I think I am starting to create more problems then I should..
In what instances are 2 vapor barriers or more a problem? is it only if we are trapping moisture between two differing temp zones?
arthur
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Replies
what?....
no one likes this question?
I believe Joe Lstiburek of Building Science Corp. has made a statement something along the lines of a vapor barrier is only needed in the far north of Canada.
Effective moisture control in buildings involves the proper use of vapor retarders. Good reading on the subject is 'Vapor Barriers and Wall Design' available at the Bulding Science web site under Technical Resources/Walls.
http://www.buildingsciencecorporation.com/resources/resources.htm
Coupled with this, and maybe more important, is control of air infiltration/movement.
Edited 4/12/2007 10:39 am ET by formulaross
thanks .. formularossarthurhttp://www.thesmallbuildingcompany.com
In what instances are 2 vapor barriers or more a problem?
All.
SamT
There are three kinds of people: Predaters, Prey, and Paladins. For the life of me, I can't see why Prey feels safer from predators by disarming and emasculating Paladins.
Just my opinion, but in most situations, ONE vapor barrier is a problem.
that's really interesting. I have just been reading Joe's building science website again. Very good resource.. He is saying many things that I have known and been using but he explains them very well.. of course what you guys are saying leads to a huge slew of often repeated questions and answers.. but at the risk of making trouble. We are western MA, what to you or others think about the following situations;1) Tyvek doubled up on entire outside of house. The first layer got old after a year of exposure and it had multiple rips so the new general contractor wrapped it again.2) 6ml under slab in a finished basement, then another 6ml under Dri-cor, then 6ml under laminate flooring again.3) exterior of (above basement) foundation has 2" blue foam.. interior finished basement has 4" icynene sprayed between studs directly onto concrete, then 6 ml on the studs.thanks
arthurhttp://www.thesmallbuildingcompany.com
1. No problem, Tyvek is permeable.
2. The 6 mil under the slab is all that was needed. If there is any moisture that will come up, the other 2 layers may cause a problem by trapping it. It is good that the first layer will slow moisture travel down. Keep the foundation and slab drained well!
3. The 6 mil on the studs can cause a problem by trapping moisture in the assembly.
From the BSC reading, do your best to prevent moisture entry, but assume that moisture will permeate into a basement (because it probably will), then build to handle it (i.e., breathe to the interior).
Edited 4/12/2007 12:22 pm ET by formulaross
Two vapor barriers ISN'T a problem. Having a barrier with relatively low vapor permeability (compared to the rest of the wall) on the cold side of insulation IS a problem.
More specifically, it's a problem if you set up a situation where the dew point of the air at specific points in the wall is apt to frequently be above the temperature at those points, taking into account all moisture and temperature dynamics.
<<Two vapor barriers ISN'T a problem>>
Well the 3 vapor barriers that are included in teh basement floor sure sound like a recipe for disaster. You've got a club sandwich with mold-food between each layer!Justin Fink - FHB Editorial
Your Friendly Neighborhood Remodelerator
Well, the concrete won't get moldy, so it's really only a regular sandwich with an extra layer of bread.Would still be a problem with only the top layer -- that's the one that's at fault, since it will tend to create the afore-mentioned dew point condition in the Dri-cor. The one in the middle may not be doing any good, but isn't doing any real harm.
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