Basement – How to find out if a vapor barrier is requried for finishing a basement to code

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I'm planning out a basement finishing project, and I'd like to do it correctly. I've done a lot of research but what I can't tell is if I do, or do not, require a vapor barrier.

I was hoping from a legal (code compliance) standpoint there would be a definitive answer, but as far as I can tell the code doesn't even touch on this.

I believe this is the correct resource for my (Delaware county in Ohio) location's building standards.

From a common sense standpoint, it doesn't seem too clear to me if it's a plus or a minus… it keeps outside water out preventing mold/mildew (positive) but if something we to happen to a pipe or the sum pump in the basement and water were to get in it would be harder for it to get out (negative).

So I was really hoping there would be another reason to or to not have it. My two questions:

  1. Does anyone know if the concept of vapor barriers ever come in to
    the code compliance of finished basements?
  2. Where would I go looking for any such information for my location? Would it be best to
    contact a specific department, or look for a contractor perhaps?

And of course if anyone knows the answer to my specific area, that would be helpful too.

Best Answer

I'll answer the second question first:

Where would I go looking for any such information for my location?

Your city's building and code inspector's office.

But note that because something is to code doesn't necessarily mean it has to be done that way--provided you can show why your way is better. Which leads to your first question:

Does anyone know if the concept of vapor barriers ever come in to the code compliance of finished basements?

It does in many places, but today is highly discouraged from most modern building science perspectives.

When I finished my last house's basement, it was in a place that required plastic vapor barriers. I did a lot of research and came to the conclusion that it's a terrible idea and was able to convince my code department of that. Details of that can be found in my answer to the question here:

https://diy.stackexchange.com/a/8644/1209

Note the links provided in the comments by Brad Mace which point to Building Science Corporation's recommendations--which were the same ones I went from.

The executive summary of why vapor barriers are bad in a basement is that a basement will often have moisture problems on EITHER side of the barrier. In both cases, you'd be trapping moisture rather than letting it escape. It's better to allow a certain amount of moisture permeability.

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