Water under house, cracks appearing in walls

[Chaser]

Looking for some advice, moved in to our current semi detached a few years back and about 18 months ago, found water under the ground floor. Theres about a foot void between floorboard and concrete pad underneath. All signs that this water has been there for some time. As i'm in the process of decorating/renovating, i'm looking to tackle this as soon as possible. I pumped it all out a couple of months ago, but found that the water looked to be seeping in through a hairline crack in the concrete pad, which appears to span across the house. I'm not sure of the full extent of the crack yet, but will be pulling the floor up to investigate further in the next couple of weeks.
Further to that, I have noticed a few cracks appearing in plaster this winter and also on the ground floor, we have oak flooring laid in the dining room which has developed a gap between the boards of around 7-8mm. Its probably been down more than 5 years but this has just happened since September/October.

First of all, I want to address the water under the house. Can the crack in the concrete be sealed and if so, whats best to use? I'd also like to treat the area underneath with some kind of impermeable layer if at all possible, to seal in and prevent the joists rotting underneath and the smell of damp eminating from the lounge area.

 

[^woody^]

In most cases it's common and you wont stop it - thats why the timber floor is above a void in the first place.

But you could check for mains or drain leaks

And all air bricks venting under the floor should be clear

 

[Chaser]

But if its common, surely there should be something in place which prevents the joists and floorboards from rotting? The smell is also apparent, as the water swills around the 50 years of dust and everything else under there. I sucked out over 100 litres of water from it about a month ago, but it came back. I intend to do it again as best as I can before looking to make the necessary adjustments. It may be that I need to dig a trench and run a drain into the rainwater drain.

 

[Mottie]

My father in law had the same problem. It was completely clear too - as if it was fresh, mains water. He called in the water board and they carried out loads of tests etc but could find no sign of mains leakage anywhere in the area. He had a considerable drive at the front of the house, around twenty metres and the front of the house was about two metres below the main road in front of the house so he suspected it was just the water table backing up under his floor as his his garden also ran down away from the house at the back so he dug a trench, broke through the footings at the rear and shoved a drain pipe just under the void and extended that well into the rear garden, leaving the end of the pipe open for any water do drain away. He never had any problem with rotting wood etc and all air bricks were clear.

 

[^woody^]

But if its common, surely there should be something in place which prevents the joists and floorboards from rotting

Airbricks

 

[Ian H]

I'd turn off your internal stoptap and monitor your water meter for 1/2 hour.

Then get some drain dye and simulate heavy use to foul and rainwater drains.

If one of those proves to be the source of the water you won't need to dig any trenches inside.

 

[Chaser]

Airbricks

Airbricks are clear and have been for last 3 years. Theres constantly at least 2 inches of water under there.