The home: shade for outdoor areas within the home
Many homes have outdoor areas such as backyards, courtyards, decks, swimming pools, play areas and sandpits. The provision of sufficient UVR protective shade for outdoor areas within the home will contribute to the health and safety of family members (particularly children) and visitors. Well-designed shade will also enhance the aesthetic qualities of the home environment, resulting in outdoor spaces that are both visually appealing and comfortable to use. It should be noted, however, that shade will not provide total UVR protection. The use of personal protection measures, ie sun protective clothing, hats, sunscreen and sunglasses is recommended. Care should also be taken to stay out of the sun between 11am and 4pm during summer, when daily UVR levels are generally at their peak.
recommendations and considerations
general outdoor areas
Partial shade is recommended for general outdoor areas, especially over grass which needs some sun for growth. Natural shade is the most appropriate option. If sufficient shade is available at all times of the day, it will allow greater flexibility for children’s play. Planting on the northern, northeastern and northwestern aspects of the site is recommended.
outdoor eating areas; decks and patios
Shade is recommended over outdoor eating and similar areas. eg decks and patios. Consider using a combination of natural and built shade, eg a trellis covered with a climbing vine, as it will enhance the visual appeal of the space. An adjustable built system and/or deciduous vegetation will allow for heat and light penetration during the cooler months.
sandpits and play equipment
Shade throughout the summer months is recommended over sandpits, although built shade may be the most appropriate option. Pull-down screens at the side of the structure will help protect against indirect UVR. Partial shade is recommended for the area which contains fixed play equipment. Natural shade is the most appropriate option. The ability to supervise children is an important issue. Inappropriately located trees and shrubs and shade structures with solid and/or opaque sides may obstruct views of children playing.
pool areas
Shade throughout the summer is recommended over the relaxation area adjacent to the pool. Consider using built shade, as tree leaves may create ongoing pool maintenance problems. Pool lounges and other seats should be placed in the shade, particularly during the middle period of the day.
verandahs
Verandahs will provide permanent shade as well as rain protection. The angle of the roof and the extent of overhang should be designed to maximise shade for the major part of the day, especially during summer. The width of the verandah should allow sufficient space for activities such as outdoor eating or children’s play to occur. Vertical pull-down blinds at the side of a verandah can provide additional protection from UVR when the sun is low in the sky.
Primary shading element: five main categories of materials for shade structures
There are five main categories of materials which can be used for the primary shading element.
standard building materials These include:
• metal or tile roofing
• timber
• concrete
• masonry
• other conventional building materials.
Significant advantages over other materials are their assured long life, non-combustibility (except for timber), waterproofing and resistance to vandalism. Given their long life, it is often possible to source these materials second hand, which reduces the need for the manufacture of new materials.
However, standard building materials are characterised by straight line geometry and, unless creatively and carefully designed, can lack aesthetic appeal. They also require a substantial supporting structure.
rigid translucent materials These include:
• treated glass
• polycarbonate
• acrylic
• fibreglass sheeting.
These materials block direct UVR while allowing the transmission of heat and diffuse light. They are most suitable for structures intended for winter UVR protection. Being waterproof, they also offer rain protection and can be used to collect water.
It should be noted, however, that many rigid translucent materials, especially the plastic-derived ones, carry a number of environmental costs. It is therefore recommended that rigid translucent materials only be used where some other environmental benefit can be achieved, for example, where their use may offset or reduce the need for artificial lighting or heating. Rigid translucent materials are typically supported at relatively close centres (approximately one metre) on metal or timber framing. Relatively high maintenance is required, both for cleaning and inspections of gaskets and fixings. If correctly installed, sealed and maintained, their life span is medium- to long-term.
Pergolas and Cabanas: Components of built shade
Built shade consists of:
• the supporting structure, which is required to maintain the shading element in position
• the primary shading element, ie the material that comprises the canopy or roof.
The properties of the shading element, such as mass and span, will strongly influence the design of the required supporting structure. For example:
• relatively lightweight materials such as metal or translucent roof sheeting, which are capable of spanning up to 1.2 metres, will require less supporting structure than a roof of terracotta tiles, which are significantly heavier and require supporting battens about every 300mm
• a project that uses structural fabric or shade cloth as the primary shading element will require less supporting structure than metal roof sheeting, as fabrics are lighter and span greater distances when in tension
• solid fabrics such as canvas or reinforced PVC do not allow wind to pass through in the same manner as open-weave shade cloth, and therefore require supporting structures that can resist a much higher level of wind loading.
This relationship between the shading element and supporting structure is significant in determining the functional performance of built shade. Short-span structural systems necessarily result in a high number of supporting columns. While in some situations this may not present a problem, locations such as school playgrounds require shaded areas substantially free of columns. The design brief should define the requirements of the area to be shaded, and the designer should ensure that span characteristics of the supporting structure comply with the requirements of the brief.
The final cost of built shade is also significantly affected by the relationship between the shading element and supporting structure. Selecting a cheap material for the shading element will not be costeffective if an extensive and costly structure is required to support the selected material. In order to achieve the most cost-effective outcome, the designer must select materials and structural systems that together provide the optimum solution for the brief.
In planning built shade, the required life of the shade structure should be determined and designed for. The post-life use of the materials, ie how they may be re-used, recycled or disposed, should also be considered and designed for.
For all built structures, large or small, it is essential to seek professional structural advice and certification from a qualified structural engineer. This certification is required for building applications and will ensure structural integrity and safety.
Pergolas and Cabanas: Providing shade
There are numerous types of shade systems, incorporating natural or built components, or a combination of these. The following sections describe the major factors and considerations for each of these approaches. Built shade is designed and constructed of manufactured components, unlike natural shade solutions that use trees, large shrubs, vines and ground covers to block direct UVR and absorb indirect UVR. A comprehensive shade strategy will most likely incorporate both built and natural shade solutions.
Natural shade
The use of natural shade can be one of the most effective and aesthetically appealing ways of providing shade. Vegetation offers seasonal variations in perfume, colour and sounds. Many species produce colourful flowers or have attractive foliage or bark, some make good habitats for wildlife and many species can be used to screen unwanted views, give wind protection and provide privacy. Other materials cannot accomplish these things as well as vegetation can.
The use of vegetation for shade also has a number of environmental benefits including:
• less need to use non-renewable resources (used in many building materials)
• energy saved in comparison with built shade systems, which often have high embodied energy (this is the sum of all energy used to produce a material, product or structure including extraction and processing of raw materials, manufacturing, assembly and transportation)
• fewer disposal problems as plants generally act as nutrients during decomposition
• absorption of carbon dioxide in the atmosphere, thereby potentially counter-balancing the ‘greenhouse effect’.
The effectiveness of natural shade depends on the density of the foliage. Foliage and timber will block direct UVR, but gaps in the canopy will allow UVR to penetrate. The size of the canopy (of a tree or group of trees) is also an important consideration. The larger the canopy diameter, the greater the opportunity for protection from scattered or reflected UVR. The height of the branches from the ground can also influence the effectiveness of natural shade, with low branches providing better protection.
It should be noted that introducing complete, or even partial shading by vegetation may affect the viability of existing under-storey vegetation. The landscape of shaded areas, as a result, may need to be treated differently to that of non-shaded areas.
Built shade
Built shade comprises all shade systems that are constructed, as distinct from natural shade. One advantage of using built shade systems, especially permanent systems, is that they can often be used for a number of purposes besides providing shade. For example, a shade structure could be used to collect rainwater for irrigation; or a structure could support photovoltaic cells, (either as a mounted array or as a laminated roofing material) for the generation of electricity.
Built shade systems can be either stand-alone structures, or systems which are incorporated into existing buildings and other facilities. They can be categorised as follows:
• permanent systems
• demountable systems
• adjustable systems.
Permanent systems
Permanent systems are considered to be those which last for at least 10 years. Their structure commonly comprises a roof with associated supporting structure and sometimes side protection, to reduce the effects of indirect UVR.
It is very important that permanent roofing systems are durable as they need to withstand the harshest of conditions, eg exposure to sun, rain and wind uplift. From an environmental and economic point of view, regular maintenance of these systems is essential to ensure their long life span, thus reducing the need for replacement of materials.
The component parts of a permanent system should either be cheap and easy to replace, or they should have a life span equivalent to that of the main parts of the structure. There is no point having a metal roof with a useful life of 60 years that needs to be replaced after 10 years, because the supporting structure or fixings did not last.
Permanent systems are likely to gain more favourable consideration from funding bodies that provide capital works subsidies.
Demountable systems
Demountable systems are likely to be a more practical and cost-effective alternative to permanent structures where:
• shade needs are infrequent
• temporary shade is required at varying locations
• a permanent structure is incompatible with the range of activities that take place at a site.
Some demountable systems can be adapted for use in a variety of situations such as above tiered seating as well as over large flat surface areas. Some can be placed on a variety of ground surface conditions such as sand, grass and pavement.
Demountable systems may be designed in modular forms that can be extended or contracted depending on the circumstances. This may consist of a lightweight framework and fabric infills which provide overhead cover, as well as walls where they are required. Alternatively, they may comprise tent-like forms, such as large marquees or lightweight tension membrane structures.
The demountable system should be easy to erect and dismantle. Complex assemblies are time-consuming and increase the risk of incorrect installation. For example, tension membrane structures are quick to erect because the canopy is in one piece. Structures using conventional materials usually take longer to erect because there are more components and fixings.
Demountable systems need to be strong enough to withstand the wear resulting from frequent transportation, assembly and dismantling. The availability of suitable storage facilities is essential to maintain the product in good condition. Their temporary nature means that they are less likely to be subject to vandalism.
Adjustable systems
Adjustable systems range from very simple devices to those which use sophisticated technology. They offer a high degree of flexibility, allowing protection levels to be modified according to the time of day or season, and to satisfy a variety of user needs. They can be either permanent or demountable.
Adjustable shade systems should be easy and convenient to operate. For example, if operation is time-consuming, difficult or requires specialist attention, use of a device may be discouraged. Systems should also be easy to operate in storms when prompt dismantling of the structure may be necessary
Components such as pulleys and cables should be corrosion resistant; use of stainless steel is recommended where possible.
Adjustable shade systems are usually attached to a permanent structure and fall broadly into the following two types:
• retractable devices such as canvas awnings
• louvred devices
retractable devices
These can cover large areas and can, in some cases, offer rain as well as UVR protection. The most common of these is of the fabric ‘roll-out’ type. One simple form is the fabric awning, cantilevered or supported by a pergola-like frame. Fabric awnings can also be supported on folding or telescopic arms, which allow adjustments to achieve the required vertical shadow angle. These devices are available in manually operated or motorised form.
Where fabric canopies are tensioned on extension, it is important that they are as taut as possible. This is because movement and flapping of the canopy will reduce the life span of the device. The canopy should be able to be tightened and adjusted as the fabric stretches over time.
It is also important to ensure that the canopy can be adequately stored when retracted. Folding back into a well-ventilated box will extend the life span of the device and prevent accidental damage.
There are positive and negative environmental impacts associated with retractable devices. The negative impacts include those resulting from the manufacture and disposal of plastic and other synthetic materials commonly used in canopy devices. On the other hand, only a small volume of material, and therefore less embodied energy, is required to produce the canopies.
louvred devices
A range of manually adjusted louvre roof systems are commercially available. These systems offer a high degree of control and flexibility for shading of outdoor areas. They can be adjusted to totally exclude the sun’s rays or to create partial shade. Most louvre designs have the added advantage of providing protection against rain.
The louvre blades are usually an aerofoil design, fabricated in pre-painted steel or aluminium. Other materials can also be used for the louvre blades. For example, corrugated polycarbonate sheet could be used in situations where UVR protection and ventilation are required, without excluding warmth and light. Louvres of expanded metal mesh could be used where waterproofing is not a priority
If the louvres are placed vertically, the louvre wall can be an effective wind deflector, or wind gatherer, in addition to providing protection against direct and indirect UVR.
Also available in the marketplace are louvred roofs which open and close automatically in response to sensors triggered by wind, rain and solar radiation.
Designing pergolas and cabanas for comfort: general principles
In designing comfortable shaded outdoor areas; e.g. pergolas and cabanas that will be attractive for users, it may be necessary to adapt or modify the microclimate (local climatic conditions) of a site. Different strategies can be incorporated during the design stage of a pergolas and cabanas to counteract the negative effects of the microclimate (yet within the broad context of the prevailing climatic conditions).
A brief discussion of the issues and strategies follows.
• provide shade which excludes UVR but admits the sun’s warmth and light. Translucent polycarbonate sheeting is ideal for this purpose
• adjustable devices may suit year-round use
• deciduous trees and other plants will allow warmth and light to penetrate when they lose their foliage. Alternative UVR protection may be needed for outdoor spaces during these periods
• provide alternative external spaces for use in different seasons. Where space is available, this may be an easier and more economical solution
• locate planned summer shade structures so as to not increase winter shade
• planting can be used to form north-facing courtyards or outdoor enclosures for social gatherings or outdoor activities. Plant shelter belts or wind screens to the south, southwest and west, leaving open sunny lawns to the north, adjacent to covered outdoor paving that is warmed by the low winter sun.
• introduce passive solar heating principles while excluding UVR. This can be done by using dark coloured external materials to absorb heat, such as some paving materials. However, ensure shading to paving in summer to limit indirect UVR and prevent the radiation of heat to shaded areas.
in all locations cooling is recommended during the summer months
• design the space to capture any prevailing breezes
• provide shade to the openings of shade structures during summer
• projecting eaves attached to buildings will cool the indoor and outdoor spaces during the summer months. Eaves will also reduce direct UVR and indirect UVR, which could otherwise reflect and scatter off wall surfaces.
shading of walls and paved areas can significantly increase summer comfort levels
• when exposed to direct sun, walls and paved surfaces gain heat, which is ‘stored’ and reradiated, increasing and maintaining the surrounding temperature. In summer, this can result in overheated, unpleasant outdoor spaces. By shading walls and paved areas, the heating of these surfaces can be significantly reduced and comfort levels enhanced
• glare caused by the reflection of bright sunlight from hard surfaces such as walls and paving can be unpleasant and increase the perception of heat. Shading of such surfaces reduces glare and results in more comfortable outdoor spaces.
cross-ventillation will provide relief from excessive humidity and prevent overheating of spaces.
• where possible, orient openings towards the direction from which cooling breezes come. However, if the requirements of a particular activity do not allow for the ideal orientation, take measures to channel the wind and change its direction
• air flow through the whole structure is due to a pressure difference between the windward and the leeward sides. Wing walls, baffles, or dense groups of bushes positioned on opposite sides of a structure will have the effect of inducing airflow.
the exclusion of wind in the cooler part of the year should be considered
• observe the direction of any unwanted cold winter winds and provide suitable windbreaks. These may take the form of built attachments (such as screens) or dense tree and shrub ‘shelter belts’ adjacent to the area requiring protection
in many locations, structures must be able to withstand strong winds.
• gabled or hipped roof forms of pitch 30 produce the best chances for equal pressure spread over the building to avoid eddying and roof lift-off. Tie-down and bracing should be designed in accordance with Code of Practice for general structural design and design loadings for buildings
• trees located in proximity to a structure can significantly reduce wind loading on the structure
• select materials that are well suited to exposed locations with high winds (eg metal roof sheeting) rather than those inherently more fragile (eg low tensile shade cloth sails).