Last winter we noticed several areas of our floor have gaps that allowed cold air in. I'm looking for suggestions on how to fill these gaps between the wall and some floorboards that don't extend far enough. This is a sunroom in the front of the home - it is an exterior wall.

closeup of floorboards not meeting wall

closeup of floorboards not meeting wall

I was going to perhaps use a gap + crack foam filler and then chip off whatever foam is visible once it dries. These areas are not as visible since a chair and side table sit in front. I'm a bit worried the foam will be unruly and end up damaging the baseboards or surrounding hardwood somehow.

I noticed that some sites recommend caulking this sort of gap. Should I caulk or try the expanding foam?

Separately I have this big gap under a baseboard on a different exterior wall where cold air gets in. It's more visible; right next to our television in the living room. Perhaps a good candidate for using a clear caulk?

closeup of gap under baseboard where hardwood floor has sagged

  • I would wad up and stuff in sandwich bags, or maybe saran wrap. It won't yellow or rot or damage surroundings, but it will block air be minimally visible.
    – dandavis
    Sep 7, 2020 at 18:48

2 Answers 2


If you have many areas where the boards were just cut too short, think about removing the quarter round molding and installing a larger quarter round that would extend further to cover those boards.

Try to determine why the boards in the last picture are sinking. Clear caulk won't make it any less noticeable unless you paint it, white caulk usually yellows. If that's an area where you'd replace the quarter round, you could bend it down to reduce that gap. The dip against the baseboard would be less noticeable than the dip in the floor. Just a thought.


Is this only in winter? If so your wood might be contracting due to dry air. If this is the case a humidifier would help fix the problem and make the environment a lot nicer for the people.

When installed correctly there is supposed to be a gap that the wood can expand into that hidden by the trim at the bottom of the wall. Either they left an excessive gap when they installed the wood or the wood has contracted.

If you do put something in the gap make sure its compressible as otherwise you might find yourself with bowed floor boards or damage to the wall.

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