When we think about energy efficiency one of the first things that we look at (or through) are our windows. This is actually a really expensive option for improving energy efficiency compared to its return. We generally only lose around 10-15% of energy through doors and windows. Most of our heat goes through our walls and roofs. However if our windows and doors are draughty then this figure can go up to around 25%. Replacing doors and windows will cost between £500 – £1500 per door and £200 – £800 per window, plus fitting and the associated disruption. So it is not a easy option even if you used the cheapest options.
However for the sake of this post we are assuming that the windows need to be replaced, so what are the various choices that face you. These include:
- Design of the windows (windows bars, number of opening casements etc.)
- Workings of casements (inward opening, outward, reversible, fixed, escape route etc.)
- Material used in the frame (wood, uPVC, aluminium, other)
- Type of glass (Double glazed, triple, argon filled, reflective glass etc.)
- Furniture (lockable windows, colour, style)
- Maintenance (accessibility of the windows, material maintenance requirements)
In an ideal world we would all get really efficient, FSC timber framed windows HOWEVER, in the UK we have no fitting standards, so we tend to use the quickest, easiest and cheapest way of doing this. This means lots of expanding spray foam, silicon sealer and cover strips. So we are fitting high quality windows in a way that is not very weatherproof, insulating or airtight. In parts of Europe there are RAL and EnEv standards for window fitting that ensures that windows are:
– Weather proof on the outer edge
– Insulating in the mid section
– Airtight on the inner edge
Using these principles is really important if we are to get the best performance out of our new windows. The great old British way of ‘it will do’ is no longer good enough.
So, things to think about when choosing windows are:
1. Design of the windows (windows bars, number of opening casements etc.)
The design of your windows can radically alter the look of your house, so care and thought is required when choosing. Like for like is the most common choice, but you can make a real statement by choosing different styles, colours and configurations of windows. Material will also have a large impact, so using uPVC on older buildings can look really out of place.
2. Workings of casements (inward opening, outward, reversible, fixed, escape route etc.)
How casements operate makes a big difference to ease of use. On first floors and above using inward opening windows allows for easy maintenance and cleaning. Outward opening reversible windows do the same, but they are not so energy efficient as the inward opening ones. You might also have to allow for emergency escape routes.
3. Material used in the frame (wood, uPVC, aluminium, other)
Being an Eco DIY blog we are obviously recommending the use of wood rather than uPVC. Wood is a natural lower embodied energy material that can last a lifetime and be repaired easily if required. uPVC requires maintenance and is much more difficult to repair and recycle (and comes from a non renewable source and has a high embodied energy). If you are worried about longevity, you can clad wood with aluminium and this effectively makes the windows maintenance free. Aluminium gives a stronger frame and so can have slimmer frames, but it does carry a really high embodied energy, but is effectively maintenance free.
4. Type of glass (Double glazed, triple, argon filled, reflective glass etc.)
Double glazed is fine for the UK climate, but on north facing aspects then triple glazing is a choice. For most refurbishment work choosing a window with a U value of 1.2 – 1.4 is fine. Only if looking for a really energy efficient is it really worth going for windows with a U value of below 1.2. It is worth noting that various gas fillings will slowly leak out, so if you are looking for a longer term solution then air-filled triple glazing will do this. Bear in mind that you will might have to have certain types of glass for security / safety reasons. For most applications standard glazing is fine, but for certain buildings you might want to look at coated glazing that can help to insulate or cool buildings. For really inaccessible areas, you can stipulate self cleaning glass.
5. Furniture (lockable windows, colour, style)
The colour and style of furniture is important, as is security (for insurance and piece of mind).
6. Maintenance (accessibility of the windows, material maintenance requirements)
Wooden windows have been around for years and good quality slow grown timber (from Northern Europe or North America / Canada) is perfectly fine for windows. But for an even longer life then hard wood is better (oak, meranti and sycamore). uPVC does require maintenance and should be painted with a UV protector, so don’t be fooled into thinking that they are maintenance free. Specifying inward opening windows does make maintenance easier and cheaper. Aluminium cladding also reduces maintenance requirements.