# Where to caulk Z-flashing?



## janralix (Apr 26, 2009)

I am going to install HardiePanels on a two-story house and will be putting Z-flashing between the upper and lower panels. Hardie's instructions aren't clear on where to caulk the flashing. Where do I caulk the Z-flashing? Behind the upper side, on top of the upper side...any help? Thanks.


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## Windows on Wash (Aug 30, 2011)

You don't caulk it on an exposed surface in my opinion. If you want to caulk it where it is tight to the sheathing, that is fine.


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## janralix (Apr 26, 2009)

Windows on Wash said:


> You don't caulk it on an exposed surface in my opinion. If you want to caulk it where it is tight to the sheathing, that is fine.


Yes, I agree about caulking exposed surfaces. I was wondering about the part of the flashing that is under the panel. Just the back side or the top of it, too, or both? Thinking about it a little, it would seem overkill to caulk both the back and top...why not just the top? Of course, overkill isn't always a bad thing except maybe in cost. Thanks.


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## joecaption (Nov 30, 2011)

It should not be caulked.
Window tape gets installed on the two sides of the window, Z moulding gets installed over the top of the window, then window tape goes over the top of the Z moulding and the two sides. 
If your dealing with the area where the two pieces meet between the first and second floor same rules apply.
http://www.na.graceconstruction.com/custom/flashings/downloads/26324_Guide-B.pdf

Are you 100% sure on your decision to use those panels? 
Have you used them before?
One of the last types of siding I'd want to install.


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## kwikfishron (Mar 11, 2010)

janralix said:


> I am going to install HardiePanels on a two-story house and will be putting Z-flashing between the upper and lower panels. Hardie's instructions aren't clear on where to caulk the flashing. Where do I caulk the Z-flashing? Behind the upper side, on top of the upper side...any help? Thanks.


 I caulk the top of the panel where it meets the wall and then seat the flashing into that. Be sure to hold the next panel up a 1/4" off the flashing.


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## Gary in WA (Mar 11, 2009)

IMO, caulk between any overlaps of the metal. No point to caulk behind the metal, it wouldn't do anything other than stop any liquid water from draining down, force it into the sheathing to wet that. What type of WRB? Where are you located?

Gary


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## janralix (Apr 26, 2009)

Thanks to you all. After re-reading Hardie's instructions it appears they don't even mention caulking either the z-flashing or the top of the panel under it. I suppose that is to let any water have a means of escape.

joecaption: I've never installed Hardiepanels and will be having the work done by a contractor. Why are you against the stuff and what other product would you use instead? I'm looking for longevity in a product and a product that won't readily absorb water. I'm in East Tennessee.


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## Windows on Wash (Aug 30, 2011)

You can caulk or seal it at the sheathing if you want as there won't be any water behind the sheathing you are trapping but you don't caulk the outside surface.


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## Tom Struble (Dec 29, 2008)

if the panel is cut at the top,it must be caulked before the flashing is installed,caulking will help windblown rain from getting under the drip cap..hopefully..


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## Gary in WA (Mar 11, 2009)

Good catch, Tom. My point was any water on the wrong side of a plastic WRB will drain, following the slick surface down; from solar drive (warming the cladding- esp. reservoir ones as stucco, cement board, etc.), fastener holes from installing it too tight, incidental water from bad window/door flashing-- then it has a way out without any continuous horizontal blocking- forcing it into the sheathing.

http://www.buildingscience.com/documents/information-sheets/reservoir-claddings

IMO, ventilate the panels; http://www.buildingscience.com/documents/digests/bsd-105-understanding-drainage-planes

Interesting read; http://www.buildingscience.com/documents/insights/bsi-066-holes-and-leaks/view

Gary


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