A-Rated Windows – The Emperor’s New Clothes?

This article started off as a rant, fortunately I was too busy to put my initial thoughts down in words. I decided I am too young to be classed as a “grumpy old man.” The reason for my ire? I realised I have been duped. Duped by the British Fenestration Rating Council, and their Windows Energy Rating Scheme.

Early last year, I posed the question “A-Rated windows, who do they really benefit?” At the time, I was concerned that the potential energy savings, and reduction in CO2 emissions may not be fully realised, while the double glazing blogger was delighted to be able to sell A-Rated windows at a higher margin than other windows, see his post  here  I fell into the trap, and assumed that because a window was A-Rated, and being marketed as “High Performance, Energy Saving, A-Rated windows”  it would be vastly superior to any other window.

Since then, I have been reading more about an issue customers have been experiencing following the installation of their A-Rated windows, and the response from the industry.

In certain weather conditions, condensation is appearing on the outside pane of windows.

External Condensation

External Condensation

When questioned about this phenomenon, the response from many of the installation companies is to congratulate the customer on their wise choice, because it shows that the windows are truly doing their job. The temperature of the outer pane is not being raised by heat transfer from the interior of the building, so moisture in the atmosphere is condensing on it.

For many customers, this explanation is enough, and they go away satisfied-ish.

My friend Matthew Glover wrote an article on this feature of A-Rated windows. It attracted many comments from within the double glazing industry, and from disgruntled customers, who weren’t prepared to accept the standard response.

The comments from unhappy customers have generated some interesting suggestions from the industry “experts”.

  • Some are facetious, “fit automatic window wipers like they have on cars”
  • some are provocative, “If they want to enjoy the view tell them to open their windows”
  • some are genuine attempts to resolve the problem “turning up the central heating a degree or two”
  • while others write off the complaints as coming from the “small percentage who would never be satisfied”.

Note: I loved the suggestion to turn up the heating, how ironic.

If I had invested my hard-earned money in replacement windows, and then found that my quality of life was worse because of this problem, I would feel justified in complaining, and would expect more than to be fobbed off with the “it proves you made a wise choice” response.

I spoke to the technical experts at Crittall Windows, and am reliably informed that it is a feature of the coating on Low-E glass which is required by many windows to gain the A-Rating. Apparently, you can now put an additional coating on to the original coating which will stop the external condensation. For an additional cost of course. Which means that the claim that the windows are so efficient has no basis in fact.

The British Fenestration Rating Council (BFRC) Windows Energy Rating Scheme (WERS) has been developed to allow consumers to compare the thermal performance of different windows. The BFRC website explains the rating scheme and what appears on the Energy Rating label:

1. The rating level  A, B, C, etc
2. The energy rating e.g. -3kWh/(m²•K) in this example the product will lose 3 kilowatt hours per square metre per year.
3. The window U value e.g. 1.4W/(m²•K)
4. The effective heat loss due to air penetration as L e.g. 0.01 W/(m²•K)
5. The solar heat gain e.g. g=0.43

I can imagine you nodding knowingly, as you take in these technical values…

I’m sure many homeowners, encouraged by their “High Performance, Energy Saving, A-rated” salesman, will fall into the same trap as I did. It stands to reason, A-Rated windows must be highly superior in performance to the others, otherwise they wouldn’t be classified as “A”

However, when every industry was clamouring for a scrappage scheme, similar to that introduced for the motor industry, the double glazing industry was no exception. Here is the government’s response to the petition (full text available here)

“The Government agrees that energy efficiency has an important part to play if we are to achieve our carbon reduction targets. The benefits of energy efficiency for households are clear: saving money on energy bills, reducing reliance on imported energy and helping householders reduce their carbon emissions.

However given the high cost of replacement windows (typically £5,000 to £10,000 for a small home), the marginal improvement in performance, particularly when replacing like-for-like double glazed windows; and given that band C windows will be the minimum standard permitted by building regulations from October 2010, a window scrappage scheme is unlikely to be cost effective on energy efficiency and carbon savings grounds.”

So the government aren’t really wowed by the performance of A-Rated windows.

My suspicions were further aroused, when I discovered that the Firmdale Group’s Crosby Street Hotel, has floor-to-ceiling Crittall Steel Windows and doors throughout, and is the most energy efficient hotel in New York City, on target for gold LEED (Leadership in Energy & Environmental Design) certification find out more here.

Front Elevation of Crosby Street Hotel, NYC

Front Elevation of Crosby Street Hotel, NYC

I decided to find out just how much better A-Rated windows really are.

On their members’ website, the Glass and Glazing Federation provide an Energy Saving Calculator which I used to produce some interesting results.

I’m just a simple Northern lad, so I didn’t do anything too complicated. I used it to calculate the annual energy cost savings, and reduction in carbon dioxide emissions and carbon footprint as a result of replacing single-glazed steel frames in a detached property with gas-fired central heating, and an average window area, with, windows of various ratings. The full results are listed below.

I have problems equating tonnes of CO2 emissions and my carbon footprint with anything meaningful, so I converted it into commuting days.
I live 15 miles from work, so travel a nice, round 150 miles a week, to and from work, and classed my car as large.

I used the carbon footprint calculator at carbonfootprint.com  and the carbon emissions comparison calculator at transportdirect.info  to work out how many days’ commuting the savings would be for each type of replacement window.

So, if I replaced my beautiful, slim, steel windows, which perfectly reflect the original character of the property, with chunky, A-Rated uPVC,  I will be able to brag to my green friends that I have reduced my carbon footprint by nearly half a tonne, and my CO2 emissions by, wait for it… nearly 1 2/3 tonnes. I will also save £321.20 pa on my energy costs. But, OMG what have I done to my once beautiful house, and where did all the light go??!!?

Common configuration of a uPVC Window

Common configuration of a uPVC Window

What if I replace my windows with the best performing steel windows? I hear you can get C-Rated steel windows these days. They won’t be a perfect replica of the originals, but maybe I’ll be able to retain the essential character of my property.


Daylight through Crittall windows - brochure cover

Daylight through Crittall windows – brochure cover

I’ll still be able to brag to my green friends, 0.41 tonnes of carbon, is only 40kg less than A-Rated windows, and CO2 emissions are 140 kg less, still more than 1.5 tonnes saved, and energy cost savings of £294.21 is just £26.99 less pa than A-rated, that’s slightly over 50p per week.

What does 40kg of carbon look like? What else can I do to match it? My annual commute to work extends my carbon footprint by 2.34 tonnes. That is 7,500 miles per year, or 150 miles per week. The weekly cost is 46.5kg, so the difference between C-Rated and A-Rated replacement windows is less than 5 days’ commuting.

My annual commute results in CO2 emissions of 3.11 tonnes, or 62.1kg per week. The difference between C-Rated and A-Rated windows of 140kg equates to 11 days’ commuting.

What about if I have a Listed Building or a building of special interest, and I need to replicate the windows. What’s the point of replacing them like-for-like? In that case, you can replace original single-glazed steel windows with the current Crittall Homelight DG Range. What do you think the results might be? (Note: Although it has not been tested, following a conversation with the Technical Department at Crittall Windows, we expected this range to achieve a D rating)

Energy cost savings: £280.71, just £40.49 pa less than A-Rated windows. Carbon: 0.39 tonnes reduction, 60kg less than A-Rated, and CO2 emissions reduced by 1.44 tonnes, 210kg less than A-Rated. In terms of commuting days, just over 6 for carbon, and less than 17 for CO2.

Below are the full results from the GGF Calculator

GGF Calculator Results

GGF Calculator Results

Try it for yourself for your own property here.

Part L of the Building Regulations which governs energy consumption in buildings is a very long and complicated document. Most people try to simplify it by taking headlines from it rather than try to understand the whole thing. The headline that most double glazing salesmen use (and the government, if you read their response above) is for existing buildings used as dwellings replacement windows must be C-Rated or better. This is, in fact, a gross over simplification, and can be very misleading for a homeowner.

A number of homeowners have stated that they have been told steel windows don’t meet the Building Regulations. This is not true.

I’m very glad I haven’t invested in A-Rated windows. The higher margins being charged, small comparative benefits and poor user experience mean that, in my opinion, they are a poor investment for the homeowner.

The largest part of the improvement comes from upgrading from single to double-glazed units, and improved weather-proofing, irrespective of the material used to fabricate the frames.

English Heritage state “Window openings and frames establish the character of a building’s elevation. They should not generally be altered in their proportions or details, as they are conspicuous elements of the design.”

In “Five Points Towards A New Architecture” Le Corbusier says “The whole history of architecture revolves exclusively around the wall apertures”

I have spoken to a number of homeowners who believe that they would be unable to maintain the character of their home because they would be forced to replace their original windows with windows which do not reflect that character, or that trying to gain approval for windows which are not C-Rated or better, would be so difficult as to be not worth the effort.  As a result, they are choosing not to upgrade.

The table above shows the potential energy improvements that are being lost as a result.

Wouldn’t it be better to encourage the switch from single to double-glazed windows by making it easier for these homeowners to get what they want?


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  • Hi John

    Interesting article. Love the example PVCu window you chose to illustrate your argument 😉

    This is a very complex issue, and as with all carbon footprint data there is a degree of guestimating. Next Monday I will be presented with our company’s carbon footprint audit information and I intend to share the results on my blog. I’m not entirely sure what the outcome will be in relation to the relative merits of PVCu and steel windows. I suspect that the embodied CO2 in steel manufacture will be higher than that of PVCu, but then you need to consider life expectancy and so on.

    What is clear to me is that encouraging homeowners to fit their homes with the best the best specification of double or triple glazing (whatever the frame material) is a far better investment from a carbon perspective than purchasing expensive cars, flying to the Caribbean etc etc. Although, I suspect that investing in loft insulation or reforestation in the Amazon beats all window systems hands down.


    Matthew Glover

  • Thanks for the comment Matthew, I agree, if we are serious about CO2 and carbon, then there are other actions we can take which will provide better results.

    My argument is that the restrictions placed on homeowners to choose their replacement windows are not justified, because there is so little difference in performance between windows which receive an A-Rating, and those which are D-Rated, Furthermore, those restrictions are inhibiting some people from taking the first, and most important, step – moving from single to double glazed units.

    By the way, the picture of the PVCu window was from a house in my street. We don’t all live in country mansions 😉

  • Fascinating article and a good read. You are absolutely right, many people just dont like the look of replacement windows nowadays and are deciding not to improve. The little difference between an A and D but still makes little difference to those mis informed homeowners insisting on an A because an A sounds better than a B sounds better than a C

    • Thanks for the comment Nick, I appreciate it. With so little difference between A & D ratings, I can’t see the point of WERS, and I am somewhat relieved that they aren’t the only route to compliance with Part L 2010. In a time of belt-tightening, cost-cutting austerity, why are we wasting money on BFRC?


    just been reading through all this. I have worked in the upvc industry for twenty five years now, the last sixteen as sales estimator for a small local fabricator installer firm. We don’t want to emulate the largest or worst of our industry( you know who you are )we just want to make a bit of profit, doing a quality product a a fair price for our customers.We got A Ratings on our windows but The WERs are to strict(from a structure pov) cost us a fortune to get and then they changed the regs to allow 1.6 u valuesfor windows and 1.8 for doors ( which weren’t even in the WERS!)I get people moaning to me nearly every call now about keeping the price as low as possible then they insist that they must have A RATED. I tell them that there is hardly any performance difference between the A RATED and the 1,6 u value and that its going to take them ( in some cases)more than twenty years to get thier money back and i am then treated like some sort of HERETIC !( I would point out that this is based on my prices which are considerably cheaper than alot of other!) The discussions that i have had with technical guys at the major profile companies have proven to me that i haven’t got my facts wrong. The public have swallowed thi eco blab hook line and sinker. Sorry bout the rant just very fed up with it!!!!

  • Denis F

    Hi John

    Thank you for writing this. I am currently trying to come to grips with the new regulations in anticipation of converting a Grade II listed office floor to residential.

    The two storey building was an early 19th C engineering workshop (but the floor in question was added in 1986) and has single glazed Crittall windows. Having spent 25 years working there, I can say that it really keeps the warmth in as it is. But new regs would potentially require that I change the windows since the exemption for listed buildings seems to have been dumped. To change to anything other than other Crittall windows would be unacceptable – the rest of the building, including the residential floor below, has single glazed Crittall windows and the effect is very attractive.

    From what you say, it may be wise to seek expert advice and assistance to argue the point with the building control officers.’Admin’ suggests that replacing windows are not the only route to compliance. Perhaps we can avoid an unnecessary and costly change.

    • Thanks for your comment Denis. For your information, exemption for listed buildings has not “been dumped” in the latest building regs.

      For existing dwellings and existing non-dwellings the exempt buildings are as follows:
      1. Listed in accordance with section 1 of the Planning (Listed Buildings and Conservation Areas) Act 1990:
      2. in a conservation area designated in accordance with section 69 of that Act; or
      3. included in the schedule of monuments maintained under section 1 of the Ancient Monuments and Archaeological Areas 1979

      Also exempt are:
      1. buildings which are of architectural and historical interest and are covered in a local authority’s development plan or local development framework;
      2. buildings which are or architectural and historical interest within national parks, areas of outstanding natural beauty etc;
      3. buildings of traditional construction with permeable fabric that both absorbs and readily allows the evaporation of moisture.

      Building Control officers are now under instruction to take advice from the Local Authority’s Conservation Officer.

  • Penny Baker

    I am one of those confused consumers you mention. I’m about to replace some windows, including with large(ish) bi-folds. I’ve asked a few firms for quotes and have received advice ranging from ‘should go for A grade’ to ‘C grade will be fine’. Is there anywhere I can find a simple comparison on performance, without needing a maths degree and calculator?

  • Penny, I wish there was an easy answer. What I’ve tried to demonstrate here is that the difference in thermal performance between A- rated and C-Rated is minimal. If it was me, I would make the choice on aesthetic grounds. Will it enhance the look of my home, or make it stick out like a sore thumb?

  • Syd Partridge

    What a breath of fresh air to read this. I was beginning to tear my hair out until I came across it in my search for the difference between A and C rated windows. I do leaded light repair and restoration and have been asked to encapsulate existing leaded lights into double glazed units. Lately, I have been told by window installers from one federation body that if I can’t encapsulate into an A rated unit I am breaking the law, contrary to advice from building control. From others who are registered with another accreditation body that for replacement windows, C rated are quite acceptable and within the regs. I have taken technical advice from major glass manufacturers who don’t seem to know what leaded lights are . I don’t know whether we are being taken for a ride, it has all become so complicated that the installers fail to understand or that the regs place too much onus on the installer so that they play safe but I give up with the lot of them!
    As an aside, when I first saw UPVC window frames being fitted on a grand scale and totally removing the character of an area I asked, and still ask a question: Is the energy required for the manufacture of UPVC from its raw materials negligible in the saving made from the installation or is it higher i.e. do we use more energy than we save and if not how does the saving and sustainability compare with wooden frames. To date I haven’t got a reply – Rant over!

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