Insulation Vapor Barrier? Yes Or No?

caseyleen

Do any of you use a vapor barrier when you insulate a new home or addition. Some guys use it and others will not.
In talking to a Owens Corning Rep, he said a plastic vapor barrier should only be used with unfaced insulation. I have heard pros and cons both ways. Any opinions?

Framer53

Vapor barrier is dependent upon where you live.

Go to the building science web site for the explanation.

Rory Read

Everything I read these days tells me I do not want to trap moisture inside a wall assembly. It's got to breathe one side or both.

I think the best article to start with is the Building Science Corporation research report titled Vapor Barriers and Wall Design. It's worth wading through, and it details different options for different climates/regions in the US.

You can grab it off their site.

Cheers,

r

Rory Read

Sorry Framer53. Just behind you there. Didn't mean to echo.

R

katoman

You need a VB if you are using fiberglass insulation. If you are using spray foam - no. If you use rigid foam panels under 2" - yes. Two inch foam does not require VB.

If you are using paper back insulation, with a tar like substance on the back of the paper, then this is the VB, and do not put another VB over this.

Normally builders use fiberglass with 6mill poly over it. All seams should be overlapped and caulked with accoustic sealant.

There are a few other considerations, and special situations, but never apply two VB

katoman

Just read the above posts, and yes, it depends on your climate.

Sorry, I assumed you were in a cold climate. I have no idea if it is required in a hot climate like Florida or California.

Framer53

You are correct for where you live, but we have no idea where this poster lives, therefor it is all hypothethical!

Ayerzee

Vapor Barrier goes to the warm side. (In warmer climates that would be facing the outside)

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Dan

rstarre

I just saw a program on cable saying it is unhealthy to seal the house airtight. People are getting an increase in respitory illnesses in the colder climates as a result of this. LOL

katoman

I'll go along with that. I worked for the first home builder here to build 'energy efficient' homes. It is all being driven by the desire to lower heating costs.

Our building code will make changes now and over the next 3 years to make every new home built to these standards. It is like living in a plastic bag, then they install air exchangers to get some air into the home, and most of them are sized wrong, or installed incorrectly.

What a mess. I prefer that a home should be able to breath. But apparently I'm in the minority. The public is basically ignorant in these matters, and only wants a lower monthly heating bill.

There's no changing it now. Wait 20 yrs. and I'll bet they start going back to the old way.

SLSTech

Install an ERV or HRV - that is what they are for

If someone can't size it properly, you need to find a new company as the math is really simple

Oh & I wouldn't connect them to the HVAC system either - a tighter house doesn't require as much heating and cooling and you have no way of knowing how the HO will actually use the system, it is better left as a standalone system

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wheeler

we don't. we would use faced bat or 2" closed cell with flame spread. around here 0.6 x 2" closed cell qualifies as a vapor barrier.

katoman

They were HRVs. The builder simply bought the cheapest units, at least half of them didn't work properly. Led to many compaints. One of the reasons I left that builder.

Now, you recomend that the HRV be kept as a seperate system? Then seperated ductwork is run to bathrooms, kitchens, etc.? The sysems they did were connected to the heating system.

Makes sense, I probably need to look into this a little further. Thanks.

KennMacMoragh

If they are not using a vapor barrier, then they are probably planning on using PVA, which is also my own preference. But yes, some form of vapor barrier has to be used.

jjcold417

In a cold climate vapor barrier prevents water vapor from entering the stud bay and condensing onto or into the insulation. Not necessary in warm climates, check local codes and reputable builders in your area to see what they recommend. In my house, a vapor barrier would be a waste of time since I leave the window vents open year round and in the warmer weather, crack at least two or three windows for fresh air. BTW, I have heard that some builders use a spray on VB with the primer, not sure if that is effective or not.

KennMacMoragh

That's what PVA is, building inspectors accept it.

moorewarner

Superinsulated homes are one of the things I am most interested in. Actually what I am most interested in is how to retrofit to a rehab.

If your house could stay comfortable in a cold climate throughout the year without even a primary heat system, why wouldn't a person want that? Gas bills for old brick or stick here in St. Louis can run $200-$600/month in winter.

Superinsulated (with proper functioning heat exchange/ventilation) is the future of building, no question in my mind, and it should be.

http://www.passivehouse.us/passiveHouse/PHIUSHome.html

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PREMIER INSUL

I have been doing Injection Foam Insulation for the past year and a half with great results. It's a BIG learning curve but really does a nice job in filling an enclosed cavity with foam insulation. The product I use has a pretty good R-4.6/inch, so I can get an R-16+ in a 2x4 wall. NO its not Retro Foam, I looked into that and its problems. I have done my homework, any questions just ask......Bryan