I never thought I could get excited about a vapor barrier installation, but as I researched the steps required to make my house truly energy efficient, I soon realized that as an integral part of the system required for a tight house envelope, that layer of translucent plastic had an immense role to play.
Cross-sections of my house walls that show the location of the vapor barrier in a cold climate. Click to enlarge.
It wasn't easy getting information
about vapor barriers (the fact that they are also known as "vapor
retarders" and "moisture barriers" didn't help much).
In this page, I describe:
This is the standard type of polyethylene vapor barrier.
It comes in widths from 12 inches to 20 feet and lengths of 60 to 375 feet. Our local store stocked the 100-foot roll, ten feet wide, which is the most common for this kind of application. This will cover 1,000 square feet, with a minimum of joints.
When buying vapor barrier, look for the gauge stamped on the product: .006 (.152 mm) represents what is referred to as "6-mil", which is the desirable thickness.
Any old plastic film will NOT do: the product in the photo has the National Standards of Canada acceptance number and the fire rating stamped on. This is important. Other countries have an equivalent label.
In order to be effective, the vapor barrier must be completely sealed.
Where pieces join and around windows and other components, a special red tape, called Tuck Tape® here, is used. It's quite expensive, but there is no substitute for it.
In corners and other uneven surfaces, acoustic sealant – the black stripes seen here – is used. They tell me there's no substitute for acoustic sealant either, which has the advantage of remaining flexible permanently.
Acoustic sealant is applied with a caulking gun. The large size
represents quite an economy, so it's worthwhile investing in a giant
caulking gun if you're going to carry out your own vapor barrier
Once the vapor barrier installation is completed provisions must be made for supporting the drywall -- and that applies to the ceiling as well, of course.
That's where strapping comes in. (Strapping is also known as furring strips.)
Strapping was applied at precise intervals, to correspond with the measurements of the drywall panels.
Measurements must therefore be very exact.
Furring strips come in very long lengths, so it takes two people to put them up on the ceiling.
The carpenter used a nailing gun to fasten it to the ceiling joists and to the wall studs.
This wall is all strapped and ready to receive drywall.
Strapping (which is just strips of soft wood measuring 3 inches wide by 3/4 of an inch thick) may seem inexpensive, at less than three dollars per 10-foot length, but when you're doing a whole house and using hundreds of lengths, the cost quickly adds up!
This short piece of wall required about eight lengths, for instance.
The last areas to get their vapor barrier were the two cathedral ceilings.
We started with the kitchen-dinette. With regular polyethylene vapor barrier, wrinkles don't matter, so the plastic just got stapled to the existing wood supports.
But each staple makes two tiny holes in the plastic, and that had me worried.
This picture shows how all the staples have been covered with tape -- we used Tuck Tape. Note how the electric box has been sealed as well.
It's crucial to seal every place where the heat could escape.
The joint where the wall and ceiling vapor barriers meet was sealed with acoustic sealant, then tape, then a strip of wood.
On this other cathedral ceiling (the sunroom-office one), a different technique was used.
The strapping went first, then the vapor barrier.
This ceiling was very uneven so the strapping had to be leveled. Here you see the men inserting shims between the rafters and the strapping.
Technically, the kind of spray foam insulation used here – BASF Walltite
(blue foam) – does not require a vapor barrier installation, but I
wasn't taking any chances.
Here's that ceiling, with its precise grid of wood, ready to receive the vapor barrier, then the drywall.
After all those surfaces were taken care of, only the crawlspace floor
remained. Because it's dirt, it's very important to prevent the natural
moisture from entering the area, especially since I had gone to the
expense of insulating the outer walls -- that crawlspace is under the
kitchen-dinette, which is exposed to the north winds.
Sealing that floor also keeps the space a bit warmer, which is good for the water pipes that go through there. One of those pipes is the water supply directly from the well.
Following the spray foam insulation specialist's advice, the crawlspace
vapor barrier was taken up the walls by at least one foot, and it was sealed to the foam insulation by two lines of black acoustic sealant.
We used acoustic sealant because tape alone would not have been sufficient, due to the irregularities in the blue foam insulation. Tape was used for fastening the edge of the plastic to the wall, and also on the seams, as can be seen in the floor portion.
No doubt the acoustic sealant would have been enough, and the taping
looks kind of messy, but the extra plastic above the acoustic sealant
had to be dealt with, and trimming it close to the sealant was not an
Crawl space vapor barriers vary and your own crawl space vapor barrier installation will no doubt differ from this one; what's important is to understand the principle, which is that a vapor barrier is only effective if it's continuous.
Keep that in mind and you can't go wrong.
To seal or not to seal the crawlspace? It's pretty obvious that with a
vapor barrier installation that is combined with blue spray foam
insulation on the crawl space walls and a tightly sealed 6 mil
polyethylene vapor barrier on the floor, you're likely to end up with a
pretty tight crawl space, impervious to outside air and humidity.
Whether this is desirable or not depends on your climate; therefore, your best bet is to contact your local authority and ask what the recommended practice is for your geographical area.
That goes for vapor barriers in general.
To achieve optimum tightness, vapor barriers are only one part a system which includes insulation and sealing air leaks (by caulking, for instance).
The following aspects have already been covered elsewhere on this site:
The air leak sealing part will be treated separately.
(Doesn't that window look like a framed photo hung on the wall or a
Photoshop trick? Well, it was the actual view from that old window!)
For the best performance, the vapour barrier installation must be made as air tight as possible by:
Since vapor barriers are applied by stapling, and I don't like
the two little holes that each staple makes, I taped over all staples,
too, for good measure.
The reason for the plural is that this vapor barrier installation was multifaceted. We installed:
Each area had its own requirements.
Polyethylene is not the only material that can be used as a vapor barrier. Foil insulation is an excellent material, but of course it's more expensive because it also acts as additional insulation. (Foil insulation is also known as foil vapor barrier and radiant barrier insulation.)
This close-up shows both sides of the type of foil insulation that we used on the kitchen-dinette walls.
We describe this installation in full step-by-step detail on our Foil Insulation page.
Our Foil Insulation Page has a section on using reflective insulation as an attic vapor barrier and/or as a basement vapor barrier.
The use of vapor barriers in attics and basements depends largely on the climate and you have to be very careful to apply them in the right place. It's important to investigate this and to use the application that is recommended for your area by the local building code. Your vapor barrier installation may differ considerably from mine.
Because of my permaculture background, and my desire to stop giving the power company a large percentage of my income, I would have done all this work anyway. But for others, the financial incentives may have added the necessary motivation to take the first step towards a more sustainable lifestyle.
The "Stimulus Package"
If you've been following this adventure, you will know there were financial incentives
attached to increased home energy efficiency in Canada. The federal
program has come to an end, but some provincial programs are still in
place. No matter where you live, there's probably an incentive plan in
place to help you achieve better energy efficiency.
How effective were all the efforts described in these pages? We found out when my second blower door test took place. (Luckily, I had been given a 3-month extension due to the shortage of contractors in my region.)
You can read all about that on my second door blower test page. That concluded the energy audit that took place with the first door blower test.
In addition to revealing a certain lack of leaks, the results determined the house's eligibility for government grants totalling over four thousand dollars.
GREEN PLASTIC? I looked, and couldn't find any truly "green" vapor barrier materials.
If you know of any, please let me know and I will gladly list them here.
Meanwhile, the manufacturer claims that his product is reusable and recyclable, and I've read somewhere that "clear polyethylene's content is up to 80 percent "reprocessed" material, which would make it environmentally sustainable."
The cost of this could be uneven quality and poor tear and puncture resistance, so I checked with the manufacturer of the product I used and was assured that their vapor barrier products are made with 100% virgin resins.
You might want to do this kind of checking before proceeding with your own vapor barrier installation. Or you might want to take the chance on recycled material. And by the time you read this, there may be some greener alternatives on the market... the green technologies are constantly evolving, after all.
A good insulation system, which includes a properly done vapor barrier installation, makes a house very energy-efficient so in spite of the materials used, it's hard not to classify this case as one where the end justifies the means.
Therefore, why is it that none the green building books that I looked at mentions their existence?
It's no surprise, then, that so many people visit this page every day!
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clicked to your site and found a great wealth of information. I'm about
the least tool oriented person there is around, but I'm passionate
about many of the topics you write about. And I find the writing to be
very well done and informative even for a non-handy person like me. Well
Prague, Czech Republic
I would just like to thank you for maintaining this resource. It's essential that information about environmental issues are easily and broadly accessible.
Thank you so much for sharing your exquisitely well-told stories! I have spent the last 2 hours reading the whole saga, and I appreciate all of the detail that went into your decision making. I hope you are enjoying your green home with cozy surroundings and energy efficiency.
Thank you for taking the time to write down your experiences. It is truly a valuable service.
Thanks for all the info on this site, it is very thorough.
Very well documented and I appreciate the work and the effort you have put into this.
Hey! Just wanted to compliment you on
your site! I'm a new, first time homeowner, with a dirt crawlspace and
have searched for hours on how to set it up.
Living here in Montreal, and the conditions aren't easy on a house and this site sure helped to answer some questions.
Thank you for displaying your work and experience!
Have to say I absolutely love your site. Really complete, well thought out, and has me clicking from page to page...
I just wanted to say I love your site! Well done!
Love your web site. You are an inspiration to me. I am 66 and I want to build a small green home on my land. [...] Your green home looks beautiful. I wish you luck in all your endeavors!
A few years ago, I bought this fixer-upper for $10,000.
It had been vacant for six years, had no water supply, needed a new roof, and was likely to conceal an unsuspected number of nasty flaws.
Don't believe me? See these "Before" pictures.
My intention was to turn it into as "green" as home as I could, within my physical, financial, and geographical limits – and to share this adventure with you, step-by-step and dollar-by-dollar.
I'm not quite finished, but I do have a few "After" pictures to show.
If you want to follow me on this exciting adventure, you can subscribe to this site by RSS feed -- see the box below the navigation bar on the left.