damp proof course correctly installed

ktj

The builders doing our extension have just put in the damp proof course below the layer of concrete that will form our sub floor. They have done this as follows. First they put a blue membrane over the hardcore and then a layer of concrete over that. All around the most of the edges, the blue membrane is long enough to lap up and over the low breeze block wall that forms the footings for the walls of the extension, however 2 things worry me. Firstly along 1 edge of the foundations the blue membrane is not long enough to lap up the side of the breeze block and secondly the layer of concrete seems very thin in places and in some areas the blue membrane is barely covered. Is this the norm or have I got a costly mistake on my hands? Any advice, especially from anyone in the building trade, very gratefully received.

03022242

did you get building regulations approval before starting the work?

owls

the blue membrane you mentoned is called visquine,
it is not designed to run up the wall it is purely there to prevent any damp rising up through your floor and not your walls, there will be a seperate dpc in the wall. in fact it is the other way there shouldnt be any over hang, they should cut it off flush to the new concrete floor.they should have also put a good bed of sand under the blue visquene to stop any puntures of it once concrete is laid on top

dstill

ktj wrote: »

The builders doing our extension have just put in the damp proof course below the layer of concrete that will form our sub floor. They have done this as follows. First they put a blue membrane over the hardcore and then a layer of concrete over that. All around the most of the edges, the blue membrane is long enough to lap up and over the low breeze block wall that forms the footings for the walls of the extension, however 2 things worry me. Firstly along 1 edge of the foundations the blue membrane is not long enough to lap up the side of the breeze block and secondly the layer of concrete seems very thin in places and in some areas the blue membrane is barely covered. Is this the norm or have I got a costly mistake on my hands? Any advice, especially from anyone in the building trade, very gratefully received.

Hi,

The DPM (Visqueen) should lap into the DPC to all sides of the sturcture. This prevents any point at which dampness can penertrate through to the internal of the building.

ktj

Thanks for all comments. Yes we did get building regs approval and the building inspector has made the builders redo the worst bit, but I'm concerned about the rest it seems a very tatty job. I don't think they put a layer of sand under the visqueen and the soil pipe that runs through the foundations isn't completely covered by the concrete. Does this need redoing before they get paid?

dstill

ktj wrote: »

Thanks for all comments. Yes we did get building regs approval and the building inspector has made the builders redo the worst bit, but I'm concerned about the rest it seems a very tatty job. I don't think they put a layer of sand under the visqueen and the soil pipe that runs through the foundations isn't completely covered by the concrete. Does this need redoing before they get paid?

The layer of sand often referred to as a blinding layer is to prevent any stones etc puncturing the DPM. If this were to happen it would offer a route for dampness to penertrate the concrete floor.

I would of expected the soil pipe to be completly covered to prevent any cracking of the concrete floor due to shallow concrete coverage. However, i would'nt think it would cause a problem, just ensure they have the correct fall on the pipe. The optimimum fall for a horizontal pipe is 7 degress which ensures the pipe is self cleaning.