Capillary break between concrete wall & PT window buck
tdbaugha
| Posted in General Questions on
My foundation contractor is going to leave the pressure treated lumber in the wall that was used to create the rough opening for the basement windows. Question is, should I remove these pieces, and reinstall new lumber with a capillary break for just leave it as is?
If I remove them, I would likely reinstall with just a 2×4 and fill the rest of the opening with foam which would certainly be better for condensation, heat loss, etc.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
tdbaugha,
Thermal issues are of lowest concern here as the opening is in concrete. I would be more concerned about insect invasion and how wet you can expect the concrete to get seasonally. It is tempting to leave the PT wood in place, but you may find that they are not anchored to the concrete as firmly as needed for the next 20-30 years. If the window bucks were set to stay and are good and square that's great. Your call.
You haven't indicated what type of windows (or size) you are installing nor if they will be set flush or inset. Also if in a window well with cover or at/near graded terrain. FWIW, when I am resetting or replacing windows in foundations I usually need to strip out existing wood. I will often find small pockets in the concrete which I patch to provide a seal-able surface. If not faced with a damp foundation I place new PT wood with building adhesive and anchors, most often Tapcon. IF the foundation has damp issues, like you suggest, I seal the opening with RedGard to slow down the uptake in the PT material.
It pays to hand pick the very best PT you can find. The stability of much lumber I seen has been dicey once it really dries out. Freshly treated stock can be a real soggy mess to work with. I have not looked at synthetics too much due to expansion issues if used in sunny locations.
Onslow, they are 3’6” x 5’ aluminum tilt turns. Head of the window is about flush with finished grade. Also, the entire foundation will be wrapped in 3” EPS so there is a thermal penalty should I leave the PT in place and not insulate these areas.
But my main concern is the longevity of the wood in this assembly, especially if I leave what the foundation contractor is leaving in place e since there’s no capillary break.
Maybe I’m answering my own question, rip out what’s there, maybe order some submersion grade PT lumber, and install with a capillary break. That should last much longer.
tdbaugha,
Do you want full depth bucks the way they are now? I'd work out a detail that left most of the opening lined with foam board, and have just enough buck depth the secure the window and casing.
No not really, but considering the other 10,000 things I have to do on this build, I was hoping to find justification in leaving them as is. 😂