# U-value of a timber window



## Doug71 (10 Feb 2020)

I am making and fitting some new windows in a commercial property we own (hairdressers), I like to do things properly so made a full plans building control application as required. There are only 4 windows, biggest 1.2 x 1.2, smallest 0.6 x 0.4 

They have passed the plans subject to the condition of me sending in some more plans with extra detail on.

They want details on trickle vents, I pointed out that on my original plans it says there are currently no trickle vents but I am hoping to fit some if the design allows.

They want details of glazing in critical locations, I pointed out that on the plans it says that all the glass will be toughened even though none of it needs to be. 

The one that is bugging me is they are insisting on a whole unit u-value for the windows, everything I make is bespoke and in the past they have always been happy with me saying the glazing I use has a U-value of 1.2 and working on a centre pane value. This chap wants more detail and has told me I will find online calculators to work out the u-value of the full window which is obviously dependent on the timber species, profiles, glazing etc.

Has something changed or am I dealing with a jobsworth? Do I just say it's 1.4 W/m2K and hope he doesn't ask to see my working out (that is what some other wooden windows seem to be)?

Thanks in advance, Doug


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## Woody2Shoes (10 Feb 2020)

Doug71":1dtdaf4t said:


> I am making and fitting some new windows in a commercial property we own (hairdressers), I like to do things properly so made a full plans building control application as required. There are only 4 windows, biggest 1.2 x 1.2, smallest 0.6 x 0.4
> 
> They have passed the plans subject to the condition of me sending in some more plans with extra detail on.
> 
> ...



You should be able to get your dg unit supplier to give you a u value based on the types of glass/spacer/gas fill and you can then use your online calc of choice for the rest, surely? Cheers W2S

PS The building regs specify trickle vent requirements - can't remember offhand but 8000mm2 rings a bell


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## Doug71 (10 Feb 2020)

Woody2Shoes":xde8lmah said:


> You should be able to get your dg unit supplier to give you a u value based on the types of glass/spacer/gas fill and you can then use your online calc of choice for the rest, surely? Cheers W2S
> 
> PS The building regs specify trickle vent requirements - can't remember offhand but 8000mm2 rings a bell



I know the DG units U-value is 1.2 and building control have always been happy with just knowing that for bespoke work. The online calculators I have found so far to work out the whole unit U-value want to charge me for it, anybody know of any free calculators?

It's an old building with solid walls, no insulation in floor, single glazed windows etc, in similar situations building control have normally just said crack on, you're improving it.

The existing windows don't have trickle vents so I don't have to put them in the new windows. Ideally I will use them but I tend to use the ones set in the head of the window that vent just below the drip lath outside so you don't see them. These windows have internal linings which are quite thick so won't leave much room for the vent internally unless I make a really deep head. It's a nice old building so I don't really want vents in the sashes with plastic hoods on.


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## Hornbeam (10 Feb 2020)

Refer to Approved document L2B or L1B if it is a dwelling
See attached link section 4.24
https://assets.publishing.service.gov.u ... dments.pdf

The problem is that teh Approved Documents are technically guidance documents so they are open to interpretation.

Ian


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## LBCarpentry (10 Feb 2020)

I thought they had stopped all the nonsense full window Uvalue and normal glass rating was enough.

I also do a lot of windows for old buildings and when a some fresh out of college jobsworth starts whimpering about things like that I tell them to stop being so ridiculous and go hassle Jelsons


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## Woody2Shoes (10 Feb 2020)

I take your point that this is not new build and therefore as long as what you provide is better than what's there you have a strong argument. The alternative is to do a very simple whole window calc knowing the relative areas and fhicknesses of timber and glass. The maths isn't hard and there are various websites that illustrate the process. Your results should be pretty close to the 'approved' software.
You might also get brownie points for using warm spacers etc to get the dg unit u value down


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## RogerS (11 Feb 2020)

Doug...you have my sympathy. It's one reason why I only made windows for listed buildings ! He sounds like a jobsworth. Could you not use one of the online calculators ? Like this site (although not looked into this specific site in detail). I used to have a PC based program that let you put in wood dimensions, DGU types etc.

You might like to ask over on woodworkuk as I know Jas is pretty switched on as far as this goes.


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## tomatwark (14 Feb 2020)

This U-Tube video might help

https://www.youtube.com/watch?v=1s9CRQ_B04U


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