air barrier

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Air Leakage Through Spray Polyurethane Foam

How thick does a layer of spray foam insulation has to be to qualify as an air barrier?

Posted on Sep 25 2015 by Martin Holladay
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Many builders use spray polyurethane foam as an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both., raising the question: How thick does the spray foam layer have to be to stop air flow? There's a follow-up question, of course: Is the answer different for open-cell spray foam than for closed-cell spray foam?

As with most building science questions, there is a short answer and a long answer. The short answer is that closed-cell spray foam needs to be at least 1 or 1.5 inch thick to act as an air barrier, while open-cell spray foam needs to be between 3.0 and 5.5 inches thick to act as an air barrier.


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Image Credits:

  1. Rick Duncan, Spray Polyurethane Foam Alliance

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The Difficulty of Stopping Air Leakage Between the House and Garage

I-Joists and open-web floor trusses, especially with flex duct running across the garage wall, can be troublesome

Posted on Jun 10 2015 by Allison A. Bailes III, PhD
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A home with an attached garage is usually a home in which people breathe more carbon monoxide (CO). Of course, having an open carport or detached garage is better for air quality (and a feature that usually gets points for you in green building programs like LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. and EarthCraft House), but what if you don't want to give up that attached garage?


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Image Credits:

  1. Energy Vanguard

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Stupid Multifamily Construction Tricks

The big disconnect between architects, engineers, contractors, trade contractors, and raters

Posted on Mar 5 2015 by Carl Seville

Although I spent most of my construction career working on single-family homes, the primary subject of this great website, I find that my current work involves primarily multifamily projects — mostly low-rise and mid-rise apartments that are seeking green building certification.

In these projects, my partner and I continue to see both new and recurring problems that are not resolved in the design phase, only to be pushed down to the field to be figured out — on a tight budget, in a hurry, and often in the cold or rain.


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Image Credits:

  1. All photos: Carl Seville

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Is OSB Airtight?

Builders and researchers in North America and Europe report that air can leak right through oriented strand board

Posted on Dec 12 2014 by Martin Holladay

UPDATED on August 13, 2015

Most builders assume — and GBAGreenBuildingAdvisor.com has long reported — that oriented strand board (OSB) is a good air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.. If a builder uses a high quality tape like Siga Wigluv, Zip System tape, or 3M All Weather flashing tape to seal sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. seams, OSB wall and roof sheathing can act as a building’s primary air barrier.


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Image Credits:

  1. Images #1, 2, 3, and 4: Richard Pedranti
  2. Image #5: Niall Crosson
  3. Images #6, 7, 8 and 9: J. Langmans, R. Klein, and S. Roels
  4. Images #10 and #11: Tom Schneider / Prosoco

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The Importance of Defining the Building Enclosure

This new home has a murky boundary between inside and outside

Posted on Dec 3 2014 by Allison A. Bailes III, PhD

The photo at right shows a common problem in new homes. It's also one that can make it difficult to pass the blower door test required by many building codes these days. If I tell you that the wall pictured here separates two rooms in a basement and one of them is not conditioned, can you see the problem? If so, how many mistakes do you see here?


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Image Credits:

  1. Energy Vanguard

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What Architects Need to Know About Attic Kneewalls

If you want your building enclosure to perform well, you need to start with good design details – especially for kneewalls

Posted on Jun 25 2014 by Allison A. Bailes III, PhD

We were working on a project, so we got a set of plans to get started. It includes the attic kneewall and vaulted ceiling section you see at right. This is typical of plans that architects draw, and builders build houses this way all the time. Unfortunately, it contains several errors. Can you spot them?


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Image Credits:

  1. Energy Vanguard
  2. Southface Energy Institute

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Understanding Air Barriers, Vapor Barriers, and Drainage Planes

These three terms refer to different materials that are easy to confuse

Posted on Feb 12 2014 by Allison A. Bailes III, PhD

Is housewrap a vapor barrier? What's the purpose of building paperTypically referring to Grade D building paper, this product is an asphalt-impregnated kraft paper that looks a lot like a lightweight asphalt felt. The Grade D designation has come to mean that the building paper passes ASTM D779 (minimum 10-minute rating with the “boat test”) and different products are called out as “30-minute” or even “60-minute” based on D779 results. At times confused with roofing felt, roofing felts and building paper differ in two ways: felts are made of recycled-content paper, building papers of virgin paper; felts are made of a heavier stock paper; building papers a lighter stock. See also roofing felt.? Who'll stop the rain? I've covered this topic in various forms before, but the confusion about what the different building materials do is so widespread that I have to keep coming back to it.

I'm going to keep it simple here so maybe we can get a few more people to use the proper terms, and especially to know when not to use the term “vapor barrier” ... and when not to use it.


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Image Credits:

  1. Energy Vanguard

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A Review of Siga Wigluv Air-Sealing Tape

To seal air leakage at OSB seams, first use a primer, and install the Wigluv tape with a J-roller

Posted on Feb 11 2014 by Matt Risinger

Every house needs four control layers. In order of importance, these layers need to provide:

  1. 1. Water control
  2. 2. Air control
  3. 3. Vapor control
  4. 4. Thermal control

The building codes have dictated the levels of thermal control and vapor control that builders must adhere to, and nearly every builder in the U.S. knows off the top of their head the R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of the insulation in their walls and attics.


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Image Credits:

  1. All photos: Matt Risinger

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Using Interior Poly As an Air Barrier

Alaskan builders still use a technique developed in the 1980s by Canadian superinsulation pioneers: the use of interior polyethylene as an air barrier

Posted on Feb 4 2014 by Martin Holladay

Back in the 1980s, Canadian energy experts urged builders to use interior polyethylene as an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. material. If the poly was installed conscientiously, and all seams were sealed with Tremco acoustical sealant, the approach worked well — at least in cold climates.


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Image Credits:

  1. Colc Climate Housing Research Center

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Air Leaks in Homes Insulated With Spray Foam

After using spray foam to create an air barrier in an older brick home, we were surprised to discover a high rate of air leakage

Posted on Nov 19 2013 by Greg Labbe

If you’re retrofitting a vintage brick building without an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both., don’t count on the spray foam to create a perfect air seal. If you plan to use the spray foam as your air barrier, it's important to test your work before you cover it with drywall so you can seal any air leaks.


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Image Credits:

  1. Greg Labbé

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