French Drain in Victorian House

Dampproblem

Hello, due to a newly built terraces the ground level is now slightly above floor level in my Vicotrian House from the 1880s. This has caused damp in the interior. I assume this is the cause as there are no damp problems where there are no newly erected terraces. I am now planning to dig a trench directly along the exterior wall, around 40cm below the interior floor level. This means that from the bottom of the trench there should be about 15cm to the floor joists (the house has suspended wood floor) and I assume (I cannot see it) also 15cm to the presumed damp proof course. I am not planning to apply any further insulation to the exposed outer walls apart from the 20cm wide layer of rubberised paint, which the vendor has already applied from ground level onwards. I think for a period building it is better to let it "breathe", rather than trying to tank it. My question is whether it is preferable to install a French drain or rather an Aco drain at the bottom of this trench. An Aco drain is easier to maintain, however, I would have to install it in a bed of concrete, which would in turn would tend to seal off the part of the outside wall (about 40cm from the bottom of the trench) that is still covered by the newly created terrace. The problem with a French drain is, that I would have to dig even deeper (another 50cm from the bottom of the trench?) and that it's gravel would be in direct contact with the house wall. Which of the two do you think is the better solution?Also, do you have an idea how I could optically improve the ugly sight of this 40cm deep trench around large parts of the house. Filling it in with gravel is not a solutions, as then the gravel would start to reach above the internal floor level as well as above the presumed damp course. I am even afraid of putting a grate on top of it, as even this will facilitate water intruding above interior floor level and (presumed) damp proof course. Finally, there is the question of how I stabilize such a deep hole (40cm +50cm if I go for a French drain at the bottom of the trench, a bit less when I install instead an Aco drain at the bottom of the trench), even if it just one side of this hole, as the outer wall of the building obviously does not need to be stabilized. Would cladding it in plywood work, or is this likely to rot away fairly soon? Many thanks for your help.

anotherbaldrick

Who built the terraces and why were they built to above DPL level ?

phill99

anotherbaldrick wrote: »

Who built the terraces and why were they built to above DPL level ?

How would the OP know? The house was built 140 years ago.

cyclonebri1

phill99 wrote: »

How would the OP know? The house was built 140 years ago.

And it also won't have any damp course, well not unless it has been inserted later.

P99, I think you have it wrong, the OP means the pavement(terrace) has been raised, unless I have it wrong:rotfl::rotfl:

Damp problem, I also misread in a different way, from the title I thought it was a french drain in a victorian property,

For my money the person who built the paths/pavements/terrace should have installed atco or similar drainage channels, and certainly not have raised it by the amount you mention.

Determining the DPC is your 1st move I think.

anotherbaldrick

phill99 wrote: »

How would the OP know? The house was built 140 years ago.

How about reading the OP ?

Hello, due to a newly built terraces the ground level is now slightly above floor level

leveller2911

cyclonebri1 wrote: »

And it also won't have any damp course, well not unless it has been inserted later.

They had slate damp courses Bri..........:D

Mark_Mark

anotherbaldrick wrote: »

How about reading the OP ?

Too hard it hurts my eyes.

cyclonebri1

leveller2911 wrote: »

They had slate damp courses Bri..........:D

Did they??? By that I mean they didn't all have. (without offense of course)

If the OP can't see a damp course then to be honest it probably never had 1.

Leveller, I've cut lead DPC's into houses from the 1870's that had no DPC whatsoever, around hear, and up to around the early 1900's DPC's were rare.

Get this, chop a course of bricks out of the outside wall for 4 feet.

Insert lead sheet, (4ft was the standard width), mortar up and brick in.

Move on 3ft and do the same again.

A couple of days later you chop out the links and overlay the lead and re-brick.

Standard practice, (and bloody hard work back in the day), :rotfl::rotfl::rotfl::rotfl:

anotherbaldrick

Mark_Mark wrote: »

Too hard it hurts my eyes.

You could always copy/paste the post and do the punctuation for him/her

Mark_Mark

anotherbaldrick wrote: »

You could always copy/paste the post and do the punctuation for him/her

Why should I?

It's not for me to moderate this forum.

Enceladus

If you check carefully there may well be a layer of slate between the brick courses, one or two layers up from the footings. Might be hard to see with erosion and pointing etc.

If the slate layer is bridged by earth or concrete or whatever then you will get damp in the walls. I had this problem where somebody had concreted over a side passage. One spring I cut out a channel along the wall and exposed the top of the footings and filled it with shingle. The difference was dramatic. The walls immediately started to dry as checked by measuring the height of the damp on the inside wall with a meter.

Also it might pay you to lift some of the floor and check it's clean underneath. If the house is Victorian then there may well be a significant build up of debris around the air vents, possibly blocking them totally. Indeed are all the air vents even present after all this time? Likewise there can be a build up of coal dust, soot, ash and similar debris against the walls beside where fire hearths are/were. All these debris mounds can easily grow to bridge the slate layer on the inside. Not to mention that under floor is out of sight and is a convenient place for the disposal of building waste following repairs over the years.

BTW I protected the slate layer with a product similar to flash banding but used with a wall primer before I repaired the concrete. Can't remember the name of the stuff, but it worked fine. At some point I intend to take up all the concrete and re-instate it at a lower level.