French Drains v Tanking

[Christien]

Hi, has anyone got any idea how much it would cost to have french drains installed to prevent water pooling in my sub floor under the boards. Or would tanking be a more effective method?

Any advise much appreciated.

 

[HERTS P&D]

£193,000 plus vat.

 

[Christien]

Dont give up your day job, you will never make a comedian!

 

[freddiemercurystwin]

What HERTSDRAINAGE2010's cryptic post means is that we haven't got a feckin clue unless you bother to actually grace us with some useful information!

 

[Christien]

I have water pooling under my sub floor every time it rains. I have checked that its not a burst pipe, had my drains checked, had a aco drain installed and have now been advised that its the water level allowing water to penetrate under the boards. I have the following options:-

Take out the timber floor and replace it with a concrete floor and provide
a damproof membrane (expensive but the best long term option)

Lower the ground externally and install a drain/sump to remove the water
(cheaper but may not solve the problem)

Provide a vertical and horizontal tanking detail to prevent the water
coming in (depends on the extent of the problem, but would entail either removal of and subseqent reinstatement of the timber floor or fairly
extensive external works)

 

[^woody^]

You are probably being badly advised

Water ingress to the sub floor void is perfectly normal. That is how your property has been designed ..... along with 000's of others

If it has been occurring since the property was built and there are no structural problems, then it can be left alone. If there was a problem with it, then you would know by now.

If there is a recent problem, and the water is getting more prevalent, then you need to locate the cause and deal with that

Tanking is not a practical solution so should not even be considered

A French drain or other drainage solution is an option, but may not be a necessity. You will need to get this properly surveyed, ground tested, and a solution designed. It wont be guesswork if it is to work

By far the cheapest, and simplest option may well be just to fit a sump pump to operate at certain water levels and pumped to a nearby drain

 

[HERTS P&D]

As above, buy a plastic dust bin and drill holes into the side and bury 1/3 into the floor. Put a sump pump into it with the hose leading into a gully. Make sure you have a RCD plug fitted to the sump lead, you could even fit a timer onto the pump to work between 6am - 11pm, this way you won't be able to hear it when in bed.

Flexible pipework:
http://www.ebay.co.uk/itm/1-5-inch-...res_UK&var=&hash=item6b1dcf2455#ht_882wt_1270

Sump pump:
http://www.ebay.co.uk/itm/Clarke-HS...ltDomain_3&hash=item5d33112198#ht_1964wt_1037

Andy

 

[Christien]

Hi,

Many thanks for your replies. If the water under the boards was not causing any problems, I would just put the carpet back down and forget about it, but there is damp rising up on my internal walls and the chimney breast (which used to have an open fire, so there is a mortar pillar instead of boards supporting tiles in front of the breast which is sucking all the water up and causing a salt like substance on the plaster on the chimney breast) It rained all day yesterday and there must have been at least an inch of water covering the entire sub floor. As i previously mentioned, there are electric cables lying on the sub floor which are being completely submerged in water. That cant be right?
I did consider a sump pump but there is only about 12 inches between the sub floor and the boards. Would there be enough space to fit an adequate pump? and where would be the best place to put it considering the whole of the sub floor is pooling water?

Regards

Chris

 

[HERTS P&D]

Dig a hole in the floor then you will have the depth you need, also the surrounding water will flow into the 'hole' where the pump will pump it away.

As for the cables, these should be fitted on or under the joists and not in the water.

Andy

 

[Christien]

Thanks Andy,

I will consider this option. would the surrounding water fall into the dug out hole if the ground is even? I am really confused as to how the water is entering my house. It seems to appear from nowhere! Could it be that it is being drawn up from under the house when it rains?

Regards

Chris.

 

[^woody^]

but there is damp rising up on my internal walls and the chimney breast
Chris

If that is the case, then the walls will still be damp whether you have ponding on the sub-floor or not

There should be a DPC in the walls to prevent this, and whether there is, or whether it has failed is the problem, and not the sub-floor water

 

[PaulJR]

Thanks Andy,

I will consider this option. would the surrounding water fall into the dug out hole if the ground is even? I am really confused as to how the water is entering my house. It seems to appear from nowhere! Could it be that it is being drawn up from under the house when it rains?

Regards

Chris.

If it is "ground water" then the water is indeed rising up out of the ground, the recent wet weather has probably saturated the ground and it's rising - what we refer to as the water "table" is getting higher. My own garden is currently under a few inches of standing water, sorry I meant standing drought.

I would suggest the sump pump is a good solution, even if just for the short term. If you dig the bucket into the ground as suggested the water will get to the sump, the pump will have a float switch and will empty the bucket once it's full and then stop.

I am a civil engineer and attempting to tank and existing basement is a really expensive idea - the joke £200k quote isn't far off. The damp is a dpc issue - perhaps the higher levels are topping your dpc, assuming you have one?

If you go down the filter drain route you need to go down to foundation level ALL around your house and then connect the carrier pipe to a sump - which will probably need a pump (so you are back to the pump) and send it to an outfall, drain, soakaway or ditch. This will destroy any paths, drives etc around the house, so will be expensive to make it all good again.

Regards the cables, as long as no joints, junction boxes or sockets etc. are wet it doesn't really matter, continuous cable is waterproof, the one that supplies your house is buried.

 

[Christien]

Paul,

Thanks for your input. I am going to get my boards up soon and assess the situation. From what I can see with a few boards loose already, some of the floor is concrete, covered in damp, what looks like sand. Would it be a good idea to clear all the floor of this so its not holding the damp?

You mentioned the dpc, there is evidence of this on the outside wall but would the internal walls have it? Forgive me if this is a stupid question, but I really have no idea about this sort of thing. Also, do you think it would be a good idea to dig out the mortar hearth in front of the chimney breast as the tiles covering it is really damp, like its sucking up all the water from below.

Regards

Chris

 

[^woody^]

Some older properties upto the 1950's had blue bricks as a DPC on internal walls. As such, these can get overwhelmed on internal walls and have some rising damp. Slate DPCs can crack too. If there is a DPC on external walls, then it should be on internal ones too.

Hearths are always problematic as they have no damp protection at all and have a solid base down to any damp ground. Chimneys can be similar

 

[PaulJR]

CHristien

I would go a step at a time. Install the pump & sump (bucket) and get that working, then see if things dry out.

If you still have damp once you have lowered the water level under the floor then look at other stuff.

As woody says the dpc type depends upon the age of the building, and it may have had an injected type installed at some point, difficult to say without seeing the building. Are the walls cavity or solid construction? cavity usually means dpc, solid often no dpc, slate, blue brick etc. These type may need a dpc adding afterwards, a very messy and expensive job.

Whatever you do, it might take 6 months for the house to dry out again, so be patient, you can run up huge bills with damp.