Green Building Forum - French drain Sat, 02 May 2026 10:19:24 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273190#Comment_273190 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273190#Comment_273190 Fri, 05 Apr 2019 15:39:00 +0100 Artiglio Pulling up the floor and redoing it, removing the tanking are neither economical or practical.
Its been suggested a french drain along the wall will at least prevent the wall getting any wetter and repointing with lime will help the wall dry out a little over time.

Plan is for a 600mm wide trench along the wall to 100mm below the concrete floor level, a studded dpm against the wall , a geotextile in the trench then backfilled , suggestion is to use cockle shells ( available locally) as this will give plenty of air space and quick drainage.

The wall will then be repointed in lime.

The homeowner understands that this will not make any immediate improvement , but that it should prevent further water being sucked into the wall and over time allow the wall to dry out a bit.

Is this a sensible way forward? Being a diy project its not overly expensive . Any suggestions to improve or new ideas?

TIA]]> French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273193#Comment_273193 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273193#Comment_273193 Fri, 05 Apr 2019 20:20:30 +0100 djh Posted By: ArtiglioI’ve a wall in an 1800 house, semi basement 9” brick,
Sorry to be ignorant but what is a 'semi-basement'?

100mm below the concrete floor level

A diagram, or at least a list, showing the levels of everything in relation to ground level would be helpful.

My instinct is that 100 mm below the concrete isn't deep enough. 600 mm width is more than enough; I presume that's because of ease of digging?]]> French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273198#Comment_273198 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273198#Comment_273198 Fri, 05 Apr 2019 22:37:34 +0100 tony French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273201#Comment_273201 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273201#Comment_273201 Sat, 06 Apr 2019 01:15:22 +0100 Artiglio
The house has differing ground levels front to back, at the rear the kitchen opens onto the garden , to the front the ground level is 1100mm above the finished floor level in the kitchen. I’ve called it a semi basement for lack of knowing the correct term.
The 600mm as you say was selected purely for ease of digging. Buildings in the area are usually built straight onto the chalk with spread brick and often don’t go much below floor level, i’d not want to go below the bottom of the wall and into the chalk. Though if the brickwork goes deeper i’d be quite happy to go down a bit further.

Thanks gents]]> French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273202#Comment_273202 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273202#Comment_273202 Sat, 06 Apr 2019 06:26:04 +0100 gyrogear Posted By: Artigliothe rear the kitchen opens onto the garden

sounds like you have a walk-out basement, then.

(like me)

gg]]> French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273203#Comment_273203 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=273203#Comment_273203 Sat, 06 Apr 2019 06:59:20 +0100 tony French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=301196#Comment_301196 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=301196#Comment_301196 Sun, 16 Apr 2023 08:51:46 +0100 cc64 https://youtu.be/bEVBOEIktr4
Usefully better than many other resources I've frittered time away on
Recommended for French drain detailing]]> French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=301208#Comment_301208 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=301208#Comment_301208 Sun, 16 Apr 2023 20:08:15 +0100 Jonti French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=305663#Comment_305663 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=305663#Comment_305663 Fri, 05 Apr 2024 16:41:08 +0100 lineweight
I am looking at a similar sort of situation and trying to work out the options.

I've seen some advice that it can be a bad idea to install a "French drain" right next to a wall for risk of destabilising the foundations, especially if they are shallow. We suspect the foundations are shallow, and it's a clay soil area.

Because of the location (a small urban front garden) it's difficult to connect any drain either to a soakaway or the public sewer. I've been wondering if a gravel-filled trench (but without a pipe at the bottom) is better (or worse!) than nothing. Because the outside ground level and inside floor level are at much the same height, if any water close to the wall could at least be encouraged to sit (and gradually soak away) say 150mm below ground level, instead of at ground level, then less of it might make its way through the lower portion of the wall to the interior.

Can anyone recommend any good technical resources for this kind of thing?]]> French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=305665#Comment_305665 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=305665#Comment_305665 Fri, 05 Apr 2024 20:18:47 +0100 djh Posted By: lineweightI've seen some advice that it can be a bad idea to install a "French drain" right next to a wall for risk of destabilising the foundations, especially if they are shallow. We suspect the foundations are shallow, and it's a clay soil area.Clay comes in a variety of types, some of which heave and others which don't. Is there evidence of heave anywhere around? Has the wall heaved, for example?

I suspect step 1 is to dig a trial hole to see exactly what the foundations are like. You perhaps can also see how deep the clay goes and you can fill the hole with water and see how fast it drains (i.e. is absorbed). If you can find out what is below the clay you'll have a better idea of how useful a French drain with no outlet will be.

I don't suppose there is any chance of lowering the whole garden a bit? That would give a much larger storage volume. Or take off the topsoil, dig out a load of clay and have it taken away, then put back the topsoil and a load of mulch of some kind.

edit to add: I googled French drain design and a couple of useful-looking hits are https://urban-water.co.uk/french-drain-design-guide/ and https://www.ths-concepts.co.uk/how-to-design-french-drain/]]> French drain https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=305683#Comment_305683 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=16086&Focus=305683#Comment_305683 Sun, 07 Apr 2024 23:40:44 +0100 Artiglio
As yet nothing has been done, however the householder has been persuaded that heating the house a bit more , using the extractor fan in the kitchen and a bit of localised removal of the cement pointing ( little more than a smear in most places) might give an indication of how bad things are.
The result has been a visible improvement in the extent of the “ wet looking “ brickwork , the plan is to keep the changes going over this summer and monitor what happens and then have a rethink on what may or maynot be the best way forward.
Basically hoping that over the drier months the walls keep drying out slowly and so convince the homeowner that keeping the house a bit warmer is worth the expense and that next winter with slghtly drier walls the cost of the extra warmth is reduced a bit.]]>