Thermal efficiency
facing views with more modestly sized, triple-glazed windows.
Triple-glazed fenestration is a strong trend right now, but it’s worth asking whether it is something we really need, or merely something that is being sold to us.
We have a maritime climate in the UK, which is warm compared to other places on the same line of latitude, so the benefit of triple glazing is not as great as it would be in, say, Canada. This means it can be argued that the energy and CO2 embodied in the manufacture of tripleglazed windows outweighs the savings they provide. As a result of this, limiting triple glazing to north and east-facing fenestration as I have suggested may be the pragmatic solution.
A window’s thermal efficiency is determined by its U value and its airtightness. Triple glazing usually offers a better U value – around 0.8W/M2K compared to 1.4W.M2K for double glazing – but it doesn’t improve on airtightness, as the same means is used to seal the casement to the frame. Speaking of seals, it is worth asking if a window’s ‘lifetime guarantee’ applies to them, as they are the element of the window that will fail first.
To really solve the airtightness issue, you need to make sure that your windows’ installation is done with it firmly in mind.
The normal fix of a couple of screws and a can of expanding foam will not do. Windows and doors need to be installed with airtight materials like Compriband 600, Pro Clima tape and Gerband mastic.
There’s also your property’s doors to consider. When we talk about doors in this context, we mean ordinary ‘front door’ types. Patio doors are essentially big windows and need to be treated as such. Doors, in this narrow sense, are less significant than windows for the sustainability of your home. The main requirement is for them to have a similar level of thermal resistance to the windows, again for good installation.
Heat storage
Passive solar gain is the phenomenon that greenhouses rely on: heat passes through glass in the form of sunlight, and is then unable to escape. This is a good thing, but like all good things, you can have too