I have no idea where it’s coming from. I have a 3’x4’ spot under my hardwood in my living room where water bubbles up from the joints when I step on it. This is about a foot off the wall that is an exterior wall with a window. I cannot find a leak anywhere in the house. The water meter is not spinning. We’ve had a lot of rain lately, but I would think that if it were coming from outside, the edge of the floor would be wet, right? This is so random, I don’t even know where to start. I don’t want to have to pay to have the floor ripped up just to find out it wasn’t coming from the slab. Any way to tell? The floor is not buckling yet.
Is this below grade or ground floor with no basement? That’s different than it being a first floor with a basement underneath.
Either way, the window is the likely culprit, at least it’s where I would start. Without knowing the building materials and/or seeing some pictures, it’s hard to say, but I’d start by taking a long hard look at the weatherproofing all the way around the window as well as the window sill (exterior) and under it where it connects back to the house). While you’re out there, check for any other place in the general vicinity where water might enter.
As for the edge of the floor being dry, but not the middle, I wouldn’t worry about that. It could be that it’s leaking under the floor and that’s just where it managed to to come up to the surface or break through the vapor barrier.
I am a carpenter that currently works for a restoration company. We deal with water and fire damage all the time. You should call your insurance and have them send their adjuster and restoration contractor to deal with this. Your floor is probably already toast.
You need to get someone in that deals with flood damage and knows how to trace the problem and mitigate the damage before it gets worse. It may as well be someone who your insurance is used to dealing with as you are going to be making a claim.
Likely they are going to open the drywall at the exterior wall to see what is going on. They will know where to look, stop the leak, dry and treat the area. You will probably get a whole new floor as hardwood is very sensitive to water.
Call your insurance now, this is why you have it. Waiting is going to cost you money and time.
Have a (large) marble?
Or a long carpenter’s level?
Is the wet spot at the lowest point in the room? If so, there may well be water under much more than what you are seeing - the difference is the thickness of the flooring - you have just one spot that is low enough for the water level to be above the flooring, but a larger area in wet on the bottom.
Get your insurance company involved before spending much on this - they may want to do things differently than you are planning.
I realize that if this is an overland flooding issue insurance probably does not cover damage in that situation. They will still send an adjuster and likely a restoration contractor to look at the issue and determine if that is the case. You can still hire the restoration guys to deal with the issue.
Otherwise you are going to have to get moving and trace down the problem. Check the exterior of the wall to see how wet the soil is and if there is anywhere obvious water is getting in. Pull the baseboard and check the gap between the drywall and hardwood for moisture. Open up the drywall to see if there is moisture in the wall from a window leak.
Once you have isolated the source of the water and stopped it you have to expose everywhere that is wet and get blowers on it to dry it out. You will need to spray affected areas with a mold control/disinfectant product. You will likely have to lift the flooring to dry it out. If the hardwood is wet it is most likely already ruined.
We do not install hardwood on cement slab where I live, only engineered floor or laminate. When my company deals with a flood on slab we pull the flooring if it is laminate, engineered, or carpet. Any kind of flooring that can absorb water is going to have to be pulled so everything can dry out.
A possibility is that you have nice reliable plastic vapor barrier across your ceiling and down the wall, and roof leaks are pooling above you in the ceiling, run down the wall (all on the other side of the vapor barrier, so no holes, no water damage). The water reaches the floor level, seeps out the bottom of the wall where the vapor barrier ends, and you see a puddle coming through the floor.
If so, crawl into the attic - the area near the top of the wall the ceiling insulation should be obviously wet to the touch.
SOme house up north here, escaping warm air condenses and freezes in the attic - come spring, these big icicles melt with the first warm day and water runs all over. However, it’s too late in the season for that.
Some years ago I found that my hall carpet was wet at the kitchen door. My first thought was a nearby radiator, but that had no evidence of leaks. The kitchen had a laminate floor and investigation found that the washing machine was leaking and the water was staying under the laminate to the door, where it could finally escape. When we lifted the laminate, the underlay and the concrete floor was completely wet.
Could be a lot of things but you can check the exterior most easily. The siding should overlap the slap but you should be able to see if there are cracks or holes there. I agree with Joey P the window is a likely culprit. There may just be a low spot on the slab that allows condensation to pool there, which wouldn’t be good. If you can find a way for water to get in from the outside you’re in the best shape because that can patched and maybe your floor isn’t totally ruined yet. Otherwise you’ll have to tear up floor or wall to work this out.