Architects
Question: Jonathan R. / Architect (Cambridge,
MA)
I’m finishing the construction documents for a new, 800-seat,
contemporary worship space, and I am trying to detail the window in the
back between the cry room and main sanctuary. I am using an STC-57 wall
construction (UL-U425; 2 layers 5/8” thick GWB both sides of metal studs
with batt insulation) between the Cry Room and Sanctuary. The window is
70” wide and 48” tall. I have attached the main level plan and interior
elevation. Logic tells me that the window should also be STC-57, but the
quoted prices from manufacturers for windows of this size and rating are
cost-prohibitive. Can the contractor build a window on site that will
perform sufficiently and if so, what would the construction need to be?
Sound-Answers.com
We assume you know about Sound Transmission Class (STC) because of the
details in your question. If not, please visit Sound-Answers.com’s
resource center to learn more about STC.
The window and wall between the Cry Room and Sanctuary should have a
STC-50 rating. (The STC-57 wall you selected is acceptable, but could
also be downgraded to STC-50.) As you noted, there are manufacturers
such as Industrial Acoustics Company (www.industrialacoustics.com)
and St. Cloud Window (www.stcloudwindow.com)
that manufacture windows with high STC-ratings, but they can be
cost-prohibitive, especially when the size of the window is as large as
the one in your project. Yes, the contractor can site-build a window
that will achieve sufficient isolation. Use solid wood (hardwood or
softwood) to frame out a 1/2" thick laminated pane, a 4” airspace, and
then another 1/4” laminated pane. This will achieve an STC-51. If the 4”
wide airspace is not possible due to stud size, then decreasing the
airspace from 4” wide to 1” wide decreases the rating to STC-46
(marginally acceptable). Try to maximize the width of the airspace (2”
is better than 1” and so on). Be sure to detail and specify a
nonhardening caulk along the entire window perimeter (both sides) where
the glass and wood frame meet and where the wood frame meets the wall.
Beyond the question ~ To help control noise levels inside the
Cry Room and thus decrease the amount of the reflected sound energy
available to transmit through the window, ensure that the ceiling of the
cry room is a fiberglass ceiling tile with a Noise Reduction Coefficient
of 0.90+ and that the floor is carpeted.
