Interpretation #6803
Published November 01, 2011
Original Request
- Code Version
- 2007
- Code
- BUILDING
- Code Description
- Building
- Chapter
- 13
- Section
- 13-404 AB.1 and AB.3
- Topic
- Acoustical Ceiling Grid
Question
Is it the intent of this code to require a second ceiling if installing a drop grid acoustic ceiling in and industrial building for air conditioned office space?
Answer Published 11/01/2011 at 4:55 PM
There are two sections of the energy code at work here: 13-
404.AB.1 and 13-406.AB.3. Sectopm 13-404.AB.1 requires at
least an R-10 in the roof or ceiling and that the roof
insulation shall not be installed on a suspended ceiling
with removable ceiling panels. The prohibition on
insulation on removable ceiling panels came down from a
national standard because of a concern that such insulation
would not be replaced after routine maintenance
displaced the insulation. Section 13-406.AB.3, Building
cavities, is a Florida-specific requirement that reflects
research done on air control problems in commercial
buildings. Buildings without an air barrier between
conditioned and unconditioned space allow air in and out
when air pressure differentials are created, typically by
the air handler cutting on. A t-bar ceiling is not an
air barrier; air pressure easily causes infiltration or
exfiltration around the metal/drop ceiling panel joints.
The code requires that for vented dropped ceiling cavities
over conditioned spaces the ceiling is both the upper
thermal envelope and pressure envelope of the building and
shall contain a continuous air barrier between the
conditioned space and vented unconditioned space. This is
particularly problemmatic in offices located in warehouses
because they often use non-structural dropped
ceilings, which may not have insulation on them or serve as
an air barrier. If the cavity is unvented, Section
13-406.AB.3.2 requires that the space be completely sealed
from the exterior environment at the roof plane and
adjacent spaces by a continuous air barrier that is also
sealed to the air barrier of the walls. This is why the
building department is requiring the walls to extend to the
roof. The easiest way to solve the problem is probably to
use a gypsum board ceiling. This makes the ceiling
the air barrier and the thermal barrier and allow
insulation on the ceiling. If the t-bar ceiling is
installed, the building department is correct: the
insulation should not be installed on the ceiling and it
does not constitute an air barrier. Some other method of
sealing the space would be required.
404.AB.1 and 13-406.AB.3. Sectopm 13-404.AB.1 requires at
least an R-10 in the roof or ceiling and that the roof
insulation shall not be installed on a suspended ceiling
with removable ceiling panels. The prohibition on
insulation on removable ceiling panels came down from a
national standard because of a concern that such insulation
would not be replaced after routine maintenance
displaced the insulation. Section 13-406.AB.3, Building
cavities, is a Florida-specific requirement that reflects
research done on air control problems in commercial
buildings. Buildings without an air barrier between
conditioned and unconditioned space allow air in and out
when air pressure differentials are created, typically by
the air handler cutting on. A t-bar ceiling is not an
air barrier; air pressure easily causes infiltration or
exfiltration around the metal/drop ceiling panel joints.
The code requires that for vented dropped ceiling cavities
over conditioned spaces the ceiling is both the upper
thermal envelope and pressure envelope of the building and
shall contain a continuous air barrier between the
conditioned space and vented unconditioned space. This is
particularly problemmatic in offices located in warehouses
because they often use non-structural dropped
ceilings, which may not have insulation on them or serve as
an air barrier. If the cavity is unvented, Section
13-406.AB.3.2 requires that the space be completely sealed
from the exterior environment at the roof plane and
adjacent spaces by a continuous air barrier that is also
sealed to the air barrier of the walls. This is why the
building department is requiring the walls to extend to the
roof. The easiest way to solve the problem is probably to
use a gypsum board ceiling. This makes the ceiling
the air barrier and the thermal barrier and allow
insulation on the ceiling. If the t-bar ceiling is
installed, the building department is correct: the
insulation should not be installed on the ceiling and it
does not constitute an air barrier. Some other method of
sealing the space would be required.
Commentary
The definition of an air barrier in 13-202 clearly
stipulates T-bar ceilings as not meeting the definition of
an air barrier by stating "House wraps and taped and sealed
drywall may constitute an air barrier but dropped
acoustical tile ceilings (T-bar ceilings) may not."