My Green Home Gets All Sealed Up:
Vapor Barrier Installation

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). That's why I wanted to put together a guide that was as complete as I could derive from my own experience, hoping that you won't have to go through the same frustrations as I did. This page is the result.

Vapor Barrier Installation, Step-by-Step

In this page, I describe:

• how we sealed up the house envelope with a vapor barrier;
• the different kinds of vapor barriers we used; and
• the techniques we used in order to achieve as tight a seal as possible.

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 installation.

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.

Cathedral Ceilings Required Special Treatments

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.

Vapor Barrier In Crawl Space

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 option.

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.

Sealing Crawl Space

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.

A Tight House Is A Good House

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:

• home insulation,
• spray foam insulation, and
• foil insulation

The air leak sealing part will be treated separately.

Why Use Vapor Barriers?

In cold climates, insulation alone is not enough to keep our costly heat from escaping. Given the slightest opportunity – in the form of a tiny hole, crack or improperly caulked joint, our precious heat will find its way out in an alarming way.

Once we understand the principle that warm air is attracted to cold air, and not the other way around, it should become almost a matter of pride to keep that warm air in!

Although some heat is lost by conduction through the insulation, most of the heat loss in a building is through air movement, or air infiltration, through the walls.

That's where vapour barriers (with or without the "u") come in. What is a vapor barrier (or vapor retarder)? It's merely a continuous sheet of impermeable material installed on the inside, i.e. the warm side of the wall, designed to keep the warm air from escaping through or around the insulation and other building components.

This applies to the cold climate where I live, in Eastern Canada. Hot climates are another matter.

There are several reasons for wanting to keep the warm air inside the house through a vapor barrier installation; among them:


3. Preventing the deterioration of the building materials (wood, insulation) by moisture (hence the alternate term moisture barrier) -- as in this photo taken in my house during deconstruction.

(It's obvious that the kraft paper vapor barriers used in the old days didn't do the job!)

In winter, as the heated air meets the cold air, it creates condensation, which is water of course. The vapor barrier is designed to prevent this phenomenon from taking place and damaging your the invisible parts of your walls and ceilings. ((That explains why the closed-cell, high-density type of insulation doesn't require a vapor barrier: it's waterproof.)

4. Health problems caused by molds.

(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!)

"Continuous" Is The Keyword

For the best performance, the vapour barrier installation must be made as air tight as possible by:

• taping all the seams with special tape,
• using plastic boxes around electrical boxes, and
• caulking any penetrations through the vapor barrier by things such as wires and plumbing pipes.

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:

1. 6 mil polyethylene on walls, over low-density spray foam;
2. 6 mil polyethylene on flat ceilings, over low-density spray foam;
3. 6 mil polyethylene on cathedral ceilings, over high-density spray foam;
4. 6 mil polyethylene on one wall, over fiberglass batts;
5. foil insulation/vapor barrier on walls, over low-density spray foam;
6. vapor barrier paint will be applied to the bathroom walls and ceilings, partly to test the product, but mostly to compensate for the fact that we're not using the special cement drywall there.

Each area had its own requirements.

Foil Insulation As Vapor Barrier

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.

Attics And Basements

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"

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 NOTES

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!

Other Strategies I'm Using For More Energy Efficiency

FOIL VAPOR BARRIER A.K.A. reflective insulation - a versatile material! SPRAY FOAM INSULATION We used not one, but two kinds. See both.

ATTIC DOOR INSULATION Attic ladders will let heat escape, unless... WATER HEATER INSULATION Fifteen minutes to save lots of money! Here's how.

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