Vapor Permeable and Non Permeable Air Barrier Systems

We are starting to see more building owners interested in air and vapor barrier systems, both fluid applied and sheet applied. These systems are related to the entire building envelope, from foundation to walls to rooftops, and have been proven to increase energy efficiency and improve air quality.

Air barrier materials resist air leakage and are designed to form a continuous plane around a building to protect uncontrolled air movement in and out of the building envelope.  Air leakage loads are significantly greater than most designers and architects realize, and a study on air barriers by the National Institute of Science and Technology revealed that the right air barrier can help improve building performance by reducing heating and cooling costs by as much as 36%.*

Vapor barrier materials limit the amount of water vapor diffusing through the wall as a result of vapor drive. Vapor drive is a phenomenon that occurs when water vapor naturally diffuses into and through wall structures and is controlled by type of structure, porosity, moisture gradients and temperature gradients.

Remember science class and studying about thunderstorms? This is the same thing just on a molecular level. It incorporates the key principles of air movement: from warm to cold. In a cold climate, vapor drive is primarily from interior of a building to exterior. If you have a hot, humid climate, the vapor drive is primarily from exterior to interior.

Source: Buildingwell.org

There are countless scientific studies and published documents about water vapor, vapor drive and air movement. With the advent of modern building science, it has been found that air leakage - and not vapor diffusion - is the real problem. The air barrier systems we incorporate, however, are a combination of both which afford us the ultimate in design flexibility. **

To manage vapor diffusion there are two types of air barrier membranes: Vapor Permeable and Non-Permeable.

Vapor Permeable Air Barriers
High vapor permeance keeps air and water out, while allowing water vapor to escape.  Positioned anywhere within the wall assembly, they are watertight and protect against air leakage. 

Non-Permeable Air Barriers
These membranes act as air barriers, vapor barriers and rain barriers. When positioned on the warm side of the insulating layer, they serve as an efficient vapor barrier, preventing moisture condensation through the wall cavity. Good for hot humid climates or an extreme mixed-humid climate.

Non-Permeable Air Barrier
Source: Henry Products

The choice of product, between a vapor permeable versus a non-permeable air barrier, is dependent on a wide range of factors, like those mentioned above, and advancements in available materials make it important to work with a professional.

*NIST Report 7238

**The Difference Between a Vapor Barrier and an Air Barrier. Written by R.L. Quirouette, Building Practice Note No. 54, July 1985

Other Sources: 
Solving the Air Barrier Riddle: Permeable or Impermeable? Written by Sonya Santos and published in the Journal of Architectural Coatings, Jan-Feb 2007

Water Vapor Migration and Condensation Control in Buildings. Written by William Acker and published in HPAC June 1998

Top 10 States for LEED-Certified Green Buildings

Back in January, The U.S. Green Building Council (USGBC) released its 2011 list of top 10 states for LEED-certified commercial and institutional green buildings per capita, based on the U.S. 2010 Census information.

The District of Columbia leads the nation, with more than 31 square feet of LEED-certified space per person in 2011, with Colorado being the leading state, with 2.74 square feet per person in 2011.

Other top states include Illinois, Virginia and Washington, with 2.69, 2.42 and 2.18 square feet of LEED-certified space per person, respectively.

The top LEED states per capita, including the District of Columbia, are Colorado, Illinois, Virginia, Washington, Maryland, Massachusetts, Texas, California, New York and Minnesota.

LEED is the internationally recognized mark of green building excellence, with more than 44,000 commercial projects participating, comprising over 8 billion square feet of construction space in all 50 states and 120 countries.

Most products used by Washington Roofing and Insulation are ENERGY STAR®, LEED, CRRC, Miami - Dade County approved and/or certified. 

Source: Press Release Jan. 19, 2012 by the U.S. Green Building Council

Flame Seal-TB

After taking an intensive training class, Washington Roofing and Insulation is proud to announce our recent certification as a qualified Flame Seal-TB applicator.

Flame Seal-TB is a waterbased, intumescent coating product that has been certified multiple times as both a Thermal and Ignition Barrier when used over a Spray Polyurethane Foam system. With very low toxicity and low VOCs, the coating qualifies for the LEED IEQ4 Credit for Low Emitting Material - Paints and Coatings.

The certification process for a LEVEL ONE applicator includes passing a detailed test and establishing a Quality Assurance and Control process within their organization.

New LEED Pilot Credits

Yesterday, the U.S. Green Building Council added nine additional Pilot Credits to their LEED Pilot Credit Library. These include:

• Pilot Credit 44: EQ - Ergonomics Strategy
• Pilot Credit 45: SS - Site Assessment
• Pilot Credit 46: EA - HVAC Commissioning
• Pilot Credit 47: EQ - Acoustic Comfort
• Pilot Credit 48: IP - Discovery - Analysis to Support Integrative Process
• Pilot Credit 49 : IP - Implementing Synergies
• Pilot Credit 52: MR - Environmentally Preferable Non-Structural Products and Materials - Prescriptive Attributes
• Pilot Credit 53: MR - Responsible Sourcing of Raw Material and
• Pilot Credit 54: MR - Avoidance of Chemicals of Concern in Building Materials. 

LEED is a rating system developed by the U.S. Green Building Council in March 2000 for buildings that are "designed, constructed and operated for improved environmental and human health performance."

From homes to commercial buildings, LEED credits can be obtained by following specific guidelines for new construction or renovation, schools, retail, core & shell, commercial interiors, operations & maintenance and neighborhood development. 

Complying with LEED standards is completely voluntary, but has been proven to benefit owners with cost-effective solutions that result from green building. To read case studies, profiles, research and resources on green building, visit the U.S. Green Building Council website.