[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 space-blanket would be would be cheap experiment,  ready-made is more expensive . Bubble-wrap made from "space blanket" is also available , (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.

[universalservices]

You should put a shed on the top of window outside so that it'll stop heating the window glass.

our site heatproofing.pk and forums: heating.freeforums.net

[Bored chemist]

Imagine you are on teh roof, looking in through the window.
If the blind is in place you see a dark blind. If yo open the blind you see the sunlight reflected by a sheet of metal.
The light you see reflected is energy that's not going into the room.
If it doesn't go in (or, at least, doesn't stay in) then it can't heat the room.
So it would be better to leave the blind open and put a mirror of some sort in its place.
That aluminised bubble warp stuff would be really great.

[evan_au]

Modern houses line the roof with insulation and aluminium foil, to reduce the amount of heat coming in through the roof in summer, and reduce the amount of heat lost through the roof in winter. Unfortunately, if your roof is already in place, it is harder to install something like this as an add-on.

I imagine that a solar panel on the roof (separated from the roof by a small gap) would also cut down heat in the loft in summer.

Previous posts have discussed the role that highly-reflective aluminium can play in reflecting light and heat back to the outside, so it doesn't heat your loft.
- But there is an equally important role it can play, even in a totally dark loft, due to its low emissivity
- Even if the aluminium gets hot by contact with the roofing material, it will radiate very little of this heat into the loft.
- It works best if there is a layer of insulation that stops the aluminium from getting hot. Hot aluminium can still heat the air by conduction and convection.
See: https://en.wikipedia.org/wiki/Low_emissivity

[wolfekeeper]

FYI you can get semi-silvered aluminium film made for this purpose that you can apply to the inside of the glass. It's not optically perfect though and you'll get a few tiny bubbles and dust trapped under it, but it will reflect ~88% or so of the light, and you'll still be able to see out through it and get some light in the room.