We are currently undergoing having an extension built on our house. The shell is complete and watertight.
When I look into the cavity at the ground floor door opening, I notice that there is standing water in it. The level is about one course (75mm) lower than the damp course. The footings are built using dense concrete blocks on the foundations and I do know for fact that there is not any concrete in fill of the cavity. The water is approximately 300mm deep.
I did originally think that the water had built up when the walls were incomplete and rain water had ran off the floor into the cavity. When the shell was complete, using a drill pump I removed as much of the water as I could (at least 200 litres!) I now realise however that the ground water will find its own level and permeate through the wall into the cavity.
Is it ok to have such water standing in the cavity? I must decide quickly if any further action is required before plastering, floor finishing etc.
I thank you in advance for any advice you can offer.
My Bungalow is built on the side of a hill. The cavity is about one metre or more deep below the DPC and you can just make out the water with a powerful torch.
Its been like that since 1934.
It never gets any deeper so I presume it gets away through the front somewhere and just trickles down the hill.
So it'll probably be OK until the place is demolished then. I'd leave well alone. As others have mentioned if it's below the DPC there won't be a problem. ALL houses are damp/wet below DPC level - that's why it's important not to bridge it (the DPC I mean).
Interesting that you've got cavity walls in a 1930s building though.
Thank you Alda, Perry for your advice. Looks like the water in the cavity is here to stay!
The ground level outside the extension is below the damp course but as the extension is cut into the land, I think this is why the build up of water is so great. I have a 1.2 m high retaining wall at 1.2 m away from the extension and as an extra precuation I have installed a 80mm perferated drain away.
It rained quite a bit recently and water built up between the extension and retaining wall, but not higher than the damp course so hopefully it will not be a problem. I am unable to put a gully drain in as the ground height is lower than the sewer drainage so have ran out of ideas!
WHERE THE OUTSIDE SOIL LEVEL IS A FAIR BIT LOWER THAN THE DAMPPROOF COURSE, THERE SHOULD HAVE BEEN A FEW VERTICAL MORTAR FREE JOINTS LEFT OPEN FROM WHICH THE WATER CAN ESCAPE THE CAVITY.
SOMTIMES THEY HAVE A PLASTIC INSERT(MINITURE GRILL)FITTED IN THEM.
IF THERE ARE NONE YOU CAN CHASE OUT THE MORTAR BACK INTO CAVITY YOURSELF TO HELP DRAIN THE WATER.
IF THE SOIL LEVEL IS HIGH(CLOSE TO DPC)YOU SHOULD TRY TO LOWER THIS LEVEL IF POSSIBLE AND AFFECT ABOVE REMEDY.
COULD YOU INSTALL DRAINAGE HOLES THROUGH THE RETAINING WALL?
THIS WILL NOT SOLVE YOUR PROBLEM COMPLETELY (AS YOU AND I SEE IT) BUT WILL REDUCE TO A MORE ACCEPTABLE LEVEL. (FOR YOUR PEACE OF MIND).
IF I WAS IN YOUR POSITION, I TOO WOULD BE CONCERNED.
I THINK IF THE WATER LEVEL IN THE CAVITY IS ONLY 75mm LOWER THAN THE DAMP COURSE THEN THE GROUND OUTSIDE IS WATERLOGGED AND/OR NOT AT LEAST TWO BRICK COURSES LOWER THAN DPC.
IF GROUND IS WATERLOGGED AND CANT GET AWAY QUICK ENOUGH, IN MY VIEW, THE WATER LEVEL COULD RISE ABOVE DPC IN CAVITY (PATH OF LEAST RESITANCE/WATER BACKING UP)
THIS MIGHT ALSO IMPLY THAT WATER IS UNDER THE (ASSUMED!!!) SUSPENDED TIMBER FLOOR!!!
WHERE YOU CAN DO SO, LOWER THE EXTERIOR GROUND LEVEL AND OPEN UP SOME VIRTICAL MORTAR JOINTS (EVEN AT TWO BRICK LOWER LEVEL) AND IF YOU CAN CHANNEL WATER AROUND EXTENTION AND AWAY TO LOWER LEVELS/THROUGH RETAINING WALL USING PERFORATED PIPING/ GRAVEL INFILLED DRAINAGE TRENCHES.
Steve, the water inside the cavity is OK as long as its below the dpc.
You indicate indirectly that the water does get away, somehow.
In as much as, with all the bad weather we've had recently it hasn't ever reached the dpc hight.
You also mention that the sewer pipe is higher up.
Seemingly one option is a float actuated pump,discharging into the drain.
The other is to dig out beside and below the sewer pipe, creating a French drain to lead the water away, to where ever the drain goes.
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