Choosing the correct replacement for an aged roof – or identifying the best choice for a new building – is no easy task. The perfect roofing solution for one building may be the worst option for another just down the street. That’s because no two buildings are precisely alike, even if they closely resemble each other. So how do you choose a new roof, given all the choices in the marketplace? You can start by asking a series of questions, before you choose the roof, the roofing contractor or the manufacturer.
1. What is this building’s mission statement?
Before calls are made to roofing contractors or manufacturers, the first item to address is the company’s mission statement as it relates to the building.
Whether you are building new facilities or managing existing properties, you want to be confident that the roofing systems you select deliver the performance you expect. More often than not, the building itself dictates the appropriate roofing system specification.
You need to know as much about the building and its future as possible. Does the company plan to keep this building as part of its real estate assets for the next 10 to 20 years? Are there any plans to expand it in the near future, or to change its use? What are its current and future occupancy, insulation requirements, aesthetic priorities and even the maintenance schedules for rooftop equipment?
These and other mission statement issues will help shape answers to types of roofing to consider and how much of the capital budget is really needed for the job.
Start your questions with what is the building going to be used for. If it’s a spec building, maybe you only need a basic roof. But, if the facility has a special use, such as an airline reservation center with computers in it, then your considerations for roofing options are quite different.
For example, as more companies move toward operating 24 hours daily, seven days a week to satisfy global customers, the data center must never spring a rooftop leak. Water on computer systems generally spells disaster.
A special set of concerns arise for cooling-dominated climates. Does the roof contribute to air conditioning savings and address other key issues? Is it part of a total energy program? There is a growing concern about urban heat islands. Reflective, white roofs have become of interest in those areas for a few reasons. They keep the building cooler, reduce air conditioning costs and also minimize the heat-loading of the surrounding environment.
2. What physical and other elements influence the roofing system selection?
After identifying the goals and mission of a facility, it’s time to evaluate the building itself. You need to begin by looking at the building’s location and the attributes of its surrounding area. You need to examine building codes, weather trends, topography – even the direction the building faces.
The physical characteristics of the building are also crucial: size, shape, design, height and age.
You also need to look at the construction materials used to build the facility and the location of HVAC and fire protection equipment, particularly if either or both of these are partially or totally housed on the rooftop.
When it comes to roof replacement, you need to list the attributes of the roof area itself. It’s best to detail the roof’s size, shape, slope, deck construction, edge detailing, protrusions, rooftop access and existing roofing system. Along with this basic information, you need to find out why the original roof is no longer adequate.
3. What flexible-membrane roofing options are available?
SPRI, the association that represents sheet membrane and component suppliers to the commercial roofing industry, identifies three major categories of membranes: thermosets, thermoplastics and modified bitumens.
Thermoset membranes are made from rubber polymers. The most common is EPDM, often referred to as “rubber roofing.” These membranes are well suited to withstand roofing the potentially damaging effects of sunlight and the common chemicals found on roofs. They are easily identified on the rooftop. Just look at the seams. Thermoset membranes require liquid or tape adhesives to form a watertight seal at the overlaps.
Thermoplastic membranes are based on plastic polymers. The most common is PVC, which is made flexible by adding plasticizers. Thermoplastic membranes have seams that are most commonly formed using heat welding. Most thermoplastic membranes are manufactured with a reinforcement layer, usually polyester or fiberglass to provide increased strength and dimensional stability.
Hypalon thermoplastic begins as a thermoplastic, but cures over time to become a thermoset. Like other thermoplastics, Hypalon materials are heat sealed at the seams.
Another thermoplastic hybrid is thermoplastic polyolefin (TPO), which combines the attributes of EPDM and PVC. TPO membranes do not cure after exposure to the elements and remain hot-air weldable throughout their service life. Most TPO membranes are reinforced with polyester, fiberglass or a combination of the two, but unreinforced TPO membranes are available.
Modified bitumen membranes incorporate the formulation and prefabrication advantages of flexible-membrane roofing with some of the traditional installation techniques used in built-up roofing. Modified bitumen sheets are factory-fabricated, composed of asphalt which is modified with a rubber or plastic polymer for increased flexibility, and combined with a reinforcement for added strength and stability.
4. Which type of membrane and attachment system are best for the building?
Many factors determine the best system for a particular building. For most buildings, there are a number of options and advantages that need to be weighed against the facility’s mission statement. The decision should not be made only on the basis of cost. Other important considerations for membranes are building height, wind exposure, anticipated roof traffic and aesthetics.
The attachment system also depends on the specific building’s characteristics. If the roof deck is able to withstand the weight, a ballasted roof may be the best option. But, if the slope of the roof is greater than 2 inches every foot, this system may not be appropriate. There are other limitations to ballasted systems, such as roof height, proximity to shorelines and other high wind zones, and the availability of ballast.
A steel or wood deck that easily accepts fasteners makes a good substrate for a mechanically fastened membrane. These systems can be designed to provide the necessary resistance to known wind forces and are not subject to slope limitations.