Do I need a vapor barrier?

[Jim Underwood]

My shop is one of those glorified sheds you can buy from HD or Lowes. So the walls are framed 2x4 with exterior siding nailed on the outside. Everything is optimized for 4x8' sheets and quick construction...

Overall dimensions are 16’ x 20’, and set on piers. The floor is 5/8” treated ply, with 3/4” oak flooring nailed over some of that roofing paper.

So if I wanted to insulate and put some paneling of some sort on the inside, do I need to first put a vapor barrier somewhere?

[Mike Wilkins]

If you use faced insulation and staple the flanges to the studs, you do not need a vapor barrier. The vapor barrier is used when you use un-faced batts (without the paper). Insulation is best installed before you move into the shop and start placing tools, cabinets, etc on the walls. A real pain to move all this stuff after the fact to install insulation. Good luck.

[Chris Friesen]

You generally want the vapor barrier on the warm side of your insulation, then panelling over that. I've never used the faced batts, around here (Canadian prairies) the standard residential construction is unfaced batts with a separate thick plastic sheet sealed to the studs with Acoustiseal and then stapled.

[Jamie Buxton]

Are you planning on heating or cooling the shop?

[Jim Underwood]

I don't know exactly what I'll do about heat, but I already have an A/C unit that I'd like to install. Doesn't do much good without good insulation though... My little ceramic heater is only good enough to keep my feet warm on a cold day. Doesn't do much in that un-insulated shell when it's 30°F outside.

[Dan Hintz]

If you use faced insulation and staple the flanges to the studs, you do not need a vapor barrier. The vapor barrier is used when you use un-faced batts (without the paper).

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.

[Mike Chalmers]

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.

Well, no one said nobody isn't direct around here.

[Greg R Bradley]

Direct or not, Dan is correct. IMHO, the basic problem is the way things are advertised and the confusion over Vapor Barrier vs. Vapor Retarder. Having no vapor barrier is much better than installing one without a good understanding, particularly in a humid part of the country that can freeze.

This will be a good start: http://www.buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers

[Mel Fulks]

Well it's not just the advertising ,the words " barrier " and " retarder" do not have enough difference between them to be useful to any one not in the know on this subject. That is most certainly by design. Many barriers are pervious ,by design. How many of us have bought the DELUXE model of something to later find out the SUPER DELUXE was real top of the line ? Virginia meets the criteria of being hot,humid but freezing aplenty in winter. I'm glad to now be better informed by the knowledgeable comments,but the common paper is always referred to around here as vapor barrier and the only caution is install "vapor barrier " to heated side. I now under stand it's not the super deluxe solution.

[Larry Edgerton]

One solution for all parts of the country is not reality. I use the "Builders Guide to Cold Climates" by Joseph Lstiburek as my go to reference. He has books specifically for other climates as well. I do not use plastic in any of the homes I build. I came to this after seeing too much damage by mold inside walls. What works for AC does not work for heat, so if you are doing both you need a controlled permeability on both sides of the wall.

Go to ***.buildingscience.com for some out of the box store thinking.

I have tried something new on my new home that I have always wanted to try. I have a balanced perm on both sides of the wall with a layer of 1/2" urethane foam on the inside and the outside. Headers are insulated with 2 1/2" of poly, and even the exterior trim is insulated. The ceiling is a double layer affair with a sealed dead air space of 3/4" in between the layers, the first layer is 1/2" urethane, spacer and 5/8" drywall. The foam layer was spaced so I could seal in between the sheets with foam. The top of the walls are insulated with poly,, cut to match the pitch of the roof, and the vent baffles are 1" foil Thermax, again any gaps sealed with foam. Windows are set with foam as are doors. No wires were allowed to penetrate the plate on the eve sides where insulation is the weakest and closest to the roof. All wires and vent pipes are sealed where they go through to the attic. There is very little contact between framing members and the interior surfaces, or the outside surfaces for that matter. Wall cavitys are 5 1/2" of wet cellulose, cealing has 24" of cellulose with a bit of binder to prevent settling above the double ceiling. I will have an air to air exchanger to control air quality and humidity before I move in.

I have set glass jars, olive jars actually, into the north and south walls so I can keep an eye on what is going on in the wall cavity as I have not seen or read of a wall system done quite this way. I heated the house to 65 last winter with natural gas and the bill on the coldest month was $72. This house is 1300 ft with 11' ceilings in the main room, 8'4" in the rest, has 25 windows and glass doors, and the basement is not done yet. I am 90 miles from Canada so it gets cold here. When I move in I will heat with wood from the property.

Rambling a bit, but my point is don't buy the "Got to have a vapor barrier" train of thought with out looking at all of the variables. For instance if you put the vapor barier on the inside in the summer when you run the air conditioning the moisture will be collection on the back side of the vapor barrier. So how you will use the building has to be considered.

By the way, with tools, the best place to have a vapor barrier is under the floor. Even with your built on stilts building you can work plastic under there. Some will say that it will have voids so it can not work but it works by percentage. If you can get 90% of it covered you will have 90% less vapor transfer, not at all bad.

Larry

[Mel Fulks]

I've been looking at insulation mfg. sites and only seeing RETARDER mentioned . I'm pretty sure THEY used to use the word BARRIER. Gonna look at old stuff,too. I'm wondering if the change is due to AC use changes. It used to be said by installers that AC was intended to bring temp down 10 to 20 degrees cooler than outside. That's gone. I still follow the old advise because any cooler than that is such a shock if I need to go back and forth frequently. My AC is never set lower than 80 degrees when outside temp is 100 or more. But I know people who stay inside a lot and always cool to 70 degrees because they want to and the equipment will do it .That makes for high inside relative humidity. Is that why this retarder term is now used?

[James Conrad]

The proper term is Vapor Retarder. The word "barrier" is no longer used because it implies that no vapor or air movement can pass through a product. It changed because it was quickly discovered that most of these products were semipermeable and that making a house as air tight as possible resulted in other vapor related problems. Products used as vapor retarders are classified into 3 groups based on there permeability and assigned a Perm rating. Kraft faced insulation IS considered a Class 3 vapor retarder when installed properly, but by no means the most efficient one on its own, not solely because of the kraft facing but that fiberglass insulation does not stop the movement of air. Stopping a structure from breathing is not always a bad thing. You should consult with some local contractors or building officials to see what the practices are is in your region.

[Jim Underwood]

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

[William C Rogers]

I went through this when trying to determine what side the vapor barrier goes on. I found it depends on where you are. I am in southern Indiana and the recommended is just using the Kraft paper ( no plastic) on the heated side. It does vary be region.

[Ole Anderson]

I can't help but think of how Mike Holmes likes to insulate exterior walls (a Canadian show). He prefers to spray the stud cavity with a thin layer of foam that looks like it seals pretty well and appears to be a vapor BARRIER. Then he might add additional bats to build the R value, then he might add a layer of poly on top of the studs, fully taped at the perimeter. Now that appears to be a vapor barrier. Question: it seems that code in the US requires an exterior wrap with Tyvek. Is that material semi-permeable, or is it just to keep the wind out? When I built my house in 1975, before the wrap was required, I had them sheath the outside with 1" of foam before they went with R-13 between the studs. Not sure how much it helped.

[Greg R Bradley]

Wow. Great information here, but I'm not sure I'm not more confused than I was to start with.... :eek: 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/documents/digests/bsd-106-understanding-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.