Double Glazing or Single Glazing

[untitled]

Hello there.

We've recently been having a very productive discussion on condensation, black mould, it's causes and possible solutions. During these threads the subject of replacing single glazing with double glazing came up and it was put forward that double glazing might make the problem of condensation in the house worse... just moving the problem elsewhere.

Assuming that there is no reasonable solution to removing the source/causes of the condensation, has anyone else been in this position and then installed Double Glazed sashes? If so, did condensation get worse (although not noted on the glazing anymore)?

My other question is regarding building regs. If we were to propose keeping single glazing are we allowed to replace all the sashes in the house with restored single glazed units or, if we replace, do we have to revert to double glazing to stay within the law? The property is not listed or anything.

Any experiences and/or notes on the regs would be gratefully received.

I've attached a couple of pictures of the front sashes and their current condition.

Thank you.

 

[TheSpid]

I 'believe' that if you replace windows nowadays you need to replace with double glazing - replacing just a pane is fine to stay single glazed - there is a firm that does slimline double glazing [I've not used them only seen them on t'internet] http://www.slimliteglass.co.uk

 

[Feltwell]

If you change the windows and you're not listed, they have to comply with building regs, which in reality means DG.

But renovation of existing windows means they can stay as SG. Yours don't look too bad, certainly no worse than mine, which I am (slowly!) restoring. If you're a reasonable DIY'er then it's not that difficult a job, just time consuming.

If changing just the sliding sashes for DG then be aware that any DG unit will be heavier and require more counterbalancing than SG. You may or may not have enough room in the sash boxes for the heavier weights required to do this and still let the windows open fully. You may also need thicker glazing bars to cover the Dg seals.

 

[Craig89]

As Feltwell has touched on, timber sash windows are almost always repairable. I had one original sash window in my property which I have almost finished restoring. I am however replacing the sashes for ones fitted with double glazing (I am having all new timber sashes made for the rest of the house with double glazing. Which in my case, is definatly required for building regulations as half of the windows are in a new extension)

If you were to have new windows made with single glazing I dont think you would ever have a problem regarding building regs. If you had to for whatever reason you could say its just been repaired.

 

[Feltwell]

There's also the definition of what is a "new window". If you're replacing the complete box frame and sliding sashes then yes, it's a new window. But if you're only replacing a sliding sash then to me that's a repair.

What you've got there is eminently salvageable though - at far less cost than a new window or even a new sliding sash - and the difference that an original sash, refurbished with modern draughtproofing seals, makes is huge - done well the sashes just glide up and down smoothly, 99% of the draught and all the rattles gone, and the difference in appearance compared to how it was originally is very, very slight. If you don't want to do it yourself then there are firms out there that will do it for you.

Just be aware the reducing the draughts - be it refurbished SG window, refurbished window with DG added, or new DG window - is pretty much guaranteed to make your condensation isssue worse if other actions are not taken as well. But it should be possible to get it sorted - I notice that my restored sashes get more condensation on the glass than they did before, due to the much reduced draughts, but I still don't have any condensation or mould issues in the rooms concerned.

I did a thread a while ago on a fairly major refurbishment of a bay window that I did here, that went down well. Next time I do a standard sash I'll do a thread to track that as it's really not a daunting job once you've got the first one under your belt. There's different ways of doing it but hopefully seeing someone else able to do it will encourage others to take the plunge and give it a go, as there really is very very rarely a good reason to completely replace an original window, they are almost always quite simply & easily repairable.

 

[MikeG]

This is a classic "all else being equal" puzzle, so let's have a think about it like that.

Let's start the mental exercise imagining an enclosed fully insulated box with a hole in the wall and X amount of moisture inside. You have a heat source (say a old fashioned light bulb) inside, controlled by a thermostat. Assume that there are no ventilation heat losses, because we are going to fill that hole in the wall. Let's single glaze that opening. What will happen, assuming it is winter and the box is outside?

For a start, the glazing will be the coldest surface in the box, and so will be the place where condensation occurs. Further, it will be the place where much of the heat from the box is lost, thus triggering the thermostat to bring the heat source on. Were the thermostat to be manually over-ridden, the colder air in the box will be capable of holding less water vapour (it's physics!), and so the rate of condensation on the glass (and potentially elsewhere in the box) will increase. In essence the heat source in this arrangement is compensating for the heat losses through the glazed hole to keep condensation to a minimum.

Now, let's double glaze the opening. The inside face of the glazing will still be the coldest surface in the box, and still be the place where condensation occurs. However, it will be less cold than the single glazed version, thus the inside surface temperature of the glazing will be higher than for the single glazed alternative, and thus engender less condensation. Further, the air temperature in the box will fall less quickly than with the single glazed version because the heat loss through the glass is less, so the air will be able to hold comparatively more moisture before condensation begins to occur. Again, it's physics.

Which box will have had the heat source on for the shortest time? Which box will have suffered the least condensation?

 

[88v8]

.... the air will be able to hold comparatively more moisture before condensation begins to occur.

Mmmm, yes, but... unless the space is permanently heated the temperature will eventually fall and condensation will occur, and if the glazing is no longer the coldest spot then the condensation may manifest on the wall.
At least the condensation can be vacuumed off the single glazing, it can't so easily be removed from the wall.

The real solution of course is to remove the damp, but that's not always so easy.

All that said, I have engaged is a degree of double-glazing. Secondary which works well to the south, less well to the west and badly to the north, and slimline units which still experience a degree of condensation but not nearly as much.
https://histoglass.co.uk/ made in Germany
and
https://www.thinsealedunits.co.uk/ made in the UK

The slimlines are 12mm overall (half inch) and have been made with hand-drawn glass, which at the same time greatly improved the look of the window by eliminating the horrible float glass that was introduced in the 70s. I had dg samples with machine-drawn glass, less costly but they were not very wobbly, so did not make the cut.
They have been face puttied, not beaded. Also important for the look. The putty of course is not putty, but stuff that comes out of a tube and I have to say is by far the worst part of the job as it is an absolute barsteward to get a decent finish. The notputty specified by Histoglass is the least worst to use.

Sashes... if the OP measures the rebate depth he will see whether he can retrofit with slimlines, yes the weights will have to be changed.
For the windows to work correctly, the rule is Pound Under Pound Over - the top sash must weigh a pound less than the weights so it will stay up, and the bottom sash must weigh a pound more than the weights so it will stay down.

in 1981 we had new sashes made for our previous house. They were hardwood - heavy - and I put 1" dg units in them, also heavy. Way too heavy for the iron weights. To get full opening I had to cast my own 2" square lead weights. More by luck than judgement I didn't burn the house down or kill myself, but it was interesting to say the least.

Ivor

 

[MikeG]

..........The real solution of course is to remove the damp, but that's not always so easy........

I don't think there is any air on the planet which doesn't contain moisture, so what you are really saying is that the solution is to remove the excess damp. This is of course correct, and my whole house ventilation system does precisely that for me. Few people have them, unfortunately. This house, if I read the OP correctly, doesn't even have basic extraction from the kitchen and bathrooms, so of course it has problems, and problems unrelated to the glazing. That's the very first thing which needs to be done here.

 

[noj]

If you're concerned about the effect of double glazing on your moisture levels/ventilation you could always invest just a few pounds in the shrink-fit window film this winter (https://www.amazon.co.uk/tesa-UK-Th...1543242921&sr=1-1-catcorr&keywords=tessa+moll or similar) and see how the place behaves?

 

[MikeG]

I say again, for the avoidance of doubt, that double glazing itself can only have a positive effect on the levels of condensation in a building, all else being equal. All else isn't equal if changing from single to double glazing also changes the amount of ventilation, which of course wouldn't be the case if it is a straight replacement of glass, but could be the case if the entire windows are replaced. To see the argument at its simplest, glass doesn't allow air or moisture through, whether it is double or single sheets.

 

[fernicarry]

all else being equal

-- same moisture in the air, same circulation, same rate of exchange of internal and external air, same temps on all the surfaces. Over a short time span, the only possible difference is that the inner surface of the windows will be warmer, maybe even above the dew point, due to the DG. There will be less condensation on the windows, which leaves more moisture to drop out on the other surfaces. Looked at another way cold windows are quite good sacrificial de-humidifiers! I think that was what Ivor was getting at.

The thought experiment assumes the window is the dominant source of heat loss which won't be the case for most of us. Keeping the room warm enough that all surfaces are above the dew point (and for some depth into the structure to avoid interstitial condensation) is tricky, at least without fairly major works. DG may make a contribution to reducing heat loss, but it could be a very small one and undoubtedly an expensive one. For my own situation I did start thinking out that DG was the way to go, but now its pretty far down the list of improvements competing for budget.

Planned ventilation to exchange relatively more moist internal air with relatively less moist external air will help address the causes of condensation. If you are extracting air from a bathroom, especially if that bathroom is quite well sealed up, there will tend to be a greater flow of air in through the adjacent spaces to replace that air. This encourages circulation in the bedrooms too. And actually leaky windows in the bedrooms works to your advantage!

We've had a central extractor for the last couple of winters -- kitchen and bathrooms -- nothing fancy, no heat recovery on it, no point. I was lucky that both kitchen and the bathroom above it were renovated so I could run the ducting relatively easily. It trickles away all the time and will boost if it detects extra moisture like when cooking or running the shower (although the setting for this is on a knife edge). I've definitely had to use the window vac less often than previous years. But not all winters are created equal so impossible to say what the primary reason is. Still think its what you should be looking at not DG.

 

[untitled]

Brilliant posts and thank you so much to everyone for the valuable input!

It seems to follow that any restoration/replacement of the windows will lead to greater potential for condensation on the walls as they will generally be more sealed and less leaky than they are at the moment. However, if single glazing is maintained then condensation will potentially be more localised to the glazing and less to the walls. At least you can see where it is whereas on the walls it's not possible.

I don't think there is any air on the planet which doesn't contain moisture, so what you are really saying is that the solution is to remove the excess damp. This is of course correct, and my whole house ventilation system does precisely that for me. Few people have them, unfortunately

MikeG... can you tell me what whole house system of ventilation you have?

I've now installed a timed and humidistat extractor in the bathroom... https://www.eleconline.co.uk/enviro...er-silver-4-230v-extractor-fan-100mm-sil100st 26l per second airflow. The kitchen is next. A brand new dehumidifier is now plugged in... windows are dry!

So back to the windows I've been convinced enough by these posts to stick with what we've got and get them restored. I did try to do it myself once but I just don't have the time so I'll check and post details when I find someone.

I DO have one last hurdle though!

My lovely other half is less keen than I am to restore and is using the potential for noise reduction in DG as a joker card to put the case forward for DG replacement. The front sashes in the picture belong to our bedroom which is street side.

Does anyone know if there may be a big difference in noise reduction with DG? I guess this thing is hard to measure and most of all hard to describe.

Thank you.

 

[Feltwell]

Our lounge went from very large SG bay window with no draughtproofing, to still SG but with draughtproofing - and it definitely made a difference to the noise from outside - we noticed even though the road outside our house if not that busy.

So if you went from leaky SG to well sealed DG you'd notice a difference in noise, but the DG itself may not be the biggest factor. General wisdom is that secondary glazing, with it's much bigger air gap, is much better for soundproofing than DG.

I tried secondary glazing here but gave up on it, the design of my windows mean the only possible sort I could use was perspex sheet held on with magnetic strips, it was just a pain, especially in summer when the loose sheets had to be stored somewhere. From staying in hotels though (something I do far too much of with work ) if you've got sash windows with enough depth inside to have a proper secondary sliding frame system installed, they work very well indeed at cutting noise out, if you can live with the looks.

Of course all this ignores the damp issue! Glad that you're comfortable now with the dehumidifier running.

 

[untitled]

Thanks Feltwell.

I actually like the chitter chatter from outside... I've always found it comforting to know that when I'm in bed someone else is still up!

I will look into secondary glazing although I have a feeling that the aesthetic visual burden might be more than the acoustic one. We are certainly lacking in storage space too.

When we finally get the windows sorted out I'll post some information. (Fingers crossed for single glazed restoration!)