Not caulking vertical seams on siding
I’m about to put up siding on a building enclosure that includes a WRB, taped XPS and furring strips. The siding will be a combination of lap wood siding (front) and ColorPlus Hardie Plank (the rest). All butt joints will be flashed. My question is limited to the seams in which the siding contacts vertical trim.
I am in agreement with Martin not to use caulking as it seems to cause more problems than it prevents (https://www.greenbuildingadvisor.com/community/forum/green-building-techniques/17939/can-wood-lap-siding-be-done-well-without-caulk)
Questions:
1) Do I need to use some sort of flashing at these seams? If so what is the best practice?
2) Hardie bulletin (http://www.jameshardie.com/pdf/install/hardieplank-hz5.pdf) seems to indicate that these seams should be caulked. However from my read, if you painted the cut ends you would not need to caulk. The bulletin states: “Terminate non-factory cut edges into trim where possible, and caulk” but also says “DO NOT Caulk field butt joints on ColorPlus siding.” SO can I just paint the cut ends and not caulk?
Thanks!
Mark
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Replies
Mark,
Your siding has nothing to do with your air barrier. Siding doesn't have to be airtight. If any water gets past your siding, your WRB and the rainscreen gap will manage the water.
So I usually don't advocate that you caulk your siding.
The only exception would be if a siding manufacturer calls for caulk. Most building codes require that all materials must be installed according to manufacturers' instructions. Following instructions also helps if you ever have a warranty claim. So you should follow manufacturers' instructions.
If a manufacturer's instructions are contradictory or confusing, you should contact the manufacturer.
Martin,
Thanks for the reply. Apologies for whatever I wrote that lead to the confusion on the air barrier part. I understand the siding is not connected to the air barrier. My air barrier is at the plywood layer.
So I think we are on agreement with not caulking the wood siding. However I’m still not clear if flashing is needed behind these joints. The photo on Scott Gibson’s post seems to indicate yes (https://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/what-s-best-approach-rainscreen)
But have not seen or read any details on such flashing.
Mark,
Some siding installers put a rectangle of asphalt felt -- or even a rectangle of metal flashing, as long as the metal is compatible with the nails -- behind each butt joint. You can also install a vertical strip of asphalt felt at the joint where the siding meets the window casing, if you want. But you don't have to.
Mark, the seemingly contradictory hardi instructions refer to two different conditions. You don't need to caulk the field joints between planks but you do need to caulk the joint between planks and corner, window or door trim.