1/4 inch gap under mudsill

This is a homeowner forum question, not news, but here's what it's about: a homeowner with a 1990s house is dealing with small gaps, about a quarter inch, between the wooden mudsill (the lowest horizontal framing piece that sits directly on the concrete foundation) and the foundation itself. These gaps are common spots for outside air to leak into a house, so sealing them is a standard part of air sealing, the work of closing up cracks and gaps that let conditioned air escape and outside air in.

The homeowner's question is narrow: whether to just run caulk into the gap, or first wedge in a foam or rubber gasket and then caulk over it. No answers had been posted yet at the time this was captured, so there is no expert consensus to report.

For a homeowner, the broader point is that mudsill gaps are a known weak spot for drafts and energy loss in older houses, and sealing them is a cheap, low-effort fix compared to bigger projects like new insulation or a heat pump. If your house was built around the same era, it is worth taking a look at where your foundation meets the wood framing above it, especially in a basement or crawlspace, since similar gaps often show up there too.