Passive Design
Designing the building and the spaces within it to benefit from natural light, ventilation and even temperatures.
Shade
Some form of shading is necessary in passive design to prevent glare and overheating.
Windows facing between north-east and south-west
Use overhead shading to cut out high angle, mid-summer, mid-day sun to reduce glare and overheating. Options include fixed, projecting overhangs (usually of the roof), louvred (adjustable) sun shades, perforated or mesh sun screens, retractable sun shades, deciduous trees and pergolas with plants.
Lower angle winter sun should generally be allowed to enter and warm the spaces.
- Shading windows by projecting overhang
A fixed, projecting roof overhang is a very cost-effective way in new construction to cut out mid-summer, mid-day sun.
- Perforated metal or expanded mesh sun shade
An overhead sun-shade using a perforated metal screen and frame reduces mid-summer sun and light – the amount will depend on the number and size of perforations. They can be retrofitted, and are a moderate cost option. But they can be visually distracting and will require cleaning.
- Retractable awning
These reduce sun and light when they’re out. They're a moderate cost option, but do require cleaning and maintenance and they may not be suitable in windy areas.
- Shade from a vine-covered pergola
The deciduous vines reduce summer sun and allow in winter sun when the leaves fall (the woody parts of the plants remaining provide about 20% shading). This is a moderate cost option, requires a high degree of maintenance, and may not be suitable for windy areas. Deciduous trees can perform the same function.
Another option is to use overhead sun-shades with solar control glass in a metal frame. This reduces mid-summer sun (the amount will depend on type of glass) while still admitting light. They can be retrofitted, but are a very high-cost option and require regular cleaning.
Windows facing between north-west and west
Fixed vertical (metal or timber) louvres in front of the window reduce direct sun and light in the afternoon, but need careful design for the specific circumstance especially for the lower angle western sun. They are a low-cost option in timber but will require maintenance. In galvanized steel or aluminium they will cost more but require less maintenance. They can be retrofitted. They must be designed to allow for opening windows and window cleaning, and, irrespective of design, will obstruct the outlook.
Adjustable vertical louvres in front of the window can be adjusted manually to cut out sun at selected times. This is a high-cost option and will require cleaning. The louvres can be retrofitted. They must be designed to allow for opening windows and window cleaning, and, irrespective of design, will obstruct the outlook.
- Vertical louvre shades for west and northwest facing windows
Adjustable vertical louvres in front of the window can be adjusted manually to cut out sun at selected times. This is a high-cost option and will require cleaning. The louvres can be retrofitted. They must be designed to allow for opening windows and window cleaning, and, irrespective of design, will obstruct the outlook.
Shade trees can also be used to reduce sun penetration. Deciduous trees will admit sun in winter. This is a low-cost option but the trees will require some maintenance/clean-up, and there is a time lag before the trees grow large enough to become effective.
Internal shading
Internal shading is much less effective at reducing solar heat gain than external shading. This is because the solar radiation has already come through the glass before it reaches the shading. The shading absorbs the radiation and while a small amount is reradiated back to the outside most remains within the space.
However, internal shading can be a useful device when:
- the sun penetrates for only a short time, and
- heat build-up will not be a major problem, and
- it is required to reduce glare.
Internal shading options include:
- Curtains are a low-cost to moderate-cost option often beyond the control of the designer. They significantly reduce light when drawn, but only reduce heat gain by a small amount. They also reduce ventilation and block the view
- Venetian blinds and vertical blinds can be specified where there is a need to adjust the amount of incoming light while maintaining some view. Blinds only reduce heat gain by a small amount. Blinds are moderate cost option.
- Roller blinds with light-admitting, UV- reducing fabric are the most expensive option for internal shading. Roller blinds reduce the amount of light coming in to the room, and reduce the amount of heat by a small amount. They can be motorised and fitted to high windows or roof lights. A range of sun filter fabrics are available to suit the desired level of light, view, and shading.