4 FM quick reads on roofing
1. Big Top: Reroofing California's State Capitol
Every single step, it seems, presented a challenge when it came to reroofing the California State Capitol building in Sacramento — scheduling, security, and maybe the most maddening challenge of all, surprises. Throw in the chaos created by the building's 3,000 occupants — including a state legislature and its committees in and out of meetings — as well as 750,000 visitors annually, and the entire process might even seem overwhelming.
For all its challenges and surprises, one main goal of the reroofing project on the California state capitol building focused on a problem every maintenance and engineering manager knows all too well — leaks.
"It was leaking profusely," says John Manning, the building's chief engineer, referring to the 98,000-square-foot surface that included several types of roofing systems and nearly 30 different sections — some sloped, others flat.
"There are actually two buildings that comprise the current state capitol," Manning says. "The first completed construction in 1869. Then in the late 1940s, a second building was built directly next to it, so it becomes one building. That finished construction in 1951."
"The roof had been on the capitol for more than 20 years, and there were leakage problems, and it was at the end of its life," says Marilyn Nelson, project manager with the state's department of general services. "When we replaced it, there were several roofing systems down below it, and we had some hazmat issues. We had to do all the demolition at night, and we reroofed it during the day. Because it is such a large roof, we had to do it in sections and phases."
The new roof is a PVC system with 10-foot-wide panels.
"We chose it because it was long-lasting and durable," Nelson says. "As you can imagine, you don't want to reroof this capitol very often. It also had a decent solar-reflective index. And it has fewer seams because of the 10-foot-wide panels."
2. How to Avoid Moisture Issues to Prevent Roofing Installation Problems
Once managers have settled on the type of single-ply system to install, the next step is ensuring that installation occurs as intended during design to prevent problems, such as the introduction of moisture.
"If the single-ply system is not installed correctly, then you run the risk of high maintenance costs by not only having to repair the membrane but also having increased risks of having to replace the underlying components sooner than with multi-ply systems because you do not have the added protection for additional layers," says Amrish Patel with Simpson, Gumpertz, and Heger. "If you don't address moisture issues within the substrate at the beginning of the project, maintain proper adhesive application, proper flashing details or proper membrane application, you may be constantly patching or prematurely replacing the roofing system.
"With single-ply membranes, your primary mode of failure occurs at the seams of the membranes. If a membrane seam has failed, you've got immediate water penetration into the roofing system, so the seams really need to be inspected to ensure they are installed properly, for example, whether they are heat-welded seams with a PVC or TPO system or adhered seams with an EPDM system."
Patel also warns managers to beware of moisture in the existing roof's substrate.
"If you install an adhered roofing system, that moisture is eventually going to start to cause debonding of the insulation and cover board and possibly of the roofing membrane," he says. "And through wind-uplift cycles, you're going to lose the adhesion of the roofing system. That often gets overlooked."
3. How Vegetative Roofs Extend Service Life
Plants, soil, and covered components of the system offer protection from the elements, including degradation by the sun's UV rays. By protecting the membrane, a vegetative roof can minimize cracks and splits due to the thermal cycle. In some areas of the country, a roof membrane surface that is exposed to the sun may reach temperatures above 160 degrees Fahrenheit during the day and drop below freezing that night. The resulting expansion and contraction wreaks havoc on the membrane. But with a vegetative roof, this can be minimized, reducing or even eliminating one of the main causes of roof leaks.
As much as a 200-300 percent extension of roof membrane service life may be achieved with the use of vegetative roofing. This is backed by the availability of manufacturers' warranties for as long as 30 years for the entire roofing system. In some cases, the warranties can even include the removal and replanting of the vegetation if a leak needs to be repaired.
In addition, using a vegetative roof over the membrane can reduce the risk of hail or wind damage to roofs. Airborne debris such as tree limbs and other windblown items is also much less likely to penetrate the roof during a storm.
Damage caused by human error is another common cause of roof leaks. A maintenance technician may have an object such as a rock or a fastener screw on a shoe bottom and cause damage or even punctures to the roof as they walk across it. Even when walkways are provided and clearly marked, workers don't always follow the rules.
4. How to Choose Best Single-Ply Roofing System
Before a facility executive begins weighing the question of which single-ply system to use, it is important to ask whether the building is suited for a single-ply membrane. "One size fits all" is as misleading for roofing as it is for clothing. Here are some situations where a single-ply membrane is appropriate when:
- weight is a consideration
- some movement may be expected in the building structure
- recovering an existing membrane
- the building is wide open and large panels can be used
- reroofing structural standing seam metal roof assemblies
- roofing in cold weather (with some precautions)
- installing a green roof
- a light-colored system is desired
Times when a facility executive may want to consider other options include:
- when vandalism or puncture-abuse is a factor
- when there is a limited number of local approved applicators
- when there is a chemical incompatibility between the existing roof and the proposed re-cover membrane
- when climatic or environmental conditions are not appropriate
- where insurance considerations favor other types of systems
- where installation is over lightweight insulating concrete decks
- where local building code officials prohibit use of particular types of membranes
Except for the last item, none of the above are hard and fast rules. They are issues that need to be addressed before choosing a particular type of roof system, regardless of whether it is asphalt-based, thermoplastic or synthetic rubber.
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