Listed Building Conversion - Double Glazing

[pdg87]

I own a 1800's Grade II listed Building, I am currently converting it from commercial to residential and have hit a bit of a nightmare with the windows. The current windows are non original single glazed sash windows, quite poorly made.

I am caught between building control and Listed building consent. For a conversion the windows must meet a certain standards and achieve a certain Uvalue. So they must be replaced or secondary glazing installed.

I've had an application in to replace the windows with double glazed sash windows, but this has been knocked back. I met with the CO last week and he stated I would have to use slim line double glazing, glazing units should be putty glazed from the front. He also said surface fixed glazing bars are not appropriate for a grade II listed building.

I met with a joiner today who makes windows and has some experience in working with slimline glazing. He seemed against using putty for several reasons and also said that if I was using multiple panes of glass ass opposed to surface fixed glazing bars it would not be possible to hide the seals on each unit with the slimline glazing bars, so there would be some of the black seal on show..

I have been provided a window sample, fitted with slimline glazing to show planning.. I'm impressed with the look of the slimline double glazing. The sample window uses chamfered wood beading to resemble putty, which I do not think the CO will go for.. but the joiner said I should try it.

Just wondering if anyone had experienced anything similar, and what solution they came up with? Also if CO might be willing to compromise on any of the above or if I am wasting my time showing him this example and should give exactly what he has asked for?

Thanks

 

[DJH]

Can you offset the u values from single glazing with increased insulation elsewhere? Not really my field I'm afraid but I've heard of similar cases where that has been a compromise.

Doug

 

[pdg87]

Not that I am aware of, I have already had to insulate the loft and a pitched ceiling. I had energy calculations carried out and was told the windows must have a Uvalue of 1.6.. I have spoke with Building regs and CO (CO seemed unaware I would have meet these standards in a conversion at first). It's a stone built building so I'm not sure where else I could increase insulation?

I don't really want to go down the secondary glazing as I don't like the look of it and it seems even worse installing it when the current windows are shoddy and not original.

 

[Gareth Hughes]

Get the CO to tell Building Control that the change they are requiring would be unacceptable
http://www.english-heritage.org.uk/professional/advice/hpg/compliantworks/buildingregs/

 

[pdg87]

Thanks Gareth,

The argument Building control would have though is that they are not forcing me to replace the windows, I could just put secondary glazing in.. but its not something I really want to have to do. Also the windows are non original (probably replaced in the 70-80's) so my CO does not see them of having historical importance.

I had not planned to replace the windows when I first bought the property but the windows are worse than I first thought in terms of design/build and current condition.

So I'd have to pay to have the windows fully refurbished, then for secondary glazing and would be left with windows that were not original nor what I wanted..

So I guess it's just as much me who wants to replace the windows as well. I think I just need to find a solution that will satisfy my CO. He has been very helpful, I'm just trying to work out if I should try and get him to compromise with the facts my joiner has put forward or not.. and whether people would agree with the points my joiner is putting forward or the stipulations my Co has stated.

 

[88v8]

Slimline DG can be face-puttied, but not with standard putty as it attacks the glue holding the glass together.

See, here:
http://www.histoglass.co.uk/content/Thin-Double-Glazing
and here
http://www.toolsforroofing.co.uk/downloads/Histoglass%20Thin%20Double%20Glazing%20Technical%20Brochure.pdf

The putty - which appears to reside in a gun-tube - is available here.
http://www.kawo-shop.de/kawo-elastokitt.html
Historischen Kastenfenstern. Just practice that until you can lob it at your joiner.

The rebates must, I presume, be primed as usual.

Ivor

 

[pdg87]

Thanks Ivor, Ive just been doing a bit of research and found which backs up your point about not using putty.

I stumbled upon this forum topic: http://forum.expertexpert.com/viewtopic.php?f=9&t=42

Which is a very interesting reading. Although started in 2010 posts continue until 2012. They seem to agree with what my joiner had said.. first of all slimline double glazing seems to have a poor life span, especially when traditionally solid-bedded in putty, as the putty reacts with the sealant around the glazed unit.. I do not fancy replacing 8 windows with super expensive glass for them to fail after 3 years.

Interestingly my CO had already approved proposed rear french doors with standard double glazing and surface fixed glazing bars, when I asked how these had been approved he said the must have slipped through without him realising. I will present him with my findings and see if any compromise can be met..

Has anyone had personal experience in the life span of slimline DG, specifically when bedded with putty?

 

[88v8]

Has anyone had personal experience in the life span of slimline DG, specifically when bedded with putty?

No, but I know that putty attacks the glue in laminated glass. And remember the delaminating glass one used to see in cars of the '30s, when they were still in use pre-MOT?

Histoglass guarantee their slimline DG 7 years, which isn't bad. I wouldn't be surprised if the reported poor lifespan has something to do with tradesmen using any old putty. Plenty of people who seem unable to read in t'trade.

Ivor

 

[skier-hughes]

We have 4mm-8-4 DG units, argon filled and use planitherm low-e glass. And self cleaning on the upstairs windows!!
Our windows are hand made, and use a special silicone to bed the units to not interfere with the self cleaning bit and wooden beads. Our oldest windows are now 8 years old, all doing well.

 

[Owain]

Not that I am aware of, I have already had to insulate the loft and a pitched ceiling. I had energy calculations carried out and was told the windows must have a Uvalue of 1.6..

That's if you consider each element of the building separately (per Approved Documents, and the Area-Weighted U-Value method of assessment). However you can consider the whole building under Standard Assessment Procedure (SAP).

http://www.english-heritage.org.uk/publications/energy-efficiency-historic-buildings-ptl/eehb-partl.pdf

 

[OriginalGlass]

Good Afternoon,

Please forgive me if I waffle but I have spent a fair bit of time working in this field recently!

I work for a company called The Original Glass Co. part of the hollseal group, Holloseal is a large sealed unit manufacturer producing around 1200 conventional sealed units per day predomintantly for wooden window manufacturers, we have recently spent a lot of time working on the development of sealed units suitable for use within period properties.

Several years ago we were continually being asked by both current customers and new if we could manufacture a thin sealed unit for the intention of replacing single glazing in Georgian and Victorian Sash's and Casements. We began by manufacturing a unit much like many other manufacturers had been constructing (Slimlite for Example) using a product called Superspacer heritage bar from Edgetec. This spacer bar is basically manufactured to a spongy consistency with an element of desiccant (moisture absorbing material) contained within its fibre, it is supplied on a roll, it is available in variable thicknesses from 4mm thick and upwards relevant to the desired cavity.

The manufacturing starts by applying the bar to the first pane of glass with a special hand held gun using not much more than a double sided tape, this tape does not form the type of primary seal achieved when manufacturing a conventional unit using Butyl to apply the bar to the Glass. This bar will be inset form the edge of the glass to allow an edge seal to be applied later. The second skin of glass is then placed on top producing a sandwich with a void of a few mm around the edge depending upon the chosen depth of seal (sightline). Some manufacturers advertise a 5mm sightline unit which will have literally 2mm of seal depth behind the bar, given the tolerances involved with the nature of manufacturing this type of unit by hand this may be literally be 10ths of a mm thick in places. The void is then filled with a Hotmelt Butyl. Some manufacturers will use a foil or tape around the perimeter to act as another form of seal.

We began manufacturing a version of the above using a sightline of 7.5mm, therefore a 4.5 mm seal at best. When sending samples of these units off to labs for the testing of Gas retention, Climatic and a life expectancy testing they failed. This construction of unit will not retain gas for longer than 12 months therefore making the initial U-Value irrelevant. The initial moisture content of the bar was also high therefore having a very limited potential for absorption, this moisture content was tested straight from the sealed packet prior to being used for manufacture. All units will ingress a certain amount of moisture over their life as they expand and contract as air pressure changes throughout the day, even a conventional unit with a thick seal depth. The main two reasons for failure seem to be due to the lack of a primary seal in combination with the seal depth therefore allowing moisture ingress and gas to escape and the low absorption potential of the bar.

Having said all of the above this type of unit can have a far extended life expectancy if they are installed in a certain manner. i.e Not installed as a tight fit in to the rebate therefore allowing a void around the edge which is completely filled with a Silicone sealant, preferably one that is tested and wont react with the Butyl Hotmelt edge seal (Hodgsons U9), fitting the units with a putty replacement such as Dry Seal by Repair and Care. (Linseed Oil based putty WILL react with and break down the edge seal.)

We do still manufacture the above units upon request but will only give a 12 month guarantee and make it very clear that we have a better alternative.

So we went back to the Drawing board, we have now developed a unit that addresses all of the above issues and has passed the tests to a satisfactory level that has allowed us to produce a product with a guarantee to match that of Histoglass. Histogalss is a great unit but is manufactured in Germany with long lead times and a price that would make anyone think twice.

Spacia is an interesting product from Pilkingtons, we are an agent, technically it is great but unfortunately practically and financially floored. Minimum size limits make this impossible to use in most Georgian applications along with the lead times cost per m2 (POA but in excess of £200.00m2+ £1000.00 per crate for shipping from Japan) and of course the vacuum plug which is not very well received

Our heritage unit uses a different type of bar and has a primary seal, we are also doing something a little different within the seal but for obvious reasons want to keep this to ourselves for now. This can be manufactured using period reproduction glass types such as Machine Drawn or Hand Drawn, the U-Value can be as low as 1.1 with an 8mm cavity. Desktop Calculations by and independent specialist say a life expectancy of around 25 to 30 years. www.thinsealedunits.co.uk

I hope this helps fill a few of the gaps, sorry to go on but I am quite passionate about this field, not just because I work within it but as a lover of period architecture and the proud new owner of a Georgian property that will be lovingly restored starting with the windows!

 

[pdg87]

Thanks for the comments

Can anyone recommend and joiners/window makers that do bespoke (or authentic Georgian Sash windows, suitable for Listed Buildings) in the the North East of England?

 

[DJH]

An interesting post OG. It's good to know that there are manufacturers trying to help us overcome onerous modern day requirements while keeping a 'period look'.

Doug

 

[88v8]

Thankyou OG. Saved your Home in my Favourites for further attention, as this is very topical for me.
Can you make units with bogus lead lights?

Ivor

 

[OriginalGlass]

pdg:- I know Ventrolla who we supply based in Harrogate cover your area, www.ventrolla.co.uk

88v8:- We can make units with lead lights depending on how well structured and flat they are however we are vary wary and always try to avoid doing it, mainly as part of the process involves closing the unit together in a press, the chance of breakage is quite high. Also if the unit fails in later life the chance of separating the lead light away to re-make in to another new unit without causing damage is slim.

DJH, Thankyou for your comment, it is satisfying now that we have made progress as it was quite frustrating for a while. The fact that the demand for the poorer units still grew even when customers were advised of the limited life expectancy made it clear how desperate homeowners are for this type of product. Its nice we now have a product we can confidently promote without question.

If period properties can be made more comfortable their long term use is ensured.

 

[pdg87]

Thanks OG,

I've already been in contact with Ventrolla, would 16mm glazed units resemble single glazing? I asked my CO what thickness slimline glazing would be acceptable and he was unaware there was different thicknesses avilable :?

What would standard double glazing measure for reference?

My CO pointed me in the direction of http://www.slimliteglass.co.uk/ When I told him there were other manufacturers he made out that they had all copied the idea from Slimlite..

I would need to achieve a U value of 1.6 so looking at slimlite that would be a 4/6/4, so 14 in total. I would need the 16mm option from Ventrolla so not too much difference..

 

[OriginalGlass]

I've already been in contact with Ventrolla, would 16mm glazed units resemble single glazing? I asked my CO what thickness slimline glazing would be acceptable and he was unaware there was different thicknesses avilable :? The very thinnest unit would be 3/4/3 (10mm overall) but there is a slight compromise in performance being this thin, a slightly wider cavity will reduce the U-Value a fair amount also the high performance Low Emissivity Softcoats are generally only available in 4mm. Ventrolla try to opt for a thicker Krypton Filled Cavity and a Softcoat where possible to ensure you get the benefits expected from a double glazed unit.

For Example a 3/4/4 (11mm overall with a 4mm Softcoat Internal Pane) would give a U-Value of 1.9. increase the cavity to 6mm (13mm overall thickness) and you get 1.5, 8mm (15mm Overall thickness) would achieve 1.2.
What would standard double glazing measure for reference? A standard unit typically measures 4/16/4 (which is the optimum cavity with Argon Gas) reaches a U-Value of 1.2, a cavity thicker than 16mm and the U value starts to increase again, which is where triple glazing starts.

My CO pointed me in the direction of http://www.slimliteglass.co.uk/ When I told him there were other manufacturers he made out that they had all copied the idea from Slimlite.. Many manufacturers have copied exactly the same make up, it is very easy to manufacture using a product called Superspacer, unfortunately the life expectancy of any unit manufactured in this manner is questionable. Our Heritage Unit is entirely different in its construction
I would need to achieve a U value of 1.6 so looking at slimlite that would be a 4/6/4, so 14 in total. I would need the 16mm option from Ventrolla so not too much difference..

 

[Gareth Hughes]

OG, this is all getting a bit "advertisy" :roll:
http://www.periodproperty.co.uk/ppuk_corporate_discussion_forum_rules.shtml

 

[OriginalGlass]

Point taken, i'll try to stick to the facts, I was only responding to questions asked in my defence!

 

[Flyfisher]

It's a fine line, I agree, but I reckon we're mostly able to separate the information from the sales pitch. I suspect PPUKers are a somewhat abnormal bunch in that we like to research and gather as much information as possible in our never-ending quest to do the best we can for our properties.

Otherwise, we'd have all succumbed long ago to the modern miracles of cement, uPVC and numerous damp-proofing conconctions. :wink:

I'm happy to ignore a side order of advertising providing the main meal is information-rich.