vapor barrier

Second Guessing an Insulation Upgrade

Posted on April 25,2015 by ScottG in insulation

Is there anything worse than getting midway through a renovation and then suddenly wondering whether you've got some important detail all wrong? That seems to be the predicament of William Lucrisia, who's in the midst of an insulation upgrade at his house north of Seattle. "The house was heated by propane," he explains in a Q&A post at Green Building Advisor. It was a cost that was hard to get hold of, especially with some of the design [features] of the house (high ceiling)."

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

Posted on April 25,2015 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.

Understanding Air Barriers, Vapor Barriers, and Drainage Planes

Posted on April 25,2015 by ab3 in air barrier

Is housewrap a vapor barrier? What's the purpose of building paper? 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.

The History of Peeling Paint, Insulation, and Vapor Barriers

Posted on April 25,2015 by ab3 in air leakage

Back in the 1930s, a rash of paint-peeling showed up across North America. One thing that most of these homes had in common was insulation in the walls. Painters put two and two together and decided that the problem was the insulation. According to building scientist Bill Rose, the painters surmised that the problem was happening because insulation “draws water,” and some refused to paint insulated houses.

Smart Vapor Retarders

Posted on April 25,2015 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 April 25,2015 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.

Do I Need a Vapor Retarder?

Posted on April 25,2015 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 April 25,2015 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.

Can Polyethylene Be Used as an Air Barrier?

Posted on April 25,2015 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.

Forget Vapor Diffusion — Stop the Air Leaks!

Posted on April 25,2015 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 April 25,2015 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?

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