permeance

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Is Oriented Strand Board as Impermeable as They Say?

An interesting look at the vapor permeability of OSB

Posted on Aug 27 2014 by Allison A. Bailes III, PhD

Oriented strand board (OSB) gets blamed for a lot of problems that are really the fault of the designers and builders. Part of the problem, of course, is the perrenial confusion between correlation and causality. OSB hit the market as we really started getting serious about insulation and air sealing.


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Image Credits:

  1. Energy Vanguard
  2. Building Science Corporation
  3. Chris Timusk

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How to Deal With a Vapor Barrier Edict

When a local code inspector insists on an interior polyethylene vapor barrier, plans for a simple addition to a Canadian home suddenly get more complicated

Posted on May 6 2013 by Scott Gibson

Christopher Solar had a simple plan for an addition to his Ottawa home. The one-room structure would have a shed-style roof with a cathedral ceiling and vertical board siding. Solar liked a wall assembly he'd read about at GreenBuildingAdvisor, which consists of exterior foam, batt or blown insulation in the stud cavities and airtight drywall on the interior. An interior polyethylene vapor retarder never entered the picture.

And that's where his story gets complicated.


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Image Credits:

  1. CertainTeed

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Should the Paper Facing of Batt Insulation Face the Inside or Outside?

The surprisingly simple answer follows from the variable permeance of kraft paper

Posted on Feb 27 2013 by Allison A. Bailes III, PhD

If you install fiberglass batt insulationInsulation, usually of fiberglass or mineral wool and often faced with paper, typically installed between studs in walls and between joists in ceiling cavities. Correct installation is crucial to performance. * with a kraft paper vapor retarder in a home, which way do you face the vapor retarder? To the inside of the home or the outside of the home? For many building science questions, the answer is, “It depends.” For this one, however, the answer is clear.

SPOILER ALERT: The answer is in the next paragraph — so if you'd rather wait and find out when you see the movie in the theater, don't read any further.


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Image Credits:

  1. Energy Vanguard
  2. Building Science Corporation (buildingscience.com)

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Do I Need a Vapor Retarder?

Someday, builders will stop asking this recurring question — but unfortunately, that day has not yet come

Posted on Jan 18 2013 by Martin Holladay

UPDATED on May 15, 2015

Every couple of weeks, someone sends me an e-mail with a description of a proposed wall assembly and an urgent question: “Do I need a vapor retarder?” Energy experts have been answering the same question, repeatedly, for at least thirty years. Of course, even though I sometimes sigh when I read this recurring question, it’s still a perfectly good question.


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Image Credits:

  1. Matthew H

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How to Choose Insulation

In this excerpt from their textbook, Green Building, Carl Seville and Abe Kruger discuss insulation and air sealing

Posted on Mar 13 2012 by Carl Seville

[Editor's note:This is an excerpt of the “Insulation and Air Sealing” chapter of Carl's new textbook, Green Building. Carl's publisher, Cenage Learning, has allowed us to make the whole chapter available as a free download.]


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Image Credits:

  1. Cenage Learning
  2. Cengage Learning

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Green Building Vocabulary Disputes

Watch out — sloppy terminology may earn you a scolding from the word police

Posted on Jul 23 2010 by Martin Holladay

As any builder knows, construction terms vary from job site to job site; one carpenter’s furring strip is another carpenter’s strapping. Like carpenters, building scientists are inconsistent when it comes to technical terms — in part because building science is a relatively young field.

In new fields of learning (including building science), vocabulary generally wanders at first, and eventually converges once consensus is reached. Reaching agreement on technical terms is useful. It helps achieve a desirable goal: efficient communication.


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