Some questions about windows...

[Wurlitzer]

Well, I've started work on my new garden studio/rehearsal room. For anyone who's interested there's a plan here.

My current concern is the window, and how to make it as soundproof as possible. I've done a lot of background reading here and elsewhere, but still don't really get some things. Help would be much appreciated on the following points:

1. Would there be any advantage installing a non-opening window over an opening one? I'll be installing a ventilation system, and figure that if it gets hot and I really want some air while working quietly, I can always open the door. The rest of the time, working at volume, I won't be able to open the window anyway.

If it makes no difference to soundproofing I might as well get an openable one, but if they can do anything better with the seals in non-opening ones, that would be worthwhile for me.

2. My building will be a double-leaf structure with 100mm dense concrete block on the outside and two layers of plasterboard (drywall) on the inside. So I'll put a window in each leaf, the inner one opening in and the outer one opening out. So far so good.

However, all the windows that I've seen sold for good acoustical properties are double-glazed units, with two panes of glass and a SMALL airgap between. They're obviously designed for just one unit being used.

Using two of these, one in each leaf, would create a FOUR leaf structure! That's bad, isn't it? So from what I understand, I'd be better off with a single pane of the thickest possible glass in each leaf, with ONE airgap of maximum width between. Correct?

3. If so, where would I get such windows, here in the UK? Would I need to go to a company catering for the industrial market or something? Even studio specialists don't seem to do this - I've found several that do studio grade doors, and various kinds of door seals etc, but none that do windows.

4. Important: I REALLY don't understand this one.

I've seen much discussion about how to seal the gap between the two door-frames or window-frames in a double-leaf building, about using flexible material such as rubber or whatever to cover the gap without coupling the leaves acoustically.

But what I don't understand is: WHY would one need to join them? Why couldn't one simply have each door and window attached to its own leaf, with the completely decoupled gap between the leaves continuing all the way round, the same at the door and window as elsewhere?

Apart from aesthetic considerations, such as opening the door and seeing bits of rockwool insulation everywhere (which I'm sure can be gotten around), what's the deal here? Why join the two frames at all? I've not yet seen anyone explain this, it just seems to be taken for granted. Is it something so obvious I'll feel like a right idiot once it's pointed out???

Thanks all for any pointers on these questions. This forum is great.

[knightfly]

1. Windows and doors that are operable (you can open them) will NEVER seal as good as fixed ones - the best you can hope for is to get CLOSE to as good, and that's with expensive seals and mucho attention to detail on mating surfaces, etc -

2. Yes, you're correct.

3. You may very well have to find a glazier, and have panes custom cut in order to get what you want. Concrete weighs almost the same as glass, so to match your concrete outer leaf you'd need a glass that's 100mm thick - not too practical. For one thing, even if you could afford it the glass, guestimating your window at around 3 x 4 feet the glass would weigh nearly 500 pounds...

Realistically, if you were to put a 5/8" (15mm) pane of glass in the outer leaf, as close to the outer edge of the blocks as practical, then a 3/8" pane in your double gypsum wall, you'd get very close to a match with your wall construction at the low frequency range; mids won't be as good as your walls however.

With a 100mm air gap between blocks and two layers of 13mm plasterboard, you would be around STC 70 with a low end TL of around 40 dB - placing your 5/8 and 3/8 glass at the extreme outer/inner edges of these would give an air gap of around 200mm, for an approximate STC of only 48 dB; but your low end would still be around 40 dB, so not a lot of bass would make it through. An increase in air gap to 300mm would help both ends of the scale by around 3 dB.

4. You just said it - mainly aesthetics. Only other reason for some sort of non-coupling cover is to keep small bits of pocket change, etc, from "shorting out" your carefully separated wall frames... Steve

[Wurlitzer]

Thanks Steve. Looks like I've got my work cut out phoning around glaziers.

I must admit I'm tempted to just do without a window. That would be a lot better, right?

[knightfly]

Yeah, for everything except sanity

[Deluks]

Thanks Steve. Looks like I've got my work cut out phoning around glaziers.

I must admit I'm tempted to just do without a window. That would be a lot better, right?

Well I've got a window in my garage (which will soon (?) become a studio) and I have every intention of keeping it. In a 12'x15' room I think the addition of natural light, and being able to look out onto the garden will make the room much more bearable to be cooped up in for hours on end.
The current glass is 3mm but I should be able to replace that with some half inch or so from a glazier, it's not so big, about 850x450mm or thereabouts. After that there will be an airgap of around 200mm and then the heaviest piece of glass I can lay my hands on. I haven't acquired the glass yet but I'm working on it. I'm looking at glass tabletops, used post office screens and all sorts to try and reach my requirements, anything to save a few quid

[Wurlitzer]

I've decided for the moment to go without a window!

I've always been a bit of a nocturnal troglodite and like the feeling of being completely shut away from the world while I work. I figure that I'll mostly be working in the room at night anyway, there'll be a ventilation system for air, and if I want more air at times when I'm not rehearsing or working at volume, I can always open the door.

More importantly, my friend/builder says that he can build it with a lintel in where the window would go, and then if I want a window at a later stage, it's not that big a job to knock one through and make one. So I figure I'll see how I go first without one.

[sharward]

. . . my friend/builder says that he can build it with a lintel in where the window would go, and then if I want a window at a later stage, it's not that big a job to knock one through and make one. . .

Good call.

[johnz]

about the double pane glass thing, i seem to remember reading in one of f alton everest's acoustic books that thermal glass has such a small airspace between it that it acts on the mass principal alone. wouldn't two thermal double paned windows act as a two leaf system then, not a 4 leaf?

[sharward]

It would be terrific if you could narrow that down to a quote and a bibliographic citation! I hope that's not too tall of an order, but the question does come up a lot and it would be great to have an authoritative answer to that dilemma, and Everest would definitely be considered an authoritative resource (may he rest in peace)!

--Keith