I live in an old house where there's a significant seam in the living room floor that leads directly to the crawl space below. After investigating, I found that one side of the gap seems to be a concrete slab—likely a later addition—while the rest of the house is built on a pier and beam foundation. This gap appears necessary for allowing the floating hardwood to expand and contract without breaking. I'm trying to figure out the best method to insulate this gap. I'm considering using some type of putty or caulk on top, then spraying Flex Seal from underneath. I know the top fill won't last forever, but I want to close up this hole into the crawl space. Any thoughts?
2 Answers
Honestly, if it were me, I would've aimed for matching the new flooring with the old by weaving them together. That’s the more permanent fix. Using wood filler or similar is just a temporary patch. The problem with fillers is they can move with moisture and temperature changes, which isn’t ideal. But if sealing the gap is the priority here, doing something well now might help for the time being.
It sounds like a good idea to use a backer rod in that gap first. Then, you can apply spray foam insulation to air seal it from underneath. Keep the backer rod level with the subfloor so patching up the finished floor later on is easier. There are some affordable spray foam kits, like the 'Great Stuff' wide spray can, which would work perfectly for this situation. Just make sure to choose a good brand based on reviews and price! These small cans are ideal for these types of gaps.
I get what you're saying, but because this is a century-old house, there isn’t really a traditional subfloor - I’m looking right at the back of the hardwood from the crawl space. A more aesthetic fix would definitely be nicer, but I don’t want to risk damaging the boards across that gap since the flexibility from the pier and beam foundation will put pressure on them, especially since we have a hole going down to the crawl space.