Home>Discussions>INSULATION & HVAC>Insulation/vapor barrier on cinder block home in Florida
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ordjen
Re: Insulation/vapor barrier on cinder block home in Florida

Keith,

There is a well documented case of an established builder in Cincinnati. Ohio who had used sheet plastic behind the drywall in his housing developement. Cincinnati is summer is very hot and humid. Buyers almost immediately started complaining of moisture problems to the extent that their carpeting was getting wet. It was determined that the hot humid air was trying to get to the relatively cool, dry, air space on the interior of the air-conditioned homes. Unfortunately, it was condensating on the back of the walls and running down onto the floors.

This old line builder who had been in business for years was forced into bankruptcy as several hundred homes had this problem. The only remedy was to tear out the drywall and remove the absolute vapor barrier behind it.

Many of today's building codes concerning vapor barriers are left over from the 40's, before the advent of common air-conditioning. As we have tightened up homes, we have created other problems. Old Victorian homes had little in the way of air barriers or insulation and had balloon construction with all kinds of air moving in the walls. Even if a wall should somehow get wet, it could rapidly dry out. I sometimes wonder what shape our homes of today will be in a hundred years from now?

keith3267
Re: Insulation/vapor barrier on cinder block home in Florida

ordjen, sorry but no way did the moisture in the walls of a house built in Cincinnati result from a vapor barrier on the inside of the insulation. Cincinnati is no where near as hot and humid as west Tennessee and we don't have that issue here.

There is another reason that the moisture built up inside the walls and i suspect what the real issue was, but you you will have to identify the case you are talking about.

ordjen
Re: Insulation/vapor barrier on cinder block home in Florida

Keith,

Fine Homebuilding Magazine has published quite a lot on this theme. Unfortuantely, I don't have the issue in which the article appeared. I will see if I can find it.

ordjen
Re: Insulation/vapor barrier on cinder block home in Florida

Keith,

Here is the website: www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/reviving-old-debate-vapor-barriers

The reference of the Cincinati homes is under the paragraph head "Beware of moisture driven inward"

Guess you have never been in Cincinnati in summer time. 90 degrees and very high humidity are common in the Ohio River Valley! It is definitely high air-conditioning country!

Please read the entire article, including the blog posts at the end. The whole concept is highly debated. I tend to agree with those that argue that poly film is generally a bad idea in this day of high air-conditioning use. An absolute vapor barrier is a bad idea. You do not want to stop air-infiltration at the cost of trapping moisture in the wall.

keith3267
Re: Insulation/vapor barrier on cinder block home in Florida

I read your article and I must say it was very confusing. It mixed references to the poly barrier on the exterior of the studs with moisture issues and then tried to transfer those to buildings with the poly barrier on the interior side of the stud. It is clear to me that the author of this article does not understand the concept of dew point.

I tried to find climate information on Cincinnati but the one source that I referenced to that does give humidity data does not have it for anywhere near the Ohio river valley. All other sources just say temps reach 90°+ with high humidity. To accurately judge, I need specific climate data, high humidity does not provide enough information.

I have been to Cincinnati and I can tell you that it was very much noticeably cooler and more comfortable than the Mississippi delta. It was during a cool spell in August though, but we never get a cool spell like that down here. The point is that you will not get condensation inside a wall cavity unless the temperature is lower than the dew point. The temperature in the wall cavity will be somewhere between the room temperature and the outside temperature.

There are only a few places along the gulf coast of LA and FL that have a dew point that high, and in most cases, you would have to cool the rooms to 68°F for condensation to occur.

The issue I do see is when synthetic stucco or brick without weep holes is used with a vapor barrier on the interior side of the stud. In this situation, especially the synthetic stucco, water will accumulate inside the wall cavity. This has been well documented and was even story on one of the TV news magazine shows (48 Hours I think). Many builders that had switched to the synthetic stucco were being sued by homeowners because the houses were rotting away after only a couple of years.

The PBS show "Hometime" did a project on a year old house with this synthetic stucco in Minnesota. They were adding a deck and needed to cut into the stucco to anchor a support beam. When they cut the hole, water poured out. I'm surprised that this didn't get edited out, Dean Johnson stood their with a puzzled look on his face and then turned to the camera and said that he didn't know what was happening but he would find out and let us know.

He never did let us know, but in the very next episode, the stucco was gone and the house was clad in vinyl siding.

BTW, my brother built a house in Utah with this. I warned him that he need to vent the exterior side of his walls but he didn't listen. His answer was that the humidity in his area ran about 3% so he didn't think it would be a concern. He is now having the same problems.

ordjen
Re: Insulation/vapor barrier on cinder block home in Florida

Keith,

Hot humid air trying to migrate to the cooler, drier environment on the interior of an air conditioned house can very well hit the dew point on the back side of an air-conditioned wall, especially on the lowere wall areas and areas close to air vents blasting cold air.

The terms vapor barrier and vapor retarder are used somewhat indiscriminately. Poly is a vapor barrier, Tyvex type products are vapor retarders. A good coat of interior prime and paint is a vapor retarder. Poly behind the drywall is an absolute vapor barrier.

If you can't prevent moisture from forming as condensation within the wall cavity, one would be well advised not to use a vapor barrier at all. The poly behind the walls in those homes in Cincinnati would not allow moisture to pass on through to the home interior, nor could it retreat to the exterior. Vapor and temperatures will transfer through a permeable membrane barrier until equilibrium is reached - Physics and Chemistry 101.

In colder climates, spraying foam on the backside of the sheathing raises the dew point of that surface preventing condensation. Unfortunately, those Cincinnati homes had no insulation on the back side of the drywall to raise the dewpoint on that surface. Moist air hit the cool poly covered drywall and literally ran down onto the floor to the point it was wetting the carpeting.

I would agree on th DryVit type of synthetic stucco products. You had better have an installer who knows what he is doing. It has caused many a class action lawsuit. It is especially bad when put over OSB. My brother-in-law in Germany has had DryVit on his house for 35 years with no problem, but then, homes in Germany are usually masonry with DryVit over it. A wood frame home in Germany is a rarity.

keith3267
Re: Insulation/vapor barrier on cinder block home in Florida
ordjen wrote:

Keith,

Hot humid air trying to migrate to the cooler, drier environment on the interior of an air conditioned house can very well hit the dew point on the back side of an air-conditioned wall, especially on the lowere wall areas and areas close to air vents blasting cold air.

The terms vapor barrier and vapor retarder are used somewhat indiscriminately. Poly is a vapor barrier, Tyvex type products are vapor retarders. A good coat of interior prime and paint is a vapor retarder. Poly behind the drywall is an absolute vapor barrier.

If you can't prevent moisture from forming as condensation within the wall cavity, one would be well advised not to use a vapor barrier at all. The poly behind the walls in those homes in Cincinnati would not allow moisture to pass on through to the home interior, nor could it retreat to the exterior. Vapor and temperatures will transfer through a permeable membrane barrier until equilibrium is reached - Physics and Chemistry 101.

In colder climates, spraying foam on the backside of the sheathing raises the dew point of that surface preventing condensation. Unfortunately, those Cincinnati homes had no insulation on the back side of the drywall to raise the dewpoint on that surface. Moist air hit the cool poly covered drywall and literally ran down onto the floor to the point it was wetting the carpeting.

I would agree on th DryVit type of synthetic stucco products. You had better have an installer who knows what he is doing. It has caused many a class action lawsuit. It is especially bad when put over OSB. My brother-in-law in Germany has had DryVit on his house for 35 years with no problem, but then, homes in Germany are usually masonry with DryVit over it. A wood frame home in Germany is a rarity.

I have nothing against Physics and Chemistry 101, I took both. There is one fact that seems to elude you, if the dew point is below the temperature of the interior of the house or the wall cavity, condensation is not going to occur, and only a very few places meet this criteria for condensation in the summer.

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