Yes because modern Scandinavian homes have huge uncovered well insulated windows to allow the sun in as a free radiator during winter. I calculated my living room window to be somewhere between 3000W-5000W worth of radiation. Due to the high insulation this doesn’t dissipate during the night in a heatwave, so it doesn’t matter if the outside temp is 18°
Why? Because housing regulations dictated it. No one expected 2018 levels of heatwaves to be the new norm (except all the experts).
My old apartment reached temps of 35° measured at midnight for weeks in the 2018 heatwave despite the outdoor temp not rising much above 30°. Morning temps where around 28° with all windows open. If the morning baseline was lower the night temps might have been possible to sleep in but the insulation kept temps high throughout.
I live in a rental on 4th floor, unfortunately I can’t add anything to the outside of the windows… And putting anything on the inside risks trapping the heat in the glass and cracking it.
As long as there is no space for air to get trapped between the glass and a reflector, it’s no issue to put it on the inside (although its more effective when on the outside) - those foils that can be put on the window using a little bit of water do a good job. Biggest problem are dark objects when only away a few centimeters from the glass - those will crack the window in no time.
At least where i live, non-permanent modifications that use things like suction cups don’t need approval from a landlord.
modern Scandinavian homes have huge uncovered well insulated windows to allow the sun in as a free radiator during winter
Which of course is why you pull down the blinds to limit heating of surfaces inside during the day and let the insulation keep heat out.
Due to the high insulation this doesn’t dissipate during the night in a heatwave, so it doesn’t matter if the outside temp is 18°
Which is why you of course open windows during the night to cool things off when temps are lower.
it’s not perfect, and helps less with high nighttime temps, but it makes the proper insulated home work with you and not against you as much as possible.
You need the blinds on the outside of the window, otherwise this helps minimally, especially if the whole southwest facing wall is glass, which turns the apartment into a greenhouse.
During the heatwave, night was the only time I could cool the room with portable AC, provided all windows were closed to not let heat in.
We have a massive south facing side filled with windows (and two double glass doors), covers about 80% of the living area, all blinds mounted inside. We still had 9°C lower temps inside compared to outside during the worst hours of the heat wave. Yes 28°C is still hot, but much better than the 37°C we had outside.
If its still 35 during the night then it will rise to that temperature inside regardless of insulation. Maybe more quickly without it. The point was insulation. If the min night temperature is 35, then you have air conditioner or you die.
This is what I do, living likewise in a well insulated northern house that sees sustained high temps.
I’d gladly take my well insulated home during any heat wave over a poorly insulated one. Anyone who thinks less insulation is the solution is misunderstanding the problem.
It’s fine to be frustrated by high temps. It sucks. But insulation is a friend in your fight against high temps, not a foe. Use insulation to resist heat rise during the day and use heavy ventilation at night to exhaust and exchange for cooler air. The alternative is to have low insulation and accept indoor temps being constantly pinned to outdoor ambient which is a recipe for discomfort.
Maybe read the last part. My current apartment is much better than my old one since I can actually create a wind tunnel, but even then it doesn’t lower it below 25°
And any apartment I’ve had didn’t allow for adding anything to the outside unfortunately. The apartments just weren’t designed for summer comfort.
I see your point. I do not see how you cannot cover the outside of thr window yet. I live on the 4th floor of an absolutrly insulated building in a much hotter region than Scandinavia. Covering window and letting air go during cooler nights keep temperature at approx -6 compared to outside temp. If outside temp doesnt go below say 26 during the night, then its air conditioning either way, regardless of insulating (but with insulation it remains cooler for longer).
Yes because modern Scandinavian homes have huge uncovered well insulated windows to allow the sun in as a free radiator during winter. I calculated my living room window to be somewhere between 3000W-5000W worth of radiation. Due to the high insulation this doesn’t dissipate during the night in a heatwave, so it doesn’t matter if the outside temp is 18°
Why? Because housing regulations dictated it. No one expected 2018 levels of heatwaves to be the new norm (except all the experts).
My old apartment reached temps of 35° measured at midnight for weeks in the 2018 heatwave despite the outdoor temp not rising much above 30°. Morning temps where around 28° with all windows open. If the morning baseline was lower the night temps might have been possible to sleep in but the insulation kept temps high throughout.
I’m Dutch and in a similar situation. There’s these stick-on sun screens with suction cups: https://huizedop.nl/wp-content/uploads/2025/06/novalux-zonwering-met-zuignappen.jpg
Works wonders, can be made to size, they’re relatively cheap. Hope it’ll help.
I live in a rental on 4th floor, unfortunately I can’t add anything to the outside of the windows… And putting anything on the inside risks trapping the heat in the glass and cracking it.
It’s fine to put aluminium foil on the inside. Sunlight is reflected out without heating up the glass. That’s what worked for me anyway.
As long as there is no space for air to get trapped between the glass and a reflector, it’s no issue to put it on the inside (although its more effective when on the outside) - those foils that can be put on the window using a little bit of water do a good job. Biggest problem are dark objects when only away a few centimeters from the glass - those will crack the window in no time.
At least where i live, non-permanent modifications that use things like suction cups don’t need approval from a landlord.
Great stuff.
Which of course is why you pull down the blinds to limit heating of surfaces inside during the day and let the insulation keep heat out.
Which is why you of course open windows during the night to cool things off when temps are lower.
it’s not perfect, and helps less with high nighttime temps, but it makes the proper insulated home work with you and not against you as much as possible.
You need the blinds on the outside of the window, otherwise this helps minimally, especially if the whole southwest facing wall is glass, which turns the apartment into a greenhouse.
During the heatwave, night was the only time I could cool the room with portable AC, provided all windows were closed to not let heat in.
We have a massive south facing side filled with windows (and two double glass doors), covers about 80% of the living area, all blinds mounted inside. We still had 9°C lower temps inside compared to outside during the worst hours of the heat wave. Yes 28°C is still hot, but much better than the 37°C we had outside.
Open all fucking windows during the night and close them and barrier them from the outside during the day.
Works perfectly when it’s still 35°c in the middle of the night 👍🏻
If its still 35 during the night then it will rise to that temperature inside regardless of insulation. Maybe more quickly without it. The point was insulation. If the min night temperature is 35, then you have air conditioner or you die.
This is what I do, living likewise in a well insulated northern house that sees sustained high temps.
I’d gladly take my well insulated home during any heat wave over a poorly insulated one. Anyone who thinks less insulation is the solution is misunderstanding the problem.
It’s fine to be frustrated by high temps. It sucks. But insulation is a friend in your fight against high temps, not a foe. Use insulation to resist heat rise during the day and use heavy ventilation at night to exhaust and exchange for cooler air. The alternative is to have low insulation and accept indoor temps being constantly pinned to outdoor ambient which is a recipe for discomfort.
Maybe read the last part. My current apartment is much better than my old one since I can actually create a wind tunnel, but even then it doesn’t lower it below 25°
And any apartment I’ve had didn’t allow for adding anything to the outside unfortunately. The apartments just weren’t designed for summer comfort.
I see your point. I do not see how you cannot cover the outside of thr window yet. I live on the 4th floor of an absolutrly insulated building in a much hotter region than Scandinavia. Covering window and letting air go during cooler nights keep temperature at approx -6 compared to outside temp. If outside temp doesnt go below say 26 during the night, then its air conditioning either way, regardless of insulating (but with insulation it remains cooler for longer).