Do I need a vapor barrier?

[Greg R Bradley]

Wow. Great information here, but I'm not sure I'm not more confused than I was to start with.... That's what comes from expecting easy answers I guess.

Easy answers do seem to turn out wrong. Building professionals have made some big mistakes. Many requirements in building codes have proven to be mistakes as people rushed for the "correct" answer.

I would strongly suggest you follow the link I provided in post #8 at http://www.buildingscience.com/docum...vapor-barriers and then look around the entire Building Science website as linked to by Larry Edgerton in post #10. There is lots of info there about different requirements for different climates and advantages and disadvantages of different types of insulation.

Even though a building professional my use the term Vapor Barrier for a Class I Vapor Retarder, it is more likely being used by non-professionals because it sounds better.

A relatives house on the Canadian prairie built to tight standards had some big challenges to fix. They simply tried to push the state of the art in insulation too hard before test results showed problems.

IMHO, Mike Holmes is dangerous and that show is about as realistic as Reality TV in general. There are different code requirements and different best practices in different areas but he has suggested code violations as the right way to do things.

You don't even want to start down the path where some houses are being built that are too tight, flunk the blower tests, and need holes opened so they can breathe. That insanity applies to new construction houses and not to your shop upgrade.

Lastly, don't forget that your shop is unlikely to be cooled all the time like a house in your area would be in the summer. There is an issue that may apply to your region where the outside of the structure gets water soaked and then the moisture is driven into the structure when the hot sun hits the wet outer layers.

[Mel Fulks]

James ,the word BARRIER is a little stronger but not an absolute term . Nets are barriers but some fish go through them. And I don't believe anyone is dumb enough to think that "vapor barrier" meant no vapor was going to get through. Professionals applied the term ,it was not a secretarial mistake. They chose the term and now we are making a mistake in useing it !? I think they have backed off in view of how AC is used and to push more expensive products.

[Chris Friesen]

You don't even want to start down the path where some houses are being built that are too tight, flunk the blower tests, and need holes opened so they can breathe. That insanity applies to new construction houses and not to your shop upgrade.

I was under the impression that current state-of-the-art for very cold climate was to build the house as sealed as possible and then add a powered energy-recovery ventilator to allow for controlled replacement of the air. Am I incorrect?

[James Conrad]

James ,the word BARRIER is a little stronger but not an absolute term . Nets are barriers but some fish go through them. And I don't believe anyone is dumb enough to think that "vapor barrier" meant no vapor was going to get through. Professionals applied the term ,it was not a secretarial mistake. They chose the term and now we are making a mistake in useing it !? I think they have backed off in view of how AC is used and to push more expensive products.

Mel, there was confusion among the trades, professionals and the consumer market with the initial use of the word barrier applied to broad market of products in turn causing moisture issues in many homes. The change clarified in the 2009 ICC presented classification to help people understand and apply these products correctly based on a perm rating. So, it wasn't a matter of people being stupid, but a failure to understand building science in a rush to make homes more efficient, it's more than the semantics of words.

[Larry Edgerton]

Something to keep in mind as far as moisture buildup is that if air can not pass through a cavity moisture is less likely to collect. If no air is passing through a cavity the only way that moisture can collect is from diffusion, moisture passing through the wall coverings.

Quoted from "Builders guide to cold climates"

{Quote}

The differences in the significance and magnitude of vapor diffusion and air transported moisture are typically misunderstood. Air movement as a moisture transport mechanism is typically far more important than vapor diffusion in many[but not all] conditions.The movement of water vapor through a 1" square hole as a result of a 10 Pascal air pressure difference is 100 times greater than the movement of water vapor as a result of vapor diffusion through a 32 sq. ft. sheet of gypsum board under normal heating and cooling conditions.

In most climates, if the movement of moisture laden air into a wall or building assembly is eliminated, movement by vapor diffusion is not likely to be significant. The notable exceptions are hot humid climates and rain soaked walls experiencing solar heating.

Furthermore, the the amount of vapor that diffuses through a building is a direct function of area. That is, if 90% of the building enclosure surface area is covered with a vapor retarder, then that vapor retarder is 90% effective. In other words, continuity of the vapor retarder is not as effective as the continuity of the air barrier. For instance, polyethylene film which may have tears and numerous punctures present will act as an effective vapor barrier, whereas at the same time it is a poor air barrier. Similarly, Kraft faceing on fiberglass insulation batts installed in exterior walls acts as an effective vapor retarder, in spite of the numerous gaps and joints in the craft facing.

It is possible and often practical to use one material for an air barrier and a different material as a vapor retarder. However, the air barrier must be continuous and free from holes, whereas the vapor retarder need not be.

In practice, it is not possible to eliminate all holes and install a "perfect" air barrier. most strategies to control air transported moisture depend on the combination of an air barrier, air pressure differential control and interior/exterior moisture control in order to be effective. Air barriers are often utilized to eliminate the major openings in building enclosures in order to allow practical control of air pressure differentials. It is easier to pressurize or depressurize a building enclosure made tight through the installation of an air barrier than a leaky building enclosure. The interior moisture levels in a tight building enclosure are also much easier to control by ventilation and humidification than those in a leaky building.

{end quote}

Drywall is an air barrier by the way so it is not some mystery product.

All of these strategies will fail in this country at this time for many reasons. Lack of education on the part of builders, people in Washington writing codes written by lobbyists that have no clue what they are doing, especially the one size fits all bologna in a country with many climates. Another big one is that way the construction industry is set up in the first place, where productivity is the number one concern, and where tradesmen do not make enough to cover their investment and make a profit.

The way it is run now and the mentality that we have to have more quantity at the expense of quality does not allow for true craftsmen to make a living generally. I have a niche market that are Crooked Tree Joinery addicts more so than customers, they love the kind of work that I do and know it takes more time to do it correctly. But not everyone could survive doing it my way, and in fact lately its not so good for me. In the last twenty years my expenses have as much as quadrupled, but my hourly rate is stagnant, so although on paper just as much is coming in the end result is that I am approaching poverty levels even though I work every day. This is with over $250K invested. Not a great business to get into unless you want to be a paper contractor who does not care.

Either way, until customers start asking the important questions things will not change, and I do not see that happening. I was hoping that Sarah Susankas ideas written about in "The Not So Big House" would catch hold, but it does not seem to be so. The house I just finished yesterday was 6700 sq. ft. with ten acres of glass and a heater that never stops. .

The problem is that with houses of this size they most often cut corners on the things that matter most long term. Energy efficiency and quality. By quality I mean the details that make a house the kind of place that gives you a warm feeling. Greene and Greene in my opinion were the pinicle of quality homes that made you, and you're guests, feel comfortable. But I wander..........

My point? Oh yea, do not compromise. There is no such thing as "Good Enough" when it comes to the insulation/ventilation package. In time anything you have saved will be lost many, many times over.

Larry

[Larry Edgerton]

Let me clarify the lack of education on the part of builders comment. I do not mean a college course, most of the mistakes that have been made lately have come from academics with little to no practical experience, as evidenced by some of the stupid codes coming out of government agencies.

What I am referring to is more pride in their job, taking the initiative to read and study what they are doing, experiment, question conventional wisdom, and strive to truely understand what it is that they are actually doing.

Not going to happen..........

Larry

[Mike Carino]

I wouldn't worry about it if its just a shed that you will occasionally heat or cool Dont sweat the small stuff and this definitely small stuff.

[Jaromir Svoboda]

This makes no sense... the paper on faced insulation is not a vapor barrier, and even if it was, a few staples along the edge is not going to seal it.

This is how it is done in Illinois.