Thursday, February 21, 2013

Feel the Warmth

The Kansas snowstorms this week remind us of a story we heard recently about a husband returning home from a hunting trip and bragging to his wife about his adventures, especially going on about the "barn with the foam insulation" the place where the hunters would gather before and after going out.

The metal building's owner, an avid waterfowl hunter, made the decision to provide an air-tight polyurethane foam insulation barrier inside the structure.

"It was amazing," the husband told his wife. "It was so warm inside because of how well it was sealed."

SPF insulation has many uses and many home-owners are finding it more economical in the long run to use it as they build or renovate houses. Steve Thomas, former host of the PBS series, This Old House and Renovation Nation on the Planet Green channel, used spray foam insulation to renovate his 100-year-old home in Santa Fe, New Mexico.

"Spray foam insulation is super insulation. It gives superior R-value, conforms to any shape . . . is a water and air barrier, which makes the house healthier, gives the homeowner amazing energy savings, and allows us to maintain the design integrity of the American Southwest," he said.

So what does spray polyurethane foam insulation have in common with snowstorms?

If the snow is the right consistency and drifts up around your building and on your roof, you can actually feel the warm in your home. It provides a wonderful insulation as it nestles into cracks and crevices, keeping the wind out and the heat in. It actually provides a better shelter than if there is no snow at all.

Snow on outside of building during the
February snowstorm in Kansas City.

But then Mother Nature changes direction and the snow melts and the insulation is gone, unless, of course, you have your building insulated with spray polyurethane foam.

Thursday, February 7, 2013

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.


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