Condensation: Leak posers on a winter day By Mel Hoffart
The new roof is cut down to the steel deck, then the curb is built with a new vapour barrier on the steel deck (right-hand side of photo). Finally, the roof reinstalled around the box.
The top of the curbs were not sloped and thus held water, which froze solid. When the snowblower was used to access the large units nearby, the resulting ice could get very thick.
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n my years of working on many projects in the north, it has never ceased to amaze me at how few individuals in the building business have any real-world understanding of condensation. Many building managers with all types of buildings have an extremely difficult time understanding how condensation and roofing can be related, and how it can possibly be relevant to a roof inspector to know how condensation works. It is not uncommon at all for even professionals to believe that condensation collection only occurs in residential situations, such as a poorly ventilated attic. In this article, I will portray how even a large commercial facility, with a flat roof, can experience major problems with condensation and the resultant “posing” of the condensation as roof leaks. The design team had been requesting for several years after completion of this project to “find the leaks”, and reports were submitted, and although possible problems were located and fixed, the real problems were still occurring, and were significant in several ways. 1. They occurred almost exclusively in the winter after a long cold spell and the weather was warming up. 2. There was a notable amount of interior damage below these “leaks”, and they were always in the same spot.
The following summer, a liquid membrane, complete with reinforcing mesh, was installed around the base of all the pipes and penetrations.
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Ops Talk • Spring 2018
The project was a design-build exercise – one of the first we were part of in the north. There were a couple of design elements on the roof that were new to us on this project, and yet, I must admit, these ideas have been used again and again. It is because of this “repetition
of mistakes” that I write this article. In my experience, when one gets down to the basics, there are only two ways to learn; from your own mistakes, or from the mistakes of others. The only aspect I will discuss here is the use of “super curbs” for dozens of smaller penetrations. In the sequencing of the construction, it was necessary to have the roof completed, with the vapour barrier and insulation and roof membrane all installed as quickly as possible on the building. Many months later, as the mechanical installation progressed, huge holes were cut in the roof system to construct these large-framed “boxes” to run the pipes and vents through. These boxes varied in size from four-foot square by fourfeet high to eight- or 10-feet square, but still four-feet high. They were framed with steel studs and fiberglass batts, not that unlike residential construction, and the outside had plywood and a two-ply SBS membrane. The vapour barrier was still on the original roof deck, albeit quite compromised by the time the various pipes, cables, and ducts were run through it. They were not considered part of the roof by the design team, and thus as roof inspectors, we were quickly and quietly told that our inspections or input were not required in regards to this aspect of the roof. After it started leaking, we were of course expected to find the leaks and have the roofing contractor fix them all as part of the warranty. To be fair, there were numerous vents and pipes run through the top of these curbs that were not well sealed. Many times this was due to the fact that the mechanical installation was too tight to allow flashings around the penetration. After
