Vapor barrier tacked to crawl decking

[Matt Fellman]

I called this out as an unorthodox installation and recommended removal since it will trap moisture and prevents inspection. I'm not sure why it was done. I think to hold up the insulation? Any thoughts?

[Phillip Stojanik]

Maybe a problem, maybe not. There is a distinct difference between a vapor retarder and a vapor barrier (Perm rating). What is needed/required should also depend on the local climate.

Whats the perm rating of the product in use as it relates to moisture difussion/microbial amplification?

[Caoimhín P. Connell]

Hello Matt:

In the last couple of years, we have seen a lot of goofy installations that are the work of “certified mould inspectors� who recommend a wide variety of “fixes� that don’t actually fix anything, and indeed, may create a moisture problem – many times, the fix involves the installation of a VB. (Although I shouldn’t just pick on mould inspector’s – last week’s brilliant “expert� was a certified industrial hygienist.)

In any event, from a moisture control perspective, I concur with your assessment and recommendation, since, unless these is a specific, demonstrable cure, the VB will probably just lower the hygric buffering capacity of the structure.

As Phillip points out, there is a difference between a vapor retarder and a vapor barrier, however, I don’t think the distinction is of any importance in this case, unless, Phillip’s point is that if the permeation is high enough, then there is no harm in leaving it in place; in which case, I agree with Philip.


Cheers,
CaoimhÃ*n P. Connell
Forensic Industrial Hygienist
Forensic Industrial Hygiene (http://www.forensic-applications.com)

(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG

[Scott Patterson]

That is how all manufactured homes (trailer homes) are sealed.

[Matt Fellman]

That is how all manufactured homes (trailer homes) are sealed.


I thought of that but it seems like those are mostly framed with metal... also, what I've seen is a mesh that I believe allows some air passage.

This is 6 mil black plastic tacked tightly in all of the floor decking (post/beam) construction. This house a DIY nightmare and really don't think this was done out of any reason other than stupidity.

Thanks guys!

[Gunnar Alquist]

Adding a comment after Caoimhin is a bit superfluous, but I would agree with the posts above. The undercarriage seal that I typically see under a mobile is not a 6 mil poly, but does have teeny holes, is woven or has some function/ability to allow moisture vapor to pass.

I particularly like Phillip's comment about moisture diffusion/microbial amplification. Anyone know what that means?

[James Duffin]

The house looks like it is plumbed with galvanized piping making the house pretty old. Could there had been an open crawl space at one time and they added floor insulation. The plastic was put in place to protect the insulation. Just another guess....

[Rick Hurst]

Gunnar,

Maybe its Moisture evaporation / Mold growth :)

[Matt Fellman]

The house looks like it is plumbed with galvanized piping making the house pretty old. Could there had been an open crawl space at one time and they added floor insulation. The plastic was put in place to protect the insulation. Just another guess....

It was right at the end of the galvanized era... mid 70's or so. I think you're right that it was put there to hold up the insulation. There was just a bunch of goofy stuff.. new vapor barrier all over the ground, mud stains underneath. The vapor barrier was in super small pieces, too. Other areas of the house were a DIY nightmare as well.... So much for a quick and easy write up... I guess that's what I get for trying to make some easy money doing a Saturday job.

[Gunnar Alquist]

Gunnar,

Maybe its Moisture evaporation / Mold growth :)

Rick,

Ummm... Yeah. That's kinda what I thought. I'm just a simple inspector and them ten cent words make my head hurt. I like your definition. However, that said, I have made mention of postdiluvian conditions in my reports. :cool: