I wanted to see if anyone had any insight to siding separation. I had this done 5 months ago and went through a semi-brutal winter. I’m wondering if this is normal to see separation. I have not checked if there was flashing on the joints.


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  • 1
    What kind of siding is this (wood, composite, fiber cement, etc)? What was done for the joints? If this is a wood product, it will expand and contract, opening these gaps. The install instructions likely specified backing the joints with a water barrier (e.g. tyvek) and caulking the joints to keep the building protected. Not all caulking is created equal, especially for outdoor applications.
    – blarg
    Commented Mar 18 at 21:38

2 Answers 2


That looks like HardiePlank siding.

The installation guide recommends that flashing be behind the ends of boards, but caulking can be done as well.


Fibercement siding does shrink a bit, counterintuitively. That's partly why butt joints should be flashed. If they weren't flashed you have a problem with the installer that'll need to be addressed.

Whether the gaps are too large is a matter of your warranty. I've seen whole houses replaced in the early days of fibercement for shrink, tension cracks, and buckling. Most of that has been resolved, but you'll need to ask the vendor or manufacturer what's considered acceptable.

I also consider it inadvisable to caulk such joints for the reasons we see here. Obviously it's too late for that in your case, but I'd not add caulk to the opened joints--it could cause problems if the siding expands when the weather gets warmer. Accept them as part of the overall appearance of the product, which is really intended to have a legacy look anyway.

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