Here a few facts about windows that I’ve come across on the quest to replace the 59 year old single glazed windows in my house.
Starting with glazing…
Single glazed windows have a u value of around 4-6 W/m2K
If you have good quality double glazed windows already, they may have a u value of around 2.1 W/m2K. (This is pretty similar to the u value of the walls in a house of solid brick construction)
Current building regulations vary for new build and retrofit so be sure to check what u value you require depending on your situation.
For really high spec windows, look for u values below 1 W/m2K. This makes sense in a well-insulated house where the walls have much lower u values than even the best windows.
I’ve got my eye on some windows with a u value of 0.6 for the glazing and about 0.75 for the whole window (EcoPassiv from the Green Building Store). A good window company should be able to tell you both u values.
And then the frames…
UPVC may be widespread, but it has its disadvantages.
The production of UPVC is highly toxic, and leads to toxic by-products. So far, UPVC windows are rarely recycled at the end of their 10-30 year life, and incineration is not an option. In the event of a fire, the toxic fumes are highly dangerous.
Timber framed windows can be far more environmentally friendly if the wood is from a sustainable source. Some come with very natural treatments to protect the outer frame from weather and the UV in sunlight, others are treated more heavily to delay the need for maintenance.
Aluminium cladding is a popular low-maintenance choice for some, but of course aluminium has a higher embodied energy which means a greater carbon footprint.
[Please see comment below]
The best windows now have a layer of insulation sandwiched between the outer and inner part of the frame. And there is an emerging range of ways to fix the windows in position to minimise cold bridging. But that’s a topic for another day.
Starting with glazing…
Single glazed windows have a u value of around 4-6 W/m2K
If you have good quality double glazed windows already, they may have a u value of around 2.1 W/m2K. (This is pretty similar to the u value of the walls in a house of solid brick construction)
Current building regulations vary for new build and retrofit so be sure to check what u value you require depending on your situation.
For really high spec windows, look for u values below 1 W/m2K. This makes sense in a well-insulated house where the walls have much lower u values than even the best windows.
I’ve got my eye on some windows with a u value of 0.6 for the glazing and about 0.75 for the whole window (EcoPassiv from the Green Building Store). A good window company should be able to tell you both u values.
And then the frames…
UPVC may be widespread, but it has its disadvantages.
The production of UPVC is highly toxic, and leads to toxic by-products. So far, UPVC windows are rarely recycled at the end of their 10-30 year life, and incineration is not an option. In the event of a fire, the toxic fumes are highly dangerous.
Timber framed windows can be far more environmentally friendly if the wood is from a sustainable source. Some come with very natural treatments to protect the outer frame from weather and the UV in sunlight, others are treated more heavily to delay the need for maintenance.
Aluminium cladding is a popular low-maintenance choice for some, but of course aluminium has a higher embodied energy which means a greater carbon footprint.
[Please see comment below]
The best windows now have a layer of insulation sandwiched between the outer and inner part of the frame. And there is an emerging range of ways to fix the windows in position to minimise cold bridging. But that’s a topic for another day.
Hi, although you are right about aluminium, it only has this high embodied energy in the first creation from electricity, but most aluminium has a high content of recycled. Also, aluminium is made in places where Hydropower is the main source, and as electricity is the prime energy requirement (unlike a blast furnace for steel), the actual Carbon Emission is very very low. Aluminium is very strong, its far more cuttable, drillable and shapable than steel, and is more resistant to corrosion than any other domestic metal. As your windows are an investment that will outlive all of us, it's wise to install the best. Wood frame, aluminium outer skin is the best (and thermally even better with additional insulation block)
ReplyDeleteIn terms of Carbon Emission, concrete is the most atmosphere hostile material in existence because it is made in such quantities and needs so much furnace heat to manufacture portland cement. It is made everywhere, in every country, whereas aluminium is mostly made in countries with high Hydropower resources.
ReplyDeleteA major public building in Melbourne, CH2 (a 10 storey building for the city government) is a reinforced concrete frame, with key differences - the aggregate is recycled concrete, and the cement is GGBS (blast furnace slag) Reinforcement is recycled steel, so this building has very low embodied energy. I didnt previously think you could use GGBS for structural work... but they have!
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