GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter 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

Is installing cedar trim boards on top of bevel cedar siding a new way of letting the walls breathe?

jerryfurlano | Posted in GBA Pro Help on

I have a customer who just moved into this house and the inside,outside, and window trim boards are on top of the bevel cedar siding.I advised him that there is air infiltration and places for bugs. Another contractor told him it is the new way to let your walls breathe. I don’t think it is, I would like some feedback. Thanks

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. Michael Chandler | | #1

    I have seen it done that way by other builders with the same rational in a house here in NC over tar paper and OSB on 2x6 walls with damp spray cellulose. It looked like a recipe for bug and moisture problems to me.

    I think the siding is there to protect the house wrap from the sun and keep it as dry as possible. running the exterior casing over the siding opens up a path for moisture to enter the wall assembly and gives insects a nice shady place to chew up the house wrap.

    I can imagine it's probably a lot faster to build houses this way, but not better and certainly no relationship to allowing the house to dry. Take the time to cut the siding to fit the trim.

    Now that your friend has moved into the house you may want to advise him or her to have the voids between the siding and trim filled with a high solids, low shrink caulk like Bostick low VOC, over foam backer rod or chunks of sill seal. The goal is not to create a solid plug of caulk but to fill the void with closed cell foam to provide a backer for the caulk and then cover that with a thin "door" of caulk that can stretch as the components of the home shrink and swell seasonally (or daily in this case).

    Does the house have decent overhangs or is the rain allowed to just run down the siding? Are there head flashings over the tops of the windows to keep water from washing in behind the head casing? Kick-out flashings?

    This detail may be just the tip of the iceberg. I'd have a full energy audit, blower door test, and durability review done to uncover other elements that need to be addressed.

  2. neo-hippie-perma-slave | | #2

    Breathe? Sure it will breathe, but more like a poor individual with OCPD. If its an old house with moused fiberglass it would be a waste of time to do anything with the siding and trim. If its a new home that is "well" insulated any "breathing" will be concentrated around those places- yielding moisture, rot, mold, stink bugs, silverfish, ladybugs, flatflies, and everyones favorite ants.

    Green Roofers Mantra-- "I am a drop of water"

  3. jerryfurlano | | #3

    Thank you for your feedback.You both said what I was thinking. I just wanted to hear it from someone else and not tunnel vision thinking on my part.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |