Adding an extra insulation to double glaze windows

alankearn

As heating is going to be a lot more expensive In three of the rooms in our house that are not used a lot I am thinking of adding another layer of insulation using made to measure pieces of two inch thick seat/bed type of foam on to the double glaze glass
Two of the the windows are approximateley two by one and half metres
The windows dont look out to anthing special so would'nt not look strange from the ouside

Does anyone think this would be a an effective

Thanks

grumbler

Do you mean blocking the light completely?

FreeBear

The current target u-value for windows is 1.4W/m²K. Your windows are likely to be older and have a value of 1.6W/m²K or lower. So yes, it would be worth putting a bit more insulation up against the window. I wouldn't use furniture type foam though. A rigid board of Celotex/Kingspan type PUR insulation will be far more effective, or even expanded polystyrene (Jablite EPS). But one thing to watch for is condensation between the window and any insulation - You will get some building up which will pool on the sill. If a wooden sill, this could result in it slowly rotting away. Certainly, mold will be an issue.

grumbler

If the insulation is sealed tight on the perimeter (e.g. with soft foam) I don't see any real reason for condensations as the amount of air trapped is very small.