Managing Connections: Roof-to-Wall

Posted on by Tremco

One of the most challenging joint connections is the roof to wall, especially when it comes to maintaining continuity throughout the entire building envelope.  In fact, callbacks related to leaky roofs may not be a problem with the roof at all.  It oftentimes is the connection between the roof and the wall causing the problem.

Air will find any way it can to travel through a building, but two conditions are needed for air to leak.  First, there must be a gap, crack or opening from one side of the envelope to the other.  Second, there must be an air pressure differential which may be caused by wind, stack effect and the HVAC system.  The taller the structure, the greater the impact.

Joints must be able to support the same air pressures as the air barrier material without displacement.  If the air pressure is not controlled across the building envelope, and within the building itself, air infiltration and exfiltration could overpower HVAC systems and result in occupant discomfort, increased operating costs, and poor indoor air quality.  Wind accelerates at the sides and top edges of the wall.  If the roof-to-wall connection is secure, it will be able to resist water penetration caused by air pressure differential outside and inside the building.

In addition, unlike the moisture transport mechanism of diffusion, air pressure differentials can transport hundreds of times more water vapor through air leaks in the enclosure over the same period of time. This water vapor can condense within the enclosure in a concentrated manner as the air hits a surface within the assembly that is at a temperature below its dew point, causing the potential for mold growth and premature deterioration of building components.

The National Institute of Standards and Technology reports that the added energy to heat and cool buildings due to infiltration and exfiltration can be anywhere from 10% in cooling climates to 42% in heating climates (NISTIR 7238).  The connection between the roof air barrier and the wall air barrier, parapets, and junctions at low level soffits as well as the sequence of making an airtight, durable and flexible connection between assemblies and whose responsibility it is to make that connection is of critical importance.  Air movement must be stopped to create a continuous air barrier at the roof plane.  It is also important to ensure that the materials being joined together are compatible.

Different climates, different practices – How do you ensure a secure connection?

Varying climates make this connection even more difficult.  While there are industry guidelines for common roof systems and wall types, within the seven different climate zones in the United States, conditions, materials, practices and sequencing vary.  With a comprehensive array of products from the foundation to the roof and a sustainable building solutions test facility, Tremco is continually putting variations on this connectivity dilemma to the test to ensure long-lasting performance and the sustainability of the options recommended.

Wall assemblies have been tested in accordance with ASTM E2357, creating various uniform levels of sustained wind loads, cyclic wind loads and gust wind loads up to 1200 Pa (100 mph; 25.06 psf) at both positive and negative air pressure differentials across the entire wall assembly, simulating real world conditions.  The roof-to-wall assemblies go beyond the ASTM E2357 testing to include testing for resistance to wind-driven rain (ASTM E331).  Comprehensive solutions to provide a continuous air barrier at this critical connection have been assembled, tested and performance has been documented at levels beyond what is generally encountered in the real world.  In addition, sequence of installation has also been documented to simplify installation and ensure success though each project is different. Tremco sales representatives work with those on the design and construction team to make sure the right products/solution is selected for the application and provide guidance through installation.

Tested solutions for the various climate regions include comprehensive vapor-permeable and vapor-retarding air barrier systems formulated for compatibility with associated flashing and sealing components.  Since every project is different, testing of variations is ongoing.  Camp Pendleton in San Diego incorporated a vegetated roof in their design and utilized different components to provide continuity.  A parapet design utilizing another roof to wall connection was also tested and documented.

The health, safety, durability and energy-efficiency of the building, as well as the comfort of its occupants, depends on the continuity of the air barrier throughout the building enclosure.  Utilizing the principles of building science, innovation and ever more comprehensive testing, Tremco is committed to helping transform the fundamental building blocks of the built environment into a truly high-performance built environment.

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Tremco

About Tremco

Tremco Commercial Sealants & Waterproofing (CS&W) is North America's foremost supplier of sealant, weatherproofing, and passive fire control solutions for commercial and residential construction and industrial applications.

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