comes into contact with surfaces
which are cold enough to cause water vapour to condense into liquid form. In
well-insulated buildings, surfaces are warmer, so condensation is less likely.

Bricks, stone and concrete are effective heat storing materials. They need to interact with
the house's internal environment. For example, a concrete slab will absorb and store the sun's
heat during the day, if it's covered with slate, hard vinyl or ceramic tiles. When the sun sets,
the slab is still warm, so your house keeps a pleasantly even temperature around the clock.
If the concrete slab is covered with carpet or cork, the heat coming in through the windows
cannot be stored in the slab, because cork and carpet are thermal insulators - these
floor-coverings will prevent heat flowing into and out of the slab. Slate or tiles
(ceramic or hard vinyl) are good choices in rooms where the sun comes in.

Internal brick walls will also act as heat stores. Brick veneer walls do not store heat inside the
house, as the bricks are on the external leaf of the walls, and do not interact with the
internal environment. Reverse brick veneer, with the bricks on the inside and a light
insulated shell (eg fibro-cement sheeting) on the outside, is a much better option.

Special thermal storage devices such as "Trombe Walls" (see above picture) are good ways to
increase internal temperature stability of cold climate houses. Heavy materials, painted black and
located just inside north facing glass act as large heat "sinks." They absorb heat energy all day
and slowly release that heat back into the interior of the house during the night.

You will be able to see many examples of efficient cold climate house designs during
Solar House Day on September 14th this year.