What are typical U-Values on windows and doors?

If you are researching new windows and doors for your home, you will see a lot of information about U-Values and Window Energy Ratings. These are all to do with the different types of glass available in windows and doors. 

U-Values on windows and doors

What are U-Values and what are Window Energy Ratings?

The typical U-Values on windows is a measurement of heat loss and the rate at which it is lost.  U-Values indicate the overall performance in retaining heat and preventing it from escaping to the outside.  U-Values are measure in Watts per square metre Kelvin, or W/m2 K. In simple terms, the lower the U-Value number, the better the thermal performance of the window.

Typical U-Values on windows and window energy ratings are similar to the familiar energy labels you see on home appliances, rated from A (the lowest), up to G, the highest or worst performing. Window Energy Ratings provide a simplified method of understanding the energy saving properties of a window.

Some window performance figures are expressed with a U-Value and others with a Window Energy Rating, although the latter has been adopted as the more commonly used.

How are U-Values and Window Energy Ratings Calculated?

A mathematical formula is used to calculate the U-Value and Window Energy Rating (WER).  In simple terms, the calculation uses a notional figure on the energy balance of a typical UK house in a year using a variety of window styles and configurations. It is important to understand these are calculations that, in a real-world situation, could be better or worse than the stated performance figures.

What is the minimum U-Value and Window Energy Rating for Windows?

All new or replacement aluminium, PVCu or timber windows require a minimum C Window Energy Rating or a U-Value of 1.6Wm2K or less.

Glass units today differ substantially from early generation double glazing.  If you have old double glazed windows and doors before 2006 it is likely these have metal spacer bars around the sealed unit and just air space in between.  Modern double or triple glazing uses a ‘Low-emissivity’ or ‘Low E’ glass coating, warm-edge (non-metal) spacer bars, Argon or even Krypton gas between the glass. All these coatings and materials enable a low U Value to a modern window.

To give you an indication of U-Values in the home, we give some approximate figures compared to your property roof, walls and floors.

 Property MaterialInsulationApproximate
U-Value
Property RoofWith insulation0.5
Property RoofWithout insulation 2.4
Cavity WallWith insulation0.7
Cavity WallWithout insulation 1.7
Typical FloorWith Insulation 0.7
Typical FloorWithout Insulation 0.9
Old single glazed windows. None5.8-5.9
Old Double Glazed windows with air space between glass. None2.8-3.0
Current double glazed units, argon gas, low-E coating. 1.2-1.2
Latest triple glazed units, argon gas, low-E coating. 0.9-1.0

As standard, our PVCu and aluminium windows come with Pilkington K™S glass, annealed (non-safety glass) where safety glazing such as toughened or laminated units are not legally required. Our double glazed units include a soft-coat low-e coating, argon gas between the glass panes and a warm edge spacer bar.

Textured and patterned glass located in bathrooms has the same glass specification with the internal pane having the obscure glass pattern.

Typical U-Values on windows and Window Energy Ratings on PVCu and aluminium windows and doors.

Origin aluminium bifolding doors.

As standard, our entire range of hinged, sliding or folding doors come toughened Pilkington K™S glass, including soft-coat low-e coating, warm edge spacer bars and argon gas fill.

Patterned glass is available where obscure glazing is required. Our premium Origin aluminium bifolding doors offer you the following approximate performance figures:

  • Origin Bi-Fold Door Double Glazed 1.6 W/(m2K)
  • Origin Bi-Fold Door Triple Glazed (with krypton) 1.3 W/(m2K)
  • Origin Bi-Fold Door Triple Glazed (with argon) 1.5 W/(m2K)
  • Energy Rating D

PVCu windows.

Our Liniar suite of PVCu casement windows feature multi-chamber profiles, specially extruded bubble gaskets, glazing flippers and other thermal enhancements.  

With a quality double glazed unit, approximate U-Values are 1.2Wm2K or alternatively a Window Energy Rating (WER) of A+. The Liniar EnergyPlus range contains 6 chambers and can achieve a U-value as low as 0.8 W/m2K with the correct glazing specification.

Our Residence 9 suite of PVCu windows provides a thermally efficient 9 chamber design and modern glass units. Approximate U-Values are 0.8Wm2K with a Window Energy Rating (WER) pof  A++

Aluminium Windows.

Our Origin aluminium products provide the following typical U-Values on windows and approximate Window Energy Ratings (WER’s) with the following glass specifications.

BFRC Energy Rating B-9

  • U-Value 1.7 (W/(m2k)
  • 28mm double glazed 4mm Diamant – 20mm 90% Argon – 4mm Total + . 20mm Swiss Ultimate spacer bars.

BFRC Energy Rating A+6

  • U-Value 1.5 (W/(m2k)
  • Origin Window with Aerogel. 28mm double glazed 4mm Diamant – 20mm 90% Argon – 4mm Total + 20mm Swiss Ultimate spacer bars.

BFRC Energy Rating A+9

  • U-Value 1.2 (W/(m2k)
  • 44mm triple glazed. 4mm Diamant – 2x16mm 90% Argon – 2x4mm Total +.  2 x 16mm Swiss Ultimate spacer bars.

BFRC Energy Rating A+21

  • U Value 1.0 (W/( 1.0 (W/(m2k)
  • Origin Window with Aerogel. 44mm triple glazed 4mm Diamant – 2x16mm 90% Argon – 2x4mm Total +. 2 x 16mm Swiss Ultimate spacer bars.

The above information is a guide and offers approximate U-Values and Window Energy Ratings, taking information from the system company websites and technical information.  Window Ratings can vary depending upon the glass specification, window configuration and other factors.  Contact us for more detailed information on window energy ratings.

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Aspire did the most beautiful job in our house. The installed our windows a few months ago, and I couldn't be happier.They were always happy to answer to our question.They came at 8 o'clock and installed the windows very swiftly with a very clean and tidy result. They decorated afterwards around the windows and you couldn't tell those weren't the original windows as the result was so good.We have a toddler in of the rooms they were installing the windows and they accommodated their work around his naps which was brilliant.If you are looking for anything window or door related look no further, I will definitely recommend and if needed use them again.
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GEMMA M.
10:20 28 Apr 21
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15:33 16 Mar 21
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Martin J.
19:06 06 Jan 21
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16:01 04 Jan 21
We were recomended to Aspire by our carpenter who was building a garden room for us, and we were not dissapointed.From the initial meeting to the completion of the work the company , and especially John Small, and the lads that came to install the doors on one of the wettest days of the year, have been excellent.The Bifolds are amazing. They look so good, and when they open and close they sound solid and beautifully made.Superb job. Thank you.
Simon B.
Simon B.
08:12 25 Nov 20
I don't usually write reviews but Aspire have been an absolute pleasure to deal with from start to finish. After replacing my neighbours sliding doors they came highly recommended. The lady on the phone was extremely helpful and understood my requirements, and my quotation was turned around quickly. I had some technical questions regarding the threshold; and unlike other companies I dealt with, I was not treated as a nuisance and Ji (I hope I spelt this correctly!) talked me through everything. The surveyor arrived within a day of me signing and despite the current situation with many delays, they still installed within the quoted lead time!The Schuco bifolds we now have look amazing and we are so thrilled we went with Aspire Bifolds!Thanks alot Ji and Team.Cliff
Cliff Bentley T.
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14:33 04 Nov 20
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Cat P.
Cat P.
10:56 23 Sep 20
Aspire were great to work with and we are delighted with the finished product. We got bifolds, skylight, large side windows and french doors all for a highly competitive price. We had some unavoidable delays due to the pandemic but we were always kept in the loop with what was going on with our order. we are extremely pleased with the quality and value we got through working with them.
Frankie H.
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12:32 11 Sep 20
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Rupert P.
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08:23 11 Sep 20
I would absolutely recommend Aspire Bifolds. They provided a great product at a reasonable price. Installation team was friendly and professional. They installed in less than a day.We also encountered a small issue with the measurement of the doors, but the leadership at Aspire was quick to cover additional costs incurred to rectify the issue. We really appreciated their professionalism on this matter.
Tim S.
Tim S.
06:54 10 Sep 20
Huge thank you to Aspire Bifolds for our external steel look doors, we’re so happy with them and the guys were quick, responsive and all around brilliant. Would really recommend Aspire Bifolds.
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Very efficient and helpful service 2 years on from original door fitting.Thanks so much Aspire!
Kim L.
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11:00 27 Jul 20
Aspire bifolds removed some old wooden sliding doors and replaced them with some lovely French doors. They did a fantastic job- they spent time with me to ensure I had made the right choice of door, it took no time to fit them and the fitter was friendly, polite, clean and courteous. Quote was competitive and I couldn’t recommend them enough!
Natasha H.
Natasha H.
19:59 23 Jul 20
We went with Aspire after getting a few quotes, they weren't the cheapest but were still competitive. We chose them on the basis of their reviews and I am really glad we did! The service has been excellent throughout, our doors were installed far quicker than we were expecting, the fitter's attention to detail is great, and the quality of the doors is fantastic.After installation we did have a few problems with finding marks on the glass, which is provided by another firm, and had a few panes replaced. John, the director, ended up coming round himself and offered to replace the final pane. I know that many firms would just have ignored our calls once we had paid everything, so to have this level of service was fantastic. This proved our decision to go with a slightly more expensive firm in Aspire was the right move!
Scott S
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12:10 16 Jul 20
After a lot of research I came across Aspire Bifolds, went to the showroom and they have a very good selection of doors to choose from.From start to finish it's been a pleasure to deal with everyone connected to Aspire Bifolds and their aftercare service is first class.Top quality product, installation and all round experience from this company. Would have no hesitation in using them again.
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Catherine Kenton M.
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18:59 08 Apr 20
We recently used Aspire for purchase and installation of smart system heritage doors for our extension. We are thrilled with the finished product. John and the team are brilliant, every person I spoke to was helpful and friendly. Email response was really fast. The whole process from start to finish was seamless and stress free.The installers were efficient and tidy, they left the place cleaner than when they arrived. Following installation we noticed a scratch on one of the panes, we thought it could be buffed out, but the whole pane was replaced without issue within a week.It is rare to find a company with such great customer service and work ethic these days. I would certainly be happy recommending Aspire to anyone.
Rebecca D.
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11:39 27 Feb 20
I visited Aspire Bifolds to discuss some technical details of the installation requirement for sliding doors. Both of the staff I dealt with were friendly and helpful and in particular Ji was able to answer all of my questions and demonstrate some of the details on the door installation in the showroom. Overall a very helpful visit.
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