Roofing Problem Areas

Flat roofs are prone to ponding water.

Flat roofs are prone to ponding water.

Facilities maintenance issues can have a major impact on productivity in industrial and commercial environments with something as small as a leaking roof causing significant disruption and downtime. Years of experience suggest that 90 percent of the problems we are presented with today will arise from a mere 10 percent of the roof’s total area. But are some roof types and roof areas more susceptible to damage than others? Moreover, how do these roofing problems arise and how can they be categorized?

Flat Roofs

Flat roofs are commonly chosen for industrial and commercial buildings, covering the vast majority of offices, factories and warehouses around the globe. However, despite their popularity, my firm’s experience indicates that the bulk of roofing applications owe to the failings of flat roofs. This begs the question; do the benefits of flat roofs outweigh the disadvantages?

Currently, the flat roofing market is in a particularly healthy state. It is easy to see why because flat roofs do in fact offer a great deal of advantages. Notably, they are a low-cost option for many projects, being easier and more economical to install, inspect and maintain. Therefore, they prove highly popular with many commercial facilities and industrial buildings.

However, flat roofs are historically problematic, suffering from an array of issues commonly arising from standing water and traditional roofing materials. Pooling of water on roofs can be attributed to inadequate roofing materials or, strangely, a roof being “too flat”. Flat roofs should actually feature a small gradient to allow sufficient rainwater run-off; otherwise, the weight of water pooling can lead to deflection and numerous subsequent issues.

Roof flashings can prove problematic due to dissimilar materials.

Roof flashings can prove problematic due to dissimilar materials.

Of course, other roof variations, such as pitched or slanted roofs, will offer their own range of complications; however, complications with pooling water are not among these. This distinct disadvantage is one of several that can lead to serious problems within that troublesome 10 percent. The most common problems can be split into three separate categories.

Dissimilar Materials
Most roofs form a veritable patchwork of materials, including anything from glass and plastics to masonry and metals. Industrial roofs can be particularly troublesome as they boast a multitude of pipes, heating units and other protrusions that make the roof geometry complex to cover effectively. Whatever the combination of roofing materials is, ensuring long-term adhesion and sealing between all these dissimilar materials is crucial—and can prove problematic.

Flashings fall into this category and are a common fixture of flat and pitched roofs, where metal, brick and felt or bitumen can often all meet. Exposed to varying temperatures and weather conditions, these materials can act differently, altering shape and size dependent upon that material’s characteristics. This can result in roofing weakness due to different expansion and contraction rates of the materials, allowing for water ingress through developing gaps. Moreover, this category includes areas where two metals may meet. Dissimilar metals exposed to continuous weathering can potentially lead to galvanic corrosion, which deteriorates the roof’s protection, loosening the materials and once again leading to issues like leaking.

Joints and Seams
Joints and seams spell considerable trouble for many roofs, predominantly due to the effects of movement. All buildings will feature a degree of movement as a result of thermal expansion, contraction and wind, making joints and seams one of the most vulnerable areas. Resulting gaps or lips can be created, increased further by wind uplift, which may allow water ingress or exposure of unprotected materials to corrosion and weathering.

Seams around skylights and roof protrusions can cause roof vulnerabilities.

Seams around skylights and roof protrusions can cause roof vulnerabilities.

Found whenever two materials meet, joints and seams are a common sight on industrial roofs and one that occurs frequently on roofs covered using traditional materials. For instance, felt or bitumen surfaces are layered in strips and require heat to fuse them together and create one barrier of protection. However, continuous exposure to the elements can lead to delamination of the roofing material, creating areas of vulnerability, such as lips.

Similarly, parapet walls can also become vulnerable at the joints, normally caused by movement between the brickwork. This can develop through movement in the building or perhaps vegetation forcing through the joint, widening any gaps further and causing moisture ingress. Furthermore, this problem is shared by the seams around skylights and glazing bars, which degrade over time due to the dissimilar materials present and associated movement.

Unlike other problem areas in this category, cut-edge corrosion does not stem from two materials meeting. In fact, it falls into this category as it is an uncoated seam of metal that, left exposed, will corrode and result in the damage spreading as the metal is slowly eaten away. Corrugated metal roofs are susceptible as they are cut and the edges never receive protection, meaning when cut-edge corrosion begins, it is important to treat it as soon as possible. In certain instances, roof sheets need to be removed and replaced, which is extremely expensive.

Metals seams are often neglected and can develop cut-edge corrosion

Metals seams are often neglected and can develop cut-edge corrosion.

Other Forms of Damage
Lastly, roofs are susceptible to various forms of damage in the immediate and long term. Long-term damage will generally arise if roofing is left unmaintained, to suffer from aging and neglect. A key example of this type of damage involves single-ply roof coverings. Over time, rubber roofing materials are subjected to the environment and constant UV exposure. Once again, over this period the material expands and contracts, becoming brittle and losing its former flexibility, making it prone to cracking.

In addition to weathering, wildlife can have a detrimental effect on roofing materials, as bird litter can chemically attack the plastic coating on some roofing systems. High levels can cause damage and subsequent deterioration of the lining, which can potentially lead to leaks or exposure of metal to corrosion.

With regard to immediate damage, working on roofs is also a common way in which damage can occur. As highlighted before, one of the key selling points of flat roofs is the ability to carry out maintenance and inspection easily. Whether it derives from maintenance or rooftop developments, such as HVAC installation, extensions or rooftop fire escapes, the foot traffic over flat roofs can lead to immediate damage of the roofing substrate, through piercing and general wear.

Over time, rubber roofing materials can become brittle and crack

Over time, rubber roofing materials can become brittle and crack.

Eliminating the Troublesome 10 Percent

For the majority of these problems, it is possible to find a repair solution. However, when left without treatment, the roof can become too damaged to refurbish, leaving costly replacement as the only option. Repair methods have evolved significantly over the years and eliminating the troublesome 10 percent is becoming far easier to do since the advent of liquid and cold-applied technologies. Not only does this signify a breaking of tradition, but crucially highlights the evolution of roofing maintenance materials.

PHOTOS: Belzona

Planning for Thermal Movement: An Essential Element of Copper Roofing Design

For centuries, copper has been used as a roofing material because of its ease of installation, adaptability to simple and unique designs, resistance to the elements and superior longevity. Copper’s warmth and beauty complements any style of building, from Gothic cathedrals to the most modern museums and private residences. Its naturally weathering surface, whether in a rich bronze tone or an elegant green patina, is a clear indication that the building owner will only accept the very best.

This detail indicates a method for terminating a copper roof at the eave. The fascia trim is bent to extend onto the roof deck to become an integral flashing apron nailed to the roof. The copper pan is secured to the apron lip to achieve vertical restraint. Horizontal movement of the copper roof sheet is accommodated by the loose-lock fold of the pan over the fascia lip. Click to view a larger version. IMAGE: <em>COPPER IN ARCHITECTURE–DESIGN HANDBOOK</em>

This detail indicates a method for terminating a copper roof at the eave. The fascia trim is bent to extend onto the roof deck to become an integral flashing apron nailed to the roof. The copper pan is secured to the apron lip to achieve vertical restraint. Horizontal movement of the copper roof sheet is accommodated by the loose-lock fold of the pan over the fascia lip. Click to view a larger version.
IMAGE: COPPER IN ARCHITECTURE–DESIGN HANDBOOK

Unfortunately, long-term performance of even the best construction materials can be compromised if the system is not designed or installed properly. For architectural sheet-metal installations, movement that occurs with changes in temperature must be considered during the design process. All metals expand when heated and contract when cooled. While this process is well understood, far too many contractors ignore thermal movement during system design or installation. Ultimately, this can lead to failure of the roofing and flashing system, causing extreme damage to the building. The Copper in Architecture–Design Handbook, which is published by the Copper Development Association (CDA) and available online as a free download, provides examples of how to accommodate for thermal movement of copper systems.

Calculating for the potential thermal movement of sheet metal is easy. Simply multiply a metal’s coefficient of thermal expansion by the metal’s expected temperature change by the length of the piece. Remember: It’s not the air temperature we’re considering; it’s the temperature of the metal. Anyone who’s touched a metal roof or the top of their car in the summer knows it gets significantly hotter than the air!

An example based on a 10-footlong piece of copper:

  • 10 feet (typical flashing piece length) x 0.0000098 per degree F (copper’s coefficient of thermal expansion) x 200 degrees F (possible metal temperature change from coldest winter night to hottest summer day) x 12 inches per foot = 0.24 inch. In this case, the calculated movement is a little less than 1/4 inch.

Remember, the coefficient of thermal expansion depends on the type of metal you are using. Aluminum expands and contracts more than copper, and most steels move less. Series 300 alloy stainless steels are very similar to copper in movement, or expansion/ contraction rate. Naturally, temperature change is dependent on building location and exposure to the elements. Many professionals feel comfortable calculating the design movement with a temperature change in the 175 to 200 degree F range, but it’s the project architect or engineer’s responsibility to determine if this is adequate.

Modern rollforming equipment allows contractors and manufacturers to make very long panels, so potential total movement is even more significant.

Let’s investigate one type of common flashing design—in this case, at the eave, which is relatively simple but can easily be installed incorrectly:

  • Based on the previous formula, with roof panels that are 20-feet long and installed at a temperature between the hottest day and coldest night: 20 feet x 0.0000098 per degree F x 200 degrees F x 12 inches per foot = 0.47 inch.

Having one of the largest copper roofs in the country, the historic Kingswood High School, Cranford, Mich., recently underwent a massive $14 million roof-restoration project. The copper-clad roof is comprised of batten seams on the upper slopes, interior gutter with internal rainwater conductors, and standing- and flat-seam panels on the eaves. An embossed copper fascia and copper soffit panels complete the system. PHOTO: QUINN EVANS ARCHITECTS

Having one of the largest copper roofs in the country, the historic Kingswood High School, Cranford, Mich., recently underwent a massive $14 million roof-restoration project. The copper-clad roof is comprised of batten seams on the upper slopes, interior gutter with internal rainwater conductors, and standing- and flat-seam panels on the eaves. An embossed
copper fascia and copper soffit panels complete the system.
PHOTO: QUINN EVANS ARCHITECTS

Because we’re installing mid-way in the temperature range and 0.47 inch is so close to 1/2 inch, dimension “A” can be 1/4 inch (one half the total potential movement). Naturally, the hem of the roof panel’s “loose lock” must coordinate with the length of the eave flashing to ensure the two are still engaged when the roof panels are fully expanded. While most contractors form eave flashings properly, some ignore the thermal movement gap “A” during installation, forcing panels to move fully onto the flashing. This eliminates the gap. When temperatures drop, the panels can’t contract, adding stress to the roofing system.

Through the years, countless thermal cycles and resulting stresses caused by expansion and contraction can take their toll. In the long run, something will fail. In some cases, work hardening of the metal can occur, causing it to crack or tear. In other cases, fasteners, such as those used to attach cleats, work back and forth, ultimately pulling them out of the substrate.

It’s easy, however, to avoid these problems. To ensure maximum performance of the roofing system, just follow the recommended design principles; understand how the different pieces of the system interact; and don’t cut corners. With a time-proven quality material like copper, proper workmanship and attention to detail can create a beautiful roof that could last the life of the building.

Learn More
For more information about architectural copper and roofing systems, visit the Copper Development Association’s website.