Adelaide Homes Design Guide 3 - Shading Protecting windows and walls from excessive solar gain in the summer can greatly reduce over-heating. Properly designed retractable or movable shades will provide this protection while also allowing the sun's heat to access the home during cold winter days. Introduction Homes are lit by the sun from different angles and at various intensities depending on the time of the day, the time of the year, and the home's orientation. While the sun's radiation is most welcome in the cold winter days, in the hot summer season the home needs to defend itself from the heat. Shades provide efficient summer protection and, at the same time, they allow solar heat to enter the home when needed. In the morning and late afternoon, the sun is low in the sky and shines on the east or west sides of the home. At noon, the sun is at its highest position in the sky and is due north, but the angle of the sun's rays is much lower and they are much weaker during winter when we want them to enter the home than during summer when they should be fended off. summer noon winter noon N summer sunrise winter sunset summer sunset 1 The wall and roof insulation is the first line of defense, preventing the massive construction (brick or concrete) from accumulating too much heat in summer and helping to hold the collected heat inside during winter. The weakest points in the home are glazed surfaces. There are various types of glazing and shading that can modify a window's performance, and they should be chosen in accordance with the window orientation. 1. External shades and screens Shades can be external, internal or intermediate. They can be fixed, rotating, sliding, folding, retracting, horizontal or vertical, manually driven, or motorized. They have different performances and different impacts on home efficiency. Overhangs Well-designed overhangs can shade south-facing windows from the high summer sun and allow the low winter sun to penetrate the home. They can be eaves of the roof, horizontal structural extensions above windows, or simple awnings.
Overhangs are not effective on east and west facing windows where the sun shines at low angles. 31 78 An eave that protects a north window from the high summer sun will allow low-angled winter sun to pass through. Pergolas Attached to a home, a pergola can shade the whole façade. Though its horizontal surface serves as a shading element, various rollups (see below) or light curtains can be added to make it efficient even in the low morning and evening sun. The width of a horizontal shade above a window should extend beyond the window's width. Diffuse light window shade Only half of the radiation that arrives at a window is direct radiation. The other half arrives from diffuse and reflected sunlight. While overhangs can effectively protect from direct sun, they still let 50% of heat inside. External rollup shades Made from cloth material, these can block sunlight in various amounts, depending on material thickness and opacity. Easily moved and rolled up, they allow flexibility in adjusting the home to seasonal conditions, but they can be damaged in storms. Trellises A trellis is a vertical net-like structure that support climbing plants. As an additional wall, they can shade whole façades or just particular windows. They are good for shading east- and west-facing windows. 2 Shutters Shutters can be wooden or metal, horizontally or vertically sliding or folding, and with or without insulation. Casting vivid patterns on a façade, they can contribute to the home's aesthetics and attractiveness. Sliding shutters
Perforated Screens Folding shutters. Perforated metal screens are typically made from aluminum, or galvanized or stainless steel. They can be perforated in geometric or more decorative patterns, adding depth or uniformity to a building. Louvres Louvres are vertical shading elements placed in front of a window. Their fins can be horizontal or vertical, and can be fixed or adjustable to follow the sun's path. They can either be positioned parallel to the sun's rays to let the greatest amount of heat inside, completely closed, or anything in between. Folding shutters. Screens are ideal for windows on all sides as they reduce heat while providing enough light, a sense of closeness and intimacy, and natural ventilation. They come in various beautiful patterns, making each façade unique. Landscaping When leaves fall from trees in winter, they allow direct solar radiation to reach the home. On the other hand, in the hot summer days dense treetops make a perfect natural shade. Opened louvres Closed louvres 3
2. Internal shades Internal shades intercept solar radiation after it has passed through a window, which is why they are not as effective as external shades. However, they are the first to stop any collected heat from escaping in winter. To block unwanted solar heat that has already passed through the window, the shades should have a reflective surface on the outer face to return as much sunlight as possible. Adjustable shades Shading systems can be designed to follow the sun's path rather than being fixed. This can be done manually, or by automatic motor-driven mechanisms that respond to a pre-set schedule or to prevailing weather conditions. This automation makes access to hard-to-reach windows (such as those above a bathtub or counter) unnecessary and saves time for occupants by controlling all window shades at the same time. Controllable shades can be programmed with solar tracking based on the home's latitude and longitude and the directions of its façades. Photovoltaic shades Photovoltaic cells can be incorporated into glass louvres of the external sun shades, either on the reverse side or laminated between two glass sheets. While reducing the amount of sunlight entering, they can generate electricity for the home. A word about windows One sheet of 3-4mm transparent glass admits around 88% of solar radiation. Double-glazed windows contain 2 layers of glass separated by an air gap and so will admit around 80%. For good winter insulation, it is recommended that the gap between two sheets be at least 12mm. For the purpose of shading and limiting the amount of heat passing through the window, glass panes can be coated with a thin transparent film with the ability to reflect the radiation. This only works in one direction. Sun heat Visible light 4
Reflective coating on the outer side of the glass pane will fend off the solar radiation, keeping the interior cool in the summer, but it will also prevent heat from entering the home in winter, when it is needed most. Low-E glass (low-emissivity glass) will block radiant heat from passing through a window, depending on which side it is positioned. Low-E glass on the outer side of a window will prevent overheating in summer, while on the inner side it will help any collected heat to remain in the home during winter. infrared (heat) inside visible light inside infrared (heat) In Adelaide and the surrounding areas, it is recommended to have low-e glass on the internal side. Heat will be kept inside during winter, and during summer it can be released by opening windows. Shading heat absorbers Excessive heat can be brought into the house by any winds that have passed over surfaces with a great ability to absorb solar heat. Directly sunlit asphalt drive ways, concrete, hard paved patios, sand or stone surfaces will absorb sunlight and radiate it as heat. Whenever possible, these surfaces should be shaded either by pergolas or by dense greenery. Home owners should also take into account that all smooth and reflective surfaces (such as water or metal) can reflect the sun's rays. Any sunlight that initially reflected off the windows may be bounced right back towards them, so these surfaces should be placed away from the house. 5 Colors White surfaces reflect all visible light, while black surfaces absorb all visible light. Colors can also have a great impact on shading. Dark-colored surfaces on the ground can absorb heat and then radiate it, but they will not reflect direct sun rays through windows. Flat roofs should be painted white to help reflect the sun's heat away. 3. Recomended types of shading in Adelaide North side Short horizontal extensions on the north side can efficiently protect the whole façade from direct summer sun, allowing low-angled winter sun to enter the home. When combined with movable shades such as shutters, blinds or awnings, the north façade can be protected from reflected sun heat too. Summer sun at noon Winter sun at noon
It is not recommended to have a porch on the north side, as its depth will shade off the sun in winter. pergola Tree shadow Trees, with their dense leaves and constant evapotranspiration, create areas of cooling shadow. In the winter season when leaves have fallen, bare branches can still create a shadow that decreases heat gain on the north windows by almost 30%. For that reason, it is not advisable to use landscaping as shading for the north windows. East and west side Lit by the low-angled sun in the early morning and late afternoon, the east and west sides of the home are defendable by vertical shades such as blinds, shutters, louvres or rollup shades. Though verandas or pergolas can provide some benefit, it is recommended to install vertical shades on the perimeter. Rollups, blinds or light curtains can make the whole space more comfortable in summer. eaves line W N trellis E East window A ten-square-meter east-facing window can permit around 100,000 BTU to enter on a sunny summer day. That is the equivalent of a home furnace running for a couple of hours, and will result in overheating. The situation will be even worse on the west-facing window where the heat will be amplified by the already-high afternoon temperatures. Landscaping is an effective way of shading east and west sides of a home, whether by a group or rows of high trees or dense climbing plants and vines on trellises or pergolas. Bear in mind that retractable shades on the roof of a pergola are more adjustable in response to environment changes. South side As south-facing windows receive a very small amount of the summer heat, they have no need for sunshades. It is, however, advisable to install shutters with insulation for protection from winds and heat loss in winter. CALL NOW TO DISCUSS YOUR NEW HOME: 0438 909 920 pergola trellis 6 Architectural Energy Efficient Homes www.endurobuilders.com.au