(Editor’s note: the following is an excerpt from the NRCA Roofing and Waterproofing Manual, 5th edition, in the section on Architectural Sheet Metal and Metal Roofing.)
Roof expansion joints are used to minimize the effects of stresses and movements of a building’s components. The effects of these stresses have the potential to cause damage to the roof system by splitting, buckling or ridging. Expansion joints in a roof assembly must be located in the same location as the building’s structural expansion joints – although they may be required in other locations.
Where expansion joints are necessary, both the structural and roof expansion joint should occur in the same location, extend across the entire roof, and continue through to the roof edge or perimeter. Expansion joints should be designed to accommodate contraction, as well as expansion. For most low-slope membrane systems, expansion joints should be detailed and constructed to a height of 8 inches (200 mm) above the finished roof membrane. Typically, wood curbing secured to the substrate on both sides of the joint is flashed with the appropriate roof membrane. An expansion joint cover is then installed.
There are three common types of expansion joint covers:
Brake-formed sheet metal cover. This type of expansion joint cover is of a two- or three-piece design to accommodate movement. The metal cap is generally formed in 8, 10 or 12 foot (2.4, 3,0 or 3.7m) lengths, and the end joints receive a cover piece or are joined with a drive-cleat or standing seam.
Premanufactured joint cover. These covers are typically a one-piece design that contain a bellows in the center of the cover to accommodate movement. Premanufactured expansion joint covers are available in different lengths, and the end joints require seaming or membrane splices, depending on the material type.
Hidden joint cover. This type of expansion joint cover is used in some thermoset roofing membrane systems. It should only be used with loose-laid, unreinforced, ballasted roof systems that are able to accommodate movement at the expansion joint. The joint in the desk is covered with a sheet metal plate fastened only on one side of the joint. The loose-laid, unreinforced, ballasted roof system is installed over the metal plate.
With certain loose-laid single ply roof membranes capable of extensive elongation, such as unreinforced, ballasted EPDM, a below-membrane or concealed type of expansion joint may be applicable in certain climates. However, NRCA recommends raised curb-type expansion joints be designed and installed in most geographic locations. Water drainage should never be designed to go through or over a raised expansion joint.
The use of low-profile area dividers that are designed to be installed in the horizontal plane of the roof is not recommended. If roof area dividers are to be used, raised curbs are recommended.
(The National Roofing Contractors Association is holding its 115th Annual Convention and Exhibit February 10-13 in San Antonio, Texas. Educational seminars, group discussions, a product show and more are planned. For more information, contact NRCA at 10255 W. Higgins Road, Suite 600, Rosemont, IL 60018; call 847-299-9070; fax 847-299-1183; www.nrca.net.)
Stone-coated steel shinglesStone-coated steel shingles are being touted as “a cost-competitive alternative to traditional roofing materials,” by Tasman Roofing Products, Corona, Calif.
According to the company, stone-coated roofing was traditionally not viewed as cost-competitive with other materials and its use was primarily reserved where harsh or fire-prone environments required added strength, protection and durability. But this new product was designed to closely replicate that of traditional roofing materials, installed over solid deck or existing asphalt roofing with no battens or special tools needed.
The Decra shingle weighs only 1.25 lb/sq.-ft. For more information contact the company at 877-GO-DECRA or www.decra.com.
Curbs for metal roofsThyCurb, Addison, Ill., says its products can make installation of roof curbs on metal buildings easier. These insulated curbs allow for unrestricted positioning on standing seam roof systems, according to the company, and are custom designed to accommodate any roof slope for rooftop equipment. The curb as an oversized, flat, prepunched base flange that can be cut out to allow perfect alignment with the seams on the roof.
Standard construction includes #18 ga. AZ-55 Galvalume, with mitered and fully welded corners, formed-in water diverter, and loose cell caps to match most standing seam configurations, for a long-lasting, watertight installation.
For more information contact Thybar Corp.., 913 South Kay Avenue, Addison, Ill. 60101; 800-666-CURB (in Illinois 630-543-5300); fax 630-543-5309; www.thybar.com.