Extension roof light efficiency

[swebb99]

Hi there,

I'm looking at extending a kitchen which will mean having a flat roof out back by about 8ft running approx 20ft across and then another 20ft along the side. The architect has mentioned fitting one or two roof light to get some light in to the room. This seems like a good idea but I'm not sure about it as I would have thought a fair bit of heat would be lost through the glass, especially during the winter. Has anyone any experience of these, do they cause heating bills to increase by large amounts ?

Thanks in advance.

 

[Notch7]

No more than any other window.

Personally the visual gain you get from increased light will far outway any extra energy cost, which wont be great.

We build orangeries often with large roof lanterns, I dont remember any customer saying energy costs had increased noticeably. Usually they go on period houses and the orangery part is far better insulated overall than the original house.

You might find that heating with underfloor heating is more efficient if you have large roof lanterns, because the heat from the floor doesnt create much heat distribution by convection. radiators in an orangery however do create a lot of convected heat, which results in hot air going up to the top of the lantern and collecting there.

Another way to look at it is that the overall energy loss cant be greater than a solid roof since a SAPS test will be needed (depending on roof light size) to prove it and may require improvement in insulation elsewhere -so in theory your energy efficiency of the extension must achieve the same level.

You will of course also have a solar gain benefit -which on cold but sunny winter mornings can be quite significant (you wont get much solar gain in the middle of the night though!)

 

[swebb99]

Great thanks for the response. Yes I suppose you are correct that i already have two windows !

I had thought about under floor heating but I already have a concrete floor so the only option would be electric which I don't want, so I will have to use either flat vertical rads or those kitchen cupboard plinths that connect to the existing combi boiler system.