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).