THE MATERIAL SELECTED to cover the roof of our historic sanctuary (later this summer) is silicone with the brand name Type S, manufactured by American Standard Coatings (ASC), based in Chatsworth (Los Angeles). It will be applied by roller according to manufacturer’s instructions at a coverage rate (thickness) that the ASC will then warranty for 15 years. Our roofer calls this “a 15-year specification.”
Below the jump, this post discusses the coating’s benefits and features, why it was chosen for our roof, and its future maintenance needs.…
(This post is a follow-up to last month’s post HERE.)
Efficient use of capital
Based on the bids received, silicone provides the longest-lasting material-warranted coverage per dollar spent:
Winning bidder: $3.5K per warranted year
Competing silicone bids: $4.9K per year
Acrylic overlay bids: $4.5–5.4K per year
Bitumen overlay: $6.6K per year.
The other option that we considered, spray polyurethane foam insulation with acrylic overlay, was offering additional benefits. The insulation would boost the building’s thermal comfort and reduce utility bills, yet at a cost of $6.2K per warranted year. Compared to the winning bid, the net difference in installed cost would be more than $40K. Much as we would love to have a much more energy-efficient and comfortable building, we could not justify spending that much extra to achieve those goals—given the other important demands for our capital. So we had to let go of that opportunity.
Improved thermal comfort and reduced energy use
That being said, we do expect a modest yet noticeable improvement in these areas. The properties of the coating should moderate summer high temps in the sanctuary, and save on AC costs. The LADWP estimates the typical energy savings from such a roof coating at 20%.
Testing has shown that this silicone product still performs well, even after weathering: its 3-year rating would be Energy Star qualified (if the federal government’s rating program for roofing materials still existed). That’s based on its measured solar reflectance after 3 years, 0.69, which exceeds the former Energy Star minimum of 0.50. The term “cool roof” can fairly be applied to the application of such a product.
Background information about ratings and “cool roofs”
The Cool Roof Rating Council (CRRC) is an independent, non-profit organization that maintains a third-party rating system for two characteristic radiative properties of roof surfacing materials: solar reflectance, and thermal emittance. Those properties are measured and certified for roof products, both new and after 3 years of outdoor exposure.
The CRRC does not set a minimum definition for “cool”; any roofing product can CRRC rated as long as it is tested in compliance with their protocols. A product's listing in the Directory does not mean that the product is energy efficient per se.
The CRRC’s two measured parameters do not, by themselves, indicate the energy savings from a cool-roof product. Rather, those figures must be evaluated in the context of local climate data, which is beyond my pay grade.
In our Socal climate zone, I expect that our “cool roof” will help avoid summer overheating, without making much difference in wintertime.
Additional characteristics of silicone coatings
- Unlike asphalt-based roofing materials (which we currently have), silicone does not oxidize and break down in UV light.
- Over time, the coating will wear away and thus get thinner (much like clothes that become threadbare after being washed and dried many times). So it needs to be monitored periodically, especially after the first 5 years.
- After it reaches a certain minimum thickness, in order to renew the warranty, a contractor will need to apply a layer that restores the coating thickness. Such reapplication can be done repeatedly, as needed, because the coating is fairly lightweight: each layer would add 320 pounds to the total load on our roof. I.e., by switching to a silicone overlay, we can indefinitely avoid the need to pay for tearing off and hauling away the present asphalt-based membrane, which would have cost more than $20K.
- Silicone coating is fluid when applied. Hence there are no seams where leaks can develop, unlike with our current membrane.
- A silicone surface is slippery when wet, so extensive dedicated walking pathways will be installed; this is normal practice. Our vendor will do so by putting down another silicone layer of a slightly different color, while embedding roof surfacing granules (ceramic beads), to provide a gripping surface. Nonetheless, some caution will be needed when the surface is moist; our staff and other workers will need to tread conscientiously.
- Silicone coatings hold on to dust and other airborne particles that will settle on the roof. Over time, this accumulation on the surface degrades the coating’s solar-reflective property (although its radiative ability can improve). The solar reflectance ratings of the Type S product predict that it will absorb 2½ times more of the incident solar energy after 3 years, compared to when it is brand new. Even so, that absorption rate will still be significantly less than the average roof in the L.A. area.
Efficient use of staff and volunteer time
We actually did receive a bid for a lower installed cost than the one we have selected. But the warranty period would only be 10 years. Because of the multi-year effort involved in re-roofing—arranging with the synagogue leadership to set aside the necessary funds, meeting with vendors, and evaluating their bids—I preferred to avoid anyone’s needing to go through all this work again in less than a decade.
Managerial energy is a resource as scarce and precious as dollars. Therefore I sought out a roof membrane that is warranted to last for 15 years. Happily, it is also a more capital-efficient approach, as explained above.
About the winning bidder
We have had a service contract with Hull Bros. Roofing for several years. They know our roof well. They also have rather extensive experience with silicone overlays, including several government buildings in Culver City.
Maintenance and future re-roofing
Because nothing sticks well to silicone, Mishkon must stick with silicone. That is, installing such a surface now is permanently committing us to it: future maintenance/repair must likewise be with silicone products.
When the time comes to pressure-wash-and-recoat, the technical choice will be simpler than it was this year: a layer of silicone. And that should cost less (in real dollars) than this summer’s initial application, because of the extensive surface preparation that is needed the first time, to ensure good adhesion.
In order to maintain the warranty, we will need to have the roof inspected semiannually, while keeping written and photographic documentation of its condition.
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