How useful is double-glazed glass for sound and heat insulation in a semi-tropical climate?

Question

I'm located in Bombay/Mumbai, and I've been trying to figure out what windows I should install for soundproofing and heat insulation.

I was talking to someone who does consultation for uPVC windows. He said that double-glazed glass (two sheets of glass with an inert gas in between) was almost useless from the point of view of sound insulation. He said double-glazed glass was mostly useful for heat insulation.

He also said that in a Bombay climate, heat insulation was not that useful For people who don't know, the climate here gets up to around the high 30s C, say like 38 C or so max, but never gets cold enough to require heating sources. So, the question is whether double glazing is useful in these sorts of conditions. In this case one would be trying to stop the heat from coming in, particularly during the summer.

So, his recommendation was that of 12 mm toughened glass, vs a double-glazed approach, which would be like 5 mm + 6 mm glass sheets, separated by a 12 mm gas enclosure.

I'm sceptical about this, so I am asking here. I had a number of other people recommend double-glazed glass as though it was the natural solution. I did find some support for this statement from this random web page - http://www.stormwindows.co.uk/index.php?id=42, which says

Typical 4mm toughened glass will provide a mean noise reduction of Rm = 27dBA while double glazing with a 12mm hermetically sealed air-filled cavity, again using 4mm toughened glass, gives Rm = 29dBA. This 2dBA difference in sound intensity between single and double glazing would barely noticeable for the average person, thus demonstrating that standard double-glazing is not always a suitable and cost effective solution for noise insulation.

Of course, one should not believe everything one reads online. So, I'm asking here if anyone can direct me to reputable sources about this.

One additional concern is whether the gas can escape over time, in the case of double-glazed glass.

Answer 1

The important comparison is not between double glazed and single glazed windows. It is between specific windows and their specifications because there are high quality single glazed windows and low quality double glazed windows and even among one group or the other, thermal and acoustical performance can vary with manufacturer and part number.

Generally speaking and so long as the sash is not open, double glazed windows will offer superior thermal performance because the separated panes inhibit heat transfer by conduction. As a relatively mature product with several decades of manufacturing and installation history, seal failure that allows the dissipation of the inert gas is not usually a problem with products from established manufacturers.

The American Architectural Manufacturers Association has well established standards for windows and doors. The Window and Door Manufacturers Association is another resource. Their building science is sound. Similar resources exist in other regions.

Answer 2

He said that double-glazed glass (two sheets of glass with an inert gas in between) was almost useless from the point of view of sound insulation.

That is not true, but it may depend on the loudness of the outside noise, it's frequency profile and what noise level you consider acceptable inside.

Double glazing window, especially when acoustic glass is used, helps to insulate against the nuisance caused by outside noise. Laminated acoustic double glazing window can reduce noise levels by up to 35 decibels.

^{double-glazing-info.com}

It isn't clear if triple glazing can offer bigger reductions but ultimately it depends on the total mass of glass, size of air gap and other factors.

Triple glazing offers no signicant improvements over double-glazing;

^{Sound transmission through single, double and triple glazing. Experimental evaluation - Applied Accoustics Journal}