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Home    >    The Manifesto    >     3. Sustainable Materials    >    Window Openings

Window Openings

Windows provide daylight, ventilation and a view to the outside. They are the eyes and nose of internal spaces, filtering light and air. Windows are key to the environmental performance of buildings, which is covered in more detail in Bioclimatic Design.

Windows and doors are the moving parts of a building and as such they need careful design for minimum maintenance. As windows are usually openable, material consideration should be given to security, privacy and protection from the elements. Windows are more weatherproof when they open outward but side-hinged casements can obstruct space outside the building. Top hung casements provide useful high level ventilation. Centre pivoted windows can be better balanced for ease of opening, and when horizontal, can bounce light deeper into the room.


Timber and steel are the most logical materials to use for opening windows and doors. Framing should be locally fabricated so that it can be easily maintained.

Much of the rest of the world has an appetite for plastic windows but these are oil based and are difficult to recycle. Aluminium extrusions are also very energy intensive but are potentially more robust. Locally made timber or welded steel windows invest in the local economy and ensure that maintenance is locally available as it is often the moving parts of  a building that are most susceptible to wear and tear. If using timber, this should be sourced from sustainability managed plantations where the trees are replanted regularly.


ECD&F Centres  Brightly coloured playful window framing adds character to the stimulation classrooms


Glass is fragile and may not be the right solution for school openings where the primary function of a window is to provide ventilation.

As temperatures in East Africa are generally benign, glass could be seen as unnecessary given there are other ways to stop driving rain. Louvred glass windows provide the maximum opening ventilation for minimum obstruction but ideally require toughened glass for greater safety, which is expensive and can shatter on impact causing injuries. Clear plastic sheet (acrylic or polycarbonate) will probably last longer in a school environment though it can scratch and yellow with age. Glass is made from sand, while plastic is made from oil based chemicals; both are energy intensive.


Mzuzu Health Centre Mechanical glazed louvres provide both natural daylighting and passive ventilation


Bamboo screens or woven materials can provide a sustainable and attractive alternative to glazing

Where glass or polycarbonate is not available or a low-carbon natural alternative is preferred, bamboo or vines can be woven into frames to create a perforated screen in place of glazing. This has the added benefit or permitting air flow and can help to screen direct sunlight. Bamboo and other natural fibres should be treated with borax or by a traditional soaking and smoking method before use. Alternatively, recycled materials such as plastic or metal waste can be woven into a colourful and waterproof lattice.


Ilima Primary  Peeled Lilian vine was dried and woven into Lifake hardwood frames to provide screening


Shutters can provide louvred ventilation as well as wind and rain protection and can help to moderate light levels.

Sliding or folding shutters can provide security, protection and variable daylight control without the need for fragile and expensive glass. Steel or timber shutters with louvred slats can admit a small percentage of daylight and allow free-flowing air movement without letting in rain. Vertically folding shutters let light in at the bottom of the window but prevent direct overhead sunlight from entering the room. Sliding shutters are easier to install and use if they have high quality roller mechanisms.


Lake Bunyonyi Secondary  Classrooms have wooden shutters instead of glazing that can be manually pushed open or closed.

Insect Netting

Mosquito netting may be necessary in some areas, particularly for buildings that are used in the evenings or night-time

Many low cost buildings are unlikely to be well sealed enough to prevent mosquitoes finding a way in so the provision of mosquito netting at windows is unlikely to be useful. With well-constructed buildings which are used during the evenings or for dormitory buildings, adding a layer of mosquito netting at the window can avoid the use of netting around beds. It is worth remembering that insect netting reduces daylight and restricts air movement and daylight considerably so window openings will need to be larger in order to compensate for this.


NTC Kaliro A layer of framed mosquito netting can be opened or closed independently of the glazed windows

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