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Coping with rooftop penetrations through standing-seam metal roofs: standing-seam metal roofing represents the state of the art when it comes to durable, sustainable, eco-friendly roofing alternatives, providing 3 or 4 decades of reliable service life.

Unfortunately, this high-tech roofing option, and the maintenance freedom it offers, is often sabotaged when it comes to mounting essential rooftop equipment and ancillary mechanicals.

Penetration-Free Attachment

Standing-seam metal offers advantages over other roof types when mounting ancillary fixtures. These roofs are particularly well suited to accept special seam-clamping hardware that grips the standing-seam systems without puncturing their membranes.

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If roof attachments are required, here are some helpful tips that will prevent problems:

* Use penetration-free attachments whenever possible.

* Never use adhesives to secure attachments to metal roofs.

* Use only attachment clamps made of non-corrosive metals.

* Use round-point setscrews to secure the clamp to the seam. This will prevent damage that could lead to corrosion.

* Any loads placed on the clamp will be transferred to the panels and their anchorage, and, subsequently, to the structure. That anchorage must be capable of withstanding the added load.

When Penetration is Unavoidable

In the case of HVAC and plumbing vents, the roof membrane is often penetrated. The soil stack must carry gases from inside out, and the HVAC unit must bring either inside air out or outside air in, or both. Consequently, holes in the roof are inescapable. The challenge is to waterproof the holes while maintaining the thermal-cycling integrity of the roof.

There are a few rules for handling these kinds of rooftop penetrations in low-slope, standing-seam metal that will help ensure trouble-free service. HVAC units and/or related ductwork penetrations should utilize preformed equipment curbs that are specifically designed to integrate with the roof profile being used. The curb is sealed to the roof and maintains the thermal-cycling integrity of the system. The best curbs are made of all-welded aluminum construction. This material is very compatible with sheet steel (or aluminum) used for roofing and should provide decades of trouble-free service if designed, fabricated, and installed correctly. Often, these curbs are load-bearing "structural" varieties that simultaneously provide support and waterproofing.

When equipment curbs are used, it is imperative that:

* Welded, aluminum curb construction is used.

* Curbs are equipped with diverters on the upslope flange.

* Curbs are shingled into the roof to avoid "back-water" laps.

* Curb walls are at least 6-inches high.

* Curb and installation are "floating," not pinned to the building structure.

* All seals are made with butyl tape/ tube grade within the joints (not exposed sealants), with careful attention paid to marrying seals at the panel seams.

* Curb sidewalls are located at least 6 inches from the nearest adjacent seam to allow sufficient drainage to the sides of curbs.

Round Penetrations

Round shapes, such as plumbing vents or pipe supports for rooftop equipment, should be flashed through the roof using EPDM (ethylene propylene diene monomer) rubber pipe flashings. The cone-shaped rubber is field cut to size and stretch fitted to the pipe. It is recommended that a stainless-steel draw band be used at the top of the flashing to ensure that the flashing never inverts itself. The part has an integral aluminum compression ring that is laminated to the rubber base.

The pipe flashing must be anchored to the roof panel only--not to the building structure or deck. To do the latter would create an inadvertent "pinning" of the roof panel, compromising its thermal movement. Ideally, these flashings should be centrally located to ensure free drainage. In any event, interrupting a seam should be avoided.

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Toy Henson is director of market development and education at The Metal Initiative (www.themetalinitiative.com), Glenview, IL.
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Title Annotation:ROOFING: SMARTER BUILDINGS[R]: BUILDING ENVELOPE
Comment:Coping with rooftop penetrations through standing-seam metal roofs: standing-seam metal roofing represents the state of the art when it comes to durable, sustainable, eco-friendly roofing alternatives, providing 3 or 4 decades of reliable service life.(ROOFING: SMARTER BUILDINGS[R]: BUILDING ENVELOPE)
Author:Henson, Toy
Publication:Buildings
Date:Mar 1, 2008
Words:600
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