From Screw-down to Standing-seam Metal Roofing

Time to reroof an old screw-down metal roof? Are you thinking about upgrading to a new standing-seam roof? Great idea! Today’s new standing-seam roofs are truly state-of-the-art; available in many profiles and finishes; and, more importantly, address many of the issues encountered in older generation screw-down metal roofs.

Caulk, roof coating and tar patches were used to cover leaking fasteners and panel end laps.

Caulk, roof coating and tar patches were used to cover leaking fasteners and panel end laps.

The screw-down metal roof and wall panel has been the backbone of the metal building industry since its inception and still represents a significant part of the total market. Screw-down panels are lightweight, durable, inexpensive and strong enough to span up to 5 feet between structural supports. Screw-down roofs and walls also have a wonderful physical property: The panels can and frequently are used as “diaphragm bracing,” securely holding the building’s roof purlins and wall girts in position, adding rigidity to the structure in much the same way drywall strengthens stud walls. This is a huge material—and labor—cost saver!

The early systems were not without problems, however; much of the technology we take for granted today did not exist in the early years of pre-engineered buildings. Many roofs during the late ’60s thru early ’80s were installed using 10-year life fasteners to secure a 30-plus-year life roof.

The fastener issue seems crazy today given the numerous inexpensive, long-life, weathertight, self-drilling screws available. Back when I started in the metal building industry, you could have the newly developed “self-drilling” cadmium fasteners or “self-tapping” stainless. Self-tapping meant you had to pre-drill a hole in the panel and purlin to install it—a much slower and more expensive process. Most of us used the less expensive but (unknown to us at the time) fairly short-life cadmium-coated fasteners and often never provided the option of a stainless upgrade to our customers.

Another shortcoming with screw-down roof panels is that, generally speaking, screw-down panels on metal buildings should be a maximum length of about 80 feet. Longer roof-panel runs frequently suffered rips or slots in the metal caused by expansion and contraction. Metal panels expand and contract at a rate of about 1 inch per 100 feet of panel run. This is normally absorbed by the back and forth rolling of the roof purlin and some panel bowing, but after 80 feet or so they can no longer absorb the movement resulting in trauma to the panels and trim. I have frequently seen this 80-foot limit exceeded.

a rusted fastener has caused the surrounding metal to corrode and fail.

A rusted fastener has caused the surrounding
metal to corrode and fail.

Standing-seam panels eliminate both of these shortcomings. The panels are attached to “sliding clips”. These clips are screwed to the purlins and seamed into the side laps of the panels securing them and thus the panels have very few, if any, exposed fasteners. The clips maintain a solid connection with the structure of the building while still allowing the panels, which can be 150 feet or longer, to move with expansion and contraction forces without damage.

This is great news for the building owner: You’re providing a more watertight roof, few if any penetrations, and expansion and contraction ability. It does come with a catch, however; standing-seam panels, because they move, do not provide diaphragm strength. The building’s roof purlins must have significantly more bridging and bracing to keep them in their correct and upright position. This is automatically taken care of in new building design but when it comes time to reroof an older building, removing the existing screw-down roof could remove the diaphragm bracing it once provided and make the building structurally unsound. Yes, that’s bad!

PHOTOS: ROOF HUGGER INC.

Pages: 1 2 3

Roof Hugger Releases Metal-over-metal Retrofit Reroofing Design and Installation Manual

Roof Hugger Inc. announces its 2014 Version 3.04 Design & Installation Solutions manual for Metal-over-Metal retrofit reroofing systems.

The 108-page manual provides design professionals and contractors with technical information pertaining to retrofit sub-framing systems for installing a new metal roof over an existing metal roof, without removal. Included in its content is information on utilizing the space between the old roof and bottom side of the new metal roof for installing insulation, dynamic ventilation and/or solar thermal hot air/water systems. Also included are 65 construction details that can be downloaded from Roof Hugger’s website in ACAD and PDF formats.

If interested in receiving a printed copy of the manual, send an email request to sales@roofhugger.com or fax (877) 202-2254.

Transite Roofing: Friend or Foe?

As Transite, or Asbestos-containing, Roofs Come to the End of their Life Cycle, Contractors Should Know When Retrofitting Is an Option

The use of asbestos dates back thousands of years. For millennia, cultures across the globe embraced asbestos’ super-strengthening properties. Asbestos’ popularity peaked in the late 19th century during the Industrial Revolution when commercial asbestos mines sprung up across the U.S. and Canada. Before its carcinogenic properties were discovered, asbestos was used in hundreds of applications, including walls, roofs, coatings, fireplaces, shingles, insulation, pipes, furniture, paper products, automobile parts, fabrics and packaging. In the construction industry, in particular, it was considered a “super-product.” Whether mixed as a binder with cement or used as a coating on steel panels, asbestos is insulating, non-combustible, corrosion-resistant, inert, humidity-tolerant and sound absorbent.

One major application of asbestos over the past 100 years has been transite roofing panels. Asbestos was essentially used as a binder in cement slurry and then formed into profiled or flat sheets. Transite roofing panels can still be found across the country; many are still in place after 50, 60 or even 70 years of life. Because transite panels acquired asbestos’ super-strengthening properties, they made (and in some cases continue to make) ideal roofing for foundries, forges, chemical plants, paper plants, wastewater treatment plants and sewage facilities. The roofing material withstands high heat, chemical emissions, humidity and other elements emitted by these facilities that other building products could not tolerate.

Transite roofing panels can still be found across the country; many are still in place after 50, 60 or even 70 years of life.

Transite roofing panels can still be found across the country; many are still in place after 50, 60 or even 70 years of life.

Despite the strength of asbestos, even transite roofs can deteriorate or require renovation. In fact, most roofing contractors have encountered or will soon encounter transite roof jobs. The job where transite is in good condition with no airborne particles may be a perfect candidate for a retrofit.

(For the purposes of simplicity, this article uniformly refers to corrugated, asbestos-containing cement roofing sheets as transite. Professionals may also encounter names like 4.2 cement asbestos or corrugated cement. It’s important to note not all corrugated cement roofing sheets contain asbestos; some manufacturers substituted wood fibers for asbestos during the height of asbestos panic in the 1980s. Few of these products successfully penetrated the market because performance did not match that of original transite.)

Leave It In Place

Contrary to popular belief, asbestos is still legally used in many commercial applications in the U.S. today, including roofing and flooring materials; in fireproofing; and in friction products, like brake shoes and clutches. With the surge of installation of transite roofs in the 1950s and 60s, the lifespan of many of these roofs’ components is just now ending. Common factors attributing to roof or structure deterioration may include longitudinal cracks along the panel highs, broken or brittle fasteners or washers, friable panel material, and/or building shifts due to expansion or contraction. Additionally, other renovations on a building may require that old roofs that are still intact be brought up to new codes.

Today, a good general rule about asbestos is “leave it on if you can,” meaning it must be in good condition with no airborne particles.

Today, a good general rule about asbestos is “leave it on if you can,” meaning it is in good condition with no airborne particles.

Professionals encountering transite roof jobs may feel confusion about how to handle asbestos-containing materials. Some may even avoid transite jobs altogether assuming they will equate to expensive asbestos-removal procedures and red tape. However, asbestos abatement (the process of removing or minimizing asbestos health hazards from a structure) can take many forms, including removal, enclosure, encapsulation or leaving the material undisturbed.

In the past, abatement through removal was the recommendation of many asbestos professionals. Traditionally, transite was replaced with fiberglass. This solution is imperfect, however, because of the expenses of asbestos removal and new fiberglass, as well as the lower heat tolerance of fiberglass-based materials. More recently, approaches have changed and several other options present themselves.

Today, a good general rule about asbestos (and in fact the position of the Washington, D.C.-based U.S. Environmental Protection Agency) is “leave it on if you can,” meaning it must be in good condition with no airborne particles. Although not always possible, when the contractor can leave the asbestos-containing material in place, asbestos should be considered friend, not foe. Regulations might prevent installation of a new asbestos transite roof, but old buildings that can keep their transite roofs in place will continue to reap the benefits of the product’s super-strengthening properties. [Read more…]