GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Older home (1950s) smells of mildew…

gerh8671 | Posted in General Questions on

I purchased a home in late 2009 and have been trying to get rid of a heavy mildew odor. Last week I discovered the seller had put vinyl siding over two layers of other siding. Underneath the vinyl was a layer of extremely damaged Boise Cascade panel siding. It was crumbling and had large holes in multiple places (no house wrap). Behind the holes I discovered clear plastic sheeting and underneath that was cedar lap siding. I continued on down to the Buffalo board that was somewhat warped and had a strong mildew odor. A couple of contractors suggested removing the top two layers of siding and clear plastic. I live in an area that it is extremely difficult to get workers due to the oil boom and will have to do a lot of work with friends and myself. Does anyone know what if that layer of plastic is the likely cause of the mildew. Had the roof re-done right away and the sheeting or deck was not wet. When I do reside, should l leave the cedar lap siding if I am going to reuse the vinyl siding or does that have to be removed and covered with OSB and house wrap? I am getting different opinions and want to do the most economical solution as the house is probably not going to be worth as much as I have put into it.

Thank you.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    When a house smells of mildew or mold, the first place to look is the basement or crawl space (if there is one). If you have a basement or crawl space, and either of these has a dirt floor, you can say Bingo!

    Here is a link to an article with more information on these issues: Fixing a Wet Basement.

    Although I've explained the first place to look, it's quite possible that your problem stems from mold and rot in your wall components, as you surmise. It's certainly true that a layer of of polyethylene plastic on the exterior side of your wall is a big no-no in a climate with cold winters. Exterior poly on your walls can easily lead to moisture accumulation, mold, and rot.

    The contractors you spoke to are correct: you need to remove all of the layers down to the polyethylene, and then remove the polyethylene. It's likely that you will find moisture accumulation, mold or rot on the layer behind the poly -- probably your wall sheathing. Any rot needs to be repaired by removing the rotten components and installing new materials.

    Once these repairs are made, you need (at a minimum) a new water-resistive barrier (like housewrap), followed by siding. If you do a careful job of removing the existing vinyl siding, it can be re-installed later.

    In the course of doing this work, you have an opportunity to improve the thermal performance of your walls by installing a layer of exterior rigid foam. For more information on this issue, see:

    Roofing and Siding Jobs Are Energy-Retrofit Opportunities

    How to Install Rigid Foam Sheathing

  2. Expert Member
    Dana Dorsett | | #2

    The oil boom is happening in both very cold and very warm climates- where are you?

    In a cold climate like MT/ND plastic sheeting on the exterior side of the insulation (and the fiberboard sheathing) is almost guaranteed to cause this sort of problem eventually.

    In a hot climate like the warmer parts of TX it can be fine to have exterior side polyethylene, as long as you don't have a low vapor-permeance layer such as poly sheeting under the wallboard or foil / vinyl wallpaper on the interior, which would be a classic moisture trap.

    It's fine to install vinyl siding over the cedar siding.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |