Thermal Performance in Extreme Hot Weather

The record-breaking high temperatures over the past few days provided great validation that good insulation and decent air tightness keep heat out in summer as well as keeping heat in in winter.

Internal and External temperatures; 17th – 20th July 2022

Any house is going to heat up a bit, through a combination of heat transfer from the outside as well as internal gains from appliances and occupants. The biggest risk is a huge amount of solar gain through windows but by keeping blinds closed (and windows closed, obviously) that can be minimised.

With such high temperatures being forecast I took the precaution of slightly over-cooling by opening some windows overnight beforehand, and then opening at night whenever the outside temperature was lower than the inside (which was not until about 04:30 on the morning of the 19th).

The master bedroom stayed below 25 degrees at all times; I’m happy with that.

CC BY-SA 4.0 Thermal Performance in Extreme Hot Weather by Marsh Flatts Farm Self Build Diary is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

4 thoughts on “Thermal Performance in Extreme Hot Weather

  1. Hi David,
    I was just looking through your website to check on a few aspects and spotted this update. We have been wondering how our (proposed) house will cope with the extreme temperatures and its great (and reassuring) to see the performance of Marsh Flatts Farm.

    • Hi Pete,
      Since the design of a Passivhaus takes account of the risk of over-heating (due to solar gain), hot-weather performance tends to be very good – so I’m sure your new house will cope well.
      A key thing is to get the heat out overnight. That’s problematic when external noise makes it difficult to sleep with bedroom windows open (e.g. in a city centre location) – so again you should be fine. It’s worth considering how to maintain security when ground-floor windows are left open overnight.

      • Thanks David,
        One aspect of our design that will assist in removing heat overnight is the high level atrium with automatic windows that runs along the majority of the house. I imagine these will act in a similar way to the windows at the top landing in your house.

        • Yes – the atrium windows will be good – ideally coupled with a low-level window or vent you can open (automatically?) at the same time, to let in some cooler air to replace what’s leaving via the atrium windows.

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