Window u values

[GreenGables]

Hello everyone,

 

I am having some bespoke double glazed windows made from accoya but the window company say they don't provide a whole window u value. How do I know if my windows will meet regs? I have chosen low u value glass with u of 1.1 and warm edge spacer in argon. I think the flush frames are 80 deep. Does anyone know if this is likely to be within building regs (1.6 w/(m2.K) whole window). How can I work this out?

 

Thanks for any advice.

GG

[Jilly]

I have triple glazing, but Building Control officer only inspected the glass marks in the corner of one or two frames. 

Edited November 12, 2022 by Jilly

[ProDave]

21 minutes ago, Jilly said:

I have triple glazing, but Building Control officer only inspected the glass marks in the corner of one or two frames. 

That was checking they were the right kind of toughened or laminated glass for the application.

[JohnMo]

You may spend a lot of money and be asked the question, not sure how you answer if building control do ask. The company can go to a third party to get the calculations done. 

 

As I understood it, it's mandatory for the whole window u value and an energy rating certificate to be issued with new windows. I may be wrong?

 

Just tell without the calculation it's not worth the risk, provide the calculation or you'll find another company to do the windows.

[SteamyTea]

A quick Google throws up a thermal conductivity figure of 0.108 W/m.K for accoya.

So you should be able to estimate the losses through the frame fairly easily, then add that to the glass losses.

[JohnMo]

Here are my door calculations, mine are krypton filled, but it shows you how they whole window is calculated, not difficult on a spreadsheet or with a calculator and a bit of time.

MOGGAN-KRYPTONDOOR.pdf

[GreenGables]

Thank you all. I will see if I can calculate it all myself. Pretty poor of the window company though. 

[SteamyTea]

1 hour ago, JohnMo said:

Here are my door calculations, mine are krypton filled, but it shows you how they whole window is calculated,

Useful document, thanks for sharing.

[craig]

On 12/11/2022 at 13:39, GreenGables said:

Thank you all. I will see if I can calculate it all myself. Pretty poor of the window company though. 

Very. They’re required to provide the information on how the window performs. If they make windows, they’ll need to have been tested (BBA, Element for example) and a certificate supplied.

Edited November 13, 2022 by craig

[ADLIan]

Agree. Window manufacturer should (must?) do this. Can you imagine an insulation manufacturer supplying a sheet of insulation but then asking you to get its thermal conductivity measured???

[Andehh]

I got screwed by my window company quote glass only. Went from 1. 3 quoted to 1.6 when I asked them about it, a month after order was confirmed ... Managed to catch it last minute and get it back down to 1.4 but still think poor form. 

[JohnMo]

They're all at it, misquoting u values, hoping they get away with it, or maybe most likely knowing little better (which if true is shocking).  I had three companies try it on, only when pushed did they give me the correct numbers, which were rubbish.

 

Neither company got any business from me.  I paid quite a bit more money, but got good service and the windows look great.

[DCG]

JohnMo

 

May I ask who you used?

 

I have whole house windows to change. Some in solid walls that will have EWI and k render applied and some new cavity walls. I am very keen to have minimal heat loss from poor installation and so if there's a company who are known for doing a good job, I am all ears!

 

thank you

[Kelvin]

I have a full window schedule for every window in the house. Lots of detail about every aspect of the window and how they calculate the U value for each window. The whole house average glazing U value is 0.79 including the rooflights.

I’d definitely consider going somewhere else but you might find it hard to get this information from smaller bespoke window companies. We had to have a timber French door replaced in the last place under the builder’s warranty and had similar trouble in getting the U value details for the door. 

[Alan Ambrose]

>>> Useful document, thanks for sharing.

 

Yeah, ditto.

 

>>> I have a full window schedule for every window in the house. Lots of detail about every aspect of the window and how they calculate the U value for each window.

 

Could you tell us who this good supplier is please.

[Kelvin]

Nordan. I expect every major window supplier to provide the same level of detail.