6 mil vapor barrier versus 10 mil vapor barrier

[Hawk94]

I am constructing a four story townhouse project in Georgia. I have been told by the Architect that a 6 mil vapor barrier shall deteriorate over time allowing water to seep through the cocrete and damage the finish floor. In lieu of a 6 mil barrier I should use a 10 mil barrier.

1. How long would it take for the 6 mil vapor barrier to deteriorate if installed over 4" of gravel?

2. How long would it take for a 10 mil vapor barrier to deteriorate if installed over 4" of gravel?

 

[concretemasonry]

You are not really talking about "vapor barriers", but vapor retarders.

Generally the permeability is a function of the thickness and age.

What is the big concern since the cost difference is minimal (only material, not labor, etc.).

The architect is concerned with the durability and his liability regarding the finished floor. I know of many builders that never use anything other than 10 mil as a matter of principal, irregardless of the specification for something less. - The cost is peanuts and it eliminates much of the extra care in installation if you really want a functioning barrier/retarder.

 

[Taro]

Another issue is how well the sheets stand up to construction activity. A 6 mil sheet often gets torn up pretty good before the concrete is poured. A 10 mil sheet holds up better. I just poured a slab for my own house and used a 15 mil polyolefin sheet. This stuff is nearly indestructible and is as close to a true vapor barrier as you're going to find.

 

[Hawk94]

Concretemasonry and Taro, thanks for your response, however the 6 mil is already installed. I need to know if there is any data indicating the life expectancy for the 6 mil versus the 10 mil.

This is considering both products are installed under the same field conditions.

 

[GrumpyG]

Hopefully, the slab is not poured!
Was 10 mil specified?

If the slab is poured, perhaps it's best to leave the slab with the 6 mil in place with a credit.

If 6 mil was specified, then the Contractor is owed an extra to remove and replace it.

 

[bimr]

Not sure that the architect knows what he is talking about. The difference in thickness probably does not matter.

Envirocon for example says that HDPE landfill liners will last 200 years.

http://www.enviroconsystems.com/faq.htm

The Residential Energy-Efficient Design and Construction Checklist recommends a "6-mil polyethylene ground cover".

http://eber.ed.ornl.gov/Residential_Products/checklist-2000/energy newchecklist.PDF

You have not said what type of "finish floor" that you are installing. Below-grade installations are not recommended for wood floors. However if you are putting a wood floor on top of the concrete at or above grade, you have to put a second vapor barrier on top of the concrete to prevent the moisture from the concrete itself from damaging a wood floor.

To install over a concrete slab, special preparations are necessary. (See NOFMA Hardwood Flooring Installation Manual.)

https://www.nofma.org/Portals/0/Publications/NOFMA Installing Hardwood Floors.pdf

If you are carpeting, you probably do not have to worry about the 2nd vapor barrier.