By Trevor Pringle - 1 February 2018, Build 164

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.

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.