The energy-efficient home: let the sunshine in… sometimes

July 29, 2015

The sun is the best way to heat your house naturally, thus cutting down on energy consumption and associated costs. As these guidelines will demonstrate, when building an energy efficient home it makes sense to use the sun to your advantage.

The energy-efficient home: let the sunshine in… sometimes

1. Windows

Appropriately placed windows are the best tool for getting the most of the sun.

  • The main windows in the house should be placed along the southern side.
  • These windows should be large (but not larger than about 15 percent of the floor area of the room; up to 20 percent for a living room) and face from about 30 degrees east to 20 degrees west of true south.
  • Windows on the eastern and western sides of the house should be small and shaded with awnings in order to minimize the entry of low-angle rays from the sun during the early morning and late afternoon.
  • Windows on the northern side of the house will not be exposed to significant amounts of sunlight at any time of the year but they should be small — or double glazed — to reduce heat loss during the winter.
  • Research has shown that double glazing is an economical and efficient form of insulation in cool climates. Eaves can be used to shade south-facing windows.
  • Maintaining an appropriate angle between the horizontal plane of the windowsill and the outer point of the eave will exclude the hot rays of the summer sun and allow the entry of warming winter sunshine, while preserving the view.
  • The ideal combination is one of large windows with retractable shading. East- and west-facing windows need to be shaded with external awnings as eaves offer little protection from the entry of low-angle rays at morning and evening in summer.

Internal shading by means of curtains and blinds is not as effective as it allows the heat to pass through the window into the room. If windows are large, then heat-reflective glass is a useful option. While large windows are needed on the southern side of the house to let in the warming rays of the winter sun, at night they can allow the trapped heat to escape. Glass conducts heat about 10 times faster than an insulated wall and three times faster than even an uninsulated brick veneer wall.

To avoid these heat losses, windows need to be equipped with heavy, lined and close-fitting curtains falling to floor level. In cold climates, windows can be double glazed to further reduce heat loss. Windows that are set high in a wall, directly below the roof line facing south should be protected by a roof overhang performing the same shading function as an eave.

2. Skylights and external shading

Skylights offer similar opportunities and problems of energy conservation. As with windows, small size, shading and double glazing help reduce heat loss. The "light tube" — comprising a small dome on the roof that directs sunlight through a tube lined with reflective material to a diffuser set into the ceiling — reduces the energy problems associated with ordinary skylights. External shading is better than internal shading.

Plant deciduous trees to the south of the house: they will provide cooling shade in the summer but allow the winter sun through when their leaves drop. Check their mature height before planting as very tall trees will simply shade the roof and not the windows. Use broad eaves that create an angle of about 65 degrees between sill and the summer sun's rays.

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