How to Choose Non-Solar Windows

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A good passive solar home design maintains a balance between solar and non-solar windows. Solar windows are those which face the sun, on the side of the house pointing true south; non-solar windows are those on the other sides.

In direct-gain designs, the north and east sides of the house should have windows with a surface area of no more than 4% of the total floor space area; the west side should have half as much, maxing out at 2% of the total floor space size. Obviously, that's a rule of thumb which must be adjusted in most situations to allow for fire escape routes, security views over side alleys and yards, or particularly beautiful vistas.

The local climate also affects the amount of non-solar glazing in a home. In particularly cold areas, for example, having a little extra glazing on one or more of the non-south-facing sides isn't too much of a problem, but in warmer regions it can lead to serious overheating. Compromises can be made with shades and overhangs to limit the effects of the summer sun, but east- and particularly west-facing windows will still be hit by early and late sunlight (respectively).

There is also the question of openable windows to consider. Passive solar homes need proper air flow, so some of the solar windows are generally openable. The same goes for the north side: one or two openable windows help generate natural ventilation, which can be further enhanced by east- and west-facing windows if necessary.

In a multi-storey home, mixing openable windows on all floors helps keep fresh air circulating as well. Remember that homes benefit from the chimney effect if windows are opened on two or more floors, where warm air rising from below helps heat the upper levels in winter. In summer, the effect can be reversed by allowing heat to rise out of the home through upstairs windows, to be replaced by cooler air brought in downstairs by openable, non-solar windows.

When you design your home and decide where to locate windows, remember that openable models are always more expensive and leak more than non-openable alternatives. Don't go overboard on openable windows or your home will struggle to maintain comfortable, stable temperatures.