[boblalux (OP)]

Our upstairs room is directly under the inclined roof in which an inclined window has been built.  Although there is a sunlight blind attached to the window (roll up - roll down), it is dark-coloured, and gets very hot during the day.  The room is now nearly 30°C!!! I get the impression that most of the heat comes through the window and heats up the blind, which radiates into the room.

If I fit a 'panel' of aluminium foil between the blind and the window (inside),  will this allow the room to cool down?

[JimBob]

The sun protection needs to be on the outside of the window. Otherwise, the glass will heat greatly and radiate heat into the room.  An aluminum foil will not trap enough heat. It will also pick up hear and radiate it into the room if on the inside.

[RD]

The sun protection needs to be on the outside of the window ...

It would be ideal to have the mirrored-surface on the outside.

However, I think having metal-foil on the back of the curtain, reflecting some light back outside, would reduce the temperature in the room somewhat*

A ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN would be would be cheap experiment,  ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN . ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN , (but it's not designed to be exposed to direct sunlight).

[ * My loft-space has no windows, but is like an oven in summer,
 i.e. with or without windows, lofts are hot in summer ].

[chris]

* My loft-space has no windows, but is like an oven in summer, i.e. with or without windows, lofts are hot in summer

The roof (which is generally dark, meaning it is absorbing light energy) gets hot and radiates long wavelength infrared in all directions, including into the living space.

For both the window and the roof situation, putting a reflective surface between the living space and the window will cut down the heat flow into the room. Most of the heating effect is because visible light heats up non-reflective surfaces which then radiate the energy in all directions. Reflecting the light back out through the glass will have an effect. But, as others have said, the best solution is to prevent the light going through the glass in the first place.

What about a nice pair of shutters?

[Tim the Plumber]

Assuming that your roof is reasonably insulated then yes the roof window is the primary cause of excess heating, the room will always be warm from the heat rising from the rest of the house.

The reflecting foil above the blind will help at bit. Screwfix do a cheap bubble wrap insulation at £8.99, at least that's what the website says.

If you put this above the glass of the window it will be much more effective. It will look rubbish though. It might be an idea to make some sort of wooden shutter to fit over the outside of the window and have some of this stuff attached to the underside of the wood.

Good luck.

[jerrygg38]

I use both central AC and room AC. One room always faced the southern sun and the room AC worked hard to get to  75 degrees I like when it is 90 or 100 degrees. Recently I placed a 1/4 inch plywood panel inside the window and cut so the AC fits through it. Suddenly the room got cold and easily reached 70 degrees. You end up with the window, an airspace, and the wood. then the blind. It works well.

[Elizabeth35]

Mirror surface will do good.