Replacing windows case study

The decision to replace windows is usually an aesthetic one. If you have inherited tired and worn out windows, they may be affecting the look and feel of your property.

Rising fuel prices now introduce a financial consideration. This case study looks into the figures in a bit more depth.

As we are repair and restoration experts we will come out and say that r&r yields immediate benefits in terms of carbon emissions and diversion from landfill. We will still look at the figures and some other popular ideas regarding replacing traditional windows with modern double glazed units.

Fuel consumption and costs

​For the case study we will only look at gas costs and consumption. Gas cost per kw/h is significantly cheaper than electricity and is the typical fuel of choice in the UK for heating homes.

According to Ofgem a typical medium sized house (3 bedroom) consumes 12,000 kw/h of gas per annum. Current costs are 8p per kw/h but are due to rise to 11p per k/wh by the end of 2022.

This means a typical gas bill will be £1,320 per annum. Standing charges add £100 giving a total of £1,420 per annum.

30% of heat loss is attributed to leakage through the windows = £426.

New window replacement costs

The average cost of replacing 10 windows (typical medium size house) with hardwood timber double glazed windows is £18,000 (June 2022 - source expertsure.com). [ We are using hardwood windows for our case study as we would empathically and categorically advise the public to never ever buy softwood windows. Even with appropriate maintenance, these units do not last 7 years before needing some urgent and serious attention. They are just not worth it.]

Return on investment

So the payback on your investment will be

18,000 / 426 = 42 years!

Clearly, from a financial perspective the investment is not worth it.

Other factors in favour of double glazing

1. Noise reduction - newly installed windows immediately improve on external noise. However, this is because the new windows fit better leaving fewer gaps. Draft exclusion will achieve similar results for a much smaller investment. Furthermore, retrofitting with thicker panes of glass and also using secondary glazing will be even more effective. Studies have shown that secondary glazing is the most effective solution for external noise especially if combined with effective gap insulation.
2. "Warmer feeling" - again this is mistakenly attributed to the windows themselves when it is more likely that draft exclusion has contributed the greatest benefit. In recent times it has become fashionable to not cover windows and doors or to use blinds instead of curtains. Thick full length curtains over doors and windows makes a significant difference to the "warm feel" of a room without changing any part of the windows.
3. Security - double glazed windows do present a more difficult target for criminals. However, laminated window panes are even more effective (think of laminated glass used in VIP vehicles such as the Presidential motorcade). Thicker panes will also improve noise reduction as mentioned above.

Retrofit vs replacement

​We can see from the case study that retrofitting makes sense, especially from an ROI point of view.

All the purported benefits of double glazing and replacement can be achieved by retrofitting options. In our case study, we have not even considered upgrading your current window panes with slimline double glazing units. As long as there is sufficient depth within the window frame, 12mm slimline double glazing units can be substituted for the current 6mm panes.

We recommend home owners with older wooden windows never replace their windows as more than likely they will be replacing hardwood timber windows with inferior softwood frames. Not only will the home owner waste money on a poor investment, they will lose value as buyers are willing to pay more for original features. 

Simply draft proving windows will achieve 70% of the benefits of replacement. If double glazing is the objective of the owner then we recommend upgrading existing windows with slimline double glazing units.