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Fenestration Products –
Design Issues

The sun's energy is free – but how you use it is critical. If you are building a new home, decisions on how many windows, doors and skylights to include in your plans – and where to install them – can have a big impact on your comfort and heating and cooling bills.

Fenestration-to-Wall Ratios

Remember the following rule of thumb: keep the ratio of window area to floor area at least 1:10. That is, for every square metre of window area, make sure you have at least 10 square metres of floor area. This will prevent solar gain from overheating the living space. Many jurisdictions also have code requirements for kitchens and dining and living rooms. Having too little glazing misses out on free solar energy – but too much glazing can result in unnecessary heat loss in the winter and excessive heat gain in the summer. The tables below give the recommended fenestration area (the area that comprises windows, doors and skylights) for bungalows and two-storey houses.

Bungalows
Floor Area Wall Area Recommended Fenestration Area
93 m2 (1000 sq. ft.) 105 m2 (1130 sq. ft.) 16 m2 (170 sq. ft.)
186 m2 (2000 sq. ft.) 149 m2 (1600 sq. ft.) 22 m2 (240 sq. ft.)
279 m2 (3000 sq. ft.) 173 m2 (1860 sq. ft.) 26 m2 (280 sq. ft.)

Two-Storey Homes
Floor Area Wall Area Recommended Fenestration Area
93 m2 (1000 sq. ft.) 149 m2 (1600 sq. ft.) 22 m2 (240 sq. ft.)
186 m2 (2000 sq. ft.) 210 m2 (2260 sq. ft.) 32 m2 (340 sq. ft.)
279 m2 (3000 sq. ft.) 257 m2 (2770 sq. ft.) 39 m2 (415 sq. ft.)
372 m2 (4000 sq. ft.) 297 m2 (3200 sq. ft.) 45 m2 (480 sq. ft.)

The placement and orientation of windows, patio doors and skylights relative to the sun are the biggest factors that affect solar heat gain. For the greatest energy efficiency, more of a home's glazing area should be oriented to the south and west, with minimal glazing on the north and east sides of the home. But it is advisable not to concentrate too much glazed area in any one location. A sunroom with limited wall space can be pleasant in the winter, but it may be too hot in the summer.

It's also important to choose energy-efficient products. As a general rule:

  • Windows that have a hard-coat low-e coating and a high Energy Rating (ER) value should be installed on the south and west side of the home – they will add more heat to the home through solar gain than they lose.
  • Windows with a soft-coat low-e coating and a low U-value should be installed on the north and east sides. Solar gain is not an issue here, but products that have a low U-value are more resistant to heat loss.

Insulated blinds or curtains can also reduce heat loss at night during colder weather and heat gain during the day in summer. They may also increase condensation and allow frost to form on windows during cold weather because they trap moist air near the cooling surface of the glass. Be sure to leave them open during cold, sunny weather to allow for solar gain.

Heat loss through doors can be prevented if the doors are situated out of the path of prevailing winds or on the leeward side of the house, or if there are windbreaks, such as a porch or vestibule.

To reduce the possibility of condensation, skylights should not be located in areas where there is high humidity, such as in a bathroom near a shower or over a kitchen sink.