Recommendation No. 4: Devise formulae or charts for more accurate selection of insulation.
In this age of computers, many programs are available to aid in this process. In addition, energy codes prescribe minimum thermal resistances. Focus at this point is more on issues of sustainability and recycling. The involvement of ASHRAE has led us to guidelines for thermal resistance by climactic region and type of construction, as well as dealing with the value of reflective roofs.
Recommendation No. 5: Investigate tilt deck construction to obtain the slope needed to eliminate water problems (ponding).
Virtually all roof insulation board systems are available in tapered form to increase slope to drain. Sprayed polyurethane foam can also provide enhanced slope. Metal roof systems are available to elevate roof areas at time of re-cover. Rules of thumb, such as providing a minimum slope of 0.25 inches per foot, have recently been revised to “provide positive slope.”
Recommendation No. 6: Determine when special means of venting are necessary.
Research by the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) has proven that roof vents are ineffective in removing moisture from roof envelopes. Today, there’s more interest in when and how to provide effective air barriers since air leakage from within a building can carry moisture (which results in condensation) and pressurize the roof system.
Recommendation No. 7 (for Manufacturers’ Committees): Develop foolproof materials and methods of installation to compensate for poor workmanship. An entirely new roof design based on new materials we do not now have might be the answer.
Single-ply materials can look with pride at this recommendation. Prefabricated roof panels, inside and outside corners, roof boots, weldable seams, termination bars, and the like are readily available. Evolution of these materials since the 1960s have seen improved primers, sealants, and seam tapes, as well as dedicated tools and fasteners.
Recommendation No. 8: Develop insulation that can be placed in plastic form (to eliminate joints), is unaffected by water, is impermeable, is strong enough to support roof traffic, and has other physical qualities making it suitable for installation over large areas and, of course, with a high insulating value.
(Sounds like a prescription for SPF, doesn't it?)
Recommendation No. 9: Construction funds should be adequate to obtain the roof required by the conditions. It’s equally important to provide adequate funds for subsequent inspections and maintenance.
Recent buzzwords, such as “sustainability,” imply that proper maintenance is provided and that the system be repairable. In many cases today, roof warranties suggest enhanced durability, but neglect and abuse will negate our best intentions.
This may be a special problem in advanced roofing systems, such as in conjunction with photovoltaics or vegetated roofs, where inspection or repair may be exceedingly difficult.
To a great extent, McCawley was able to address these issues in the nine chapters of his 1959 book. To his credit, as well as that of the National Academy of Sciences, all of the above issues have been addressed to some degree, although some issues, such as reflectivity, self-cleaning of roofs, seeking the perfect membrane, and thermal insulation, are still being addressed today.
If you’re lucky enough to have access to a copy of McCawley’s book, there’s a great deal more in it than just historical significance. It can provide insight into today’s systems and materials – even those not imaginable 70 years ago.
Unfortunately, despite their historical significance, McCawley’s books are no longer in circulation. Perhaps the MRCA or the NRCA should consider republishing McCawley’s book as a celebration of just how far we’ve come in the past 50 years, and where the roots or customs of many of today’s roofing systems originated. It would be a shame to let this gateway to the past be lost, especially since so many of our peers are fading away. (The NRCA is considering reissuing 100 Years of Roofing in America in 2011, and the Manual of Low-Slope Roof Systems [McGraw-Hill] was last updated in 2006.)