# Sash windows build advice on compliance..



## JC800 (21 Dec 2022)

Hi all,

I want to build my own sash windows for an Edwardian semi and not quite sure what the requirements for compliance are given my circumstances. When I bought the house upvc double glazed windows were and still are in place. I’ve salvaged a set of original sash windows from a neighbouring property which require some repairs so first question is can I get away with installing these with the necessary repairs made? If so I’d be wanting to upgrade the glass to double glazing so my second question is what would be the maximum thickness I could use given the sashes are 44mm thick?

That would be one set of circumstances, but in the event the rules won’t allow for the above option then it’s on with making my own. I am under the assumption I would not get away with like for like construction methods? So if that is the case then is there any available resource online I can seek guidance from?… I’ve done many a search but only window companies come up. Say if I wanted to use 10mm double glazed units would I need to alter the spec of the sash and casement thickness? Again, does anyone know of any available resource that stipulate the requirements for frame thickness to glazing thickness?

Thanks in advance.


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## Ollie78 (21 Dec 2022)

You should be fine using a slim DGU with 8mm sightline and krypton or xenon ( I forget which is the best now ) use Hodgesons heritage putty for glazing, never use linseed oil on double glazed units, and silicone is a nightmare.
You will need to make new sashes to accommodate the additional glass thickness. 
Old ones can be adapted sometimes but by the time you have messed about with them it's quicker and easier to do new ones.

16mm (4/8/4) maybe 18mm ( 4/10/4 )units should go in a 44mm thick sash if you make them right this will allow a 6mm putty line. 
Glazing bar thickness is going to have to be the sight line of 8mm twice plus whatever you can get away with 5mm being the minimum I would allow before it gets too skinny
So 16mm plus 5mm is 21mm which is still pretty slim.

You may need custom knives if they are going force you to copy the mouldings of existing ones exactly but often you can just use a small flat ovolo and adjust the rebate to allow the glazing.

You will not be complying with modern part L, you are "restoring and upgrading existing as best you can"
This is "conservation "work not new build so this is the angle you need to use.

Have fun

Ollie


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## deema (21 Dec 2022)

If it’s not in a conservation area, locally or nationally listed, rip the hell out of it. Modernise it as much as possible. Sod heritage, the lefty idiots on the council can just for the fun of it slap a local listing on your ‘castle’ and then your royally ‘flocked’ at being able to upgrade it to make it habitable for the 21 century. Triple glazed modern units all the way. The less ‘heritage’ there is the less likely you are to get a local order. This is talking from bitter experience.


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## niall Y (21 Dec 2022)

Pilkington Spacia? ................ but God knows how much it costs!
Ooops... just found out £250 per sq. metre


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## Ollie78 (21 Dec 2022)

deema said:


> If it’s not in a conservation area, locally or nationally listed, rip the hell out of it. Modernise it as much as possible. Sod heritage, the lefty idiots on the council can just for the fun of it slap a local listing on your ‘castle’ and then your royally ‘flocked’ at being able to upgrade it to make it habitable for the 21 century. Triple glazed modern units all the way. The less ‘heritage’ there is the less likely you are to get a local order. This is talking from bitter experience.



I agree in some ways I would love some nice Internorm aluminium and wood composite windows with internal blinds. They are great windows. Then I finally managed to get a price for one (small ish one fixed one opening side) it was nearly 3 grand.. for one !!!

Ollie


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## Jacob (21 Dec 2022)

If you want replica period sashes then forget double glazing, it's totally incompatible with trad design. Instead look at having internal shutters or secondary glazing, or even just thermal blinds.


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## Jacob (21 Dec 2022)

deema said:


> If it’s not in a conservation area, locally or nationally listed, rip the hell out of it. Modernise it as much as possible. Sod heritage, the lefty idiots on the council


Nothing lefty about conservation. There's a clue in the name - think "conservative".


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## deema (21 Dec 2022)

Labour council. Hardly describe them as right wing conservatives? They also slapped a Tree Preservation Order on the entire front garden…….which hasn’t any tress in it. In the village another of their imaginative decisions was to slap a local listing on a house that was in the process of combining a cattle shed into it……the shed had and now has to have an asbestos corrugated roof on it. The house roof is now half modern and half corrugated lung disease: you simply can’t make this stuff up.


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## JC800 (21 Dec 2022)

Ollie78 said:


> You should be fine using a slim DGU with 8mm sightline and krypton or xenon ( I forget which is the best now ) use Hodgesons heritage putty for glazing, never use linseed oil on double glazed units, and silicone is a nightmare.
> You will need to make new sashes to accommodate the additional glass thickness.
> Old ones can be adapted sometimes but by the time you have messed about with them it's quicker and easier to do new ones.
> 
> ...


Thanks for this Ollie. Good to know I’m not obliged to go supersized thickness to cater for 10mm dgu’s. I’m planning on boarding the outer walls with the insulated stuff so if I make new sashes I don’t mind going a bit wider, but not so much as to look odd. I’m not in a conservation area… So I’m wondering if becoming Fensa certified myself is the get out clause from having to deal with council inspectors


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## Jacob (21 Dec 2022)

deema said:


> Labour council. Hardly describe them as right wing conservatives? They also slapped a Tree Preservation Order on the entire front garden…….which hasn’t any tress in it. In the village another of their imaginative decisions was to slap a local listing on a house that was in the process of combining a cattle shed into it……the shed had and now has to have an asbestos corrugated roof on it. The house roof is now half modern and half corrugated lung disease: you simply can’t make this stuff up.


They are only trying to stop the place going to the dogs! Sometimes they get things wrong.


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## deema (21 Dec 2022)

Just ‘repair’ the windows. I had a really interesting conversation on what is repair and what is replace with a building inspector. In the end, as long as any part of the original exists, or remains from what was there before you started to repair, it’s a repair. So, taking it to an extreme, if you reuse a screw, it’s a repair. I know, madness, but that’s the literal interpretation as I understand it of the rules.


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## JC800 (21 Dec 2022)

deema said:


> If it’s not in a conservation area, locally or nationally listed, rip the hell out of it. Modernise it as much as possible. Sod heritage, the lefty idiots on the council can just for the fun of it slap a local listing on your ‘castle’ and then your royally ‘flocked’ at being able to upgrade it to make it habitable for the 21 century. Triple glazed modern units all the way. The less ‘heritage’ there is the less likely you are to get a local order. This is talking from bitter experience.


It’s not a conservation area, but imo worthy of being conserved. Modding out is the no brainer for all the obvious reasons. I’ve just got the itch to restore, I’m on a 50/50 street ratio of conserved to modified. It’s a nice street in an average area. If most of it was modern I’d stick with my existing set up. Possibly I’m guilty of purist snobbery but I see worth in keeping things original… It’s one of them where charm trumps practicality.. but at least I ain’t a leftie


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## JC800 (21 Dec 2022)

deema said:


> Just ‘repair’ the windows. I had a really interesting conversation on what is repair and what is replace with a building inspector. In the end, as long as any part of the original exists, or remains from what was there before you started to repair, it’s a repair. So, taking it to an extreme, if you reuse a screw, it’s a repair. I know, madness, but that’s the literal interpretation as I understand it of the rules.


If I get an inspector who approves repairs then great. Just concerned as they’re salvaged they won’t qualify as the original, that coupled with no sashes having been in for at least 30 years..


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## Fitzroy (22 Dec 2022)

I’ve been messing around with the sashes on my place and put a thin 14mm (4-6-4) krypton DGU in one of the sashes. I’m not impressed with the performance. It steams up whilst cooking, whereas the 24mm DGU in the door doesnot.


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## Bristol_Rob (22 Dec 2022)

Ollie78 said:


> never use linseed oil on double glazed units.



What makes you say this?


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## Seascaper (22 Dec 2022)

JC800 said:


> Hi all,
> 
> I want to build my own sash windows for an Edwardian semi and not quite sure what the requirements for compliance are given my circumstances. When I bought the house upvc double glazed windows were and still are in place. I’ve salvaged a set of original sash windows from a neighbouring property which require some repairs so first question is can I get away with installing these with the necessary repairs made? If so I’d be wanting to upgrade the glass to double glazing so my second question is what would be the maximum thickness I could use given the sashes are 44mm thick?
> 
> ...


Hello,
I repaired my window frames which were single glazed. The frames had come apart through age so I removed them one by one, took out the glass and nails, stripped, repaired and refastened with a good resin glue and dowels. The glazing units can be made up to a variety of thicknesses but building regs does specify a recommended width and depending on sill height you will have to have toughened glass, from 20 to 28mm. Once I had removed all the old putty, glazing nails etc it was then a question of routing out the frame for the addition depth needed for the glazing units. Quite simple to do with a half inch router and a sharp straight cutter finishing the corners with a chisel. The frames were then reassembled with new hinges and then the new glazing units, in this case 24mm put in with silicon and some wood beading that I had specially cut. No putty was used as from previous experience the small birds just ate it!
It was undoubtedly a lengthy process but rewarding when you saw the completed job. These were large windows which suited the house and matched all the others. And yes a labour of love and a good upgrade from single glazing.
Regards


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## Doug71 (22 Dec 2022)

I generally avoid making windows these days because of all the regs, I find it's a hassle making one offs and proving they meet part L and part Q of the regs ( don't think part Q will apply in your situation). Some inspectors aren't bothered but others want all the details.

I don't use the slim double glazing very often, it used to have a bad reputation for breaking down, I don't know if they have improved the design or if it was just bad installation. You shouldn't use linseed oil putty with DG as it sets hard and DG need to be able to move a bit, it probably also affects the edge sealant.

If you create a log in on the Mumford and Wood site you can view all their drawings and sections they use which can be helpful

https://www.mumfordwood.com/


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## Fitzroy (22 Dec 2022)

Doug71 said:


> I generally avoid making windows these days because of all the regs, I find it's a hassle making one offs and proving they meet part L and part Q of the regs ( don't think part Q will apply in your situation). Some inspectors aren't bothered but others want all the details.
> 
> I don't use the slim double glazing very often, it used to have a bad reputation for breaking down, I don't know if they have improved the design or if it was just bad installation. You shouldn't use linseed oil putty with DG as it sets hard and DG need to be able to move a bit, it probably also affects the edge sealant.
> 
> ...



Fab, I’d seen these guys before and looked at the sections and then lost the website name in my head. Great to have it back, and favourited now!


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## Ollie78 (22 Dec 2022)

JC800 said:


> Thanks for this Ollie. Good to know I’m not obliged to go supersized thickness to cater for 10mm dgu’s. I’m planning on boarding the outer walls with the insulated stuff so if I make new sashes I don’t mind going a bit wider, but not so much as to look odd. I’m not in a conservation area… So I’m wondering if becoming Fensa certified myself is the get out clause from having to deal with council inspectors


Fensa is a scam and not relevant for restoration work anyway. Don't give them your money.

Ollie


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## Ollie78 (22 Dec 2022)

Bristol_Rob said:


> What makes you say this?



Experience, I worked for a company who used putty for a while and it caused no end of problems.
Birds eat it, it can't be painted straight away even when dusted properly, it shrinks, and it dries too hard and is prone to crack.

The DGU manufacturers state not to use linseed oil putty and won't warrenty them. And if you really must they say first you must completely encapsulate all the edges with silicone. However, paint hates silicone so I refuse to use it.
The solution is hybrid polymers like Dryseal, Timbaglaze or Hodgesons heritage putty.
Solves all the problems, looks like putty rather than beads which have their own problems.

Ollie


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## Ollie78 (22 Dec 2022)

Jacob said:


> If you want replica period sashes then forget double glazing, it's totally incompatible with trad design. Instead look at having internal shutters or secondary glazing, or even just thermal blinds.


It is possible to do a pretty good job of disguising it, it has its limitations of course but most people wouldn't notice until you get less than a meter away. 
It's a compromise but can increase the warmth noticeably in conjunction with draughtproofing.

It's not perfect but if you need new sashes anyway then it won't hurt.

Ollie


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## Ollie78 (22 Dec 2022)

deema said:


> Labour council. Hardly describe them as right wing conservatives? They also slapped a Tree Preservation Order on the entire front garden…….which hasn’t any tress in it. In the village another of their imaginative decisions was to slap a local listing on a house that was in the process of combining a cattle shed into it……the shed had and now has to have an asbestos corrugated roof on it. The house roof is now half modern and half corrugated lung disease: you simply can’t make this stuff up.


I worked for a guy in a wonderful old water mill. He had lovingly restored it and I made him a few windows. 
They made him keep a corrugated iron roofed coal shed from the 60's. 
So I can certainly believe it !!


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## JC800 (28 Dec 2022)

Bristol_Rob said:


> What makes you say this?


Not answering for Ollie.. but to share my one experience with it it stuck well to the knife and stuck well to my fingers but not in the frame. It didn’t take long before resorting to no nonsense belt and braces and did it with milliput. Obviously I’m not pro and I imagine theres a good few reasons it’d be considered awful practice but 3 months in and going strong.


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## JC800 (28 Dec 2022)

Thanks for the input everyone. Sorry I’m a bit late back to resume the discussion. I’ve been told by a few people I should be good to go with making repairs on what I salvaged and keeping them within spec. I’m going to stick with the original glass and thinking I’ll add some strips to extend depth of the casements so’s I can run up to the inner edges with the insulation board then fit the architrave once I’ve skimmed. In theory it seems like a feasible way to improve on heat loss through the weight chambers. Then from there obviously draft proofing, and the insulated blinds recommendation sounds like a good one.

One final thing I wanted to ask.. the windows are made from pitch pine so for sections that need replacing.. what timber should I go with? Can I go with a hard wood or should I just stick to as closer match as possible which I assume will be redwood pine? Whats the done method in that scenario?

Thanks again.
Dave


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## Ollie78 (28 Dec 2022)

Southern yellow pine is a fair choice and not hard to find, you can use reclaimed old pitch pine floorboards if you can find some. Redwood is ok if you can find good stuff. 
I always use hardwood for cills, Jewsons stock it in Meranti but they call it door cill.

Ollie


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## deema (28 Dec 2022)

In Manchester, you should be able to easily find Douglas Fir, and if you feeling flush Accoya which is excellent for window frames too. Personally I would use either Accoya, Oak or Sapele for window cills


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## Doug71 (28 Dec 2022)

Don't want to put a downer on things but I can't see how replacing your existing windows with single glazed ones would comply with the regs, maybe you realise this and are willing to take the risk? It's not just the U values but also things like escape, protection from falling, safety glazing in critical locations etc. You will find single glazing cold if you are used to double glazing.

You could swap them over and all be fine but I would hate to think you went to all that trouble then had to remove them again because of some jobsworth.


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## HOJ (29 Dec 2022)

I'm afraid I have to Agree with @Doug71.



JC800 said:


> If I get an inspector who approves repairs then great. Just concerned as they’re salvaged they won’t qualify as the original


Answered you own question really, BC isn't going to help you.

I've been asked to make 10 big windows for a Farm house (existing are far too gone to even consider repair) it's listed, client doesn't want to go down PP route (cant repeat what she said) problem is liability, I'll end up getting prosecuted for doing it, if we get found out, would be a nice job, but I'm not prepared to take the risk.


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## deema (29 Dec 2022)

@Doug71 @HOJ 
The rabbit hole is repair versus replace. My understanding, and I’d really appreciate your perspective, is that repair is allowed, you can actually replace the entire window and frame under repair…..if you don’t agree with the screw definition…..you can replace the frame and refit the original sashes, and then replace the sashes! Now, again it’s my understanding that apart from fitting the correct glass ie safety were required you are not required to under repair to upgrade to the latest standards. Equally, again my understanding, if its listed, even the rules required for safety glass go out of the window (pun intended)


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## eribaMotters (29 Dec 2022)

Bristol_Rob said:


> What makes you say this?


Getting back to Linseed Oil Putty. It will break down the DG unit. Over 30 years I fitted probably 180-200 DG units in wooden casements and fanlights, softwood and hardwood frames. My method was always the same. Preserve windows and beads with with green Cuprinol, allow to dry thoroughly, use an aluminium oil based primer and then glaze with double sided sticky glazing tape on the vertical rebate with a smear of Butyl putty on the top edge and on the face of the beading where it sits against the GD units inside surface. I've had 3 units break down, so not a bad result.

Colin


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## Doug71 (29 Dec 2022)

@deema there are a lot of grey areas around the regulations for windows as it often comes down to the officer who you speak to on the day. I was once told that a repair over a certain amount (think it was 80%) was classed as a new window but I'm sure there is an argument for the Triggers Broom replacement method.

One of our local inspectors used to be great, he understood older buildings and bespoke joinery, he had the opinion that as long as you were improving things he was happy, unfortunately he has moved on and his replacement is the total opposite wanting every detail and calculation possible to prove that things comply.


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## JC800 (29 Dec 2022)

Doug71 said:


> Don't want to put a downer on things but I can't see how replacing your existing windows with single glazed ones would comply with the regs, maybe you realise this and are willing to take the risk? It's not just the U values but also things like escape, protection from falling, safety glazing in critical locations etc. You will find single glazing cold if you are used to double glazing.
> 
> You could swap them over and all be fine but I would hate to think you went to all that trouble then had to remove them again because of some jobsworth.



No downer Doug, I appreciate the input. As it stands I’ve become accustomed to freezing my ass off. I’m on half building site and there are a dozen or so other remedies I need to implement. I dare say if the original sashes went back in tomorrow it would make diddly squat with the absence of the dgu’s. So rejuvenated originals with the rest of the insulation measures in place should be a vast improvement.

The property I salvaged them from was a real time capsule as the previous occupant had been their her whole life. Before it’s new landlord gutted the place I managed to rescue all stained glass, internal doors with all original furnitures still intact. It was the only property with original rear windows along with the stained glass which I also acquired. I even took a moulding from one of the corbels. So I’ve gotten all passionate and insistent upon restoring what’s been gutted from mine. I reckon as I have managed to get the original parts the restoration approach would be a sound investment in terms of financial value also.

Like many others I’m prepared to deal with the shortcomings of original sashes but you’re right. I’m biased towards what I want to hear with no absolute confirmation the positive advice I’ve been given is definitively the correct advice. I guess really I should keep digging before I make a start.


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## GweithdyDU (30 Dec 2022)

deema said:


> Labour council. Hardly describe them as right wing conservatives? They also slapped a Tree Preservation Order on the entire front garden…….which hasn’t any tress in it. In the village another of their imaginative decisions was to slap a local listing on a house that was in the process of combining a cattle shed into it……the shed had and now has to have an asbestos corrugated roof on it. The house roof is now half modern and half corrugated lung disease: you simply can’t make this stuff up.


"half corrugated lung disease:". My understanding is that the corrugated stuff, which is encased in cement, is not the issue that the stuff used for lagging, and so on is. They still charge a fortune for removing it though!


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## LBCarpentry (Yesterday at 13:11)

On a 44 / 45mm sash you can use 16mm heritage double glazing for best effect. 15mm moulding, 2mm butyl tape, 16mm glass and remainder is putty. Approx 10 - 12mm.

Modifying an old sash for larger units has never worked for me tbh. Often the glue has long gone and after bashing them about they are in no state to hold the extra glass weight. It always amazing me how easy old sash’s break apart. They are often only held together by the putty on the glass! Usually one diagonal bash in the floor and the entire thing folds down like a folds thing into 4 neat peices

Quicker and more satisfying to make new ones. Remember to allow for brush seals though.


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## Jacob (Yesterday at 13:22)

LBCarpentry said:


> On a 44 / 45mm sash you can use 16mm heritage double glazing for best effect. 15mm moulding, 2mm butyl tape, 16mm glass and remainder is putty. Approx 10 - 12mm.
> 
> Modifying an old sash for larger units has never worked for me tbh. Often the glue has long gone and after bashing them about they are in no state to hold the extra glass weight. It always amazing me how easy old sash’s break apart. They are often only held together by the putty on the glass! Usually one diagonal bash in the floor and the entire thing folds down like a folds thing into 4 neat peices
> 
> Quicker and more satisfying to make new ones. Remember to allow for brush seals though.


If you do use brush seals don't put them across horizontally at meeting rails and bottom of bottom sash or you block condensation escape route and create a whole set of new problems.
Sashes work really well as de-humidifiers.


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## JC800 (Yesterday at 14:34)

LBCarpentry said:


> On a 44 / 45mm sash you can use 16mm heritage double glazing for best effect. 15mm moulding, 2mm butyl tape, 16mm glass and remainder is putty. Approx 10 - 12mm.
> 
> Modifying an old sash for larger units has never worked for me tbh. Often the glue has long gone and after bashing them about they are in no state to hold the extra glass weight. It always amazing me how easy old sash’s break apart. They are often only held together by the putty on the glass! Usually one diagonal bash in the floor and the entire thing folds down like a folds thing into 4 neat peices
> 
> Quicker and more satisfying to make new ones. Remember to allow for brush seals though.



Thanks both for the very helpful additional input. I don’t suppose either of you know definitively what the situation is with the legalities. DGU’s were installed sometime in the 80’s (very poorly)…

So with the sash windows being salvaged from another property on the same street, can I replace the DGU’s with restored salvaged units? I understand if the original windows are still in place then maintenance is permissible. But my circumstances differ in that I’m essentially down grading already fitted dgu’s with less energy efficient windows that, albeit match the street spec, are not original to my property. I’ve had a mixed range of answers both on this thread and externally and it’s a big chance to take without the full knowledge applicable to my specific circumstances.


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## Jacob (Yesterday at 14:51)

JC800 said:


> Thanks both for the very helpful additional input. I don’t suppose either of you know definitively what the situation is with the legalities. DGU’s were installed sometime in the 80’s (very poorly)…
> 
> So with the sash windows being salvaged from another property on the same street, can I replace the DGU’s with restored salvaged units? I understand if the original windows are still in place then maintenance is permissible. But my circumstances differ in that I’m essentially down grading already fitted dgu’s with less energy efficient windows that, albeit match the street spec, are not original to my property. I’ve had a mixed range of answers both on this thread and externally and it’s a big chance to take without the full knowledge applicable to my specific circumstances.


If it's your own property I'd just go for it. They aren't out there to get you and who is likely to shop you in the first place? In any case you could always retro fit thermal blinds, thick curtains, shutters, etc etc, if called upon.
The only issue is your EPC certificate should you come to sell but replacing DG with other DG isn't going to make any difference


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## Dibs-h (Yesterday at 15:05)

Jacob said:


> If it's your own property I'd just go for it.


I'm with Jacob - I'd just do it.

Replacing some of our ugly uPVC windows with DG sash windows (which I think the house originally had) is on my list of things to make\do. I'll just end up doing it.


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