The specified slider does not exist.
Conclusion
Since 78 WUFI models were simulated, it would be difficult to describe all the models with their drying profiles. For the purpose of this article, four models are explained. Figures 2 and 3 are the self-drying models from Toronto with a white and black roof membrane and ventilation moving moisture out of the metal roof deck’s flutes. It is important to note the baseline was no ventilation moving the moisture out. Ventilation had to be added, as there was increased moisture. As previously mentioned, the beginning of the WUFI model began October 1, 2016, and the simulated leak occurred April 1, 2017 (as indicated on the graphs). There was minimal moisture ingress into the roof enclosure during the winter months, even with a smart membrane due to the ventilation introduced between the metal deck roof flutes. This ventilation allowed for the vapour attempting to diffuse into the roof assembly to be greatly reduced—the effect of this reduction will be evident when ventilation is not occurring. The black roof membrane assembly in Toronto (Figure 2) dried in nearly half the time of the white membrane roof assembly in Toronto (Figure 3). A higher membrane temperature and high vapour pressure were critical to the effective diffusion of the moisture/vapour to the interior. Based on the graphs, it appears the roof drying was effective when a single wetting event took place. If several wetting events had occurred, the results would be different. In a colder climate such as Edmonton (Figures 4 and 5), by not venting the moisture attempting to diffuse into the roof enclosure, there will be added diffused moisture due to the installed smart membrane. Even in Edmonton, if a black membrane is used in conjunction with a self-drying roof enclosure there is still enough energy to diffuse the moisture to the interior, where it can be accommodated. On the other hand, the white roof does not have adequate energy to move all the moisture out of the system before the interior moist air reverses and diffuses back into the system (around mid-September). In this scenario, the author does not believe a self-drying roof with a white membrane will be an acceptable approach.
The tight time constraints of planning, designing, and constructing have placed a strain on available resources, especially finances and labour. A saying in the construction industry is, “Speed, Quality, and Cost—you can pick two, but you cannot have three.” Developing durable and efficient building enclosures, even when problems arise, should be the way of the future. Developing a self-drying roof enclosure would be a giant step forward in minimizing the monetary impact of construction on an owner and the environmental burden on society.
The proposed self-drying roof design was developed with economics, environment, durability, and ease of construction in mind. The roof membrane is to be continuous and have very low vapour permeability and a specified colour to suit the respective climatic zone. The thermal insulation in the assembly is to be a highly vapour permeable insulation material with a varying smart membrane below the insulation. Ventilation of the metal deck may be required in some climatic zones to remove the vapour attempting to diffuse into the roof assembly.
Results from the 78 hygrothermal models prove the potential for a self-drying roof enclosure is suitable in almost every location (Figure 6). Several outliers show self-drying roof enclosures with a white membrane were not ‘functional’ in colder climates. The performance of this self-drying roof enclosure design could minimize the rate of litigation and provide the additional benefits of increased resiliency and reduced financial burden for building owners and the environment. Though there is much more work required with modelling and testing, the design of a self-drying roof enclosure appears to have some promise.
With the life cycle of standard roof systems (typical industry types) averaging 17 years, the potential for increased durability and resiliency is needed. A self-drying roof system will allow for increased material performance and longevity, as the insulations’ effectively recover when moisture loading occurs. The cost of the overall system will increase by 30 to 35 per cent, but if the roof system can reach the industry standard 25-year warranty (with proper maintenance) the operational and environmental costs could be reduced.
Rockford Boyer is the technical manager, building enclosure at Elastochem Specialty Chemicals. He has a diploma in civil engineering, a degree in architecture (building science option), and a master of building science degree. Boyer has more than 15 years of experience in the enclosure design field, including five years with AMEC, Earth and Environmental, 10 years with Roxul/Rockwool Insulation, and two years with Elastochem. He can be reached at rboyer@elastochem-ca.com.
