Monthly Archives: January 2017

Determining The Condition of a Roof

Roofing problems seem to show up at the worst possible times and, often, in the worst possible places. They also can quickly turn from small drips into large, costly headaches. Among the numerous options managers have in trying to prevent roof leaks and other problems is the use of roof coatings. Options in coatings have expanded and evolved in recent years as manufacturers seek to address customer demands for performance, flexibility and cost-effectiveness. To make smart coating decisions for their facilities’ roofs, managers need to answer three questions related to specification, coating type, and post-installation inspection and maintenance.

What shape is it in?

Managers need to understand the condition of the roof in question before deciding on whether or not to apply a roof coating. Is the goal to preserve and maintain a roof that is performing relatively well, or is it to repair and restore a roof that has developed leaks?

“A reflective coating would be a good choice for a facility looking to preserve a roof and make it more reflective,” says Michelle Carlin with GAF. “A liquid membrane is a fabric-reinforced coating system that restores a roof by forming a fully adhered and seamless roof system. This liquid-applied membrane is a system that a facility might choose for restoring a roof that has begun to show signs of failure via leaks or cracked seams.”

Weather and climate conditions, as well as the type of facility, also should play a part in the decision. Managers in facilities such as schools and hospitals with occupants who could be sensitive to solvent fumes should specify odorless coatings.

Silicone roof coatings tend to be more resistant to grease, fats and oils than water-and solvent-based coatings.

“That makes them a better choice for use on restaurants, airports, food processing facilities and other commercial buildings,” Kate Baumann with Mule-Hide Roofing Products says. “The other things to look at are temperature, weather, humidity and other climatic conditions likely to be faced during and just after the coating application.”

Silicone and solvent-based coatings are more cold tolerant than water-based coatings, Baumann says. Technicians should conduct adhesion tests following the coating manufacturer’s specifications to make sure the coating selected will adhere properly to the substrate.

Coatings are not always the solution, however.

”Managers should look at all solutions,” Baumann says. “Coatings are often an excellent choice, but sometimes there are other choices with reroofing, and you really need to take the soundness of the current roof under consideration and make an educated decision overall with all of the choices.”

Managers who do decide to apply roof coatings could see multiple benefits for their facilities, both immediate and long-term.

“Coatings have always had an edge when it comes to benefits for facilities,” Carlin says. “Facilities save money on initial installation costs, they save money by choosing a reflective coating, and they save money by allowing existing roof components to perform better.”

Because coating application can take place while occupants are in the building, the process does not need to disrupt them or their activities. Reflective coatings have been proven to save facilities up to 30 percent on cooling costs, Carlin says. Coatings also help address the urban heat island effect by not contributing to a rise in surrounding air temperatures.

What You Need To Know About Flat Roof Coatings

Flat roof coatings can be a good investment for many facilities. A flat roof coating can extend the life of a roof because it lowers the roof temperature. It can also lead to additional energy savings as the temperature is reduced.

Still, because there are so many different types of roofs in use today, specifying a flat roof coating isn’t easy. Different substrates require different coatings. A coating’s adhesion might depend as much on the substrate’s characteristics as on the coating type. In general, it is more difficult for coatings to adhere to hard, smooth, chemically inert surfaces and easier on rough, irregular, chemically active surfaces.

A coating’s adhesion to a substrate often improves when the installers put down a primer or base coat. Coatings manufacturers recommend certain primers or base coats for managers trying to match a specific topcoat with a specific substrate. Managers should use only the base coat or primer specified by the coating’s manufacturer.

With the introduction of roof membranes such as ethylene propylene diene monomer (EPDM), polyvinyl chloride (PVC), thermal polyolefin (TPO), Hypalon, modified bitumen, and built-up roofing, manufacturers have developed a variety of roof coatings to address multiple substrates with different adhesion and weathering characteristics.

Managers can specify asphaltic and tar-based coatings for use with coal-tar-pitch built-up roof systems. Non-asphaltic coatings, including urethanes, acrylics, and polyureas, are most commonly used on single-ply systems.

Each of these coatings has different cost and performance factors. Due to variations in coating formulations, a manager should work closely with a roof consultant and the manufacturer to make sure they specify the right coating for the roof substrate and that workers perform the correct repairs before applying the coating. Manufacturer representatives and product data sheets also can assist in specifying coatings.

Wet Roof Deck?

Wet roof decks simply can’t be ignored. Recovering a wet roof deck won’t make the problem go away. That’s because recovering a roof deck will likely only cause the roof to blister, or cause other serious problems that won’t be covered by a warranty.

Here’s how to tackle a wet roof deck the right way. First, identify wet areas in the roof. To do so, one of three types of moisture surveys should be completed: infrared, nuclear or capacitance. None of these actually measure moisture. Instead, they measure the effect moisture has within the roofing materials.

For best results, match the type of moisture scan with your roof since each moisture scan works differently. Infrared surveys measure the heat retained or lost in insulation that has become damp. Ballasted roofs aren’t a good candidate for infrared surveys because the rock itself retains a lot of heat, giving potentially false readings. Nuclear moisture surveys measure hydrogen atoms in the roof, meaning that any membrane with a large hydrogen chemical component will send positive readings. Water is a good conductor of electricity, and capacitance surveys measure electricity traveling through the roofing material. This won’t work on a roof with wet or ponded areas, and may require modified instruments on EPDM roofs.

The amount of moisture found in the roof, if any, may dictate the choice of whether to recover or replace. The more areas of moisture found, the more expensive it will be to replace those areas.

If you have 100,000 square feet of roof and four 8-by-10-foot areas are wet, replacing those sections makes sense. But if 30 percent of your roof is wet and it’s scattered throughout the roof, the labor to replace all of those sections probably equals the cost of just tearing off the entire roof.

But what if the roof is leaking just after a recent replacement? It’s not that farfetched — due to poor design or installation, many roofs experience water leakage soon after construction.

In many instances, water leakage through a roof membrane can go unnoticed because a vapor retarder at the bottom of the roof system captures the water. The captured water absorbs into the insulation, significantly decreasing the thermal value of the insulation and causing premature deterioration of the roof system.

A properly prepared and implemented design can prevent water from migrating into the roof. Generally, the membrane in the roof’s field does not allow bulk water leakage. Most leaks through a system arise from unreliable detailing.

Roofing system manufacturers provide standard details for perimeter conditions, which typically have the flashing exposed and terminated on the wall surface. They rely on sealants to prevent water infiltration. Manufacturer details typically do not address leaks around the roof system.

For example, in most instances, roof terminations consist of surface-mounted conditions — exposed termination bars or metal flashing — or reglet-set flashing — a small cut in a wall system to insert the metal flashing. In a brick masonry wall, these types of terminations are not appropriate because water can bypass the flashing, infiltrate through the masonry, and migrate into the insulation. Instead, the design of roof flashing for a masonry wall should incorporate a through-wall flashing that extends through the masonry to capture and divert water out of the wall above the flashing.

Picking A Cool Roof

Most roofing industry experts agree that a cool roof is one that exhibits a combination of high reflectivity and high emissivity. But the questions have always been how high is high and what combination of the two yields the most benefit?

One way to make a decision is to use the Solar Roof Index (SRI) to evaluate a cool roof. The U.S. Green Building Council’s LEED 2.2 uses SRI as a way to evaluate a cool roof. LEED version 2.2 is the first national specification to use a relatively new measure of reporting a cool roof’s properties. LEED 2.2 sustainable sites credit 7.2 states that to receive one point, building owners should use a roof with a Solar Reflective Index (SRI) of 78 over at least 75 percent of the roof’s surface for roofs with slopes less than 2:12.

SRI is a unit developed by scientists at Lawrence Berkeley National Laboratory. SRI incorporates reflectivity and emissivity properties into one, easy-to-read, standardized measure so that roof buyers won’t have to scratch their heads and try to figure out if a high reflectivity and low emissivity is better or worse than a medium reflectivity and high emissivity.

SRI is calculated with a complex formula spelled out in ASTM E 1980 and is a scale of 1 to 100 that is a measure of a roof’s combined thermal properties. It is defined so that a standard black (reflectance 0.05, emittance 0.90) is 0 and a standard white (reflectance 0.80, emittance 0.90) is 100. But some hot roofs can have negative values, and some white thermoplastics and white roof coatings have scored as high as 104 to 110.

SRI as a method for reporting cool roof data will probably take a little while to catch on. Most manufacturers still report separate emissivity and reflectivity data in their literature, but the Cool Roof Rating Council, an organization that verifies and labels cool roofing products has begun using the measure, while retaining reflectivity and emissivity measurements.

Different roofing technologies have different SRI values.  Asphalt coatings for example have aluminum pigments added to asphalt cutbacks and emulsions to give coatings solar reflectance index (SRI) values of 21-30 on a scale of 0-100.

Acrylic elastometers on the other hand, a new-generation coatings, have a highly reflective surface, often with an SRI greater than 100. Most highly reflective acrylic elastomers are white, and workers can install them over existing bituminous or non-bituminous roofing. Acrylic elastomers typically are specified at 12 mils for five-year warranties and at 20 mils for 10-year warranties. Some manufacturers specify up to 40 mil applications.