So you’ve moved into your dream period property, only to find that it’s draughty and cold in the winter. There are, of course, measures that can be taken to make the place more cosy and warm, which I shall touch on later, but what I really want to look at here are the windows. In particular, the original sash windows and the dilemma of keeping them along with the cold and draughts, or installing modern double glazed windows and losing the building’s character. In this article I shall examine the alternatives to leaving the original windows in place and see how different options can affect energy use.

Before getting onto the windows, I will quickly mention two other main sources of property heat loss. First is the loft. The vast majority of heat is lost through un-insulated loft space. To insulate the loft is an easy job and doesn’t cost very much at all. If using the most common insulation material, mineral wool, the recommended level of insulation is 270mm. Compared to a loft with no insulation, this will save about a tonne of CO₂ a year. (Energy Savings Trust) So, if you haven’t insulated your loft – do it now. Enough said. If you do live in an old property, the chances are that it will be constructed from stone, so you do not have the option of cavity wall insulation. It is possible to improve the insulation of stone walls, but this can be costly, loose you interior space or affect the look of the exterior of your property. In the future I will do some research and hopefully write a piece on this very subject. For now, however, it will suffice to say that the windows in your character property are one of the biggest sources of heat loss, but they can be improved relatively easily.

Space heating represents by far the largest proportion of household energy use (see below), so the fastest way to save energy, save carbon and save money, is to reduce your heating bill.

Because of the large proportion of energy loss through windows, one of the fastest ways to reduce the heating bill is to address this issue. The most common way of doing this is by replacing your windows with double glazed ones. However, if like me, you bought your house partly because of its period features the last thing you want to do is put in modern – albeit energy efficient – UPVC windows. When writing these articles I always try and speak not just from what I have learnt at university, but also from my experience as a homeowner as well. Up until recently, on the advice of two double gazing companies, I couldn’t get good, authentic-looking, wooden double glazed sash windows. This is not true and a quick Internet search will uncover a few specialists in this field. So with this in mind, what can be done to the windows?

I am going to go through the options that I have looked at and, hopefully, there should be some ideas in there for all budgets.

Without replacing windows:

• Do nothing, just learn to live with the noise and draughts and turn your heating up in the winter (not recommended).
• Place some draught excluder around the joins in the window. I am referring here to the strip of plastic that has small brushes fixed to one side. This doesn’t look very nice, but will reduce draughts significantly.
• Put up a pair of heavy lined curtains in front of the windows.
• Install some shutters. These are very trendy at the moment, and although they will not be quite as effective as curtains, they do have the advantage of not taking up as much room as curtains because they are usually fitted within the frame of the window.
• Have the frames repaired/reconditioned. This will reduce noise and draughts.
• Convert existing single glazed sashes to double glazed units.

Replacing windows:

• Replace the window completely for modern double glazed UPVC windows – this is the cheapest option, but, will look slightly out of place on a period property.
• Replace the window for modern double glazed UPVC ‘sash style’ windows – this will look better than normal double glazed units, but will still sacrifice authenticity.
• Replace the window for authentic-looking, wooden double glazed sash windows. Although this is probably the most costly option, it will give you both the insulation and noise reduction properties of modern windows, but will also keep the character of your home – also worth thinking about if you’re considering selling in the future.

Use a combination of any of the above, whatever your budget will stretch to – all improvements, no matter how small, soon add up. And remember, as soon as you lower the heat loss, you will see a big saving in your energy bill and reduce your carbon emissions.

Finally, light a big warm fire, pour yourself a glass of hot gluhwine, roast some chestnuts, put your feet up, watch It’s a Wonderful Life on TV and just forget all about the cold weather outside. Lovely.

So, now that we know the windows can be replaced without sacrificing character and charm, what savings can be made? Let’s take, for example, five single glazed sash windows in a small Victorian terraced house (like mine). If they were upgraded to double glazed – but still authentic looking – sash windows, the saving in energy could be around 256 kilowatt-hours (kWh) and 235kg of CO₂ emissions per year. At today’s gas prices that’s about £45.00 off your energy bill annually.

Please note these figures are just examples. You can see all the sums at the end of the article under U-Values.

 

The cost of replacing your windows is completely dependent on which option(s) you go for so I’m not going to provide a price guide. However, to keep costs down, you my want to consider replacing just the front windows for double glazed traditional sashes, to keep the character of the property, and putting modern double glazed units at the back. The choices are endless and are completely reliant on your budget.

Finally, there are a few other methods that you can use to reduce draughts and noise.

• Place a heavy lined curtain around exterior doors.
• Place some draught excluder tape around the frames of both internal and external doors. This is a very simple job to do and will take about 5 minutes per door, but you will notice the difference.
• Purchase a draught excluder for the bottom of doors that lead to places like porches and external exits. I’m referring here to the sand filled ones that cover the gaps in the bottom of the doors.
• If you are lucky enough to own an open fire, make sure there is a damper plate – or some other way of closing the hole – in place at the back. An awful lot of heat is lost up an open chimney when the fire’s not in use.
• If you have the original exposed wooden floorboards, seal the gaps between them and also look at the gaps between them and the skirting boards. Running a wet hand along any potential gaps on a cold, windy day will soon tell you where the drafts are. You could also cover them in carpet and a quality underlay – but that will cost you 100 times as much as draft excluding and again you will loose a period feature.

So hopefully there are a few things to mull over here. If you do want to pursue the window repair/replacement options take a look at these companies listed below. They will also help to give you an idea of the costs involved.

• The Original Box Sash Windows Company – www.boxsash.com
• Timber Windows. Com – www.timberwindows.com
• The Sash Window Specialist – www.sashwindowspecialist.com

U-Values

By way of illustrating the differences in energy loss between certain types of window I will now give a brief explanation of the arithmetic of thermal transmittance using the U-Value of different windows. Please bear with me, it’s really not that complicated.

Basically, the U-Value is a measure of the performance of any building material. Using the U-Value we can measure the rate of heat loss through a window. This is calculated by multiplying the area in square metres (m²), by the U-value, by the temperature difference between inside and outside. The lower the U-Value, the lower the heat loss.

U-Values are expressed as W m^-2 ˚C ^-2(Watts per square metre per degree Celsius)

So assuming you have window that is 2 m² in area, the U-Value of the window is 5 and it’s 20˚C inside the house and 5˚C outside (20 – 5), then the rate of heat loss will be:

2 x 5 x (20 – 5) = 150 Watts

If we assume that this rate of temperature difference is the average for the heating season of 6 months and the house is heated for 12 hours per day, then the loss in energy per year would be:

150 watts x 12 hours = 1.8 kilowatts hours (kWh)

1.8 kWh x 182 days (or 6 months) = 328 kWh

At an average gas price 3.5p per kWh this would cost £11.48 (per window)

Comparatively a double glazed unit with a U-Value of 1.1 would cost around £2.55 per window – a saving against the above single glazed unit of around £9.00 per window. (see below)

2 x 1.1 x (20 – 5) = 33W

33 x 12 = 0.4kWh

0.4 x 182 = 73kWh

73 x 3.5p = £2.55

£11.48 – £2.55 = £8.93

If we assume that a property has 5 windows, all of similar size, then by replacing the windows the house owner could save £45.00 per year on their energy bill.

Assuming 0.184kg of CO₂ of per kWh (Carbon Trust, 2009) the saving in carbon emissions would be around 47kg of CO₂ per window.

Below is a table highlighting the different U-Values of windows and the amount of energy that is lost through each window on a hypothetical year and how much this would cost. This is only a rough guide.

So by using the above sums and simply inserting the area of your windows, you can compare the heat losses of any windows you may have now, compared to what you may wish to purchase in the future; just another tool in the box of the conscientious home owner.

References

Boyle, G. 2004 Renewable Energy: Power for a sustainable future. Oxford University Press. The Open University, Milton Keynes.

Energy Saving Trust. www.energysavingtrust.org.uk/Home-improvements-and-products/Home-insulation-glazing/Loft-insulation/All-about-installation.

Pilkington United Kingdom Limited. www.pilkington.com/resources/defaulttable.pdf

Timber Windows www.timberwindows.com/content/More_Information/Technical/technicaldetails.pdf.