low level windows needing to withstand the uniformly distributed load of minimum 0.74 kN/m without breaking

[Adsibob]

So we had our building control inspection. Various issues have been identified, all of which appear to be administrative with the BCO wanting to see certificates that I was expecting him to see. One that I wasn't expecting was the following that has come up in respect of our aluminium 2G windows:

 

Low level windows installed to extended parts of the dwelling house to be evidenced to be able to withstand the uniformly distributed load of minimum 0.74 kN/m without breaking; window specification to be forwarded for review; (for further information please refer to Approved Document K, section K2 3.2

 

I raised this with the supplier and in response he provided paperwork which states that the windows we have which are low level (by which I mean the bottom of the window is just above knee height) are as follows:

 

"6.8 Laminate clear / 4mm toughened planitherm/ 16mm black warm edge, 18mm warm edge duplex, argon gas" 

 

Is this going to satisfy the BCO? I can't see how the info that is being provided by the supplier is sufficient to confirm the 0.74kN/m requirement. All the panes have a kitemark on them reading BSEN121501 and KM8462 SUPERTUFF, but then anyone spelling "tough" like that doesn't really win my vote of confidence for toughness.

 

Hopefully I'm just worrying about nothing, but this was one of the queries I didn't instantly know the answer to.

[Dan F]

Have you seen my thread from couple of weeks ago when our BCO visited?

 

 

[Dan F]

13 minutes ago, Adsibob said:

Low level windows installed to extended parts of the dwelling house to be evidenced to be able to withstand the uniformly distributed load of minimum 0.74 kN/m without breaking; window specification to be forwarded for review; (for further information please refer to Approved Document K, section K2 3.2

This is a guarding requirement for first-floor low-level windows.  This, is not AFAIK, a requirement for ground-floor low-level windows.  Instead ground-floor low level windows simply need to "break safely".  To prove safe-breakage they need to comply with EN12600.  Are your windows ground floor or first-floor?

 

 

13 minutes ago, Adsibob said:

"6.8 Laminate clear / 4mm toughened planitherm/ 16mm black warm edge, 18mm warm edge duplex, argon gas" 

If they are anything like out BCO this won't be enough if they want "design loadings".  But again, "design loadings" should only be required for first-floor load level windows.

 

What you need to fully satisfy this requirement (if they are first floor windows is):

- BS1680 compliance.

- Design loadings calculated to using EN 16612 which show they meet 0.74kN/m requirement as specified in BS1680. 

 

Our supplier was unable to get this paperwork from the european manufuactur and our BCO didn't insist in the end.  Our glass is triple-glazed with all three panes toughened.   One thing that helped put his mind at rest though was the report I generated, for the same glass unit make-up using the AGC calculator.  What size are the glass units in your case?

Edited May 11, 2022 by Dan F

[JohnMo]

Your supplier will have to go back to the manufacturer and the manufacturer should be able to issue a certificate.  Supplier is being lazy.

 

Your lucky, we had a wind loading of 1.07kN/m requirement.   So had to get structural engineering approval, prior to purchase.  We ended up with triple glazed with each pane being 6mm thick toughened glass.

[Temp]

I googled to see if 6.8mm laminated met 0.74 kN/m. Found only this..

 

https://www.pilkington.com/~/media/Pilkington/Site Content/UK/Reference/BRGlassMechanicalStrengthPDF.ashx

 

[Nick Laslett]

3 hours ago, Temp said:

I googled to see if 6.8mm laminated met 0.74 kN/m. Found only this..

 

https://www.pilkington.com/~/media/Pilkington/Site Content/UK/Reference/BRGlassMechanicalStrengthPDF.ashx

 

“The table has been based on maximum glass area of 3.4m2.” E.g. a 6.8mm laminated pane, 3.2m2 in size can take over 0.25kN concentrated load. That was my interpretation. 

 

On page 7 of the FH Brundle doc there is table for DGU units.
 

 

https://www.fhbrundle.co.uk/files/pdf/co1/Technical/Glass Loading Data Sheet 7.2.pdf

It is pretty clear to me that a 2.0m2 DGU with 6.8mm laminated pane and 4mm toughened pane would pass the 0.74kN test. How you convince the BCO is a different matter. Not to mention how astragal bars effect the calculations, SHMBO has our windows in full prison bar look, so each pane is essentially reinforced. 

Edited May 11, 2022 by Nick Laslett

[Adsibob]

Thanks all, that's helpful info. I'm a little bit miffed that I even have to worry about this because the supplier of the windows came to survey the house and really should be responsible for making sure it complies with building regs. It's their area of expertise, not mine. But such is life.

All the windows in question are first or second floor. In total, we have four such windows, and one of them is my son's bedroom, although directly outside it is a pitched roof over our ground floor, rather than a straight drop to the ground. He is only 2 but already built like a 3 year old and likes to charge around like a mini bull, so I'm glad the BCO is making a fuss. The areas of the individual panes are as follows:

 

So the panes vary in sizes from 0.84m2 at the small end to 1.49m2 at the large end.

 

I don't really understand the table that @Nick Laslett has posted, but if a residential property (a conversion, not a new build) counts as class 2, then the only figure on that part of the table which is below my window sizes is 0.15m2 (which doesn't make much sense because who could fall out through such a tiny opening and my windows are all significantly smaller than the other areas in that part of the table. However, that table shows 4+4 and 6+6, whereas I'm going to be some sort of weighted average of the two being 6.8 + 4. I wonder if this is going to be another lawsuit?

 

 

[Dan F]

22 minutes ago, Adsibob said:

Thanks all, that's helpful info. I'm a little bit miffed that I even have to worry about this because the supplier of the windows came to survey the house and really should be responsible for making sure it complies with building regs. It's their area of expertise, not mine. But such is life.

You should insist they provide this documenation.  Or have you already done this and got nowhere?

 

22 minutes ago, Adsibob said:

 

I don't really understand the table that @Nick Laslett has posted, but if a residential property (a conversion, not a new build) counts as class 2, then the only figure on that part of the table which is below my window sizes is 0.15m2 (which doesn't make much sense because who could fall out through such a tiny opening and my windows are all significantly smaller than the other areas in that part of the table. However, that table shows 4+4 and 6+6, whereas I'm going to be some sort of weighted average of the two being 6.8 + 4. I wonder if this is going to be another lawsuit?

 

Right. I had a similair issue. In my case it was no no such tables for triple-glazing in your case your glass make-up isn't listed.  I agree, if you just use this table then you need 6+6, but the reality is that your units are almost certainly fine, it's just a paperwork issues.

 

What is you cill height for the largest 1.026x1.448m windows?  This is important as the line and area loads need to be calcuated 1.1m from floor level.

[Adsibob]

6 minutes ago, Dan F said:

What is you cill height for the largest 1.026x1.448m windows?  This is important as the line and area loads need to be calcuated 1.1m from floor level.

I haven’t got a tape measure to hand (just moved in yesterday - not sure which box it is in!), but it is about 66cm I would estimate for that window.

[Nick Laslett]

Most of your house is Occupancy class 1. Protective barriers in this class only need to pass 0.36kN load. Occupancy Class 2, covers balconies, landing, stairs & corridors. Protective barriers in this class need to pass 0.74kN load. I’m not sure if any residential dwelling windows should be in Occupancy Class 2. Document K, section K4 refers to glass in windows with chills below 800mm needing to pass Class 3 of BS EN 12600, most toughened and laminated glass satisfies this requirement. 
 

I thought this web page explained it well. 
 

https://www.bereco.co.uk/blog/navigating-complying-uk-building-regulations-windows-doors-v1-new-homes

 

Edited May 12, 2022 by Nick Laslett

[Dan F]

45 minutes ago, Nick Laslett said:

Most of your house is Occupancy class 1. Protective barriers in this class only need to pass 0.36kN load. Occupancy Class 2, covers balconies, landing, stairs & corridors. Protective barriers in this class need to pass 0.74kN load. I’m not sure if any residential dwelling windows should be in Occupancy Class 2.

Landing, stairs and corridors are Class 1.   Balconies, julliete balconies and "edges of roofs" are Class 2.  Our BCO and window supplier were both consistent is saying that low-level first-floor windows (with no roof flat roof outside) fell into Class 2 and not Class 1. 

 

That table you copied isn't particulalry clear, take a look at this for example, which adds more colour: https://techhub.uk.saint-gobain-building-glass.com/sites/default/files/document-files/Guards %26 Barriers 2A - Applied Loads - 17-09-2018.pdf

 

Edited May 12, 2022 by Dan F

[Conor]

Just had our final inspection and he never asked for anything, the toughened watermark on the glass was enough. Just in case anybody else is panicking!