Standing water in subfloor

RA2020

Hi,

I'm a longtime browser of the forum but this is my first post, as I would really appreciate some  advice. I've recently purchased my first home & am a complete novice with DIY/Building/Renovating. However, last week I noticed around 1.5 / 2 inches of water in large areas of the subfloor.

The house is currently empty as it requires some renovation, and I've had a few of the living room floorboards up for a couple of months. The subfloor surface looked soggy when I took the boards up and I have noticed small puddles when the weather has been bad but last week there was a lot of rain and it appears a lot more water has come in the usual.

The house had damp issues, so I've removed the defective plaster and have been advised to get a damp course put in and membranes applied to the walls.
The floor joists are also rotten. To resolve this, I was originally going to replace the timber floor with solid concrete (as the back of the house is already concrete - only the living room floor is timber). But I'm now wondering if that's a good idea if all this water is coming in, could a concrete floor lead to any issues if water is seeping in?

The waterboard came out last week and they weren't able to find any issue on their side. They poured some dye down the gully at the side of my house, but they said it looks like the gully is blocked & even if it wasn't blocked, they have no idea where the gully actually goes. They also asked about the neighbors house, as it's a semi-detached, but I was told by the previous owners in February that the neighbor is an elderly person who went in to hospital & their housy has been vacant since December.

The water has pretty much gone now, and the surface is just soggy again with a few smaller puddles.
I did upload some videos to youtube to try and explain further, but I'm unable to add links to my posts. However, my youtube channel name is: Subfloorwater

As I mentioned, I really have no knowledge or experience with this type of stuff & just want to resolve the problem correctly so it doesn't lead to further issues down the line.
Any advice would be greatly appreciated.

Thanks,
Rachael

FreeBear

RA2020 said: The house had damp issues, so I've removed the defective plaster and have been advised to get a damp course put in and membranes applied to the walls.
The floor joists are also rotten. To resolve this, I was originally going to replace the timber floor with solid concrete

You don't say how old the property is - Anything built after ~1850 or so will invariably have a DPC. This will be a layer of slate, a bitumastic layer, or even a course of hard engineering bricks. Injecting chemicals in to the wall will not give you a DPC, and slapping waterproof coatings on the walls will only mask the problems for a few years.

The water is getting in somewhere - The gully drain is one suspect, so a CCTV survey may throw up some clues and also give you some idea of where it runs. There may also be a leaking pipe, but the waterboard would have told you if the water was rain water or tap water (they test for chlorine). By the sounds of it, it is rain water, so you should be looking at drainage and surface water run-off.

Is there hard paving up to the outside walls ?

Does the ground levels bridge the DPC ?

Are any air bricks visible and free of obstruction ?

Replacing the suspended timber floor is one option, but you still need to fix the source of damp or it will just keep causing trouble. If there are any pipes (or cables) under the floor, you must plan any replacement so that pipes/cables can be accessed for maintenance. With a timber floor, lifting a board is easy. Digging out a ton of concrete is messy.

RA2020

Thanks for the response. The property was built around 1930, it does seem to have a layer of slate or something similar in the wall, but I was told it is probably now porous and may not be effective. 

The waterboard did test for chlorine but the water only turned slightly pink, so they said it wasn't conclusive enough & may just be natural.

Yes, the hard paving does go up to the outside walls all around the property, I think the ground may bride the DPC, I've attached an image of where the DPC looks to be. 

We do have air bricks at the front, but I don't think there are any at the side or back (Although the back of the house contains concrete floor) 

My thinking behind the concrete floor was that (if) I can identify what's letting the water in then the floor will never need to be replaced again. Apparently our detached neighbors have solid concrete floor in their front room, but I think that was done by the council after the house I now own was purchased from the council.

RA2020

Also, I forgot to mention. I'm having a full re-wire and the pipework re-done. The wires and pipes will be coming down the walls rather than through the floor.

FreeBear

RA2020 said: The property was built around 1930, it does seem to have a layer of slate or something similar in the wall, but I was told it is probably now porous and may not be effective.

Yes, the hard paving does go up to the outside walls all around the property, I think the ground may bride the DPC,

I'm guessing the same person that recommended chemical injection & waterproof membrane/plaster told you the DPC is now porous - He is feeding off your fears and lack of knowledge.

First step would be to reduce the ground levels around the outside walls and possibly install a French Drain (check surface drainage as well) - The cost will be minimal. Monitor the damp issues over the next 12 months and see if things have improved. If damp is still an issue, get an independent expert in who doesn't work for a damp proofing company or has links to the PCA - It will cost a few hundred, put you should get an honest assessment.