How does the external heat get into your house? Thermal bridging, solar gain or air leakage?

The answer is…  more than likely is a bit of everything.  You aren’t alone, many homes all over the world can suffer from overheating.

During summer, the upper floor of a two-storey building often experiences severe overheating and stratification because of the following:

  1. Windows and skylights are primary entry points for heat energy, with bottom-floor windows also significantly contributing to overheating.
  2. Insulation gaps of just 5% can account for 30-50% of heat loss/gain.
  3. Downstairs heat sources like cooking, appliances, and halogen lighting heat transfer 20-25% upstairs, exacerbated by downstairs window-induced warmth.
  4. Air Leakage: Throughout the building envelope, both upstairs and downstairs
    • Lack of draught stoppers in exhaust fans.
    • Open holes around ducted heating returns or outlets.
    • Internal cavity sliders connected to the roof.

A typical reaction of occupants, when faced with an overheating upstairs in a double storey home…

Heat Rises.Abandon the second floor, and only cool downstairs. – The net effect: A greater temperature differential, exacerbated air leakage at the top and bottom of the building.  A large difference in temperature inside a leaky building creates greater pressures and air moving faster through gaps.

In winter, if you have an overheated upstairs, some people might try to close off ducted heating outlets upstairs.  This can aggravate air leakage via the ducted heating system and again, this will “NOT” help.  Click here for more information on this.

Heat will always find its way to the highest part of the house, no matter where the heat outlets are. A principle demonstrated perfectly by hot air balloons.

Solutions to reduce over heating

  • Fix up gaps in your insulation.
  • Make the building more airtight.
  • Install a split system on the second floor to reduce temperature stratification.
  • Add some shading to your windows in the west and east.
  • Add tinting onto your windows.
  • Install some ducts to transfer air from upstairs to downstairs with an inline fan.  (Avoid depressurisation induced air leakage in the ducts)
  • Shade windows, upstairs and downstairs, stop heat absorption via glazing throughout the home.

Extreme solutions to reduce over heating

Separate the first and second floor entirely with the installation of a doorway at the top or bottom of a staircase.  After doing this it’s good practice to ensure insulation is placed in between floors, to contain thermal bridging. It could also be a good idea for each floor to have its own dedicated ducted heating system or at least zoned off area. When the ducted heating is used upstairs, the door must be opened to connect upstairs to the return inlet, otherwise air leakage is induced.

Extreme solutions for new builds

Installing a centralized ERV/HRV ventilation system, reduces stratification considerably, especially when combined with air tightness in the building envelope.

For an ERV/HRV system, ensure the building has:

  1. Consistent insulation
  2. An airtight envelope
  3. Well shaded glazing
  4. Alignment with passive house principles.

Overheating is a very common issue in Australian homes, especially in double storey builds, contact us for any queries on your home.