Okay so we’ve lived in our 1950’s Terraced ex council house for 3 years,
Each summer, upstairs gets stupidly hot,

Throughout the house we have upvc double glazing although some of it is in need of updating,

In the loft there’s probably around 300mm of fairly recent (5years?) insulation between and over the joists,

I imagine replacing this would be pointless,

My questions are;
Can I add insulation boards between the rafters or staple that shiny bubble wrap stuff to the rafters?

If I can, would it really be worth it?

Are you saying the house is hot today?
Or you want it hotter in winter?

Dont think the heat is coming downwards, sounds like the insulation is doing its job.

The loft is obviously really hot, surely if it’s too hot it can heat the rooms below?

Winter it gets somewhat cold but we have quality central heating so maybe don’t notice the poor insulation so much.

sounds like the insulation is doing its job

This – the insulation is stopping the hot air escaping. My house is the same after the insulation was replaced and upgraded – it’s like a bloody sauna.

Nice and warm in winter though.

More insulation above laid on top of existing. Shut the curtains on the southeast, south and southwest sides when you hot out in the morning. Open the windows when you get home. Have plants on the windowsills , water them in the evening.

Leave the loft hatch open so hot air can vent into the loft. Add more vents in the loft, it’s designed to be a “cold” space.

Lightweight, fluffy insulation is great at keeping heat in. Not great when it is overheated.

Look at houses on continent that have much heavier roofs – trying up up the specific heat capacity so that sun is less likely to warm it all up and thump heat in house. It’s called decrement delay, few of our houses a rebuilt with it in mind.

Ap’s advice re curtains and plants is best – change your behaviour, not just throw more insulation in.

As per Murray

I’d also look at venting the loft space… it’s probably also humid which may lead to its own problems.

By far the most effective per £ we had was fitting left over reflective under-laminate insulation OUTSIDE upstairs South facing windows..
This made a HUGE difference.

It’s OK inside but outside is much better.

The only cost was some removable velcro stuff…

A cheap extractor would probably make a big difference

Must admit that I’ve toyed with the idea of AC in the house for those really warm days.

Got to persuade Mrs Gti to turn the ****’ Aga off first though…. why do women always moan that they are cold?

Since having new insulation laid a few years back, as others have done, we open the loft hatch during heatwaves to help cool the rooms.