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

How do I keep bugs out of this old wall?

canada_deck | Posted in General Questions on

This part of the building was a car garage built in the 1980’s in Canada and has since been converted to living space.  As far as I know, wall construction is:
Drywall-Vapor Barrier-2*4 studs with fiberglass insulation-OSB or Plywood-Black building paper-Cedar lap siding

I am having a hard time with bugs. I’d especially like to reduce the amount of spiders that are crawling around inside.  Today, I pulled off the electric baseboard heaters and it appears that spiders, ants and wood bugs are getting in from the walls.  I will be sealing those electrical penetrations but would ideally like to also prevent them from getting into the walls in the first place.

I am fairly confident that they are getting into the building by crawling up the concrete wall and into the gap behind the water table trim board.  That board is tight to the wall in some places but leaves a meaningful gap in others.  

My first thought is to fill the gap using spray foam or backer rod and caulk.  However, I am conscious of the fact that could potentially create an issue f it is a drainage plane.

Note that the second picture is taken looking into a mirror looking up into the gap under that trim board at the same location as the first picture. 

Any thoughts?


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. Expert Member
    BILL WICHERS | | #1

    You could use some stainless steel mesh cut into a strip, then pressed up into that gap to form a springy "U" shape that would stay in place. That would allow for ventilation and drainage while still keeping most little critters out. You could also try the "pest block" canned foam variant -- I don't think you really have a drainage gap there, although it's hard to tell for sure from those pics.


    1. canada_deck | | #2

      Thanks. That is a good idea. Unfortunately the gap is non-uniform. It only exists due to warping of the wood. However, I will riff off that. I found some stainless steel scrubbers for cheap at a hardware store and will be able to stretch them out and jam them into the crack. It's like something in between wire-grid and steel wool.
      This isn't a drainage plane as-in a rainscreen assembly but I believe that it would technically qualify as it is tar paper with some relatively loose siding on top.

  2. canada_deck | | #3

    Found some packages of stainless steel scrubbers at a local hardware store. They could be easily pulled/stretched out so that a single scrubber would cover many feet of gap. Used a bent piece of composite shim to jam it into the crack of varying width. Obviously I will have to see if it stands the test of time but I am very happy so far. Got it done in a single evening with very little mess. Will allow any water that gets trapped behind siding to drain down.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |