Design A Better Shaftwall System
August 29, 2017
With the continued popularity of high-rise corporate headquarters, institutional buildings and high-density housing, the gypsum shaftwall system, known as the Cavity Shaftwall System, provides economic benefits – and also peace of mind due to its fire-resistant qualities. Originally designed for the 110-story World Trade Center in 1973, the Cavity Shaftwall System replaced heavier, more expensive masonry walls. This shaftwall system utilizes gypsum board framed with metal studs and tracks to enclose elevator shafts, stairwells and service shafts. These shaftwalls withstand the positive and negative air pressure forces exerted by high-speed elevators. Cavity Shaftwall Systems are also ideal for fire-rated, interior partitions where access is restricted to one side and as fire-rated, horizontal membranes.
Advantages Of The Cavity Shaftwall System
Cavity Shaftwall Systems provide many benefits. They are lightweight, easy to install, weather-, sound- and fire-resistant and more economical than masonry shaft construction. Four to five times lighter than traditional masonry enclosures, gypsum shaftwalls weigh approximately 10 pounds per square foot of wall compared to 40 or 50 pounds per square foot for a masonry wall. Buildings utilizing this shaftwall system require less structural steel and extensive underground support pilings. In addition, the core of the gypsum panels in the Cavity Shaftwall System contains about 21 percent water by weight, creating a fire barrier with 1- to 4-hour fire-ratings from either side. When gypsum board is exposed to fire, the water turns to steam and slows the passage of heat through the assembly, keeping the building safe for a longer period of time.
Typical installations use 1-inch thick gypsum shaftliner panels inside a minimum 2-1/2-inch metal framing system with an integral space to hold the panels in place on the shaft side. Metal J-tracks are placed horizontally at the top and bottom and vertically at partition ends. They also frame openings. Depending on the fire-rating you are trying to achieve, install one to five layers of 5/8-inch fire-rated gypsum board to the outside of the stud, creating a corridor side of the enclosure.
To construct lightweight fire barriers for cavity shaftwalls (1-4 hr.), we recommend Gold Bond® BRAND eXP® Shaftliner. It is an approved component in specific UL fire-rated designs, including G586 (horizontal, 2-hr.) and W419 (vertical, 1-4-hr.).
Questions About The IBC 2009 Code Updates For Buildings?
If you are designing a building of occupancy category III or IV with occupied floors over 75 feet tall and all buildings over 420 feet tall IBC Section 403.2.3 require increased impact resistance for exit stairways and elevator hoistway enclosures. If you have questions, contact your construction design manager for clarification and for assistance with the best and most affordable options for your project.
Company: National Gypsum
Of: Scott Hughes and Thad Goodman
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