That would be a problem. But an inside flat screen with a hole in it could work.

This is what we have but our windows open inwards.

It's the bit about the window staying behind the screen I'm not getting, since they open outwards. I expect I'm just heing dense

He was definitely thinking the window opens inwards!

So our (inward opening) bedroom window has an externally fixed fine mesh screen, with a ceiling fan and the window open we can manage the heat just fine!

This may be a good bet. The flexible mesh kind come with velcro tape.

This conversation has a definite air of déjà vu about it, and LiW, I think you were also the subject victim! 🤣

Well yes, but I'm married to my very heat intolerant OH, not you .

Luckily for both of us.

It doesn't get that hot in the UK!

It's all good. I gave some workable ideas to explore

When the window is opened enough for the vent tube to go thru is the inside perimeter of the window a flat surface where an inside screen could be placed?

Not really, no. I think the flexible mesh thing may be the best bet.

Hope you get it sorted!

I gather summer temperatures in southern England have gone up in recent years to the point where air conditioning is worth having. I have not lived in England since 1997 and that was in the Midlands.

I'm currently working on a garage pit. My place came with a double garage and at first I did keep the car in there but the current car is too long to fit. It is ideal for motorbikes though and there are 2 in there at the moment. When they put in the concrete base for the garage they left a rectangular hole for a potential pit but did nothing more. The wooden shuttering was still in place and there was a load of ballast (sand and stones for concrete making) in the hole. My plan is to use the pit to provide a comfortable working height for doing jobs on the bikes. A lot of bikers have a lift for that purpose but this seems cheaper and safer. I think I have discovered where the ballast came from as it is what was used instead of hardcore, under the concrete. Rubble would have been a better choice as some of the ballast has escaped into the pit hole, leaving voids under the concrete. I am trying to stabilise it by hammering lumps of rubble left from previous projects into those voids. As I dig deeper I can insert retaining bricks around the edge of the hole.

Aren't UK windows typically devoid of screens? How are you blocking insects on all your other (openable) windows?

Mesh roll cut to fit, with velcro fixings. But we don't open all the windows, not necessary.