What folks sometimes think is settlement of a foundation, is actually just the wood shrinking.For example, I have seen a house where the floor joists shrank a 1/4 inch each, and on the 3rd floor there was a 3/4 inch gap at the floorboards and baseboard. All wood shrinks and doors go out of plumb and pipes pitch backwards.
Sounds like you need to caulk the cracks with a silicone caulk and monitor it for further issues.
If the gaps get bigger than 1/2 inch, you may have more serious problems.
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