We've recently bought a Grade 2 listed farmhouse and some of the rooms are suffering from penetrating/rising damp as some of the external paths surrounding the house are higher than the internal floors and the building has no DPC as its c1650
Having spoken to a heritage conservation specialist he has suggested installing a land/french drain up against the wall so the rain/ground water is drained away rather than held against the wall.
The walls are ~600mm solid stone and have been rendered in modern cement based plaster internally which is also part of the problem we have as the palster is blowing off. I have been advised tanking is not appropriate for this type of wall and really it just needs to be allowed to properly breathe again with suitable drainage and lime plaster.
i fully understand the concept of the french drain the problem i think i'm going to have is that it appears that modern surface water drainage has been installed around the perimeter wall already, ie where the land drain really needs to go.
What would the experts suggest is the best plan of action?
options i've thought of are
a) digging up the existing drainage installing the french drain next to the house wall then re-laying the surface water drainage next to it and redirecting the down pipe spouts to the drains which would now be sitting slightly away from the walls (might look a bit weird)
b) expose the existing drainage and install the french drain around it. I'm concerned that if its not right next to the wall then the damp problem will remain.
you don't really want a french drain along the house wall, the idea is to divert water away from it. Ideally you need to reduce the ground levels as it is causing 'bridging' . I am wondering why the ground level is so high? As you say tanking is not an option as you need the old walls 'to breathe'. If for some reason the ground levels can't be reduced then maybe one of the 'work arounds' on the drainage pages will do the job.
If 'modern drainage' has been installed where the proposed French Drain is supposed to go, why isn't it acting as a French drain? It should have been laid on pipe bed and covered with same, which is effectively a French Drain.
Maybe it's hasn't been laid with granular material, in which case you have your answer: lift and re-lay using granular material.
Unusually for him, Sean is actually talking sense!
French Drains are rarely an effective remedy. They are 16th C technology and we have moved on a bit since then. High ground levels and the potential for bridging are more relevant.
.........i do have the odd light bulb moment, only trouble is i'm like a modern bulb, turn on and it's dim then takes a while to brighten up ??? :laugh:
the problem might be just caused by useing modern cement based render on the inside pulling the damp in. but like they say reduce the ground outside if you can.
i agree with all of the above
cement renders on old building cause loads of problems
the reason the ground is high on old properties is 400 years of deitritud rotting down then building up
why do you think old churchyards are always 3 foot higher than the outside road?
LLL
This is where an expert polish builder would have good advice, even now they build without damp course and have less issues than us. Our damp course is a joke to them. Do it right, do it once. Lower the ground levels, remove the render the rest should work as nature intended
I've been having a look round and i think we certainly can lower the levels somewhat so i've got a local guy and his mini digger coming next week to drop the paths.
We'll also be adding some additional drainage as currently some of the gutters just pour onto the path around the house which obviously won't be helping things.
However i'm not sure we'll be able to drop all the paths sufficiently to be below the internal floor levels as some of the internal floors are a good 18" below the current outside path levels and there's quite a lot of existing drainage thats already set and can't be moved without a huge redevelopment ie pipes that go under extensions, inspection chambers etc
Ideally what sort of level below the internal floor levels should we be aiming for?
Also if there's existing drainage pipe work against the walls can the fin drains mentioned above be fitted under/around their current location? or would that drainage need to be lifted and relocated?
I've included some more pictures which hopefully help clarify the job we've got on
Problem guttering section
No downpipe or end caps, effectively useless, water from the roof has essentially been pouring onto the steps and soaking into the wall
Conservatory Guttering just pours straight into ground
You can see the property is on a bit of a slope
I found the airbricks for the suspended wooden floor all blocked
There was also a buried inspection chamber
More of the path round the rear of the property
This pipe work runs under the extension and feeds into the main inspection chamer at the front of the house, it's not possible to adjust this so this is really setting our minimum level on this side of the house
having unsuccessfully found any plasters/builders that seem to have any experience or knowledge of old buildings and that don't want to drill and inject or just use modern materials I'm going to have to attempt to tackle this myself (well the drainage anyway)
basically we've had the paths lowered as best we can till we've hit existing rain water run off pipes so we can't really go any lower now and in fact we'll have to raise the paths back up with new gravel to sufficiently cover them.
the soil under the paths seems to be clay from what I can tell as when it rain they puddle with water and don't drain away
so basically they plan is to install a French drain but i'm in 2 minds whether to also do some sort of external tanking as well, whether it be some sort of paint or cementatious slurry. Does anyone have any recommendations for products? or will just gravel up against the wall be sufficient?
The footings aren't particularly deep below the level we've lowered the paths too at the moment maybe ~25cm. Would it be ok to expose the foundations along the length of that wall or will it need to be done in sections?
cheers for any advice
The path as it stands now
one of the holes dug to discover the depth of the foundations
