vapor retarder

What Happens When You Put a Plastic Vapor Barrier in Your Wall?

Posted on March 31,2015 by ab3 in polyethylene

A lot of people have heard advice about vapor barriers and vapor retarders. Many of them have walked away confused. A big part of the problem, I think, is that they've been told what to do — "Put it on the warm-in-winter side," or "Never use one" — but they haven't had the physics of what happens explained to them.

Smart Vapor Retarders

Posted on March 31,2015 by AlexWilson in polyethylene

Nowhere in building design has there been more confusion or more dramatic change in recommended practice than with vapor retarders. Thirty years ago, we were told to always install a polyethylene (poly) vapor barrier on the warm side of the wall. Then we were told to forget the poly and go with an airtight layer of drywall (airtight drywall approach). Insulation contractors, meanwhile, often said to skip the vapor barrier; we need to let the wall or ceiling cavity dry out. It made for a lot of confusion. And I’m not sure we’re totally out of the woods yet.

How to Deal With a Vapor Barrier Edict

Posted on March 31,2015 by ScottG in MemBrain

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.

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

Posted on March 31,2015 by ab3 in Batt insulation

If you install fiberglass batt insulation* 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.

Do I Need a Vapor Retarder?

Posted on March 31,2015 by user-756436 in perm

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.

Vapor Barriers Redux

Posted on March 31,2015 by ScottG in Building Science

Few topics in building science seem to have caused as much confusion as the use of a polyethylene vapor barrier in exterior walls. Once routinely used by builders to prevent the migration of interior moisture into wall cavities, polyethylene is no longer recommended for houses unless they’re built in extremely cold climates.

Joe Lstiburek Discusses Basement Insulation and Vapor Retarders

Posted on March 31,2015 by user-756436 in basement insulation

Dr. Joseph Lstiburek needs little introduction. The well-known Canadian engineer is a principal of the Building Science Corporation in Massachusetts. He’s also a regular GBA podcaster and Fine Homebuilding author. On Wednesday, June 6th, I attended an all-day building science class presented by Dr. Joe in Westford, Massachusetts. As usual, his presentation combined salty language, corny jokes, light-hearted insults, and rock-solid building science information.

European Products for Building Tight Homes

Posted on March 31,2015 by user-756436 in air sealing

A new distributor of building products from Europe has set up shop in Brooklyn, New York. The company, called Four Seven Five, was recently founded by a trio of Passivhaus consultants: Floris Keverling Buisman, Sam McAfee, and Ken Levenson. Four Seven Five plans to import air-sealing products and ventilation fans from Germany, as well as HVAC equipment from Denmark.

Can Polyethylene Be Used as an Air Barrier?

Posted on March 31,2015 by ScottG in PERSIST

Polyethylene sheeting has had its ups and downs as a preferred building material over the last 20 years. At one time, it was routinely used in wall assemblies as a vapor barrier. As building scientists learned more about air and moisture movement through walls and ceilings, however, they began to advise builders that an interior vapor retarder is better than an interior vapor barrier, and the perceived usefulness of poly plummeted.

Vapor Profiles Help Predict Whether a Wall Can Dry

Posted on March 31,2015 by Peterbilt in drying potential

Today’s walls, roofs, and floors are better insulated, tighter, and made with a much greater variety of components than they used to be, making them a lot more susceptible to moisture problems when they get wet. Compared to the old days, today's walls and ceilings are more complicated and can be very slow to dry.

Forget Vapor Diffusion — Stop the Air Leaks!

Posted on March 31,2015 by user-756436 in air barrier

Last week’s blog answered some common questions about vapor retarders. This elicited a comment from Bill Rose, research director of the Building Research Laboratory at the University of Illinois in Champaign. “We might imagine a future in which the building code sections that address the vapor barrier would all go blank,” Rose wrote.

Vapor Retarders and Vapor Barriers

Posted on March 31,2015 by user-756436 in polyethylene

Although building science has evolved rapidly over the last 40 years, one theme has remained constant: builders are still confused about vapor barriers. Any energy expert who fields questions from builders will tell you that, year after year, the same questions keep coming up: Does this wall need a vapor barrier? Will foam sheathing trap moisture in my wall? How do I convince my local building inspector that my walls don’t need interior poly?

Air Barrier or Vapor Barrier? - Building Science Podcast

Posted on March 31,2015 by JoeLstiburek in air barrier

_This podcast series is excerpted from a two-day class called "Building Science Fundamentals" taught by Dr. Joe Lstiburek and Dr. John Straube, of Building Science Corporation._

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