Open Web Steel Joist Roofs Require Metal Screens

by Jonathan McGaha | 31 December 2013 12:00 am

Overcoming screen attachment limitations on steel joists

When it comes to choosing products for the building exterior, architects and contractors are always on the lookout for systems and solutions that offer the best combination of aesthetics, quality, efficiency and cost. So it goes with rooftop equipment screens.

Rooftop mechanical equipment, while essential to a building’s performance and comfort, can adversely affect its aesthetics. For decades, architects have specified some sort of screening system to hide what is perceived as unsightly equipment. One of the most common types of roof structures where equipment screens are required are open web steel joists with metal decking.

Through the years, contractors have employed various methods to meet the spec when attaching mechanical screens to open web steel joists. However, those traditional attachment methods are prone to shortcomings which can now be overcome by innovative, engineered framing systems. There are a variety of methods for employing mechanical screens on roofing supported by open web joists. Considerations before installing a roof screen of any type include height and weight of the roof screen, as well as local wind loads. With any roof screen, you’re basically installing a sail on the roof.

Common screening limitations

Any system installation must be waterproof or you’re creating a problem that didn’t exist. Any kind of water infiltration creates an environment for mold and other problems.

One type of equipment screen system that does not penetrate the roof is the “shroud style.” It attaches to the rooftop equipment itself. Manufacturers of these screens have systems designed to match a particular model number of air conditioning unit or other rooftop equipment. The problem: this system can’t effectively screen multiple units and it ultimately hinders access to the unit, making it more expensive to service.

Another method of roof screen construction can be installed by the steel erector who runs structural steel columns up through the decking and roof. The columns are welded into the structure of the building, and therefore, can’t be modified during construction or in the future without great expense. Steel tubes are welded in place between the columns above the roof to mask the equipment. This method is comparatively expensive and usually “overbuilt.” And if not assembled carefully, it may allow for multiple points of entry of water and moisture where the columns penetrate the roof deck. Plus, this system will eventually rust because it is field welded and painted.

The most common system involves the construction of a “sleeper.” A wood curb, usually a 4 by 4 or 4 by 6, is attached to the joist
(through the metal decking) and capped with sheet metal. These curbs disrupt the flow of water to roof drains, leading to a gradual buildup of debris and a premature deterioration of the roofing membrane. The screen, typically constructed from steel studs, is easily attached with an L bracket on the curb. Another issue with the sleeper is the L bracket penetrates into it, creating leak potential and the penetration is relying on a sealant where it is lag bolted.

Watertight roof attachment system

RoofScreen Manufacturing of Santa Cruz, Calif., developed and patented a pre-engineered and watertight system to address the shortcomings of traditional equipment screen construction methods. RoofScreen is counter-flashed and sealed, and meets the NRCA roofing standards and warranty requirements of all roof material manufacturers. The small attachment footprint does not inhibit water flow.

Its patented sprocket lock feature is particularly important when dealing with open web joists because it reduces twisting, a vulnerability of open web joists. It allows the installer to adjust the system to the slope of the roof, then lock it together. When locked, the sprocket connection absorbs the torque that would otherwise be transferred into the open web joist.

Ryan Bruce, CEO of Santa Cruz, Calif.-based RoofScreen Manufacturing, has decades of experience in the roofing and construction trades with deep familiarity of all aspects of rooftop structural, waterproofing and installation considerations. For more information, visit www.roofscreen.com[1].

Source URL: https://www.metalconstructionnews.com/articles/open-web-steel-joist-roofs-require-metal-screens/

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