Vapor Barrier Advice


We are lucky to have another guest blogger today! Today’s post comes from a Super Cubes client in Florida, Sterling Cox, founder of Southworth LLC, who is converting a one-trip 20’ container into a prototype living space, to be used as a production model. You can follow the pictures they are posting to Instagram at Or, if you’re in the Jacksonville area, they’ll be debuting the finished product at a festival called OneSpark from April 9th-13th ( Like so many other container projects, they are balancing their goal of using green building practices with being cost-conscious and also energy efficient. They recently added a vapor barrier to the container before insulating it.

Tonight's process:

We adhered a layer of Tyvek Home Wrap to the inside of the container for the vapor barrier using 3M all-purpose spray adhesive. This process was difficult with two people, and I imagine nearly impossible with...

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In the basement of my house (built in 1900) in NE Ohio…Half of the basement floor is finished, the other half is dirt floor covered by a few inches of crushed stone gravel. I had a mold issue, so looking to put a vapor barrier over the gravel floor. Also am getting slightly elevated radon level about about 4.9 to 5.1. I’m hoping maybe to solve both issue with one fix.

Here’s my dilema…I’m looking for a vapor barrier material that would withstand occassionally walking across it. The furnace is located on the gravel side of the basement, as well as we use that area for storage (holiday decorations, etc). There wouldn’t be heavy traffic, but would need to walk over to change furnace filters, swap out holiday decorations, etc. Can anyone recommend a product that would act as a vapor/moisture barrier that could withstand some foot traffic? Also, the barrier would be installed on top of the gravel, so looking for something that wouldn’t be easily punctured by the crushed stone...

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• Massachusetts' building codes are mandatory for all buildings statewide. Local jurisdictions may amend the codes only with state approval.
• For more information about statewide codes and enforcement issues, visit

Massachusetts Building Code
Vapor Diffusion
Molecules of water vapor will move through building materials, driven by differences in vapor pressure from one side of the material to the other; higher vapor pressure on one side will drive water vapor through the material to the lower pressure side. The vapor molecules move right through the molecular spaces in the building material in a process called diffusion, and different materials have different diffusion rates.

The code requires that certain materials be installed in the envelope assembly that will limit vapor diffusion to a slow enough rate that moisture does not accumulate within the system. Such materials are considered "vapor retarders" (sometimes called...

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You have probably heard a lot of advices about vapor barriers and vapor retarders. And maybe you have walked away, even more confused than before. The problem, I think, is that you've been told what to do "Put it on the warm-in-winter side," or "Never use one" but you haven't had the physics of what happens explained to you, and that’s why I think you didn’t understand it.

In this article, I'm not going to get into the details of vapor barriers, I'm simply going to explain what happens in a wall cavity with and without a plastic vapor barrier installed. Here is said, if you have used plastic paint inside or outside on the walls it is to be seen as vapor barriers or vapor retarders as these paints will prevent the vapor to move or even prevent the condensation inside a wall to evaporate.

Plastic on the inside
1. Hot Humid Weather
I'm writing this article because I see a lot of houses having problems with humidity on the inside or their outside walls, or even...

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Best practices: Vapor retarders and air infiltrationbarriers

Vapor retarder overview

Editor's Note: This story is excerpted fromThe Rehab Guide: Exterior Walls -- one in a series of new guide booksproduced by the U.S. Department of Housing and Urban Development (HUD) to keepthe construction industry abreast of innovations and state-of-the-art materialsand practices in home construction & remodeling.

Vapor retarders first appeared in building construction in the 1920s. Earlytheories held that moisture vapor will migrate from a region of highconcentration towards a region of low concentration along a linear path. Theamount of moisture transfer is dependent on the differences in concentration andthe vapor permeability of the membrane separating the two regions.

This is the theory of vapor diffusion, which viewed the flow of moisturevapor directly analogous to the conductive flow of thermal energy. In thistheory, air movement, and the moisture...

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I am also in N. Virgina (Arlington) in a cape cod style house built in the late 40's. I finished our basement 2 years ago. It went from a dark mildly musty space to what's now a nice cozy dry one.

Among the work, I first had several foundation cracks filled with urethane ("crack team"). I also regraded to allow the 3 day rainstorm runoff that we get often enough (couple times every year!) to go elsewhere instead of pooling next to the foundation and finding it's way in. Also added a second downspout out front (if one spout gets blocked by oak leaves in the middle of a storm, the water still can flow without running over the gutters down to the wall).

As for insulation of the walls, first I went around the inside perimeter (rim joist area) and sealed every last air gap with caulk, etc. and then applied solid pieces of foam in each space, followed by spray insulation around the edges. Very much a pain, but the results were worth it. (another option would have been to...

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No Primer Required Extended Temperature Range Translucent - Stud Identification Superior UV Exposure Resistance Lighter Weight Energy Savings Ease of Installation Meets LEED Criteria

An innovative air and vapor barrier membrane
3M™ Air and Vapor Barrier 3015 is an innovative, proprietary, translucent air and vapor barrier that uses non-asphaltic-based adhesives, which permit an extended application temperature range between 0°F to 150°F. It does not require primer for most substrates and can withstand up to 6 months of direct UV exposure. The 10-mil engineered sheet membrane self-seals against nail fasteners and penetrations. It also conforms to contours for continuous bonded contact. Available in widths up to 4 feet wide, the air and vapor barrier can be specified locally and delivered globally.

No Primer Required

3M™ Air and Vapor Barrier 3015 does not require a primer for most substrates so fewer products are needed on a jobsite. Worker productivity can increase,...

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The last thing you want your customers to envision when thinking of a concrete floor is a damp, cold basement slab. One of the reasons those old basement floors were like that was because they had no vapor barrier beneath them, leaving an easy path for water vapor from the soil to migrate into the slab, assuring that the cold clammy damp feeling never went away. And dampness is only part of the problem, water vapor moving through a concrete floor can delaminate sealers and overlays, discolor acid stains, produce efflorescence on the surface, damage aggregates, cause the slab to curl, and condense beneath objects on the floor.

But it doesn't have to be that way. On new interior slabs, moisture can be easily controlled and mostly eliminated. Here is information to help you understand how moisture moves in a slab and how using a vapor barrier can help control the problem.

Vapor Barrier Information


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Vapor barrier insulation is insulation which comes packaged with a vapor barrier, eliminating the need to install one. Typically, this form of insulation comes in rolls which can be unfolded and cut to create strips of insulation for installation in a structure. The advantage to vapor barrier insulation is that it eliminates the additional step of installing a vapor barrier. The disadvantage is that it cannot be used in a structure which already has a vapor barrier, because two vapor barriers can create a vapor trap, which is very undesirable.

In most regions of the world, vapor barriers are strongly recommended. A vapor barrier prevents water from entering the walls, floors, and ceilings of a structure, preventing rot, mold, and mildew. Typically, the vapor barrier faces the living quarters of the house, preventing moisture from leaching from the interior of the house to the walls. In very humid climates, the vapor barrier may be placed on the outside, so that moist air...

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High-Performance Vapor Barriers

On more than one occasion, I have had to slither across the damp dirt in a crawl space. I would emerge from the space encrusted with dirt. Sometimes, the dirt would smell of chemicals. The air in the crawl space was heavy with a dank, musty smell.

Three years ago, a friend of mine was considering leasing a house. He asked me to inspect it, as the lease had an "option to buy" clause. The house had been vacant for approximately one year. As I crossed the threshold into the home, I knew instantly that this modern house had been built over a crawl space. I asked him about this. He said that there was a lower level storage area. The house had been built on a hillside. We went around the back of the house. Yes, there was a storage area alright. The entire house was constructed over a giant walk-in crawl space. I guess you would call it a walk-space in this instance. In any event, the musty odor was overpowering. There was gravel spread...

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W.R. Meadows

Form stakes sealed to the barrier prevent vapor intrusion. VaporStake in Chino Hills, CA

Install boots around all penetrations and blockouts. Fortifiber in Reno, NV

To be effective, a vapor barrier must be installed in a way that prevents any water vapor from getting to the slab. ASTM E 1643, "Standard Practice for Installation of Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs," provides details, but here are a few tips:

Most exterior slabs do not need a vapor barrier. If you are going to seal an exterior slab, find a sealer that transmits water vapor (breathes). For some tips on this, see Sullivan's Corner. In general, place the concrete slab directly on top of the vapor barrier, with the subbase below. If the subbase is sharp angular gravel, a thin layer of sand can be placed on top of the gravel subbase next to the vapor barrier. See below for more discussion on this. The vapor barrier can be placed under...
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This article is reprinted here with permission from Backpacking Light Magazine.


Occasionally during the FAQ portion of my slideshows, and frequently at the start of every winter, I receive questions about vapor barrier liners (VBL’s). The content and tone of these questions suggest a general misunderstanding of and slight mystery about them, so in this article I’ll attempt to offer a comprehensive review of VBL’s based on my understanding of and experience with them – basically, what they are, how they work, and when to use them.

I believe that VBL’s can be a critical and pivotal component of winter clothing and equipment systems—and, to a lesser degree, shoulder-season systems. Unfortunately, there is not much information available on VBL’s—an internet search returns information that is mostly outdated, incoherent rambling, or mistaken. My hope is that this article will result in (1) a greater understanding of VBL’s and (2) increased use of...

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I have pergo installed in a kitchen and recently was notified by my tenants there are small bubbles of water coming up between pergo planks. The property is located in Tucson, AZ. This is a very dry climate, except in the summer during Monsoon season, which even then the humidity might hit 60% on a very rainy day.

The localized area is right in front of the sink cabinet. The pergo planks are now starting to slightly buckle. I contacted my home owners insurance company and they sent out an Adjustor. He was unable to determine where the water was coming from. He then contacted a water leak detection contractor. The water detection contractor found the swamp cooler on the roof could be the cause of water slowing accumulating under the pergo. He stated the overflow valve for the unit needed to be adjusted and the timed overflow spilling of water that drains thru pvc pipe was entering thru the roof near the sewer vent pipe. Upon inspection of roof vent pipe, this roof area is...

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We all make mistakes (including me) but I would hardly characterize Lsiturbrek as 'the most respected and studied man in the country' in this matter since his advice conflicts with most all building codes for vapor barriers and proper basement contruction across the US. (maybe Piffin is in Canada?)

But after Domino's great handling of the vapor issues in a basement (with some disagreement) I thought I'd give my 2 cents toward his last response yet again:

First, vapor flow into a basement is from 2 sources:

One is from the wet ground into the basement thru the foundation...

The other is from the living space thru the framed wall toward the foundation.

Without addressing BOTH these directions of vapor flow we are all talking passed one another.



Vapor flow in from the soil, thru the foundation, occurs despite any temperature differentials, because the the soil...

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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.

In this article, I'm not going to get into the details of vapor barriers or all the possible scenarios of different wall assemblies and moisture loads. I'm simply going to explain what happens in a wall cavity with and without a plastic vapor barrier installed.

Plastic on the inside

1. Hot Humid Weather

I'm writing this article because one of our HERS raters came across a house in Charleston, SC that had poly under the drywall, on the interior side of the wall assembly. If you're at all familiar with the climate in Charleston and understand moisture, you know that can't be a good thing.

I was there one day in June a few years ago...

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