Author Topic: A sound attenuating flat roof architecture  (Read 3385 times)


  • Guest
A sound attenuating flat roof architecture
« on: March 19, 2008, 02:00:15 AM »
I'm in the architecture phase of a house contstruction.  Planning approval is granted,
and the house has a 1-meter thick flat wetland roof.  The roof deck is 500mm of that meter,
where the rubber membrane sits - then 250 of foam insulation and 300-700mm of living wet landmass.

I have to span several spaces about 6 meters with this heavy roof.  And despite the
supplemental beams, i'm curious if anyone has tried using engineered' truss's as a noise abatement feature.
Because of the extremely heavy roof, i've been considering using the kind of engineered truss called
a posi-joist.  My thinking was to place them (made 250 deep out of 2x6 timbers) 3 inches apart across the
whole ceiling... and to call the ceiling *done*.  This makes the gap above the timbers in to a 250mm dead
space that will be pretty much invisible to the room proper - can serve as a flexible electrical wiring area,
and serve as a ventilation return... but also serve as an acoustic absorber from the room below.

So my question is: do posi-joists placed at 3 inch spacing create an acoustic absorber?
picture of posi-joist:

My crude acoustic understanding is that a ceiling of slats with a dead air space above is a good acoustic
absorber, would this work better using posi-joists 400 deep made of 2x4's instead, or with a different spacing?
What percentage of the ceiling should be slats and dead air space to create the optimal sound absorption?


  • Guest
Re: A sound attenuating flat roof architecture
« Reply #1 on: March 19, 2008, 10:15:18 PM »
I think you need to consult a structural engineer first, considering how much load you'll have on these trusses.