1. The original RC-1 used in most lab tests no longer
exists. USG stopped making the product in 1985. Most test
results are based on STC tests conducted 10 or more years ago
on different fabrications. As there is no standard for RC
channel fabrication, the various resilient channels available
vary greatly in their resilient (stiffness) characteristics. Using
currently available RC channels that are often too stiff or that
have holes the wrong size or shape results in reduced STC
values. There are few current RC channels available that have
recent test results based on their actual fabrication and design.
2. Dead on arrival. RC channels are thin and prone to damage
from shipping or on-the-job storage. Any bend in the channel
can cause shorting. We have multiple reports of damaged RC
channels that are deployed because by the time the damage is
perceived, it is too late to re-order.
3. The RC channels are placed too close together. If this
happens, the composite stiffness of the wall will be too high
and will result in reduced sound insulation.
4. The RC channel is often drawn on the architectural
plan and/or installed upside down. In such instances, the
weight of the drywall pushes the channel into the studs
(instead of pulling it way from the studs when installed
properly) thus causing a short circuit in the wall, resulting in
poor sound insulation.
5. The RC channel extends too far and touches an
adjoining wall. This error causes a short circuit in the wall
resulting in radically degraded sound insulation.
6. A screw is placed incorrectly. While the drywall is being
attached to the resilient channel, a screw that accidentally
attaches into a stud or touches a stud at any point will short
circuit the wall and result in poor sound insulation.
7. Insufficient gap between the wall with the resilient
channel and any adjacent wall. If the drywall attached to
the RC channel touches the drywall on the adjoining wall, the
wall will be short circuited, resulting in reduced STC value.
8. Drywall is not installed properly. If the subcontractor
adds drywall that is beyond spec (e.g. adding a layer of Type X
to meet fire code), the resulting structure can sag, and the
weight of the drywall on the resilient channel can cause the
wall to touch the floor, causing a short circuit in the wall,
resulting in poor sound insulation.
9. Electrical junction boxes attached to the stud and to
the wall. This common error causes a short circuit in the wall
and result in poor sound insulation. This mistake is easy to
make with the faceplate, which must also be isolated, or by not
cutting enough of the drywall away around the junction box.
The same principle applies to ceiling attachments such as
lighting and fans.
10. Gaps around the junctions. If junction boxes at the wall
are sealed with standard caulk that hardens over time (instead
of non-drying non-skinning acoustical sealant), or not sealed
with anything, this will cause a short circuit (or air gap) in the
wall, resulting in poor sound insulation.
11. Resilient ceiling. If the ceiling is also resilient, the walls and
the ceiling cannot touch each other. To achieve this, it is
recommended the walls be put up before the ceiling. This is
counter to standard drywall installation practice.
12. Actions of other subcontractors. When RC channels are
used in floor/ceiling assemblies involving stuffing materials
into the open truss, the risk is magnified. Plumbing, HVAC
and electrical materials are routinely attached inside the small
cavities in ways that guarantee short-circuiting the RC channel.
13. Green wood warping. Most multifamily housing (such as
west of the Mississippi River) is made of the less expensive
green wood, which dries after installation. The drying process
can distort the framing by as much as 1/2" in extreme
situations; 1/4" is common. This torque can bring the RC
channel in contact with other elements and cause a short
circuit.
14. Moisture & humidity warping. In high-humidity areas
(such as the Eastern seaboard), humidity can bow and buckle
drywall, 1/4" to 1/2" in many cases. This distortion can bring
the RC channel in contact with other elements and cause a
short circuit.
15. Foundation settling. Foundation settling, the #3 cause of
litigation, is a common occurrence. A 1/4" or 1/2" settling
distortion can bring the RC channel in contact with other
elements and cause a short circuit.
16. Language barriers. The high incidence of RC failure
contrasts with good results established in the top labs. This
discrepancy points out the need to have highly trained,
disciplined personnel supervising and performing the
installation. In many construction crews, many of workers are
foreign-born. The ability to communicate in English fluently,
understand and execute written and verbal instructions for
something as delicate as RC channels is required.
17. Owner/tenant actions. If, during the life of the property,
the owner or tenant installs materials to the wall, such as a
picture or lighting, the wall can easily be short circuited. In the
case of hotels, many products are routinely attached to the
walls for various reasons, including anti-theft and seismic
restraint: bed head-board, writing desks, open shelving system,
closet shelving, refrigerator, safe, sconces, mirrors, paintings,
bathroom shelving, television wall stands, decorative wall
hanging, crown molding, baseboard, wainscoting. For rigidity
and security, these products are attached to the studs by
screws, which invariably cause a short circuit and significantly
reduce the STC rating of the wall. Similarly, if RC channels are
used in ceiling construction, any lighting (including track lights
and ceiling fans) introduced post construction could reduce the
ceiling’s STC value. Also, any retrofit for new communication
technology, that requires a junction box to be attached to the
wall will significantly reduce the wall’s STC value. This is
particularly risky because the location of the studs and RC
channels is hidden and difficult to find post construction.
Either the wall or ceiling has to be left alone for the life of the
property or significant post-construction risk occurs.
18. Furniture. If the owner (or hotel guest) moves heavy
furniture (e.g. bed, desk) against the wall with force, it can
cause the resilient channel to bend slightly and touch the studs,
thus causing a short circuit in the wall, reducing the wall’s STC
value.
Resilient Channel aka Soundbar - 90% Failure Rate???
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