Hi everyone, first time poster here so apologies in advance for any faux pas.
I currently have a damp problem in two walls in my kitchen which back out onto my patio. I suspect part of the problem is poor design and drainage of the patio, along with inappropriate rendering of the wall down to ground level and possibly a bridged/broken DPC. I've had a new chemical DPC injected to no avail and so need some advice on whether to/how to rectify the patio drainage issue. I've got a few pictures to help explain:
This is the rear face of the house, and the damp problems are on the other side of the white rendered surface. As you can see, the patio step is laid pretty high up, the top being less than 2 inches below the internal floor level. The step is sloping slightly to the right, such that water poured on the left half of the step runs away from the house towards the main patio area, but on the right it runs towards the gulley where the green iron soil pipe is. Once it hits this gulley it flows towards us along a concrete base towards the end of the step then seems to flow into soil, draining quite slowly. The house is built on London clay, which might explain this.
This next picture is a better view of the gulley on the right.
This next picture shows the height of the patio step in relation to the doors and the surrounding patio level. As you can see, the step comes right up to the wall.
Now what I'm thinking is that this damp in the kitchen could be caused by one or a combination of all of the following:
1) Degraded DPC, in which case I don't know what more I can do after having a new DPC injected.
2) External render bridging the DPC, in which case I think I need to hack off the waterpoof cement render to about a foot above the ground level and finish with a bell cast to stop capillary action and allow the lower brick courses to breathe.
3) The patio step bridging the DPC, in which case I'm not sure what to do. Do I need to remove the step in it's entirety, cut it back by a distance from the wall so it becomes a floating step, or install something like a linear drainage channel between the step and the wall.
4) If I install drainage, where can I drain the water to? Is there a way of draining it into the green soil pipe on the right, or do I need to run the channel round to the left of the building where there's an actual drain which takes the guttering run off?
For further info, this next picture shows the side return patio with the rainwater drain and an airbrick visible on the left.
The patio slopes away from us down towards the garden but it still looks fairly high compared to that airbrick. Also down at the end where those grey plant pots are is prone to pooling of water when a high volume of water comes down the patio (think torrential rain or pressure washing, not normal British everyday rain).
I'd really appreciate any thoughts on where I go from here. Am I barking up the wrong tree with my diagnosis? What trade do I need to install drainage - a paving expert or a builder? Is this likely to be an enormous, expensive, or even necessary job? Any advice gratefully received! Thanks for reading!
1) Degraded DPC, in which case I don't know what more I can do after having a new DPC injected.
It may well be fine im going to assume your place is 1920-1930,s? And an injected dpc should make that even more likely.
2) External render bridging the DPC, in which case I think I need to hack off the waterpoof cement render to about a foot above the ground level and finish with a bell cast to stop capillary action and allow the lower brick courses to breathe.
I would find your dpc ( should be aboutthe height of the door sill (top of step) and cut away an inch above that then a drip bead fitted and new render down to the bead. This will allow the brick to dry as it was intended plus stop the bridging of dpc. Only good can result from this.
3) The patio step bridging the DPC, in which case I'm not sure what to do. Do I need to remove the step in it's entirety, cut it back by a distance from the wall so it becomes a floating step, or install something like a linear drainage channel between the step and the wall.
Well no water can cappilarate (sp) up a upvc patio door so under the sill is not a problem, the section of step to the right of the doors is definately pointless and the water has a good chance of going over your dpc as it rains and bounces off the step. I would cut that section of step away (its had it anyway, install a new one)
4) If I install drainage, where can I drain the water to? Is there a way of draining it into the green soil pipe on the right, or do I need to run the channel round to the left of the building where there's an actual drain which takes the guttering run off?
Hmmm i cant see whats going on with the soil pipe from that picture but can it over flow? Is it blocked? Could be related as an issue.
I notice your airbrick is breached by the paving and while i would expect your dpc to be sat on topof the air brick i still dont like to see that, it can only increase chances of your building getting damp.
Thats great, thanks for the advice! The house is around 1900-1910, solid brick walls, no cavity. I've had rising damp on both sides of the doors internally, but having had a chemical DPC done and the walls lined internally to 1m height with damproofing membrane the damn stuff is now starting to appear above the membrane, so I'm pretty keen to tackle the route cause before it trashes the entire wall!
The render changes should be a relatively straightforward job which could be done quickly. I'd be quite happy to lose the outer section of step on the right hand side, as you say it's not doing very much (apart from making a nice stand for a plant pot) and the bricks beneath are giving way.
The soil pipe is a bit fiddly to photograph, this is a slightly different angle.
It's basically a solid, cast iron pipe which disappears into the ground. There's a fairly chunky cement curved fillet around it (imagine sticking a pipe into the top of a Christmas pudding for a rough shape). This is the white painted stuff around the base of the pipe. Previously the gulley between the step and the side retaining wall was filled with soil and gravel and general rubbish built up from having a plant trough on top of it for 5 years. I've dug all that out today and basically the there's a concrete base extending out from the house at the same level as the main patio before it appears to drop away into mud. This drains really slowly and seems to be where any water from that quarter of the patio drains to, which is why I was wondering if there's a way to place a drain there and discharge it into the green pipe.
As to overflows, I've certainly never seen that in the 7 years I've been here. The base of the pipe is pretty firmly encased in that cement fillet and the junction between the plastic and iron sections seems sound. I've had no history of blockages or anything backing up, although getting it CCTVed and plastic lined is an option if there's doubt over it's integrity.
One more question about the DPC - how the heck do I find it? The whole base of the building is surrounded by the red render stuff that around the airbrick and I can't see any obvious line between the brick courses and change in brick style. I'm actually really relieved you think the DPC would be just under the door sill as I had visions of it being 2 inches below the step with water leaching into the house!! Thanks again!
