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Roof Coatings Breakdown
By Michael R Slattery
Concerning flat roofs and elastomeric roof coatings, it is shocking to stand on a home in Miami and see all the neglected flat roofs that have turned black with stains. In 2016, people are much more aware of their home’s energy efficiency but have yet to fully realize the potential savings on their roofs.
In Miami, almost every homeowner either has a shingle roof, tile roof or metal roof. The majority of those have a flat roof attached, usually in the back over a patio, addition or Florida Room. What many don’t realize is how important roof maintenance is to their flat roof. Out of sight, out of mind? Sloped roofs require little maintenance other than keeping them clean and free of debris. Flat roofs, as a consequence of being flat, require a more rigorous maintenance regimen or they are doomed to a short life cycle.
Many homeowners perceive a flat roof as a maintenance free system. This idea has been perpetuated by roof salesmen and manufacturers who point out the white granular surface of modified bitumen and mineral surfaced cap sheet products which cover the vast majority of residential flat roofs today. Nothing in South Florida is maintenance-free.
Gloeocapsa Magma is a cyanobacteria which grows on everything down here eventually. Also known as black algae, it is the black film we see on sidewalks and pavers as well as our roofs. Flat roofs also develop this film and though there is debate over whether it directly damages the material, there is one indisputable fact – it is black! When a roof turns black it absorbs the sun’s rays rather than reflect them and, as a consequence, the roof membrane’s aging process accelerates. Specifically, the aging process is thermal shock, the deterioration of the roof’s material caused by daily expansion and contraction due to temperature changes.
Elastomeric roof coatings are a proven remedy for the effects of thermal shock. Their elastic characteristics and durability have been documented by such authoritative entities as ASTM, CRRC and Energy Star®. A roof that is stained black can reach surface temperatures of 150º or more on a sunny 90º day. The temperature range the roof experiences is much narrower with the application of a quality roof coating, from about 75º at night to about 100º on a sunny 90º day. Without coatings that range goes from 75º to 150º - that’s a lot of expansion and contraction going on.
Some folks turn to roof coatings after several years when a roof begins to leak and develop problems - by then it is usually too late. The primary use of roof coatings is to protect the roof from the effects of solar radiation, not to fix or prevent leaks. I have never given a warranty against leaks on a project where roof coatings were used as a maintenance application. You will not see anything on manufacturers’ warranties about stopping leaks either, despite the claims you may see in their marketing materials. Coatings can help prevent leaks but when used without re-enforcement, are strictly a maintenance application.
My mantra for roof coatings is “You can do it, we can do it or you can have someone else do it – but DO IT – and the sooner the better”. Roof coatings are an investment. If 25% of the roof’s cost is invested in a roof coating application and applied within the first five years of the roof’s installation, the roof’s life cycle can easily double. That is good math. Every year that goes by renders the roof coating that much less effective. Indeed, a roof can be too old and worn for coatings to be practical and may even cause the roof to fail faster than if it were left alone. Occasionally I must give a client the “zero option” when their roof is too far gone with not much to do other than replace. Sometimes roof materials crack under the stress created by the slight shrinking that occurs while a coating cures after being applied. A roof must first be inspected closely to determine if it is strong enough to support a coating.
Ponding is an important issue when considering a roof coating. Ponding water is any water left standing on the roof after it has stopped raining. Standing water is not good for the roof’s membrane and, unfortunately, flat roofs in Miami are mostly designed as perfectly flat, have settled a bit and developed ponding areas. Some are so badly designed they completely fill with water before they start draining. That is a 100% ponding situation – not good. Some flat roofs are built as additions that are sloped the wrong way and have negative drainage built into them by the original contractor. Ponding can be corrected with a well-designed system at the time of replacement through the use of tapered insulation. Sadly, many contractors will not even offer this option and when they do, the owner often declines due to its considerable cost.
Small ponding areas which dry soon after the rain stops are fairly inconsequential. Moderate ponding is a problem, however. I have not seen a good definition but I consider any water left on the roof after a sunny day to be moderate ponding and serious enough to cause problems. Dirt will gather in these areas and if the material is organic, as many are, the roof will deteriorate faster there.
Miami-Dade County considers any water still on the roof after 48 hours to be excessive ponding. You will see this standard mentioned in the literature of many coatings manufacturers because that is the point at which they recommend correcting ponding areas as their water-based coatings are not made to withstand extreme ponding conditions. Ideally, ponding conditions due to structural defect are corrected during a re-roof through the use of tapered insulation. There are three ways to address severe ponding on an existing roof: 1) Build up the area with additional material. This usually does not completely eliminate the ponding water but “pushes” some over the edge while mostly displacing the water and spreading it out over a larger area. It then evaporates more quickly as it is much shallower. 2) Rebuild the structure. In extreme situations ponding can be so widespread that filling the area may be impractical or even against Code. It is not uncommon for Miami-Dade’s 25% rule to come into play here. It states that if a repair covers more than 25% of the roof it must be replaced. That rule applies to many trades in the Code and has sent me back to the drawing board a few times. The problem with rebuilding the structure is that it is outside of the scope of a roofing contractor’s license and requires a General Contractor – that is “code” for very expensive. 3) Solvent-based roof coatings. Generally, water-based roof coatings can be used on roofs with little or no ponding. Solvent based coatings should be used on roofs with moderate to extreme ponding.
Be aware that solvent-based coatings are much more expensive. It is advisable to use solvent-based coatings only on the ponding areas and water-based on the rest of the roof to save some money.
Acrylic roof coatings account for a vast majority of the residential roof coating market, are available in water-based or solvent based formulas and are ideal for the flat roof systems typically found on most homes. Other coatings available are polyurethane, butyl rubber, hypalon, and silicone. Without going into great detail on each we can say three things about them. They are all generally commercial applications, solvent-based and expensive.
There are literally hundreds of different roof coatings on the market in the US with local or regional manufacturers in almost every major city and several national brands. To become familiar with the coatings we favor and use regularly, go to the Cleaning and Maintenance Page on this site.
The successful use of a roof coating system is dependent on a thorough examination of the roof’s condition, followed by a well-executed cleaning, surface prep and coating application. Homeowners, roofing contractors, maintenance managers and architects are recognizing the economic, environmental and performance advantages of elastomeric roof coatings.
Michael Slattery is a Florida Certified Roofing Contractor and President of Roofer Mike Inc, a roofing company in Miami, FL.