Damp - Victorian House - Investigation

[bmartinlevy]

Hi everyone,

First time posting, as I've found the forum really helpful as a first-time house buyer and caretaker of a Victorian property. My girlfriend and I recently purchased a Victorian house built in 1862 in London in a conservation area in SE18 (Woolwich/Plumstead). We have a damp issue we've been trying to investigate and determine the cause of. We want to do what is best for the building and are restoring many of the elements to their original Victorian style and would appreciate any advice on the below. I've included some photos of the issue against the floor plan which hope are helpful.

• 1. The damp is located in these two walls, both brick, one exterior and one interior. We had the regular run-of-the-mill damp survey done which stated rising damp in the x2 affected walls and recommended a damp proof course. We have resigned ourselves to doing the DPC, however we see this as extra insurance. We are mostly concerned with eliminating any on-going cause though that could be behind it and don't want to be ignoring an underlying cause outside of moisture from the ground type. The build is early-Victorian so don't believe there is an original slate DPC, as from my casual research, this came into fashion in later Victorian builds. Our Build Site Director who is overseeing our renovations commencing in June agrees that there may actually be a leak that needs investigating. The guttering is newish and clear and no obvious leaks going into the walls themselves.

• 2. We've spoken with our adjacent neighbour who has no rising damp issues, and their cellar is dry. There are damp spots on our cellar walls though, but the damp is spotty and not uniform.

• 3 & 4. Other images from the interior of the damp.

• 1. The most immediate cause we thought was the concrete which has been laid in the back garden. It's old and broken apart now, and we will eventually have removed and put a conservatory in its place. We've had conflicting advice, as some have said this could be causing the damp and is not-levelled correctly. However, our Build Site Director says it's actually not necessarily a levelling issue, as it's not blocking the vents going under the house floors which are shown in the additional photos. We were tempted to immediately remove this regardless, but as we aim to eventually put a conservatory here, we didn't want to spend the money to put down clover or something similar to prevent the garden turning into mud in the interim.

• 2 & 3. As part of renovations, we aim to ensure these are completely unblocked, but they are not currently obstructed by the concrete. We were worried that the concrete may be causing rainwater to drain under the house though? This was put to us by another Build Site Director quoting renovations.

• 4. One major concern is that we have drainage pipes from both the bathroom/toilets as well as the guttering going beneath the concrete. From what we gathered from neighbours, the drainage system goes out under the back of the garden into a system in the parallel terrace behind us. There is no manhole on our property or the neighbours. The backs of our gardens sit against the one from the parallel terrace. I've contacted two companies who specialise in leaks to get quotes (£400 approximate + VAT) who said they can use cameras to see if anything is leaking. We think this might be a good thing to do regardless, but we want to make sure we aren't barking up on the wrong tree?

As mentioned, any advice would be appreciated! Thanks in advance.

Best wishes,
Benjamin

 

[88v8]

Hello and welcome to the Damp & Other Things forum.

Jolly good photo-montage there. No idea how one does that.....

Leaving aside potential plumbing leaks which could account for the damp in the cellar and yes I would spend the money investigating, or just dig some holes which is cheaper if you have the inclination... the concrete: and airbricks...

Airbricks... so there is a suspended floor? And whoever laid the concrete knew not to block the air bricks. Which is good. I wonder as an aside if there were more air bricks, that they did block. But often, original builders did not put in enough air bricks so maybe that's all there were.

You know btw, that when you build your conservatory you must leave through-ventilation for the underfloor? To the outside air?

Anyway, back to the concrete; what bothers me is that if there is a dpc, it would usually be just under the air bricks. In that case, the concrete has bridged the dpc. You need to check:

Inside, take up a board or two adjacent to the damp, you will see the dpc if it's there. Shining a light around under the floor you will also be able to see if there is damp under there. Dry rot, etc.
At the same time, see if there's a nice draught coming up all the way along the wall. That may tell you whether you need to put in more air bricks. It's almost impossible to have too many air bricks.

So, if the concrete has bridged the dpc you need to remove it, or for the time being at least remove it in a strip to leave a clear gap of 12" say, away from the wall, and lower the external ground level so it's at least 6" below the dpc.

Establishing whether there is a dpc and if so where, is also the first step in determining the floor height of your conservatory. If it's to be a solid floor, the floor should finish at least 6" below the dpc. If it's to be a suspended floor then the sub-floor needs to be 6" below, but the suspended floor will of course be above, that is to say at the height of the existing wood floors.

If resolving the bridging of the (possible) dpc removes the cause of the damp, you may expect the wall to dry out in about a month per inch of thickness. Do not try to be in a rush to decorate over it.

We're all agog to know what you find...

Ivor

 

[plasticpigeon]

I think Ivor has said it all really, but in addition I think it is possible that the concrete was poured on top of whatever was there before rather than the area being lowered before the concrete was added. Therefore I think it very likely that the ground level is too high. The air bricks are usually a brick height above ground level not at ground level, which strengethens the idea that the ground level is too high and as Ivor says, could be bridging the DPC if it is there at all.

 

[Lacan07]

As Ivor has already said that concrete patio is your nemesis, its almost certainly bridging the DPC. (Are you sure you don't have a slate DPC?) The moisture underneath is unable to escape the screed surface which is too high so it just moves sideways into the walls. Rising damp is very rare, there's usually an alternative an explanation.

I would forget about the liquid DPC, either hire a skip and a breaker and dig all of that area out, or just cut a gully along the side of the house. Make sure the interior walls are breathable by stripping the wallpaper / modern paint back to the original lime and it will dry out in time.

The cellar could be a potential leak as others have already stated

 

[CliffordPope]

The airbricks do look dangerously close to the level of the concrete, with only very low and apparently crumbling copings to keep surface water at bay.

What happens in a cloudburst? Can the concrete area really drain rainwater away fast enough to prevent the water level overtopping the defences?
Where does it drain to? There's no point in removing the concrete if that merely creates a muddy padling pool that still cannot drain properly.

 

[RBailey]

Hi,

Welcome to the joys of old properties.

I also noticed the crack in the concrete in way of the drains(?) in picture 4.
There may be a crack in the pipe in / below the concrete, especially if it is clay pipe (which is probable) and the if builder was less than careful when they put the slab in.

Cheers,
Richard B.

 

[MatthewC]

I think it very likely that the ground level is too high.

Absolutely! What is the relative height of the floor inside compared to the concrete outside?

If you have a suspended floor inside then the concrete (or whatever) immediately outside MUST be well below the level of the joists inside. I had this issue and the immediate solution was to cut away the concrete for a width of about 10 inches all along the wall, and dig down to give a decent depth of wall (about 10 inches) so that it was able to breathe. I put a small amount of gravel in that trench; this helps avoid splashback as well (which keeps the base of the wall forever damp).

The longer term solution was to dig up the concrete entirely and re-lay it at a lower level. Also, I had to replace the joist along the wall inside which had zero strength, and all the floorboards had the end 3" rotten. It will not be so bad if you have joist ends up to the damp wall.

You need to do this and let it all dry out for months. Do NOT do a DPC in a hurry - if the base of a wall can breathe then it really isn't necessary. Honest. If you have time, have a look at my old blog: http://houseintheenchantedforest.blogspot.com/

 

[bmartinlevy]

Thank you all for your replies! They have been immensely helpful, and we understand a lot more now including bridging DPC and air bricks.

Hopefully will have a leak company by next week. We've discussed with our Build Site Director about lifting some of the floorboards to get a good look under the suspended floor as suggested to better understand the situation and going to work at addressing the concrete ASAP. We'll look at getting it cut away from the wall at least 12 inches and dug down to the appropriate level and temporarily cover with gravel we're thinking, including potentially installing some more air bricks.

We've already discussed with the potential conservatory company that when it's installed we need it dug down to the appropriate level, so we hope to permanently address the issue then and ensure the floor of the conservatory is appropriately installed.

I'll post some more photos as soon as we lift the floorboards!

 

[worms]

In a house with a cellar, it is normally possible to see the underside of the groundfloor, without resorting to lifting floor boards.

Indeed the pic of the cellar seems to show just that and allows enough of the wall to be visible to see if there is a slate DPC (can you also see the air-vents from the inside?). That pic also suggests that part of the damp wall was previously behind something that had pipes leading to it - presumably a boiler? If that had been historically leaking, it could take quite a while for the wall (and the ground behind it) to dry out. Do you know how long it is since these pipes were disconnected and capped off?

I'd ask a similar question about the "newish" gutters - these back areas on the inside of an 'L'-shaped building often get very little sun and wind, so can be quite damp, even if everything is working as it should. It takes an awful long time for historic damp to dry out in these corners, so I'd support the suggestion of digging a trench around the concrete outside, which might help a lot with this.

Having a drain company look at the drains behind the property will certainly provide interesting info, but it might not be a priority if cash is limited. In my experience, drain companies tend to always find something that looks dodgy and "needs" extra work - it would be surprising if a 160 year-old drain was in perfect condition, but that doesn't necessarily mean it is causing a problem.

 

[MatthewC]

Hopefully will have a leak company by next week.

"Leak company"??

We've discussed with our Build Site Director about lifting some of the floorboards to get a good look under the suspended floor as suggested to better understand the situation

You should be able to judge the condition of the suspended floor just by standing on it. If it moves, there is probably rot. Lifting floorboards unnecessarily is not a good idea. I knew I had to do mine before I bought it - the young estate agent stood near the door and said "bit of movement here" as she gently flexed her knees!

And you have a "Build Site Director"? I'm impressed!!

 

[bmartinlevy]

Thanks for the further replies! Have tried to previously look for the DPC in the cellar but didn't notice anything, going to have another look this week and try to see if we can see air vents as mentioned. We're definitely anticipating some rot being present, the floorboards give a bit and dip slightly around the exterior wall with the most damp as @matthewc described. Going to try to avoid lifting the floorboards as much as possible though but expecting some remedial work will be needed.

In good news, we did have some success with the inspection done by the leak detection/drainage services company (sorry, called them a leak company previously)!

We've received our written report, diagram included above which I've added photos to, but to summarise: there is no manhole access, so the only pipe they could access currently with the CCTV camera was the 'Soil & Vent Pipe'. However, this yielded interesting findings. @Rbailey was correct, at about 0.8m down it meets the old earthenware (clay assuming) pipe, turns 90 degrees, and at that junction already has multiple fractures. A further 1m into the back garden it has a full 'circumferential' fracture. Heavy scale deposits of course noted throughout. You'll notice that the pipe goes out through our neighbour's garden and report notes this becomes Thames Water's responsibility at that point. Unfortunately we are none the wiser on the 'Rainwater Pipe' or 'Waste Pipe' as currently inaccessible. We suspect they also will have similar fractures however. They did inspect the cellar and believe the damp there most likely caused by the leaks as well as noting two cracks in the first floor bathroom walls that could be caused by resulting subsidence.

To quote: 'It was apparent from the CCTV camera inspection that the accessible private drainage system is not in a satisfactory structural condition having multiple fracturing which will be allowing the loss of water into the surrounding ground area particularly at the base of the soil and vent pipe which is in close proximity to the damp and therefore could be connected.'

There was also something we hadn't really clocked, but there is a bit of a cowboy gully where our kitchen sink just pours out the wall. The drain it attaches to in the middle of the garden concrete has broken pipes and it's absolutely not connected properly or fit-for-purpose.

This all being said, and as mentioned by @worms, they quoted over £5k w/ VAT to do just the first bit of work to fix the gully and excavate the Soil & Vent Pipe to fix all the fractures as well as doing a further survey on the inaccessible pipes. Obviously very expensive and doesn't go to solving the overall issue on a long-term basis. But in good news, we scheduled a call with our Build Site Director on Friday who have experience and are currently installing a sewer system--they have quoted £1k (£2k maximum) to remove all of the concrete, dig everything out, and replace all the pipes with a new system. They recognise this is almost certainly the cause of our damp issue and understand our wish to remedy this in as permanent a fashion as possible. We believe this is our best bet, as we want the concrete completely gone and assurance that we have a decent drainage system which isn't going to cause us issues in the future. This would also mean we can ensure that area is levelled at the appropriate depth, as multiple people have noted is really needed to ensure proper ventilation.

In a year's time, we are still hoping to have a conservatory built where the concrete currently is at the same time we renovate the kitchen. For the time being, we were thinking we could plant grass/clover once pipes are fixed to prevent a mudbath right out the back door. We have been looking into the possibility of a conservatory with a suspended floor even. We really are hesitant to go and put another concrete foundation on top of pipes making accessing them very difficult in the future.

We really would welcome any advice on the above. Couple of extra points: as @worms noted, we recognise where this damp is located even once the drainage system is fixed could take a long time to dry out due to it's L location in the corner and if there's anything we could do to encourage drying. Also even if we get all of our pipes fixed, we still have it connected to a pipe crossing boundaries which is certainly filled with heavy scale deposits and possibly cracked, does anyone have any experience with this and Thames Water, is there anything we should do?

Thanks for all the advice already! Best wishes.