Hollow/cavity wall

Hello everyone, I’m thinking about building a room-within-a-room-construction and wondering if the width of the cavity between the in- and outside wall matters. My idea was to leave a space of approximately 40 centimeters (15-16 inches) between both walls, which won’t be filled with insulation. Would this make a significant difference as far as soundproofing is concerned or am I just wasting space? Thanks a lot in advance! Kind regards, 74Loveplane

This is probably a question for the construction forum but....all the papers I've read suggest that low frequency attenuation is to a large extent dependant on the seperation between the two walls of a double wall construction. So, no it's not wasted space. That said, there is likely a point of dimineshing returns. When you say 40 cm between the walls, is this the distance between the two inner most edges of the drywall? I would recommend putting insulation in between. Technically this will lower the attenuation somewhat as it couples the walls slightly, but it will be more forgiving to imperfections in wall assembly and holes (such as those for outlets and tie lines). It will also help damp out any cavity resonances. Check out the BBC and NRC papers on wall construction for more details. Cheers, Kris

Thanks Kris, You’re right of course, I should have posted this question on the construction forum. (a bit too hasty, Dutch you know) anyway: The idea of the rather large cavity came to me after reading articles of several building experts. I was wondering (and desperately looking for answers) if a completely filled (with insulation) normal cavity could cause problems with condensation building up between the walls. The experts (on the Internet) I’ve read so far, totally disagree on that subject. So I thought, go for the old fashioned way. Here in Holland houses are build, since decades, with a cavity in which the air can flow freely, thus keeping it dry and free of fungi and other stuff. This of course gives me a problem in the soundproofing area, so I thought what if I make some small triple pane windows in the in- and outside wall. This way I can get air floating through (leave ‘m open at night for example), have some daylight in and solve the fresh air problem without an AC system. So the reason to make a small corridor (between 40 and 50 cm’s wide) between both rooms was the necessity to be able to open up the windows from the inside. Could you tell me at which point it will be no longer effective or like you said: what’s the point of diminishing returns? I saw, in a lot of studio designs on this forum, a space between rooms of approximately 1 foot. Thanks, And kind regards, 74 Loveplane My apologies for being so elaborate! :oops:

Check out these BBC research pubs for better info than I can provide from memory. Cheers, This one is quite good, and the one I was thinking of. In particular check out the graph on page 12 to see why you will want some kind of damping (insulation) inside your wall. I have no information on the moisture issue, it's probably regionally dependant, so you may want to check with an expert in your area. http://www.bbc.co.uk/rd/pubs/reports/1995-06.pdf Here's another...not as good, but still okay http://www.bbc.co.uk/rd/pubs/reports/1991-09.pdf Cheers, Kris