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Posted: Tue Dec 29, 2009 11:29 am
by harryp
Hi,
The area I live in has a high water table. This resulted in 3 to 4 inches of standing water under the floors prior to installing a sump pump. The sump has remedied the standing water however water still creeps in around the perimeter and then trickles down into grooves I have cut and on into the sump.
I would like to intercept the rising water via perforated pipes feeding into the sump. I intend to cut channels into the subfloor around 12 inches deep and install perforated pipe with pea gravel.
As it appers the water comes in at the perimeter of the house; would I be better going for perimeter drains internally or externally?
The soil is clay which makes it difficult to predict the path the water will take.
Any tips would be very welcome
Thanks
Harry
Posted: Tue Dec 29, 2009 11:56 am
by lutonlagerlout
quality post harry
I would say externally as its better to get it before it comes in, in the first place
LLL
Posted: Tue Dec 29, 2009 2:54 pm
by flowjoe
Hi Harry
LLL is correct in that intercepting the water would be a better solution, are you sure its a high water table and not water tracking through to the sub-floor.
I would be very wary of installing any form of land drainage at a level lower than your foundations as this can lead to subsidence, secondly you dont want to be draining too large an area and have the pump running all the time. The pump will burn out and your leccy bill will be ££££.
Some outside trial pits would probably help to confirm the source of the water and the best way forward.
HTH
Posted: Tue Dec 29, 2009 3:51 pm
by harryp
Thanks for the replies. Yes it is definately a high water table as it effects a large number of properties in the area.
Digging the sump and channels in the subfloor resulted in water accumulating about a foot down. I am concerned about external drainage close to the house as it would need to be around 3 feet deep to reach the same depth.
I have had a number of trenches outside due to replacement of the surface drains. The rising water accumulates in certain areas. I presume this is due to varying porosity of the clay soil.
The other option would be a shallow internal perimeter drain such as 'U' piping or guttering which feeds to the sump.
Posted: Tue Dec 29, 2009 4:10 pm
by cookiewales
harry when you cut a new chanell in clay water will allways follow it try a shallow cut to perimiter see if that helps sometimes you can try and do to much cheers cookie :p :;): :;):
Posted: Tue Dec 29, 2009 4:28 pm
by harryp
Thanks I'll give it a whirl!
The floors are currently up and I want to get any digging done before they go back down. I really don't want to have to revist it :;):
Posted: Tue Dec 29, 2009 5:29 pm
by cookiewales
sorry you may be better tanking it on the outside and inside.but it is allways better to stop water coming in from sides maintain sump pump aswell do outside as french drain find somewhere to drain this water to and you should be fine have done this job myself on high water table 12 inches below ground in winter. i laid aco drain level all round with spurs coming off took it to a storm drain nearby they have had no trouble since give me a call if you need any more info cheers cookie :p :;): :;):
Posted: Tue Dec 29, 2009 6:36 pm
by lutonlagerlout
what surrounds the house at present?
is it paving or soil?
some pictures would be handy
as cookie rightly says if you dig a hole in clay it will fill with water,
this doesn't necessarily mean the water table is high,we have had a lot of rain recently too
oh lastly,have you got issues with damp in the house?
LLL
Posted: Tue Dec 29, 2009 6:57 pm
by flowjoe
I can not recall being involved with a job that was the result of a rising water table in 27 years, its usually water tracking from somewhere due to heavy or prolonged rainfall or someone down the lane trashing through a land drain causing a surcharge.
Foundations and footings cut into a clay sub-soil creates a path of least resistence that water will always take, and usually some kind of interceptor drain will do the trick.
Harry you only need to drain down to an inch below your sub-floor level, if you do use a pump make sure its in a sealed unit that only allows water in ay the desired level.
Posted: Wed Dec 30, 2009 1:48 pm
by harryp
I have recently purchased the house so can't comment on how long standing water has been present underneath. However it has been long enough to cause extensive damage from the damp conditions - damage joists, floorboards and plaster resulting in a lot of remedial work. From speaking to the neighbours the same problem affects all houses on the road and up to 3 roads over.
The house has a paved drive to the right, small garden at the back and a small garden area at the front. The diagram represents the overall area.
I only have a couple of pics to hand. One of them shows the drive ripped up due to replacement of the drains.
http://www.flickr.com/photos/45979532@N05/sets/72157623100533120/
Would an interceptor drain be installed as a french drain on the external perimeter against the wall of the house going down to subfloor depth?
Posted: Wed Dec 30, 2009 2:49 pm
by flowjoe
Harry
Yes we would normally try to intercept the water with a french/land drain on the external walls. Some contractors also render the below ground brickwork or use some kind of barrier such as visqueen.
Again do not install it below foundation level AND i wouldnt dig a full length trench any closer to that gable until i knew the condition and spec for the foundations, we usually work in sections backfilling as we go.
You dont want to end up with a pile of bricks 
Posted: Wed Dec 30, 2009 3:19 pm
by harryp
Thanks everyone for the info. It is really helpful and greatly appreciated!!
Would a geo membrane be required to line the french drain? I can only find it 100m rolls.
I'm about to fill the driveway trench with concrete so it covers the new PVC piping and then use the existing material to backfill. Would expansion/contraction joints be required?