Has anyone experienced a collapsed floor in an addition to their home, and if so, what repairs are needed, especially in cases of water damage and cracked plywood?
Asked by Angèle Adam 
7 months ago
Last Updated: April 26, 2024
While we were having dinner in the dining room, we heard a loud noise and felt a big thud coming from the floor. It turns out that the floor caved in at the corner of the room. This part of the house is not directly above the foundation and is actually an addition built on a slab. There’s a noticeable crack in the floor and what looks like a hole in the concrete leading outside. We removed the floor and discovered that the plywood had cracked, causing the collapse. Has anyone experienced this before and knows what repairs are needed? It could be due to water damage. Do we need to replace the entire floor structure? Any input would be appreciated.
Oh no, that’s terrible. If this happened in my house, I would definitely consider consulting a structural engineer for some expert advice.
Were you referring to the room being an addition, or were you trying to say “in addition, we think the house is on a slab”? Not trying to nitpick grammar, just looking for some clarification.
It appears to be an addition at the back of the house. The rest of my home doesn’t have a basement underneath. I think the stairs in that room that used to have bilco doors leading to the basement.
As others have mentioned, having a qualified contractor is crucial when dealing with the structure. Maybe not the best place for that discussion though, seems pretty busy here. Good luck! 👍🏻
It appears there’s an inadequate foundation and footings under the addition. It’s probably best to consult with a structural engineer and follow their advice. Best of luck!
Maybe there’s a secret entrance or one that needs to be created. I suggest examining the exterior further. That small hole is not the root cause. Does the floor sound hollow? It’s hard to believe a concrete slab could just drop like that.
The first photo you showed me seems to be the base of that room. And it seems to be falling apart. I love a good DIY project. But I think it’s best to bring in a foundation expert. It’s a good thing no one got hurt this time. But it’s a warning sign to take action before it gets worse.
Do you have home insurance? Consider reaching out to a local home inspector for an inspection, as they may be able to provide more assistance than engineers. They will be able to assess the situation in person, which is more accurate than trying to do so from your pictures.
It seems like there is a crawl space instead of a slab. In any case, you’ll need to do more demolition to assess the extent of the damage and the best course of action.
Check the basement or the perimeter of the addition to see if there is a crawl space entrance. If not, you may need to cut out the floor where it collapsed to check for a damaged pier or joist. Can you see concrete or cinder block from the outside?
Sorry, it’s not something you can do yourself. Give us a call for assistance.