Landlords are looking to try and upgrade there homes to a Band C on the EPC. They are considering every aspect of the house, in some cases, to squeeze out every point possible. Will upgrading your windows to a modern highly efficient triple glazed window make all the difference? Below we'll look at a recent EPC we've completed and test the difference between double and triple glazed. We'll also take a look at the complexities of the EPC on this topic.

How Do Triple Glazed Windows Affect The EPC?

To answer this question, first, we need to understand how window energy efficiency is measured. As far as the EPC goes, we are looking for two values, a 'U-Value' and a 'G-Value'. The quick explanation of these is that a U-Value measures how much heat is stopped from escaping your home. The lower the U-Value, the lower the amount of heat escapes. A 'G-Value' is related to how much of the suns natural heat is able to enter the house via the window. This is measured on a scale of 0 (none) to 1 (all). Its really important that you keep the specification document from your window installation. Documentation is the only way we can identify the these values. If we do not have the figures, when completing an EPC we ALWAYS have to use default U and G-Values which are more often than not, higher than the actuals.

Window EPC Example

We recently completed an EPC in Warrington on a Semi Detached house in Sankey. The home had double glazed windows throughout and achieved a score of 62 points on the EPC putting it firmly in a Band C. After the EPC we went back and played with the inputs a bit. We changed the double glazed to triple glazed without adding any further and the result stayed exactly the same, 62 points from 100. This is because the default U-Value for double glazed is 2 W/m²/K and the triple glazed is 1.8 W/m²/K. A very small difference.

Quick note here. When completing the EPC we input the type of window that makes up the majority of the windows in the house. i.e. if you have 4 triple glazed and 3 doubles, we'd input triple glazed only.

I found a U-Value for triple glazed windows on the Everest website of 0.8 W/m²/K from their Ultimate range. This U-Value by itself would improve the EPC score on this house to 64 points out of 100. However, when we introduce the G-Value of these windows (0.2), it drops the score right back down to 62. This is because the house now gets no free heat from solar gain. In an ideal situation we'd need a window with a low U-Value and a higher G-Value to boost the EPC score.

I've scoured loads of window manufacturers websites looking for the best combination of U-Values and G-Values to improve the EPC score. Both double and triple glazed. The double glazed have a higher U-Value and higher G-Value. The triples I found had lower U and G-Values. For **this property** the only window which made a difference to the EPC score was again from Everest, in there triple glazed (44mm) Energy Saver range. The difference was a whopping one point improvement. You might get different results on your property. My results are for a specific property with its own unique energy retention profile. What is clear though, is that upgrading windows from double to triple will not see a significant improvement in your EPC score.

Single Glazed Vs Triple Glazed

If your home has single glazed windows, what improvement will you get from installing triple glazed? There are not many domestic buildings with single glazed windows, but we do see a lot of businesses with them on Commercial EPCs. For instance, in this example house, if we adjust the windows to single glazed, the result is 59/100. Only a 4 point difference to the window that makes the most difference on the EPC.

The real world tangible results will be must larger than the 4% EPC improvement. From experience, I know that going from single to double glazed windows makes a huge difference to energy bills and overall comfort of the home. You can expect to add a bit of value to your home too.

Other Ways to Boost Your EPC Score

Based on this example only, it seems there are better areas of the home to focus on that will provide a higher return on investment. With uncertainty around MEES for landlords, some are looking to improve their result to a Band C. We recently did a similar test on cavity wall insulation which had a more positive outcome for those looking to improve their EPC scores. We'd recommend checking your current EPC for specific advice for your property. Some common improvements are energy saving light bulbs, loft insulation and boiler controls. These usually provide a quick, inexpensive boost to your EPC score.