The Hambro® system is well-suited for all types of ceiling systems and is specifically included in a host of U.L. designs.
Fire Rated Gypsum:
For example, the Hambro® system can be used with a fire-rated gypsum ceiling.
The most commonly used thickness is 5/8”; however, our
U.L. designs are promulgated on ½” thickness.
Traditionally, gypsum ceilings are used in residential applications
such as assisted living, condominiums, apartments, etc. These
ceilings provide a finished appearance, and coupled with Hambro®’s
4’ joist spacing, allow the mechanical systems to be
interfaced directly into the structural plenum, minimizing
or eliminating unsightly bulkheads or soffits.
|Furring channels are wire tied perpendicular to the Hambro bottom chords.
|Unprotected ceiling penetrations for ductwork are allowed (see UL Fire Ratings for details).
|As an option, recessed light fixtures are permitted to be unprotected as well.
Gypsum ceiling installation is normally done sing a standard
or non-resilient 7/8” furring channel. Per U.L. design
these furring channels are wire tied perpendicular to the
Hambro® bottom chords using a double strand of No. 18 SWG (.048
in diameter) galvanized steel wire. When creating a 1½
or 2 hour rated assembly, the furring channels must be attached
at 16” O.C. and can be attached at 24” O.C. when
a 1 hour rating is required. In addition, these gypsum ceilings
may also be dropped to accommodate short span conditions,
such as corridors, where the joists may be very shallow but
the ceiling needs to be at an appropriate elevation. For example,
in a corridor condition where the joists are framing between
the corridor bearing walls, a Hambro mini joist may be used.
The joists will protrude down from the bottom of the slab
approximately 4”. Deep mechanical systems may then be
installed, and a ceiling would be installed beneath the mechanical
systems. Since there are no webs or bottom chords, the gypsum
ceiling is hung from the pre-punched holes in the Hambro top
There are many ancillary advantages of using Hambro and fire
rated gypsum ceilings. Per U.L. design G-524,
unprotected ceiling penetrations are permitted for 1, 1½
and 2 hour fire rated assemblies. Per 100 square feet of ceiling
area, 256 square inches of unprotected ceiling penetrations
are permitted for a 1 hour rating; 196 square inches of unprotected
ceiling penetrations are permitted for a 1½ rating;
and 100 square inches of unprotected penetrations are permitted
for a 2 hour rating. Other traditional steel and concrete
floor systems will require these penetrations to be protected
with fusible link registers or dampers. In lieu of the unprotected
ceiling penetrations for ductwork, as an option, recessed
light fixtures are permitted to be unprotected as well based
upon the same 100 square feet of ceiling area. Other advantages
of using Hambro® include the permissibility of using Romex
in lieu of BX or conduit within the plenum for a 1 hour rating.
Romex is less costly, and without having to use conduit within
the plenum saves on the cost of conduit as well as the installation.
Fire Rated Acoustical Ceiling Grids:
In many building types, fire rated acoustical ceiling systems
will be used so as to provide access to the HVAC and other
mechanical systems. This situation may occur, for example,
throughout an office building to provide tenant flexibility
or in residential buildings in the public areas and corridors.
Hambro® has been tested in accordance with U.L. design G-229,
whereby fire rated acoustical ceilings are permitted with
Hambro®. Unlike fire rated gypsum ceilings, fixture protection
and/or tenting over light fixtures is required with Hambro® as it is with other steel and concrete systems. The U.L. web
will list many manufacturers of these ceiling grids and the
permissible sizes they offer.
Fire Rated Lay-In Grid Systems:
Recently, both USG
have developed fire rated gypsum ceilings that utilize a lay-in
grid system for dropping the ceilings, while offering the
same benefits of Hambro® as U.L. G-524.
These grid systems allow for flexibility in the installation
should the ceiling need to be hung to allow for mechanical
interfacing while maintaining the high-end appearance of gypsum