In Part II and Part III of this blog series, we looked layer by layer at the components of a low-slope roof, exploring the options available and the role each plays in creating a high-quality, long-lasting roof. In this post, we’ll discuss how to sift through those choices and select the right system for a job.
Match the Roofing System to the Building’s Purpose
What happens inside a building has a significant impact on the type of roofing system that should be installed on top. Still, this important consideration is often overlooked in roof designs.
To illustrate, let’s consider an imaginary street in a city in a cooler climate. An office building, a hospital, a manufacturing facility and a restaurant are neighbors. Each will have characteristics that should be considered when selecting their roofing system.
- Office Building: A black EPDM roof would absorb more of the sun’s rays, helping warm the building’s interior during the winter, reducing heating costs.
- Hospital: The building operates 24-7-365, and its many occupants and constantly running equipment can make the building warm, even in a cool climate. If this will cause the building to have more cooling days than heating days, a reflective white TPO roof could help reduce cooling costs and maximize the performance of HVAC equipment while keeping patients, staff and visitors comfortable.
- Manufacturing Facility: Many manufacturing plants have long I-beams that run along the ceiling across the entire building. Large machinery operating in the plant can make those beams – and the roof – vibrate. That could cause a roofing system with low elongation, such as built-up roofing (BUR) or self-adhering SBS modified bitumen, to fail prematurely at the seams. An EPDM system would be a smarter choice; with its greater elongation, it would better accommodate the building’s movement and be much more durable.
- Restaurant: A restaurant’s roof will often have a trap to capture the grease and oil that are vented from the kitchen. If the trap is not emptied frequently enough (a common occurrence) and its contents spill onto the roof, it can damage an EPDM membrane over time. PVC KEE is the ideal solution for restaurants and food processing facilities. It is the most chemically resistant single-ply membrane and will best withstand regular exposure to animal fats. PVC is a strong second choice, delivering excellent resistance to chemicals at a lower cost.
Four buildings. Same environment. Distinct purposes. Different roofing needs.
Evaluating an Existing Roof
If a project is new construction or a complete tear-off and replacement, the roof designer has a blank slate in planning the system that will best meet the needs of the building, its occupants and its owner. When working on an existing roof, however, a few more questions must be answered first ... Is the roof a candidate for recovering or coating, or is it no longer sound and in need of replacement? What products are already there, and what condition are they in? Are there repairs that must be made before the roof is recovered or coated?
Answering these questions requires a thorough assessment of the roof.
Start with a visual inspection, walking the roof to experience it up-close. Things to look for include:
• Peeling and chalking of existing coatings.
• Poorly attached vents or other projections.
• Open seams and side laps.
• Insufficient slope.
• Areas of ponding water (evidenced by the accumulation of dirt or debris).
• Damaged membrane.
• Loose membrane on fully adhered roof systems.
• Broken or improperly flashed pipes.
• Broken or missing drain components.
• Loose or damaged perimeter edge metal.
• Deteriorated, damaged or loose flashings.
• Damaged or wet insulation or substrates.
A moisture survey should then be completed to locate any leaks and determine their severity. This can be done by making core cuts in several specific areas of the roof or by completing a moisture scan using other technology.
Core cuts are the roofing equivalent of soil samples, with cuts being made to remove samples of all roof layers down to the deck. This deep dive reveals the components used initially and added since; the installation methods used; the quality of the installation; and the roof’s current condition. The contractor can then answer several key questions, including: Does the roof have adequate slope or should tapered insulation be added? Is the insulation wet, and how extensive is the saturation? Is the roof deck deteriorating? Has the roof already been recovered and the number of layers allowed by local building codes reached? Core cuts should be made in all elevation areas and where different roofing system compositions are apparent.
Moisture scans are non-intrusive ways to find potential areas of moisture. Options include:
- Surface Meter: A device placed on the roof surface shoots electrical impulses into the roof to a desired depth, pinpointing where moisture may be present.
- Infrared Camera: A handheld or drone-mounted infrared camera is used to scan the roof for moisture. Wet areas will glow “hotter” because the moisture will retain heat longer. The roof should be scanned at dusk when the distinction between “hot” and “cool” areas will be greatest.
- Electronic Leak Detection (ELD): These tests require that a conductive material, such as Detec TruGround Conductive Primer, has been applied to the substrate directly below the membrane. If the initial roof design did not include such a material, ELD is not an option. In the test, water is applied to the roof surface, which is then scanned using an ELD device. If leaks are present, the water will create electrical connections to the grounded roof deck, enabling the device to pinpoint their locations.
- Nuclear Resonance Imaging: This is an alternative to ELD when a conductive material is not present. A robot sends radio impulses into the roof to detect water. The impulses can penetrate up to 2.5 inches (6.4 cm) and are effective in assessing one layer of roofing.
If the scan detects moisture, core samples should be taken from those areas to confirm the results and determine how saturated the roof may be. High levels of moisture throughout the roof likely mean the roof should be replaced. Roofs with isolated, lower levels of moisture often can be coated or recovered after repairs have been made, including replacing areas of wet insulation or damaged roof deck.
When planning a coating project, an adhesion test should also be completed. A coating’s long-term performance depends on how well it adheres to the substrate and whether the existing roof is sound and has adequate drainage prior to coating. An adhesion test will determine whether the coating is compatible with the substrate and whether encapsulated moisture or other underlying issues that could impact adhesion have been properly addressed.
In the test, a small area of the roof is cleaned and coated. Strips of polyester-reinforced fabric are embedded in the coating, with several inches at the end of each strip left outside the coating to serve as pull tabs. After the coating has fully cured, a fish scale is attached to the pull tabs and used to remove the strip from the roof. The test is a “pass” if the coating remains adhered to the roof membrane and a “fail” if the coating separates completely from the roof surface.
With this analysis completed, the contractor can choose the type of system that is best suited to the building’s location and purpose and the building owner’s priorities. And on retrofit projects, the contractor has identified any repairs or alterations that are needed. The design work is not complete, though.
Just as important to the roof’s long-term performance are how the insulation and cover boards are fastened and how the roof covering is attached. We’ll cover that in the final installment of this series.