Secondary glazing + double glazing: sound insulation?

[Garald]

Where can I find information on the dB reduction (on top of that provided by double glazing) I am likely to get in the following scenario?

 

Existing acoustic double glazing + thick layer of air (windowsill created by insulation!), between 16cm and 20cm + secondary glazing (single)

 

This was a solution proposed in another thread: 

 

Calculating the effect on heat insulation is probably simpler: just add the R of the secondary glazing itself (poor, like any single glazing) and the R of the air laye (skimming https://www.wufi-wiki.com/mediawiki/index.php/Details:AirLayers suggests it's only a bit worse than a 3-5cm thick layer (R<0.16); is this right?).

[SteamyTea]

6 hours ago, Garald said:

Where can I find information on the dB reduction

You could try modelling it in LISA.

https://lisafea.com/

Pretty sure it does acoustics.

[Bozza]

Not a direct answer to your question, but I used to live in a city centre apartment near noisy pubs and clubs  - a converted 100 year old post office.  Massive 2m high original single glazed wooden sash windows.

 

we installed secondary single glazing and the sound reduction was remarkable.    The secondary glazing Sat about 3-4” from the sashes.  If you’re  looking at establishing the effectiveness  of secondary glazing for sound insulation I’d say if used in tandem with good quality double glazing you ought to get a great outcome.

 

our secondary was from Everest, don’t know if they still do it or not.

[Garald]

2 hours ago, SteamyTea said:

You could try modelling it in LISA.

https://lisafea.com/

Pretty sure it does acoustics.

 

Thanks, though that does not seem to be made for Linux-based folk...

[SteamyTea]

25 minutes ago, Garald said:

 

Thanks, though that does not seem to be made for Linux-based folk...

Try WINE

[Garald]

3 hours ago, Bozza said:

we installed secondary single glazing and the sound reduction was remarkable.    The secondary glazing Sat about 3-4” from the sashes.  If you’re  looking at establishing the effectiveness  of secondary glazing for sound insulation I’d say if used in tandem with good quality double glazing you ought to get a great outcome.

 

That sounds very encouraging.

 

3 hours ago, Bozza said:

our secondary was from Everest, don’t know if they still do it or not.

 

I can look into that; I got a reasonable-looking quote from a place called Clearview. I am based in the Paris area, though, so I'd much rather find a EU-based manufacturer. Brexit shafts us again.

[saveasteading]

In double glazing, a narrow gap works best for heat, but is worst for sound. 

A wide gap allows heat to circulate so is very poor for heat.

So if you use double glazing first, then the secondary glazing can be as far as you like inside it for best sound reduction.

I'm pretty sure the suppliers of secondary systems have figures.

From memory you should have at least 40mm gap, up to 100.

 

I fitted a diy polycell system as we were next to a main road, and it worked very well. Was decades ago so can't help on current options.

 

[Garald]

15 minutes ago, saveasteading said:

In double glazing, a narrow gap works best for heat, but is worst for sound. 

A wide gap allows heat to circulate so is very poor for heat.

So if you use double glazing first, then the secondary glazing can be as far as you like inside it for best sound reduction.

I'm pretty sure the suppliers of secondary systems have figures.

From memory you should have at least 40mm gap, up to 100.

 

We are talking about a 160mm-200mm gap - this should be OK for sound, no?

 

I don't know whether an air layer that deep is 3/4 as good or 1/10 as good as a 30mm-deep layer (I'm getting contradictory information), but that's a secondary consideration - my energy rating is very good, it's the noise from the street that still bothers me (particularly when I sit close to the window, and particularly in the higher frequencies: I simply dislike the sound of motorbikes).

 

Edited October 21, 2023 by Garald

[SteamyTea]

  

3 hours ago, SteamyTea said:

Right, rather than get my old PC out and boot up the CAD, some pictures instead.

I used the outside of my window as it more closely resembles the inside of yours. Having said that, is fitting secondary glazing outside a viable option.

One thing to remember is that it should be easily removable, in a hurry, in case of a fire.

 

First picture is how a new frame would be fitted. This can be screwed, bonded or just double sided adhesive taped. Paint will match the colour.

 

 

Then make up a glazed panel.

Mine are cheap clear styrene, but of painted moulded timber, stuck to the styrene with double sided tape, with some foam draught seal stuck to the other side. Now I used a cut of saw to cut the mitres, but a hand saw, and a butt joint (with some filler maybe) would do. Then drill some screw clearance holes through the timber and styrene sheet.

Screw into secondary frame.

 

 

 

 

 

[Garald]

1 hour ago, SteamyTea said:

  

 

That does look very nice (and inexpensive). I don't have manual DIY skills I know of, so I guess I'll have to order a kit and install it together with the contractor and his guys.

 

What CAD do you use, by the way? I've been using OpenSCAD, since, at the same time that it's free, it is much programmer-friendly than the supposedly "user-friendly" free software I've been able to find.

[SteamyTea]

5 minutes ago, Garald said:

I don't have manual DIY skills I know of

A rule, hand saw and a sharp knife is all that is needed.

6 minutes ago, Garald said:

What CAD do you use, by the way

I have a legit copy of TurboCad, been using TurboCad for 25 years, never got on with AutoCad.

Shall have a look at OpenSCAD.

[Temp]

4 hours ago, Garald said:

 

We are talking about a 160mm-200mm gap - this should be OK for sound, no?

 

I don't know whether an air layer that deep is 3/4 as good or 1/10 as good as a 30mm-deep layer (I'm getting contradictory information), but that's a secondary consideration - my energy rating is very good, it's the noise from the street that still bothers me (particularly when I sit close to the window, and particularly in the higher frequencies: I simply dislike the sound of motorbikes).

 

 

When the M3 was built next to our house in the late 60s my father fitted secondary glazing with a narrow air gap. Can't remember the exact width but it was on the inside of the wooden single glazed windows so probably 30 to 40mm. Then the government offered to fit secondary glazing. My dad ask if we could just have the money as we already had secondary glazing. They said no because the gap on what we had was too small. So my dad got them to come fit another lot. This was fitted to the inner face of the wall so a gap more like 175mm. It opened so you could still put things on the window sill etc. So we had a sort of triple secondary glazing.

[Garald]

Someone here https://engineering.stackexchange.com/questions/56707/secondary-glazing-16-to-20cm-away-from-double-glazing seems to be implying that the additional sound reduction would be of only 2dB, which is very little indeed. Is that correct? Or are there effects that they are neglecting?

 

I suppose much of it depends on whether the secondary glazing is airtight?

[saveasteading]

2dB doesn't seem right.

I would have to study it properly, but there are lots of R numbers and dB in graphs and charts on a website called selactaglaze. 

 

The immediate obvious difference is between a 50mm cavity and 200. The bigger gap is most noticeably effective for lower frequencies.

[SteamyTea]

22 minutes ago, Garald said:

Someone here https://engineering.stackexchange.com/questions/56707/secondary-glazing-16-to-20cm-away-from-double-glazing seems to be implying that the additional sound reduction would be of only 2dB, which is very little indeed. Is that correct? Or are there effects that they are neglecting?

 

I suppose much of it depends on whether the secondary glazing is airtight?

Have you got two phones, then you can download a decibel o meter app, play around with a sheet of clear plastic or glass  and see if the readings change.

Not perfect, and uncalibrated, but will give you an idea of what is going on.

Unlike mathematics, physicist don't let the better be the enemy of the best.

[Garald]

23 minutes ago, SteamyTea said:

Have you got two phones, then you can download a decibel o meter app, play around with a sheet of clear plastic or glass  and see if the readings change.

Not perfect, and uncalibrated, but will give you an idea of what is going on.

Unlike mathematics, physicist don't let the better be the enemy of the best.

 

Hey.

 

On the other hand, this mathematician does not have a sheet of clear plastic at hand - he'll have to get one.

 

And that opinion came from an *engineering* stack exchange! The applied-maths friend I talked to liked the idea of secondary glazing.

Edited October 22, 2023 by Garald

[SteamyTea]

5 minutes ago, Garald said:

 

On the other hand, this mathematician does not have a sheet of clear plastic at hand

Just make an imaginary one, you lot are good at that.

6 minutes ago, Garald said:

The applied-maths friend I talked to liked the idea of secondary glazing

Get them to make one.

Applied mathematics is only using a simple rule, rather than complicated algorithms.

[Garald]

3 minutes ago, SteamyTea said:

Just make an imaginary one, you lot are good at that.

Get them to make one.

Applied mathematics is only using a simple rule, rather than complicated algorithms.

 

Applied people care an enormous lot about algorithms. Admittedly they care about practice performance rather than just about asymptotic complexity.

 

And believe me, applied math can get complicated. If anything, it's pure mathematicians who find unnecessary complications (and decimal points) unaesthetic.

 

There's also a lot of crossover - said applied friend keeps telling me about applications of my field to his.

[SteamyTea]

26 minutes ago, Garald said:

There's also a lot of crossover - said applied friend keeps telling me about applications of my field to his.

Now that would make for an interesting statistics project.

Statisticians are allowed to be wrong, as long as the reasoning is right.

Or is that economists.

[Garald]

The conversation in https://engineering.stackexchange.com/questions/56707/secondary-glazing-16-to-20cm-away-from-double-glazing is getting interested; people seem skeptical.

[Garald]

There's also the question of how to design the secondary glazing so that I can still open my existing windows (which open towards the inside, both "à la française" (like a book) and by tilting; let's call this combined operation "the German way"). I was just asking in a French site, and someone was saying that sliding windows wouldn't do - the rail would get on the way. (Perhaps window rails are thick in France?) Is the only option to have windows that open in the same way as my existing windows - be it in exactly the same way (four panels, side panels fixed, middle panels opening in the German way) or else having two large panels, both opening in the French way?

Edited October 22, 2023 by Garald

[SteamyTea]

13 minutes ago, Garald said:

There's also the question of how to design the secondary glazing so that I can still open my existing windows

4 secondary panes with the two middle ones hinged so that they double back onto the adjacent panes.

 

I think you may be overthinking all this.

It is never going to be invisible, so has to show the function in the best possible way.

[Garald]

8 minutes ago, SteamyTea said:

4 secondary panes with the two middle ones hinged so that they double back onto the adjacent panes.

 

I think you may be overthinking all this.

It is never going to be invisible, so has to show the function in the best possible way.

 

Right, that's one of the possibilities I was mentioning. 

 

I'm a bit alarmed at how skeptical people at https://engineering.stackexchange.com/questions/56707/secondary-glazing-16-to-20cm-away-from-double-glazing seem to be - are they right, or are they just not getting that we are talking about two separate window frames?

[SteamyTea]

3 minutes ago, Garald said:

are they right, or are they just not getting that we are talking about two separate window frames

They are probably guessing.

 

While I did not do any calculations when I secondary glazed my windows, intuition, backed by theory, meant I knew there would be a sizable improvement.  The noise reduction was much better than I imagined.  Thermally I probably benefited most because air leakage was reduced (I have 36 year old timber frames).

Have you checked that all your windows close properly and the seals are sealing well?  Can usually tell by dirt marks that have bypassed the seals.

 

[Garald]

2 minutes ago, SteamyTea said:

 

Have you checked that all your windows close properly and the seals are sealing well?  Can usually tell by dirt marks that have bypassed the seals.

 

 

Everything is closing properly; these are new windows and new window-frames. (Well, at one point one window wasn't closing properly because we had not closed it right after opening it fully, and we could really notice the difference.)

 

Don't get me wrong - these are good windows. All the same, it's a first story right in front of a busy two-lane street.