Product Information

Hambro Fire Ratings

Hambro® D500 brings you one of the finest fire rated structural floor systems in the world.

There are many accepted methods to achieve satisfactory fire protection with the Hambro floor system. Extensive fire testing has been performed by Underwriters Laboratories (U.L.), resulting in many milestones, and again proving the superior performance of the Hambro system. The full scale fire tests are performed while the system is loaded to its full design capacity and the results are as follows:

NOTE: See U.L. Designs for details.

Gypsum Board Membrane:

Fire rated Gypsum “drywall” ceiling membranes installed directly under Hambro joists are generally used in residential construction. They are economical, aesthetically pleasing, and can safely accommodate integrated sub-systems, recessed light fixtures and ventilating units without impairing their fire rating capabilities. U.L. Design No. G-524 has been the most popular Hambro rating for residential applications due to its enormous flexibility. For each 100 square feet of ceiling area, it allows unprotected ceiling penetrations up to 256 square inches for 1-hour (See U.L. item 10Q), 196 square inches for 1.5-hours (see U.L. item 10F) and 100 square inches for 2-hours (see U.L. item 10K).

This design permits unshielded, non-metallic electrical wiring for up to 2-hours. For 1-hour, as an alternate to the unprotected duct outlet, 2 inch & 4 inch PVC pipe is permitted per 100 square feet of ceiling area to run throughout the Hambro plenum, penetrate the ½ inch ceiling and run down through non-rated partition wall (see U.L. item 10E).

In lieu of the unprotected duct outlets (dampers), up to four unprotected recessed light fixtures, 6-½ inch diameter, are allowed per 100 square feet of ceiling area for a 1-hour fire rating.

Fire Rated Gypsum:

The Hambro system can be used with a fire-rated gypsum ceiling. The most commonly used thickness is ⅝ inch type C; however, our testing was based on ½ inch thickness. Traditionally, gypsum ceilings are used in residential applications, such as assisted living, independent living, condominiums, apartments, and student housing. These ceilings provide a finished appearance, and coupled with Hambro’s 4 feet joist spacing, allow the mechanical systems to be interfaced directly into the structural plenum, minimizing or eliminating unsightly bulkheads or soffits.

Gypsum ceiling installation is done using a standard, non-resilient ⅞ inch furring channel. Per U.L. design G-524, these furring channels are wire tied perpendicular to the Hambro bottom chords using a double strand of No. 18 SWG (.048 inch diameter) galvanized steel wire. When creating a 1-½ or 2-hour rated assembly, the furring channels must be attached at 16 inches O.C. and can be attached at 24 inches O.C. when a 1-hour rating is required. In addition, 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 inches. 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 slots in the Hambro top chord.

Fire Rated Lay-In Grid Systems:

In addition to the standard installation of the fire rated ceiling using ⅞ inch hat channel, manufacturers such as USG and Armstrong have developed a hung dry wall grid system, 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 ceilings.

Gypsum Board Membrane U.L. Designs:

Suspended or Lay-in Ceiling:

Accessible ceiling panels commonly referred to as “lay-in” ceiling tiles are generally used in office, commercial, and institutional construction. These removable fire rated panels allow access to the ceiling plenum for alterations to mechanical or electrical equipment. Any penetrations to the assembly need to be protected as per the U.L. design.

Fire Rated Acoustical Ceiling Grids:

In many building types, fire rated acoustical ceiling systems will be used 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 site will list many manufacturers of these ceiling grids and the permissible sizes they offer.

Suspended or Lay-in Ceiling U.L. Designs:
G-229 (most commonly used)
G-201, G-213, G-222, G-227, G-228, G-236, G-243.

Sprayed-on Fireproofing:

Protecting the Hambro joists by sprayed on fireproofing is another accepted option of fire protection. This option is typically selected when there would be so many protected openings that spray becomes a cost effective alternative, or spray can also provide flexibility to future tenants who want the option to use a non-rated ceiling of their choice.

Sprayed-on Fireproofing U.L. Designs:

Through-Penetration Firestop Systems:

Through-penetration firestop systems are intended to restore the hourly rating of fire-resistive assemblies that have been breached due to penetration by electrical, plumbing, or mechanical items.

Through-Penetration Firestop Systems:
F-E-1001, F-E-1002, F-E-1003, F-E-2001, F-E-2002, F-E-2003, F-E-2004, F-E-3001, F-E-3002, F-E-3003, F-E-3004, F-E-5001, F-E-7001, F-E-7002, F-E-8001, F-E-8002, F-E-8003.

Always check your U.L. Directory for the latest updating of these listings and applicable building codes before detailing ceiling construction.

Furring channels are wire tied perpendicular to the Hambro bottom chords.
Unprotected ceiling penetrations for ductwork are allowed (see U.L. Fire Ratings for details).
As an option, recessed light fixtures are permitted to be unprotected as well.