Why U-Values Are the Future of Energy Efficiency in PVCu Products

June 28, 2024

In the evolving landscape of energy efficiency, VEKA’s Technical Director, Paul Kennington, sheds light on why the industry is shifting focus from traditional Energy Ratings to U-values for PVCu products. This shift promises greater accuracy and reliability in measuring a product’s thermal performance, aligning with upcoming regulations and the UK’s net zero target for 2050.

Why U-Values Are Superior to Energy Ratings

“I’m going to say it upfront. I think the days of Energy Ratings are limited. When it comes to accurately indicating how a product will perform, U-values are the way forward.”

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Whilst most fabricators tend to use one method or the other, as if they were comparable, there are significant differences between the two.

Energy Ratings, with their banding index ranging from E up to A++, serve as a marketing asset with the minimum acceptable rating for building control being B or above. The rating indicates energy loss through the product, as well as energy gain and air leakage.

U-values on the other hand, which building regulations stipulate must be 1.4w/m²k or less in the replacement market, focus solely on energy loss.

Energy Ratings vs. U-Values

So, why are U-values a better indicator of how a window system actually performs?

Firstly, it’s important to consider how the ratings are calculated. U-values are designed to solely indicate thermal energy loss through the entire product. Energy ratings, on the other hand, provide an overall rating of how energy efficient a window or door is, considering several different factors. Plus, there are several external factors such as location, shading, etc., that can affect performance, so it doesn’t always reflect reality.

Another major factor to consider is the consistency in how the ratings are calculated.

U-values are an international standard. Energy ratings are determined by several different private organisations – all of which have their own methods for calculating the rating. Unlike thermal transmission, for which there is an international standard with methodology, there is no such standard for energy ratings.

The result is that whilst the methods used are very similar, small inconsistencies can often mean the difference between an A+ rating and an A rating. Calculation methods change over time, plus, further confusion arises when designers take a U-value from the calculation sheets of an Energy Rating calculation – as these are calculated in a more accurate way than the International Standard used to calculate U-values – and inconsistencies can arise, especially with triple glazing.

It’s clearly a mixed-up situation and no one standard approach exists.

Regulatory Changes: Future Homes Standard and Approved Document L

Perhaps the obvious need for consistency, clarity, and credibility across the sector is what’s behind the government’s focus on U-values moving forward. This is clear from what’s been included in the recent Future Homes Standard Consultation

Change is Coming

Moving forward, replacement windows will need to meet the requirements of both Table 4.2 of Approved Document L and must perform as well as the window being replaced. Although this change will already affect some replacement windows, it will really come into play in the future as properties being built now often meet the lower notional values of 1.2w/m²k.

On top of this, there are proposed changes to the calculation methods for windows in new dwellings. Currently, it is possible to use the value of a window of standard size and configuration to represent all windows in a property. The proposal is that this will no longer be the case. The calculation will need to reflect the exact size and configuration of the window being installed. Energy ratings are based on standard windows, therefore, unless a major change is made to the scheme calculation methods, how can energy ratings be a true comparison for replacement windows in the future?

And that’s not all. Included in the consultation is a call for evidence on overheating. Not just in terms of whether this should be applied to material change of use scenarios, but also the potential for overheating in existing dwellings. Both are highly likely to have an impact on whether or not Energy Ratings will be an acceptable form of proof of performance.

The Bigger Picture

What’s the drive behind all of this? Well, with the UK’s net zero target in mind for 2050, changes need to be taking place now. It makes sense for these to be applied in the newbuild market first – but make no mistake, the longer-term plan will surely be for the replacement market to follow soon. Consultations happen for a reason. And for the government and the market itself to demonstrate performance and progress, we need accurate data – central to which is consistency and credibility, which U-values provide.

This is why at VEKA we intend to focus on referring to U-values for all of our new product suites moving forward. It’s the right thing to do and clearly what the regulatory environment is calling for.

We’re also dedicated to continuing to develop products that meet changing requirements and innovative software that makes the process of calculating U-values as straightforward as possible.

Our focus is not only on supporting the change that needs to happen, but also on driving what that change looks like and how it’s introduced. By commenting on forthcoming standards, we continue to be a leading voice for the industry and encourage everybody across the sector to do the same.

Some will no doubt be apprehensive about developments that might lie ahead. However, others will appreciate that change needs to happen, and legislation suggests it will happen – those that are at the forefront of enabling that change will no doubt benefit commercially and we are here to support that growth.

The next step in that journey? Follow our lead and adopt U-values as the best indicator of how your products perform, as we advance into the next generation of fenestration.

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