Damp in Victorian house dining room


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Thank you toolsntat, for the kind offer. I will try that tonight when the family have gone to bed. If I think it's not clear either way (leak or no leak) I will PM you.

Don't be too downhearted, sammyse. You are doing all the right things, and although it may take a time, you will succeed in the end.
Hi Boschboy,
I think it's too early to say. I've spend any spare time I have (from the day job & family time) trying to fix the route causes and implement some of the recommendations from this thread (Thanks MikeG and others!).

So far, I have:
  • Lagged the cold water mains pipe, the full length
    Added a new airbrick, and unclogged two existing vents
    Added a fan, with built in humidistat, to aid the airflow
    I have dug a channel around the exterior wall, to the depth of 150mm below the DPC, and added drainage (which required me to find a way to connect it to the gully without having backflow/smell coming through)
    Removed the exterior plinth to just above the DPC, which was bridging the DPC (when I removed it, the bricks were quite damp behind it, so I'm glad I did that)
    Removed the cement render from the external walls, about 1.5m high. I was really pleased that most of the bricks were not damaged by the render coming off - it never bonded fully, probably because it was added while the wall was damp!
    Fixed the guttering, there was a couple of leaks and now it ends tighly against the gully, no chance for splash back against the wall.


Still a lot to do though:
  • I need to tidy up the plinth and add a bellcast bead
    Need to re-point some brickwork using lime (never used lime before)
    Internally, I need to remove the concrete hearth (which is acting as a cold-bridge, as MikeG explained above)
    Remove gypsum plaster and foil backed plasterboard (previous owner!!) from the external walls, and replaster with lime
    Fix/replace the joists and wall plates which have been damaged due to years of damp
    Re-decorate the room.

One day, i hope to have a chance to do some actual woodworking!! :)
Seems like all my time and money is going on fixing stuff like this, but I do hope I can do something more fun soon.

I took some pictures of my progress, will post them up later.
Not relevant to your problem, but one to remember for damp in old houses - look where the cast iron downpipes are. More often than not they were fixed with wooden wedges driven between the stones - and they rot. The water then tracks in and downwards. I had only two noticeable bits of damp in a late Victorian house - one wasn't very obvious until I took ceilings down and then I could see the water mark about three feet along the joist.* Fortunately there was no long term damage done. The other was a wooden block built into the wall to carry the fascia and to which the wall plate fastened down to - that had rotted away completely allowing the water to wick through the dust and dirt. From the internal plaster repairs I would imagine that had been a problem for several decades. I could lift the corner of the roof clear of the wall ......... not good for a high house on a hill overlooking the west coast of W. Cornwall. :shock: Six inch fascias on eight inch roof timbers weren't doing any favours, either ................. :D
* which was about two feet below the source.
Well that's interesting. I have one original cast iron downpipe at the front of the house. No visible damp problems that I can see but I will have a look tomorrow for any wedges type thingies. Cheers.

Sent from my Nexus 5X using Tapatalk
So it's been over a year, and now it's time to get back to solving this problem of damp in the dining room. I’ve did a fair amount of work last year, but this year is the big job – I will no doubt need some advice from your good selves.
All the advice on here has been great – THANK YOU!!! - which I have taken on board and here's what I've implemented so far:

I’ve created a trench around the external wall, to take it to as low as possible, which is almost 150mm under the DPC, but not quite. It’s the best I can do because unfortunately the mains waste pipe is higher than it should be (a problem caused when the house was built). Any lower and the drainage wouldn’t work.
As well as digging the trench, I had to replace the channel drainage with low profile (very short!) channels, and had to create u-bends from the new channel drainage into the bottle gully at the lowest possible point. This was done using flexible waste pipes, rubber grommets and some carefully placed cement. The drains all work and water flows freely into the mains waste.

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I’ve taken off the horrid cement rendering off the external wall, about 1.5 meters high. I wasn’t planning to do more, but please shout if you think I should!


Gutters and downpipes have all been sealed and fitted correctly – no leaks.
Inside, the mains water pipe has been lagged for the entire length.
I have fitted a bathroom extractor fan (with humidistat) under the floor, venting out from the dining room via an airbrick. This has been running for 12months+ now. It is powered from a fused switched spur in the dining room.


These are the next steps, and I have a few questions I hope you can help me with. I’ve taken a couple of weeks off work this month:

Inside the room:
  • Remove the concrete hearth completely from the sub-floor
    Remove the mixture of cement render and foil backed plaster board from the walls (yes, cement render with finish plaster on top – previous owner’s attempt to cover the damp)
    Remove the rotted floor joists and any rotted floor boards
    Remove the rotted skirting boards
    Remove all debris/rubble from the subfloor
    Build new honeycomb walls to support the new joists where the hearth was, using slate to pack and level the joist where needed.
QUESTION 1: Should I use a specific type of brick, and what should the cement mix be? (I was thinking engineering bricks?)

  • Install new joists matching the existing size (2x4), either replacing the entire length of a rotted joist, or sistering if only a portion of the joist is rotted. New joists will also be laid over the space left by the hearth.
QUESTION 2: I’m not sure how to deal with the ends of the joists (pic below), and how they should be supported. It looks like they are resting on a wall plate (which is rotten and needs replacing as well). Should I replace like for like with a DPM underneath, or is there a better way, e.g. Joist hangers?

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wall plate 1.jpg

wall plate 2.jpg

QUESTION 3: Should I place a DPM (Visqueen) under each joist, to prevent moisture transfer?

  • Install 100mm slab insulation (Rockwool Flexi) between the joists, supported by netting
QUESTION 4: I confirmed with the manufacturer that this is suitable - does anyone have better suggestions?
QUESTION 5: For the narrow gaps between the joists and the brick walls, I was thinking of using expanding foam, is that OK?

  • Install new floorboards (I bought solid timber flooring to match the original, but now I’m thinking I might replace the lot with the green sheet floorboards used in modern construction)
    Replace the extractor fan with three PC fans (one for each air brick), powered by a 12v adaptor plugged into a regular socket above floor level I was thinking of using these fans: https://www.amazon.co.uk/dp/B00650P2ZC It's quiet, and a 6 year warranty.
QUESTION 6: Is there a better way to power these? I don’t like the idea of a plug that has a cable going down through the floor. E.g. would it be better to have a 12v driver installed in the subfloor powered by the fused spur?

QUESTION 7: What wood preservative do you recommend for cut ends of the joists, and should I give everything (new and old joists) a coating of a preseverative?

  • Re-plaster the walls with lime (and use a lime paint as well)

  • Fit bellcast beading to channel the rainwater away from wall into the channel drainage
    Repoint where needed with NHL 3.5
    Remove a rogue airbrick that is bridging the DPC and make good the DPC with slate.


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Hi all, quick question:

It's very clear now that the room has been stripped that the air vents are above the internal floor level, which is most likely hindering air flow.

Do you think raising the internal floor level is a good idea? About 80mm will mean the vents are below floor level.

I was thinking of laying treated CLS along each joist to achieve this.

What are your thoughts?
I will be adding some 12v fans under the floor also.

It would mean the kitchen door opening would lose 8cm of height, from 200 to 192cm
It's an old granite house 1875, in the adjoining room (original servants kitchen) there was solid floor with no damp course and was nastily damp. We ripped it up and installed a new insulated concrete one with damp proofing etc. Which says to me there is the opportunity for the floor in this room to be also damp. I have not seen any evidence of damp in the room. The room is 4m long and has two vents on the external wall. So from my statistically irrelevant sample of 1, yes they are effective ;)
It's an old granite house 1875, in the adjoining room (original servants kitchen) there was solid floor with no damp course and was nastily damp. We ripped it up and installed a new insulated concrete one with damp proofing etc. Which says to me there is the opportunity for the floor in this room to be also damp. I have not seen any evidence of damp in the room. The room is 4m long and has two vents on the external wall. So from my statistically irrelevant sample of 1, yes they are effective ;)
Thank you :) the room you describe is similar to my situation...
Do you think raising the internal floor level is a good idea? About 80mm will mean the vents are below floor level.
View attachment 90631

The vent doesn't have to just be below floor level. I has to be below the bottom of the joist. Therefore you'd have to raise this floor getting on for a foot. As that clearly isn't possible, you either need to lower the vent (that will depend on the external ground level), or put in a periscopic vent, which are cheap and very effective. It should be hidden by the skirting. Cross flow is the critical thing here, so there should be clear open vents on the opposite wall, and a clear air path between.
Thank you @MikeG. (and all). Looks like periscopic vents are the way to go.

Sadly, the 'opposite' vents are perpendicular to these, at the front of the house, so I don't seem to be getting good cross flow. Hence I shall add fans to get the air moving a little
Hi All,

I had been working flat out on the dining room the last couple of weeks (took time off work), so I thought I'd give an update since, well, this is the last thing I 'made', and it may help others stumbling on this thread in future.

As mentioned above, it's been flat out - I wish I had taken more pics but to be honest I just wanted to get on and squeeze every minute from every day. My teenage lads were a huge, huge help as well.

The aim was to remove the hearth, rotten wall (sole?) plates, and any rotten joists. Plus, I would also remove the internal plastering which was the wrong material.
Started off well enough, but I discovered that not only was there bad rot, but also woodworm. While I was here, i decided I would replace the lot - and have peace of mind. This is what it looked like once everything was ripped out:


There had been a catalogue of errors/bad building work throughout the years before:

Concrete render on walls;
Foil backed plasterboard on damp walls;
No DPM at all between wood and masonry;
The hearth, which was a cold bridge, was also bridging the DPC, causing the damp to spread up the walls;

This was all ripped out.
Here's a pic of a socket back-box, that was on a cement rendered damp wall - shows the extent and duration on the damp problem:

The hearth is now also gone - that was 1 cubic meter of cement and clay, all very damp:

Woodworm had spread to the passage as well, quite bad, but very luckily completely localised to one joist (above the un-lagged water mains pipe that attracted condensation, not a coincidence, I'm sure) and some local floorboards. All were also replaced:



With all the joists, wall plates replaced and installed properly this time, I also took the opportunity to install 3 under floor fans to keep the air moving:


This, together with three new telescopic vents, and a much clearer sub-floor, is helping with airflow. (The fans may not do much - some might say it does nothing, but it makes me feel I've done what I can...)

Slab (Rockwool RWA45 100mm) Insulation added, with netting - which is really a backup since the slabs fit quite tight.


So next on the list is re-plastering with lime, and then the cosmetic decorating/flooring etc.
I love a rip it all out and have a gander underneath thread! You'll be relieved when it's over knowing you've done the right thing.

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