Drainage and damp problem/solution/maybe???!!!

[davidward89]

Hi everyone,
Thought I would post on here after coming across this super helpful forum. I've read around the issue I have in some other threads but I thought I'd post a detailed explanation of my issue and possible route forward to see if anyone can help/advise/tell me I'm being completely stupid!!

I live in a 1906 terraced house in Pembrokeshire, a property that My wife and I moved in to with our four kids last year, and which is likely to be our home for many many years to come hopefully!! The house is absolutely amazing and in need of full renovation. We've tackled a lot of the main issues and am now on the the following:

At the rear of our property is a kitchen area with a utility area right at the back of it, from which I assume there was some sort of covered coal store at some point in the rear garden, dug in to the ground. It would have been accessed through a doorway which has been blocked up with breeze block with a cavity. All of the rest of the walls in the property are aprox 20inch thick stone with no cavity.


Th issue is as you can see that water makes its way through the bottom of the breeze block wall and in to the utility area. To complicate matters the area to the left of the breeze block wall is not a pit, its the garden height, making the pit about 3 ft lower than the garden.

Here is the height of outside shown from the inside:

Ideally my first thought was to excavate on the outside, digging down all the way down the length of the utility and down the side of the outisde toilet which is attached to it, but the more I think about it the more I think that this is not feasable. The wall of the utility not behind the pit and of the outside toilet are relatively damp free and having dug down a small amount they are built straight on the rock in the ground, which I would rather not start having to disturb if at all possible.

My current thinking is this;
- Dig a pit on the outisde, lower than the breeze block wall (which I have already begun as seen in the outside picture)
- Dig out a channel on the inside of the utility and through to the outside toilet where there is a existing manhole)
- Lay a land drain beginning in the pit on the outside of the breeze block, and run it through/under the breeze block wall/step, along the channel dug on the inside of the utility, through to the outside toilet and terminating in the existing manhole.

This is my first idea just to see if that will control the movement of the water, past this I plan to use a geotechnical membrane on the outside pit breeze block wall and backfill the pit completely to the existing adjacent level, laying a membrane and concrete pad for that area. Installed along the new continuous level of the outside of the utility to the top of the steps will also be an aco drain to aid with surface water removal, down the steps and into a further set of aco drains to a drain gulley that already exists.

My primary concern is the land drain idea though; is this a good idea? Am I missing something huge? I'm very keen to stay away from just tanking everything as seems to be all I hear everyone tell me to do, but understand that if this will work alongside perhaps its also an option, but if I can stay away from it I would rather do.
I'm approaching the land drain idea as a first sort of test to see what happens.

I'll attach further pics in a second post as I think I've reached the max, and a rough plan which I hope will make it all clear!

Thanks in advance!!!
David

 

[davidward89]

 

[davidward89]

Or perhaps because I plan to backfill the pit and bring the level up the existing pathway this is completely unnecessary?!!!

 

[Zebra]

The drain - the green lines in the images above - makes sense, provided you wouldn't be damaging any sort of DPM that might have been laid beneath your utility room floor, or any pipes and cables etc. But by "land drain" do you mean of the perforated type? It wouldn't make sense to be perforated, I think, once it gets indoors at least. I wonder whether simply a yard gully and normal 100mm drain pipe would do as good a job. It depends on where the water is coming from: is it rain that simply falls there? does the pit slope downwards towards the house? or is that the height of the water table? Would a similar hole dug a little away from the house fill to the same height? Where is the downpipe dumping all the rainwater from the guttering on the back of the utility room?
In principle I think it's not a crazy idea, to run a drain under the house to the existing manhole, if it's not feasible to drain it away in the other direction to a soakaway.
Backfilling the pit though seems a terrible idea, I would imagine that will only make your problems worse, as will any sort of membrane against the breeze block wall.
An Aco drain along the back wall where it abuts the raised area - the red line on the drawing - seems unnecessary depending on the fall of the land there - if it falls toward the house then maybe - but sending the runoff down the stairs is asking for trouble - it'll make the stairs very green and slippery and might cause damp ingress into the outside loo and even perhaps into the neighbours house.
The Aco drainage in the yard seems reasonable, to deal with surface water there, if necessary.

 

[davidward89]

HI Zebra, thanks for your reply.
That's a good point about possibly damaging a dpc, I've no idea what's under there!
I was thinking of the perforated type but the more I read about these the more I'm put off by them to be honest. A solid pipe sounds like a better idea. What do you mean by a yard gulley?

In terms of where the water is coming from, yes it's purely rainwater, and the pit does slope towards the house. The issue is the whole garden gets higher as you go away from the building so its pretty impossible to drain anything away from the building.
The guttering is just a temporary at the moment, we've just had the utility reroofed and I've not got round to attaching a downpipe yet, and the water naturally drains down the steps at the moment as that's the only way it can go, but I need to add in relevant drainage to prevent it running down the steps, but this is all good, I can sort that.

Not backfilling the pit isn't really an option...if we don't backfill it and bring it up to adjacent garden levels then we are just left with a pit in our garden, which is no good at all!
So it seems to me I have two options:
1. Backfill the pit, laying a concrete pad on a dpm with adequate drainage against the exterior utility and toilet walls to direct surface water away from the building
2. Dig out around the entire outside utility and outside toilet area, building a retaining wall and installing drainage and the pit level all the way around the building to the yard area. This would mean removing the steps also. If this is the best option, then it is something I am willing to do, but I'm trying to explore other options as this is a huge task and I'm not keen to loose more space than I need to in what's already a compact garden.

What do you think? It needs to become a usuable space somehow.
And if it is possible to backfill sucessfully, is the drainage pipe talked about initially laid inside the house (green line on the pictures), a completely unnecessary task?

Thanks again

 

[Zebra]

This is what I mean by a yard gully, something like this.

What about a partial option b. If the steps and existing raised external area aren't causing a problem, then there's no need to dig them out, especially if as you say, it's rock down there not soil. But what about a retaining wall say 400-500mm away from the newly filled in doorway.
On here we are constantly advising people to dig soil and concrete away from the external walls of their houses, as it's a recipe for penetrating damp. See here:

The Zebcolm Trench

The Zebcolm trench is so named because I made one, and then malcolm made one. If you make one, let us know and we can elongate the name. The Problem: ground levels higher on the outside than inside, causing penetrating damp through solid wall, with no possibility of lowering external ground...

www.periodproperty.co.uk

Could you do a Zebcolm trench behind the filled in doorway and the full width of the pit, topped with a grating which would be removable for access, and then landscape the rest of the garden as you like.

Then you'd have to link it all up: if the raised area of garden slopes towards the house then I can see the necessity for the Aco drain along the existing raised area (back of utility and toilet), but instead of sending it down the stairs, it could go into the trench and join up with the yard gully.

If the newly filled in pit has no option but to slope towards the house then some sort of drainage system - either an aco drain at the top on the garden side of the retaining wall, or simply letting the water run into the trench and dealing with it at the bottom, or perhaps if the retaining wall were higher than the garden beyond then you could slope the ground towards another yard gully up there, and send it down into the trench to join up with the rest of the system.

Food for thought? You really want the ground level in the trench lower than the floor level inside the utility room.

 

[Zebra]

Just to add, this would be very similar to my own arrangement in that within the bottom of the trench I built here, there is a yard gully, into which the gutter downpipes are routed, which connects to a plastic drainpipe which runs under the house to a manhole at the front.

 

[davidward89]

Okay yes this is an interesting idea, I had seen your post with the zelcomb trench but was unsure if it would work for me.
In terms of the retaining wall, is it necessary to make sure that water can't permeate through this? I.e. if this is built of breeze block it's going to just seep through?
Although if it's heading down towards a yard gulley I guess this maybe isn't an issue

 

[Zebra]

I don't know the answer to that one. In most cases it's just to do with allowing the house wall to have air circulating against it. Most cases aren't dealing with large quantities of water falling towards the house.

When you say breeze block what do you mean specifically? I would take breeze block to mean thermalite blocks, that you would build an inner leaf of a cavity wall from, and not something you would use structurally. If you mean medium density blocks then that would be a feasible material, and I don't suppose it would matter if moisture seeped through... depending on the quantity and where it goes then I suppose.

 

[davidward89]

I don't know the answer to that one. In most cases it's just to do with allowing the house wall to have air circulating against it. Most cases aren't dealing with large quantities of water falling towards the house.

When you say breeze block what do you mean specifically? I would take breeze block to mean thermalite blocks, that you would build an inner leaf of a cavity wall from, and not something you would use structurally. If you mean medium density blocks then that would be a feasible material, and I don't suppose it would matter if moisture seeped through... depending on the quantity and where it goes then I suppose.

I've finally got round to doing this!
I've dug down the outside of the utility wall and it's just built on the bedrock in the ground. The bottom fourish foot of the wall is bedrock with about 3 ft of stone built on top.
So......
I can't dig any further down than I am now, but I'm figuring that this is better than no trench at all right?! I reckon I'm down to the level of th wall that the bedrock stops and the stone wall above begins
I'll send a picture when I'm back home which might help

 

[a twig]

Anything you can do will always help - don’t let the perfect be the enemy of the good

 

[davidward89]

I've some making good to do on the wall! It's about 18inches thick, no cavity so thankfully solid

 

[davidward89]

Id actually like to somehow reinforce the lower part of the utility wall in some form also if anyone has any bright ideas?!

 

[Zebra]

You have won the prize for the biggest Zebcolm trench. However, the rule is supposedly that you can dig down to the bottom of the lowest foundation course of your wall, and then at a 45 degree angle from there. If you keep digging vertically, you undermine the wall, which I fear you might have come close to doing, although it does look fairly solid at least.

 

[davidward89]

Okay that's helpful. Perhaps I should've stopped sooner!
I'm considering pouring a concrete angled form against the utility side so I guess it would make sense to bring this up to the bottom of the lowest foundation course?