External Ground Level Help

[steanywhere]

Hi this is the my first time posting so I hope I'm providing all the information properly (and yes I've taken photos...!)

We moved into a late Victorian terrace house with some damp problems and I've been doing some digging....

From what I can tell the rear addition is built with quite shallow foundations and over the years the external ground level has been raised with more and more concrete and rubble. This has meant the external ground level is now at least as high as the internal floor level. Added to this the rear bay gutter drains directly into the corner of the rear addition (and guess what that is where the most damp is....!)

I've discovered two things after digging out the pseudo-French drain that had helpfully been filled with soil and pea shingle and thus keeping a lot of water directly next to the solid wall.

1. The old air vents aren't blocked from the outside but I'm guessing could very well be from the inside.
2. If you look below where the render has fallen off under the air vent there seems to be a slate DPC two rows of bricks up from the brick foundations.

Also there is what may well be an original drain - and thus possibly an original ground level?? - about 15cm from the top of the concrete path down.
This would have made the original ground level about one row of bricks above the foundations and one row below the DPC.

Another view of that shows also that the concrete hasn't been cut away from the wall next to the drains and goes right up to the kitchen door (ground and internal level the same) and again unsurprisingly this is the second most damp area internally....

So some questions....

1. Should I break up the concrete and reduce the ground level? If so to what level above the foundations?

2. The drains are running down the side return would it be good to get a drain survey done to establish that they are working properly?

3. If I do reduce the ground level what should I replace the concrete with?

4. Anything from the pictures that I've not picked up on please feel free to let me know...

Thanks in advance for your help....

 

[MatthewC]

Hi steanywhere

Welcome to the forum. What a lovely set of photos! You seem to be on the right track with your questions, but I'm not sure exactly what is the depth of the gully beside the wall in relation to the floor inside? Also, what is the floor inside - suspended wood or solid?

Firstly, you need that drain near the corner to do its job and take the water away - does it drain well especially when raining hard? If not, you need to get it sorted,, either by rodding if you know where it goes, or else by some serious digging!

Secondly, the concrete up to the wall does not help, especially if it's at the floor level inside. I suggest you cut that back as far as you can and as deep as you can - even six inches will help a bit, but preferably more.

I would do just those two things and wait and see for a good while, assuming that you have no other obvious nasties around the place. You need to check that gutters do not overflow and that the downpipe is not split and chucking water down the wall.

I had a concrete path up to the wall at floor level which rotted the suspended floor, and another path held earth against the wall at about 6" above floor level. Then there were the blocked gutters, broken downpipes and ivy growing up the wall to the roof! See my blog - there some interesting photos at http://houseintheenchantedforest.blogspot.co.uk/2010/11/is-it-really-only-three-weeks.html

Matthew

 

[malcolm]

Here is what I did: http://www.periodproperty.co.uk/forum/viewtopic.php?f=1&t=14273&p=201613&hilit=fibregrid#p201613

I replaced a French drain with a trench which seems to be working. My foundations were also shallow in the botched Georgian extension so I filled the bottom of the trench with concrete to help avoid the foundations moving into the trench. It might be more convenient to lower your path tather than have a trench. Any material should be OK so long as it is below the damp course.

 

[Flyfisher]

I agree with MatthewC. The right questions are being asked and there seems to be a good correlation between visible external problems and internal damp effects, which I'd say is quite encouraging - a problem with a clear cause is a problem much easier to solve!

That trench looks pretty good to me and will save lots of work (other than keeping it clear). If a similar thing can be done all around the walls then it must surely help.

After all that it will hopefully just need some patience for the damp walls to fully dry out. We generally say one month per one inch of thickness of wall - a very rough guide but indicative of the fact that it probably won't be a couple of weeks, so don't panic for a while.

If the internal floors are suspended wood then pay particular attention to underfloor ventilation. If possible, ventilation on more than one side of the building will help improve airflow as the wind will create slight pressure differences around the house, enough to influence the underfloor airflow.

 

[Zebra]

Either the trench will have to be kept open as it is, or the path should be lowered. The trench can't be filled in again, even with something like gravel, which, although it is free-draining, still holds moisture against the house, as I learned to my cost. Really, the path wants to be made of something other than concrete, because concrete causes water to splash up against the wall of the house when it rains. As a temporary measure to prevent this you could stand a board - a piece of ply or something similar - up in the trench which will stop this while still allowing air to circulate behind it. In the long run, shingle or gravel would make a better path.
What you've done so far seems very much on the right track though.

 

[88v8]

Excellent start.

The original dpc was a bit low relative to the foundations, but the fact that there is a dpc at all is good.
It should have been 6" above ground, so yours at 3" is too low, really, but nowt to be done about that.

As has been said the ground needs to be lowered to original as-built level. Then gravel will make a good path and prevent rain bounce.

Your pic shows clay drainage, which is great if it's still sound, but yes I would have someone poke a camera down and check it's clear and working as it should. We had a survey done a couple of years ago by someone near Gloucester, cost was £300.

Is it an optical illusion, or is your garden already lower than next door's? If so, one can see why the level would tend to creep upwards.

That iron vent, which would look fine if cleaned up and gloss painted, appears too high to be underfloor. If it opened into the room, perhaps because there were once gas fires, I can quite understand why it was blocked up and there would seem no point in reopening it. Otoh if you have suspended floors then underfloor ventilation is crucial and it would be as well to review the original provisions and see if they were adequate, ensure there are no dead corners in terms of airflow.
Workmanship and materials were often better in the old days, but in terms of protecting houses against damp, design was sometimes lacking.

Ivor

 

[plasticpigeon]

I live in a house quite similar to yours, and I am a bit surprised by the layout. I'm guessing that the soil pipe is on the side wall of the rear addition and not on the back wall of the main house. As Ivor says, the air bricks look to be above ground level, and I wouldn't expect them lower as the back bit of the house usually had a solid floor. However the slate dpc looks very low, my early Edawrdian terrrace has little in the way of foundations, but I still think there are 4 bricks between the corbelling on the foundation and the slate dpc. Could it be possible that the slate you have found is to rest floor joists on (unusual at the back of the house but possible) and there is another dpc 1 or 2 bricks higher up, meaning that the original ground level was roughly where the dpc you have found is. This is the situation on the main body of my house.

Yes getting the drains checked is a good idea, and I don't think concrete is good, it causes splashing, and doesn't allow for drainage through it or evaporation from it. I have pavours in my yard, which also encourage splashing but do allow water to drain so it never (or rarely) pools. I don't have any damp so I'm happy with the situation.

 

[plasticpigeon]

Also gutters draining on the ground are a terrible idea so yes get that fixed, although if only a bay roof it will not be much water. Also for what it is worth, the ground level at my place (or at least the top of the pavers) was originally and is still only just over 1 brick below internal floor level. Not what would be built today, but the way it was sometimes done back then.