Yet another thread about an Edwardian Semi-high external ground level / internal damp

[mccostas_83]

Hi,

House newbie / competent DIYer here. After much reading and educating myself (thank you to every single one of the contributors, it has been my therapy reading through how to tackle various jobs, mainly the above-mentioned damp problems which we uncovered after ripping out a musty kitchen at the rear of our property. I even bought the Haynes manual and have thoroughly read Heritage House etc) we realised the external ground level of our patio(s) where much too high, in fact, equal to the kitchen and this was probably the main cause of the damp / condensation we were seeing in the kitchen. (definitely a combination of factors i.e. no radiator/gypsum plaster / a failed damp-proof injection done by the previous owners/cement external render/slabs right up against the external wall and splashing / sitting water)) With fab suggestions from A Twig and Zebra (amongst many others I decided to have a look at what I could do myself. So, I planned to dig a channel along the external walls which were adjacent to the problem-patio. Easy, I lifted the slabs around the edge of the house, and whilst this would be too large a trench, it would at least help in the interim and offered me plenty of space to dig etc... until I hit another poured concrete slab and on the other side, some sandstone slabs. Now what?...

What I will say is the external ground level is now 6" below the internal kitchen level, but the poured slab is butted right up against the wall and the cement render is still sitting right on top of it. (so, the slab was installed first then the render by the looks of it) I continued to lift the remaining slabs and whilst the poured concrete slab isn't what I wanted to find it is at least directing water toward the drains. Please see the photos attached of what the patio looked like slabbed, then the poured cement slab i uncovered, and also the moat which i have accidentally dug hoping it would help.... the soil is clay and the water just gathers. I have my concerns obviously, as this is right at the corner of the house...the poured slab is in a quarter-circle from corner to corner and i can't decide whether this is decorative, or not... Should i just fill the moat back in, and concentrate my efforts on digging the trench along the wall? (ignore the plastic, I have tried to mitigate the moat filling up...in vain i may add after the weeks of rain up here in Scotland)

I'll need to cut the cement slab along the wall, remove this and dig a trench, but I'm worried about sitting water here. Do these trenches need to run into a drain?

Also, will I have a damp proof course (the house was built in 1904) and if we will have a DPC, where will it be?

Thanks in advance for all your help and any info offered.

 

[Cubist]

Your photographs show that the land slopes heavily toward the house and, assuming the clay bed you have discovered extends up that slope, rainwater will flow over the clay toward your house and is gathering in this low spot you are calling a moat. Are those drains I can see in the photograph open and working properly? Presumably these connect either to the waste water exits from the property or flow to other exits lower down the hill? If they are not working it may be a good idea to clean them out as silt and other detritus may have built up to limit/impeded their performance

It seems to me that the concrete slab was poured to create a dam to prevent water gathering at the back/foot of the house and while its worked to keep peoples feet dry its done nothing to really help the house. Assuming the drains are working I would suggest you consider installing a lateral drain alongside that retaining wall with a feed to the round drain in the photograph. This would at least prevent the water from standing for any length of time and may help to reduce penetration under the concrete slab

 

[mccostas_83]

Thanks Cubist, your insight is much apprecited. The drains are functioning, yes. So, for my understanding you would look to do something similar to the below? Would you cut into the side of this drain though in order to get the water into it? (apologies for my lack of experience)

key: purple being the lateral drain, the yellow are drains, the light blue is like a u-bend from the kitchen sink waste, green is soil and orange is rainwater downpipe.



Would you bother with cutting the concrete slab around the walls of the house to form a trench?




Thanks again!

 

[mccostas_83]

Would you fill the moat back in?

 

[Cubist]

I think my first move would be to open that round drain to examine the drain fitting below. You may find its a manifold to which the waste water drain from the kitchen is connected and perhaps also the other drain next to the dining room wall. Try also to determine the direction of flow and whether it empties out into any of the other drains. If its not connected to these you will need to find out where it drains to. Depending on age, the below ground fittings may be manufactured of terra cotta or plastic though other materials are not unknown. If plastic there's a chance it may have a 'knock-out' or 'cut-out' blank conveniently sized and positioned to allow connection of a 100mm perforated flexible pipe, but you could also use 100mm waste pipe with lots of holes drilled in the top and sides and covered with weed inhibiting fabric to prevent blockage. both of which are commonly used with garden/land drainage and would be ideal for use as I suggested next to the retainer wall.

If necessary, it may also be practical to remove the current fitting and replace it with a suitable manifold that is in turn connected to the main waste water drains.

Would you bother with cutting the concrete slab around the walls of the house to form a trench?

Not yet as you may be able to avoid it altogether.

Would you fill the moat back in?

Once you are satisfied that water is not collecting there then yes - but not before.

Hoping this helps.
cheers,
Cubist

 

[mccostas_83]

Thanks cubist! Sorry, I thought I replied!