NEW TRENDS AND EMERGING TECHNOLOGIES Acoustic ...

NEW TRENDS AND EMERGING TECHNOLOGIES
Acoustic Separation in New Townhomes
By Don Gratton, PEng
GETTING AWAY from concrete demising walls and floors, and going to lightweight composite
walls and floors is a break with tradition. But, performance audits done for the New Home Warranty
Program, Tarion, are uncovering serious complaints of “neighbour noises” due to inadequate sound
dampening by the demising walls.
Such was not the complaint in traditional row housing where concrete block walls separate one unit
from another. With strapping and regular drywall on each side of block walls, Ontario Building Code
(OBC) gives the assembly a sound transmission class rating (STC) of 57. STC 57 is much better than
the minimum sound proofing of STC 50 required by OBC 9.11.2.
To achieve an STC 57 level with drywall and no masonry or block requires insulated, double stud
walls, faced with Type X gypsum board, and an air space between the rows of studs. In addition, the
studded wall needs complete sealing of the inside of the gypsum boards at all edges and electrical
boxes. Building this kind of demising wall requires a good deal more attention to detail than the
simple, old block-based separations.
Stacked Townhouses
Stacked townhouses have the additional problem of soundproofing the floors between lower and
upper units. Whereas older designs like the Estonian development on Corinth Gardens in Toronto had
concrete floors, new ones are relying on the wood sub-flooring, insulation between supporting beams,
and double drywall supported on resilient channels for the ceiling below. This meets the STC 50
requirement, but is inadequate judging by the dissatisfied responses to surveys of residents on lower
floors. They complain that the worst noise transfer is below any kitchen or bathroom that cannot be
carpeted, below stairs and beside laundry rooms.
Although the above-designed floors have an STC of 50, OBC Appendix 9.11 recommends a margin
of 5, i.e., STC 55, for quality homes. Their supplementary guidelines give examples of how this is
achieved with floors, namely either by using a 1.5 inch concrete layer over the sub-floor and two
layers of the superior Type X gypsum board on the ceiling, or with about an inch of lightweight
concrete on the sub-floor and absorptive insulation between it and the double layer ceiling, to achieve
STC 55. Appendix 9.11 goes on to say that “impact noise requirements are being considered in future
revisions.” The tone of the Appendix is that acoustic separation is still somewhat experimental.
The author saw three stacked townhouse projects that employed acoustics consultants to certify that
their architect’s designs met requirements. In no case was concrete topping used on the floors. For one
of these, a 78-unit two-level project, all floors and stairs were specified to the minimum STC 50, with
sadly predictable results.

Plumbing Noise
In another project, plumbing noises were so severe in some lower units that the performance auditor
had walls and bulkheads opened to find that absorptive insulation or sealing within the walls was
inadequate, both in performance and in comparison with builder’s specifications.
But even within established units, and also in detached houses for that matter, more could and
should be done so that use of an upstairs bathroom does not disturb those enjoying the space below.
The technology is there and continues to evolve, and the costs to install sound-absorption during
construction or major renovation are small.
Conclusions
New townhouses must be acquiring a reputation for being poorly soundproofed, which certainly
hurts the condominium industry. Builders could enhance their competitive position by being able to
guarantee a certain level of acoustic dampening. That required more care and supervision during
construction than seems to be the norm. And the regulators, namely Tarion and the Ministry
responsible for building codes, could increase their efforts to see that home buyers get what they
expect in the area of sound separation between units. Even the real estate salespersons could better
inform themselves on this subject in order to help clients differentiate between prospects with good
versus poor sound control.
Don Gratton has been a registered professional engineer in Ontario since 1969. For the past two
years, he was a reserve fund planner and engineer for First Condo Group Ltd., a firm serving
southcentral Ontario for over 20 years under the direction of Hans Moehring of Toronto. Email them
at info@firstcondo.ca, or firstcondo@sympatico.ca.
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* Condominium Manager Magazine – Winter 2005