Designing to beat the heat

By - , Build 164

Don’t underestimate the importance of good design and orientation in determining how well a home invites in winter sun while dealing with peak summer heat. For established homes, there are also retrofitting options.

Shading can help reduce summer overheating.
Shading can help reduce summer overheating.
Figure 1 Midday sun altitude angles for summer and winter solstice.
Figure 2 Features of passive design for cooling and to reduce interior heat build-up.

THIS SUMMER is being forecast as one of our hottest. Having an unusually hot summer can have an effect on how comfortable our houses are over the summer period.

Domestic spaces overheat as a result of:

  • too much unshaded north, east and west areas of glazing
  • lack of cross-ventilation
  • lack of insulation
  • lack of thermal mass.

Limiting summer solar heating

Options for reducing the potential for summer overheating that can be incorporated into new dwellings include:

  • louvres, roller blinds or movable shutters:
    • vertical for east and west elevations
    • horizontal for north elevations
  • designing layout of spaces to facilitate cross flow ventilation – include low-level and high-level opening windows on each side of the building
  • projecting eaves – design eave widths to limit summer sun but allow winter sun into north-facing living spaces (see Figure 1)
  • fixed projections and verandas – verandas also limit desirable winter sun entry
  • a pergola
  • awnings that preferably are retractable to allow winter sun to enter
  • maximising the level of insulation
  • glazing selections:
    • clear – transmits heat, maximises winter and summer gain – radiates 80% to interior
    • tinted body or film glass – absorbs heat, radiates 60% to interior, blocks UV, reduces solar gain by 30–70%
    • reflective – reflects heat, radiates 40% to interior, lowers summer and winter gains
  • deciduous planting to provide summer shading.
Figure 1 Midday sun altitude angles for summer and winter solstice.

Maximising summer cooling

In addition to minimising the potential for heat build-up, the building design should also facilitate cooling air movement (see Figure 2) by:

  • orienting buildings to maximise their exposure to the prevailing summer wind direction
  • elevating the building to catch stronger winds
  • having a relatively narrow plan across the prevailing wind direction to facilitate passage of air through the building
  • locating window and door openings to facilitate the passage of air
  • incorporating vertical ventilation pathways (roof windows, opening clerestory windows) to utilise the air movement created by the stack effect
  • having opening windows and doors to the prevailing cool wind − horizontal openings near floor level are more effective than vertical openings particularly when paired in open plan spaces with high-level windows on the opposite side of the building
  • installing ceiling fans to increase air movement
  • specifying vents that are installed into window joinery
  • specifying light or cool-coloured exterior finishes to walls and roofs to reflect rather than absorb heat
  • minimising external surfaces, especially adjacent to windows, that reflect heat into the building
  • creating taller internal spaces – provides more space at ceiling level for warmer air to accumulate but keeps it above occupants’ heads.
Figure 2 Features of passive design for cooling and to reduce interior heat build-up.

What about existing houses?

For an existing house, the options to minimise summer overheating are somewhat limited in the short term. Research shows that there is a significant increase in heat pumps installed for winter warmth now being used for summer cooling.

Other options include:

  • installing external retractable sunshades or shutters or shade sails provided they can be securely fixed to the building without compromising the weathertightness of the cladding – internal sunscreen blinds and shutters do not stop the heat passing into the building through the glazing
  • fitting restrictors or double tongue catches to existing windows so that some natural ventilation can occur during the day
  • constructing pergolas if permitted, preferably independent of the building, and encouraging the growth of deciduous vegetation
  • ensuring that openable roof windows are left open to allow rising warm air to exit
  • installing ceiling or wall fans to increase air movement where people sit or stay
  • retrofitting vents into window joinery
  • increasing the levels of insulation particularly at ceiling level
  • applying light or cool colours when repainting walls and roofs.

Resources available

Various resources assist in passive design that allows the sun in for winter heating while keeping it out to prevent summer overheating. Examples include:

 

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Articles are correct at the time of publication but may have since become outdated.

Shading can help reduce summer overheating.
Shading can help reduce summer overheating.
Figure 1 Midday sun altitude angles for summer and winter solstice.
Figure 2 Features of passive design for cooling and to reduce interior heat build-up.

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