First post on this excellent site which I've found to be a goldmine of info. Sorry that this is a bit long winded.
I had an extension built and since completion we have had a problem with damp on a wall in the original part of the house, where it meets the new extension. See photo.
To investigate I have dug up the ground in the side alley of the house adjacent to where the damp is . I have noticed that when it rains, water is accumulating low down and is finding its own level beside the drainage pipe in the photo. This photo was taken after bailing out a couple of buckets of water out of the hole.
Although this area of water is quite a bit below the brick footing of the old part of the original house (1927), I think it could be causing the issue.
The foundations for the extension were dug into thick clay. This Alley area to the side of the extension was dug out and filled with gravel and quarry dust (blinding!), after the extension was built and the drainage pipes were installed. The alley was flagged up to about 4 weeks ago, until I lifted them and dug this area up to check for leaks in the drainage pipes and MDPE pipe.
I appreciate that the lack of cover here isn't helping the general situation but after it rains I am able to bail 6 or so builders buckets out of the wet area and it still fills up to the level of the drainage pipe connecting to the old clay pipe. In a dry spell the water stops appearing here eventually after it is bailed out.
To stop the water building up I was thinking for putting a land drain along the width of my extension at the back and down the side alley to include this wet area in the photo. I have a notion that water is running off the clay below the soil in the garden (soil is about 12" deep) and down to the top of the foundations where it is running to this area. The garden at the back of the extension slopes very gently towards the house.
Is it a bad idea to put a land drain in so close to the side of the house, particulary the original part of the house with the brick footing? I'd ideally like to stop the water accumulating in this area.
its difficult to ascertain levels from your pictures but it seems to me that levels have been altered
is the side alley higher than the internal floor?
if so what did the architect specify to alleviate surface water
it is definitely damp,
I would look at levels first
LLL
Before I lifted the flags, the level in the side alley beside the new extension was just below floor level. There is a DPC in the outer skin of the extension a couple of brick courses above the outside level.
The extension was built with the floor level in the new part of the house being the same as the old. The garden level and side alley are the original heights. There is no problem with damp in the new part of the house.
Where the old part of the house starts the ground level was as before the work was done. The ground level was my first thought on the damp so I dug down the level here about 4 months ago and nothing improved.
I then dug the ground away fully outside the damp area, about 5 weeks ago, as it the photo and have not seen any improvement in the house.
I checked the plans and there is no mention of drainage.
the pic of the damp wall looks like the wall had not been perfect in the past. how old is the house, whats the floor constrution, what type of brick, thickness, cavity?. have you had new central heating installed? just a few pointers.
First thing is do not put a land drain lower then any foundation.
Was the ground wet when the found was dug ?, dig a hole along side a lot of properties and you will find groundwater, drains leak all the time but it is rare to find damp caused by leaking drains.
Is the damp consistent, does it get worse after rainfall, have you checked any overflow pipes upstairs in the original build ?, many a plumber in his haste to get to the golf course has left an overflow short and dripping into a wall cavity.
was the old brickwork plastered or cement rendered?
I have seen similar to this before and it is efflorescence i.e, salts coming out of the old brickwork
also is the old wall cavity or 9 inch?
LLL
The house is 1927 with no DPC. There is no cavity just a solid brick wall. It was originally a floating floor with joists over a void with soil under. When we had the extension done we had the floor filled with hardcore, insulation and concrete over a DPM. This DPM wasn't incorporated into the old wall. The spec of the new floor was passed by Building Control.
We had underfloor heating installed throughout in a concrete screed. All the internal walls were re-skimmed and the lower part of the wall giving trouble was taken right back to the bare brick.
The outside wall of the area giving problems had a brick boiler house up against the wall, which was removed when the extension was done. The pipes entered the wall in the rectangle area that has been cemented up. The pointing in the area looks ok but also looks original.
When I lifted the flags I thought I had found the problem as this cemeted area extended below the flags and was not cemeted up.
I put the silicone in here when I lowered the ground level about four months ago.
At this time I also put more silicone in the gap between the outer skin of the new wall and the junction of the old wall. This was open below the flags. There is a fibre board sandwiched between the new bricks and the existing wall. Basically a spacer I think.
The damp in the wall does not get any worse in wet weather and doesn't improve in a dry spell.
There is no plumbing in the room above in this area.
The area of water has filled up more with some rain today.
Would the water in this area soak up through the clay far enough to make the wall damp do you think?
i think you have efflorescence ,when we have to plaster brickwork that old it normally has to have 3 coats of centaprufe the last one with sand incorporated to aid adhesion for the plaster
my house is 1922 and you will find they used slate for DPC
the thing is when the wall was exposed and was lime mortar any moisture could evaporate,but now its plastered it has no where to go so shows itself in the form of salts
of course i could be wrong but I have seen this scenario before especially when old brickwork gets plastered
i will look for a link for you to explain what might be happeneing better
LLL
the bottom line is that true rising damp is very rare,normally other factors at play
good bed time reading for insomniacs
cheers LLL
Great info there Luton.
I have read before about the rising damp fraud. What I'm bascially doing is looking for my 'other factor'. I'll give all this a good read.
Just to be clear. The inside wall that is showing damp was plastered originally and painted and was replastered when we had the extension built. We didn't have an issue before. The room now smells damp and the damp meter gives high readings in the affected area.
the damp meter is an electrical resistance meter, but it sounds bad
as flow joe correctly said check all gutters pipes etc
check your water meter isnt turning when all the taps are off
the job we are on has 3 water mains of which we pierced 2
1920 2 inch iron 1963 1/2 inch galvanised and 2008 20mm polypropylene
although they shouldn't have been all 3 were live,due to them just being disconnected at 1 point
good luck
LLL
I don't think its water pipe related as the wet puddle area clears up in a dry spell. I exposed the MDPE pipe the full length of the extension and it was sound. No water meters required in N. Ireland (yet!) :laugh:
There are no gutters affecting this area as it is the gable wall of the house.
All valid points though. Thanks for pointing them out.
you say on the outside of this damp wall there was a boiler room, this would have kept wall warm. new central heating=more heat, pulls damp from walls. fibre board between walls? i would say that is not right, sponge? i would say your problems are not on the outside. also i bet you have had double glazeing in the old part of house aswell as new build.
Sorry that this is a bit long winded. 
