Bird Holes in Spray Polyurethane Foam SPF with Roof Coating System
Birds also come into play on some SPF with roof coating systems because they often feel the need to peck through the surface of the roof coating into the SPF creating holes in the roofing system. And while the closed cell nature of spray polyurethane foam SPF is advertised as being waterproof in and of itself, there are plenty of low-slope roofs with wet SPF on them.
Some solvent based roof coatings such as butyl, silicone & urethane are better able to resist leaks from ponding water, but they are also not breathable meaning that any moisture already within the existing roof system will not be able to get out through the roof coating. When the drive from any moisture in the existing roof meets the resistance of the roof coating, the roof coating will eventually blister. The blisters, especially in unreinforced roof coating systems, will often rupture allowing bulk water to enter the existing roof assembly and building. Trapped moisture in unvented flat roofing systems is not unique to roof coatings. Blisters in BUR built-up roof systems go all the way back to moisture being present during installation.
Acrylic roof coatings are not able to withstand ponding water and will emulsify, creating a hole in the waterproofing coating. Some roof coating manufacturers consider the need to re-apply a roofing coating in areas of the roof that pond water a maintenance item but in reality it is a repair that may or may not be able to be properly made at the time the roof starts leaking based on the season, the weather, and how wet the roof system becomes where the leak has occurred.
Do roof coatings really save money?
The biggest reason most building owners are interested in roof coatings is that they are often marketed as being a less expensive way to a “new” roof (“your roof reborn” or “restore your roof” are common tag lines). As in most cases though, reality is somewhat different than the advertising. While unreinforced roof coatings, if applied while a commercial roof is still in good shape, can extend the life of the current roof and are often initially less expensive than a new roof, what you get for your money is far different in a number of important aspects.
One primary attribute of a new roofing system is that it has a ply component to it. Single-ply roofing systems such as EPDM, TPO & PVC are, as the name implies, comprised of one stand-alone layer of roofing membrane. Additionally, but of fundamental importance, is that single-ply membranes are manufactured under factory controlled conditions vs. roof coating membranes are made on-site. The majority of roof coating systems are unreinforced and merely an addition to the existing roofing membrane. They not able or approved to function as stand-alone commercial roofing systems.
The primary reason many people are under the impression roof coatings are an inexpensive way to repair a leaking roof is that many roof coatings are inaccurately marketed as waterproofing when they are primarily reflective. The ability of most retail roof coatings to “seal hairline cracks and pinholes to increase water resistance of the roof and prevent leaks” is about the same as most latex paints.
A large part of the potential cost savings of professional quality waterproofing roof coatings is predicated on not having to tear-off an existing roof the existing roof. And while not having to tear-off an existing roof will save on average 1.50/SF-2.50/SF in tear-off costs alone, many existing roofs are not torn-off anyway. Although the IBC International Building Code specifies low-slope roofs with two or more systems be torn off down to the deck, most municipalities recognize that the older BUR built-up roof systems that primarily drove this requirement (typically weighing 8-12 LB/SF) were far heavier than most single-ply systems weighing .25 LB – 1 LB/SF and so allow a maximum 8 plies being the nominal equivalent of two 4-ply BUR systems. If however you are in a municipality that would require the existing roofing to be torn off before installation of a new single-ply roofing system and the existing roof is suitable for a roof coating system, the roof coating system may be less expensive even over a 20 year period.
Labor costs are often higher on reinforced waterproofing roof coating systems than for traditional single-ply systems due to the time required for cleaning and prepping the existing roof, embedding the reinforcing fabric, and applying the 3-5 individual coats of primer, foundation, and finish.
On a cost per mil or cost per year basis, professional quality reinforced waterproofing roof coatings are usually more expensive than some single-ply roofs. In fact, the better manufactures of these roof coating systems often do not claim to be less expensive than other roofing systems, but better. For some applications, they do have one or more clear advantage.
What’s the warranty like?
Perhaps not surprisingly, most retail roof coatings have material only warranties. Material warranties merely provide additional quantities of the roof coating should a manufacturing defect in the coating be able to be proved. This is a very high threshold and very limited responsiveness to be sure. Some professional quality waterproofing roof coatings have system warranties available at additional cost, covering both materials & labor, but they’re often split in responsibility resulting in the very real possibility of the manufacturer and contractor pointing a finger at each other. Many professional quality waterproofing roof coatings have a 10 year or longer warranty implying an effective life of at least that long but due to the many variables affecting adhesion, roof drainage, DFT dry film thickness, moisture content of the existing roof, condition of the existing roof membrane, and because roof coating warranties are so weak, assuming a shorter effective life than the stated warranty is often prudent. In fact when viewed from a truth-in-advertising standpoint, the warranty term of many roof coatings is more than a bit suspect.
Climate condition application challenges
While the Southwest and much of the Western US offer solid climatic conditions for the application of roof coatings due to their typically longer periods of dry, warm weather and lower number of deciduous trees, in other areas of the US these factors as well as wind have a significant impact on the application of roof coatings.
First and foremost, having the total number of warm sunny days needed to apply a roof coating system doesn’t mean much if they are separated by frequent rain which is often the case in the East, South, Midwest and Northwest. Obviously this is compounded if the roof substrate is already wet and/or the roof drainage is less than optimal.