Damp Proof Course - Mid Terrace Victorian

Hi All,

I've got some moisture coming up a party wall from the bottom in the middle of a ground floor room. I've removed some render and a section of the floorboards. I'll try to provide as much information as possible but ultimately I'd like some advice on how to prevent this from re-occuring.
- ground floor room
- party wall, non cavity
- area of concern starts in the middle of the room
- suspended floor
- air vents clear all around the house (could do with bigger vents)
- unsure if neighbouring property has any/similar problems
- the brickwork the joists were resting is damp
- the brick above appears to be dry although the mortar seems damp
- the end of the joists have rotted (will be re-instated once the damp is controlled)
- the lowest level below the floor is dry ie the ground below the floor
- unsure how far it extends along the wall but suspect it runs along to the external wall
- a chimney breast was removed at some point 1m plus away from the exposed area but remains in the adjoining property.
- musty smell which could be a combination of the wet debris and timber, not evident before exposing the area.

Some photos - corner joist has been cut as it was rotten and wet.


The black 'pad' appears to be some sort of epoxy. Is this the DPC? It's easy to pull away and has failed at some point, possibly leading to the moisture getting into the joists. I excavated quite a bit of dirt/debris around the joists which was on top of the black pad. Some could have been from removing the render.
I'd like to sort the joists out and rest them on something that won't allow damp to propagate. I'd also like to make the wall good and prevent the damp re-occurring up the wall. Any advice appreciated.

I would talk to your neighbour first if possible as it is likely they have some issues their side too and it is important to tackle it jointly if atall possible, though I appreciate this may not be realistic.

With damp it is often a few things but one thing I have noticed is your plaster seems to go right to the floor which means any rising damp could bridge the dpc and get trapped in the plaster. The plaster should be a couple of inches off the floor. I imagine your dpc will be a layer of two engineering bricks.

Is there any ventilation in the sleeper walls under the floor? If the sleeper walls are solid then the air might not circluate properly.

Looking at your airbricks, they can get very blocked with spiders webs and what you think is giving ventilation isn't. It is worth checking with some dowel rods etc.

I would leave the wall to dry out for a while and engage a reputable builder unless you diy skills are very good.

Thanks for that, will try and get hold of the neighbours and see if they have similar issues. Their place was gutted and re-rendered/skimmed 12 months ago so maybe nothing has reared it's head just yet. I find it odd that this is happening in the middle of a room and there is no moisture below the footing.
When I make good the render I'll leave it above floor level as you mentioned. I can't see an existing DPC (not sure what I'm looking for). All the bricks look the same. By finishing the render above the floor, will this stop the bridging?
I'm going to keep working along the room to the external wall and rule out things like radiators leaking or any excessively damp areas. I started where I did because it was damp. There is some efflorescence on the same wall but quite high, about 1.5m up. I expect this is from the neighbours chimney breast which remains.
What would be best to render with? Sand/cement with waterproofer, limelite, other?
No vents in the sleeper wall but the area I've uncovered is in the same 'bay' as 2 air bricks to front and rear. The air bricks are clear but as mentioned could be undersized. Will be interesting to see if it dries out now that I've removed a load of debris. Possibly condensation build up in the corner? There was a bookcase in that corner for a number of years which wouldn't have allowed any air flow. I expect that it has been happening for quite a bit longer considering the amount of rot in the joists.
I can turn my hand to most things including a loft conversion so this shouldn't be too much of a challenge with a bit of research and help from here. I just wanted to make sure I hadn't missed anything obvious which people with more experience may be able to help with.

YW. You might want to invest a few quid in a book called 'The Damp House' by Johnathan Hetreed, it proved very helpful with issues I had, which included plaster to the floor level. Raising the plaster line will stop any bridging that was happening, it can only help.

As for where your dpc line is, it should be right above the airbricks.

It could be condensation in the corner as you say, it is often more than one thing so good to look at everything. I wouldn't waterproof/tank anything though as that is often the worst treatment and can trap damp in the bricks, forcing it upwards. For an old house you want something that will allow the wall to breathe and the moisture to pass out.

As for underneath the subfloor, they started using honeycomb walls that allowed the air to pass through so it may be possible to adapt your sleeper wall to allow more airflow.

Regarding using a builder, it may be that they would build a new sleeper wall for the joists to sit on. Then there is the joist ends to consider. What I am saying is the solution needs to be right, there are pointers on youtube for sure. I am sure you can do it but it is important to get it right first time.

The Peter Ward damp videos on youtube are very good, especially for older houses.

Thanks for the recommendation of the book, I've tracked a copy down.

I'll check for the dpc but may have to remove some external render to get a better look.

I'll probably need to go back to near sleeper wall to make good the joists so will look at a honeycomb style construction at that time.

I have been enjoying the work of Peter Ward on youtube for a week or so now. I can adopt a few techniques I've picked up from him. Really great stuff. For a while now I have been against injected DPC's and creams etc. This was done to another area of the house before moving in and hasn't done a lot except move the problem somewhere else (other side of the house to this current issue).

Will post back after a drying out period.

Just a random thought- when you talk to the neighbours, see if they have still got a back boiler in the fireplace (or possibly the central heating pump in the vicinity). And if they (and/or you) aren't actually using the flues you might want to cap them or at least put a cowl on top (so you don't get rainfall down them).

(The back boiler thing was a problem for my neighbours until I moved in to my first house 25 years ago and ditched the back boiler- it looked as if it had been gently leaking for years, no problem my side but they had damp, efflorescence, you name it in that wall til then).

For those following along at home, I finally got around to a bit more investigating under the floor. The boards aren't coming up very easily but need to keep them in reasonable condition until replacement.
There appears to be a low wall running parallel with the joists which has a load of rubble/debris blocking airflow. Since I lifted the original floor board and removed the rubble the wall has been drying out nicely. Not sure why the wall is there. The joists either side of it appear quite different in age. Original wall maybe?

Location of wall under joists


View under floor from left hand side of wall


View under floor from right hand side of wall (copper pipe from rad for reference).



When I take the floor up I'll look at what this wall is actually doing. Currently I'm guessing not a lot so will be modified/removed to allow airflow and sort out my condensation problem.