2012 Spring Seminar

Synthetic underlayments in the roofing market serve as secondary water shedding barriers under roof shingles. Organic asphalt felt has traditionally served this purpose, but durability of the material is known to diminish over time and is inferior to newer synthetic products made with composite layers. While traditional felts are permeable, allowing moisture vapor transfer over time, newer synthetic materials are typically non-permeable, allowing very little moisture transport.
Recent testing and evaluation at Owens Corning™ Science and Technology Center demonstrates that "adding" breathability to synthetic underlayment provides no advantage to the performance of an asphalt roof assembly.
A modified American Society for Testing and Materials (ASTM) E 96 "Dry Cup" testing method demonstrated that standard overlapping shingle construction creates its own vapor barrier system, preventing both the transport of moisture from exterior weather elements, as well as preventing moisture vapor escape from the building interior. Moisture transfer through the roof cannot be achieved simply by making the underlayment material breathable. Because the experimental data indicates that the multi-layered shingle system creates a vapor barrier, a properly designed and installed attic ventilation system, or a properly designed and installed unvented roof assembly, is necessary to protect the roof sheathing from moisture within the home.
The focus of this paper is to investigate the system performance of standard asphalt shingles and to evaluate the impact of installing nonbreathable underlayments between the shingle layer and the roof deck. The research performed indicates that nonbreathable underlayments may be installed below asphalt shingle roofing materials with comparable or better moisture performance.

Sometimes soon after installation of a highly reflective "cool" roof condensation is discovered. Did the cool roof cause the condensation? Most of the time the answer is no but sometimes it is yes. This presentation explains how installation of highly reflective "cool" roofs can cause a moisture problem on roofs where it had not been a problem before. The focus will be on examples where wood decks, with insulation below, had been accumulating relatively large amounts of moisture for years but old non-cool built up roofs had helped them avoid problems by heating up and facilitating drying every time the sun came out. In such cases, installation of highly reflective cool roofs can inadvertently disrupt the balance between seasonal wetting and drying – causing increased moisture accumulation, condensation, and even mold growth in localized areas. Topics include:

• Why wood decks with insulation installed below tend to accumulate more moisture than wood decks with insulation installed above.
• How hygrothermal modeling can be used to simulate the effects of lowering roof membrane temperatures.
• Selected aspects of the new ANSI/ASHRAE Standard 160-2009 "Criteria for Moisture-Control Design Analysis in Buildings".
• The overwhelming influence of air intrusion on moisture accumulation in roofs.
• Building Code provisions for ventilating "enclosed rafter spaces".
• How adding insulation (above) can help combat the potentially negative impacts of installing "cool" roofs over wood decks with insulated spaces subject to air intrusion.
• Why roofs with vapor retarders can sometimes accumulate more moisture than roofs without vapor retarders.

RICOWI deployed 7 hail inspection teams to Dallas Texas in June 2011, inspecting over 100 roofs that were impacted by the May 24th 2011 hailstorm. The goal was to determine if the impact resistant roofing systems performed differently from standard products. Roofs inspected were impacted with hail sizes from 0.25" to 5". Results of the analysis of the data gathered will be presented.

In 2011, commercial and scientific journals published articles that describe hundreds of millions of dollars of building envelope damage associated with moisture. In an energy conservation program, avoiding such damage can be challenging because the very actions that reduce energy loss, such as increasing insulation and reducing airflows, can also increase the likelihood of moisture-related problems. Fortunately, research funded by DOE and other government bodies has provided the initial design tools needed to solve these problems. This previous research (started by DOE in 1999 in response to mold issues) has resulted in the first edition of an ASHRAE standard, has produced design tools that can be used by architects, engineers, or other researchers, and has created a limited set of material property data for US building materials.
A major goal of the DOE’s Building Technology Program's roadmap is to provide affordable, reliable and deployable technologies to maximize cost-effective energy efficiency for envelopes and to reduce heating and cooling bills by 50%. If the envelope technologies are not designed with moisture control in mind, the resulting damage will add cost (no longer affordable); create call-backs (no longer deployable), and will alienate building owners if problems are perceived to be associated with increased energy efficiency. This presentation will summarize their efforts over the past several years.

About one fourth of North American low-sloped buildings are roofed with mechanically attached assemblies and its popularity continues to grow. In such systems, because of the flexible and elastic nature of the waterproofing membranes and their attachment mechanisms, wind and building mechanical pressurization from the interior causes the membrane to balloon or flutter. The volume change of the membrane deflection causes negative or bubble pressure below the membrane, which is equalized by the indoor conditioned air moving into the assembly, which is termed as air intrusion. To measure the air intrusion in MARS, an experimental study was started and control data was developed at the National Research Council of Canada as part of the SIGDERS (Special Interest Group for Dynamic Evaluation of Roofing Systems) research. To relate the air intrusion with the moisture transport in the mechanically attached roofing system, a spin off project was started in collaboration with CRCA, NRCA and four major roofing manufacturers. The present paper discusses the research findings from this ongoing study, which addressed the following tasks:

1. Test additional systems for air intrusion quantification and provide comparison with the SIGDERS control data.
2. Impact of air intrusion on moisture transport in mechanically attached roofing systems compared to vapour transmission, and to establish air intrusion limits for potential condensation in these roofing systems.