Maximum indoor temperatures

It is well known that indoor temperatures above 25°C are not advisable and that figure is in the Passivhaus standards for new and retrofitted buildings.

Does anyone have a corresponding number for bedrooms? Surely it should be cooler?

My problem is 1st floor overheating. I want to avoid fixing anything to the walls because of thermal bridging and likely problems fixing future EWI.

A 2 storey pergola doesn’t seem practical.

Edit: I have found advice to not heat above:
16 °C
18 °C
18.5 °C.

I haven’t found any advice on “cool to” temperatures.

We heat our well insulated new build to 18oC and its fine.

A really airtight house doesn’t need to be heated to such a high temperature as there is no air movement to give a cooling effect.

@epickering, thanks for your reply. That can certainly be a target heating temperature but seems low for summer cooling. Do you have any overhearing issues in summer or is that temperature maintained passively?

This American site says “the U.S. Department of Energy recommends the best AC setting during summer is 78°F (26°C) when you are home” and then goes on to say in relation to night temperatures that “a study found the best sleep happens as the body reaches “thermoneutrality” when environmental temperatures are at 86°F [30ºC] (nude and uncovered) or 60 to 66°F [16ºC to 19ºC] (wearing pyjamas and covered by a sheet) This suggests one tactic to help enjoy a good night’s sleep during the summer is to raise your AC to a warmer setting, say 80°F [27ºC] while using lighter bedding and sleepwear.”

The inference is that Passivhaus’s 25ºC should be reasonable for bedrooms too for most folk, but perhaps with modification to their customary bedding/clothing.
I lived in Jakarta for a couple of years. Mean daytime max/ night time min are remarkably consistent at 31-33/25-26ºC throughout the year. We found that we could sleep comfortably (naked+sheet to be pushed off on the hotter nights), with windows open, provided that we had run the AC for half an hour before bedtime to flush away some of the day’s heat.

Humidity is also key of course. It’s 11:30pm in Jakarta now and the weather app tells me that it is 26ºC/89%RH which sounds about normal. I think humidity tends to be lower on the hottest UK days? The Met Office says that during the July 2022 heatwave, “temperatures soared in mid-summer sunshine, with the relative humidity below 20% in the dry air.”

My conclusion is that 25ºC as a design target should be OK for most people, with perhaps fans to help on extreme days.

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Thanks @Gabriel_Hyde, that is interesting. Jakarta temperatures seem pleasant. My tropical experience is in Zambia, which has much wilder swings, leading to greater discomfort. At least where I was, in Lusaka province, the humidity was normally OK.

We just turn the boiler off in April and open the windows!

Opening the windows only works when the outside air temperature is tolerable. I’m in the south east and recent summer temperatures have been really high.

When I was in India the AC was set to 32C while the outdoor temperatures breached +40C. the decrement factor of the concrete walls radiated heat for most of the night. So it all depends on the prevailing conditions.

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