Water keeps seeping in

[Basecoat]

Hi All

My extension is progressing well but one big problem I have is water keeps seeping in through foundations into the new build area. Water seeps in when it rains especially heavy.

My area suffers from water table. It is an annoying problem. I have done a number of things to eradicate the seepage. Concrete filled base areas around foundation walls. Rendered drive side wall where water was seeping through foundation blocks. The water has slowed but not stopped it. My lawn slopes down to my extension that doesn't help. I have put in a temporary gully between the my new wall and the lawn it works but not 100%.

I have been told by two builders that the seepage will eventually stop but I not am sure and I find hard to believe them. I have 30-45mm depth of water inside my extension. Surely this is a perfect recipe for dampness and wet rot. So all of you please help me find the solution. What is the solution to this problem. I wish to thank you all in advance for your input.

 

[noseall]

presumably you have either timber or block and beam type construction to the ground floor of the extension?

 

[Aqua]

Could you construct a sump near to the extension and drain the area in question to the sump with a gravel drain and perforated plastic pipe.

You would obviously need a sump pump to move the water into a main drain. Grunfoss do a very good float switch protected sump pump for this type of job which can lift the water upto 10 meters.

I forget the exact price for these pumps, but they are not that much.

 

[snozzer]

Construct a french drain around the extension, run it to a sump and then pump (or store and reuse in the summer on the garden)

 

[anobium]

If it is due to a high water table and I presume that your ground floor is of a timber suspended construction, then you are unlikely to achieve a bone dry sub floor area.
I go along with what everybody else has suggested but more important than anything is to ensure that you install effective underfloor airbricks in accordance with current building standards.
From what I recall it is approx 1no 225x75mm airbrick every 2.4 m.
This will prevent the moisture vapours on the oversite condensing and wetting the timbers.
PS Also use pretreated joists and boards.

 

[JohnD]

As you are still in build I wonder if it would be worth laying dpm over the oversite and laying some readymix over the top of it? Just has to be enough to give weight to prevent it floating up. Folding up the edges inside the walls and I suppose you would have to put a couple of courses of blocks to prevent water pressure pushing it off?

 

[Basecoat]

Hi All

I wish to thank all for your input in response to my problem with my extension. I dug 600 wide X 250 deep strip foundations. BCO passed them. I had them filled with premix concrete. A week later I started to build the foundation wall using foundation blocks to required level. Again building BCO passed them. He said he satisfied the standard is good and that I can start taking the walls up.

Next I laid the visqueen membrane in the ground and had 150mm deep premix concrete poured in. A couple days later it rained heavy the water started seeping in. I marked the areas water was coming in especially from the base of the foundation wall. I have reinforced base with more concrete. This has helped but not stopped the water getting in.

I was wondering if there is some sort of water repellent/sealant that I can use to seal the foundations to make them water tight. I have also constructed a visqueen membrane gully between the garden and the extension wall the outlet from this gully goes into the drain. Again this works vey well but some water still gets through.

In essence I wish to employ a permanent solution rather then a temporary. I am no expert but water in foundations is got to be bad although I do wonder how city of Venice in Italy works. Their foundations are submerged in water.

I have six airbricks instead of four. The joists for subfloor are in. I intend to fit flooring last when all messy work is done therefore have put down cheap plyboards.

I am very disappointed with this problem. My walls are going up but this problem keeps hindering my progress. The weather is not helping. Please help.