Diagnosing dampness in a Victorian-era cavity wall

As far as I remember that downpipe has always discharged directly on to the pavement, even before the pavement was raised and the channel added. The downpipe shoe (didn't know what it was called until I looked it up!) has been added relatively recently; before that the end of the pipe just discharged directly into the channel. There was never an elegant route from the pipe to the gutter.

Good point about the rainwater goods further up. Next door's downpipe has always discharged into my guttering. No obvious reason to believe that it isn't still functioning correctly but of course I haven't seen it working in heavy rain recently, and a blockage could cause the gutter to overflow.

But we still come back to two points - the outer skin is dry (a bit of moss notwithstanding) and the damp is only inside, which is why I wonder about water getting into the cavity.

Anyone got any thoughts about the advantages and disadvantages of adding ventilation to the inside of the cupboard? There has been some casual ventilation via a loose brick for a long time, so I don't know if adding an internal vent would make things better or worse.

The house is 50 miles away, so inspection at short notice isn't quite trivial. I'm visiting on Wednesday with a builder, and will report any further findings...

The most common cause is condensation. Typical causes: interior RH too high, damp handling measures messed with. A water leak in the abutting ground can also cause it. Cavity walls were common in Vic times, so were walls that looked like one sort of construction but weren't - don't judge a wall by its cover. Also houses with a whole bundle of different wall constructions in one house are often seen.

I'd start by looking at the rainwater goods. It's not clear but looks from one of the photos that the drainage slots are filled with dirt.

Then I'd plug a dehumidifier in - that deals with most damp problems quickly. You may still need to sort out the cause - not always - but the dh prevents unnecessary extra damage & health damage too.

NT

DPCs are in most cases immaterial, ie usually don't make a snigificant difference to whether a house can deal with damp or not. They are BR required to deal with edge cases.

NT

to be expected. Condensation prefers lower areas where ground contact chills them more.

Partially blocked guttering partially overflowing there is a common cause. Good to get out in pouring rain & see if any rainwater issues are visible.

entirely possible

perhaps

Neither sounds like a good solution :)

NT

if there's moss on it it's not dry, it's consistently damp enough to support moss.

An airbrick is unnecessary heat loss. Sealant is normally not the solution to damp problems in old houses either. Solving the cause is. If there are signs of damp around the rainwater goods, fix em. Cast iron often rusts through at the back where it's hard to see. And I'm struggling to believe those shallow grooves, even when kept clear, would have much hope of handling 2 house roofs' worth of heavy rain.

NT

missed that - most bulders don't understand damp in old properties and want to get paid for unnecessary or harmful work.

NT

Thanks for the various bits of advice. It sounds like one of the first things I should get the builder to do is inspect the guttering and check that it's clear and functioning correctly (I can do a fair few jobs myself but am not great with heights).

When I referred to 'sealing' I just meant repointing the loose brick back into place rather than using some kind of sealant. Before doing that I'll probably be well advised to knock another couple of bricks out and check that there isn't any debris bridging the cavity.

Another thing I noticed when I was there over the weekend was that the pressure gauge on the combi boiler was at zero - I added water to the system to get 1 bar before firing the heating up. I'll check the pressure when I go back. There could be a leak somewhere, and it's probably a good idea to check around the radiator on that wall particularly carefully.

So I'm not sure of the root cause but will have plenty of things to look at :)

Check pressure vessel hasn't failed.

Plus one of the downpipes is above a grill. Is the pipe connected to this grill blocked or broken ?.

The grille is a couple of doors down the street and is only shown to demonstrate where the channel discharges to. I poured a bucket of water down it and it drained freely.

They are called "Slot Drains" eg:-

Even so, discharging a downpipe immediately next to the outside wall is a bad idea. Try getting that past the BCO on an extension or new build.

The slots could never cope with anything other than a light shower, so the whole area in front of your house would be awash during proper rain.

Historic photos would be interesting (local library ?) which might show the drainage arrangement before these slotted slabs were installed.

My house is typical Victorian. Suspended wood floors about a couple of feet above ground level. So any damp in the walls is below room level. Seems to work OK - provided you don't raise the ground level, as so many do with concrete or paving etc.

Visited again this week and had a chat with a local builder. Since my visit he went back and happened to see the house while it was raining - he spotted some overflow from the guttering and a fair amount of water running down the outer skin, so that's where I think we need to start. I've asked him to clean the guttering and check that everything is flowing well.

While I was there he removed a couple of bricks inside and I had a dig around in the cavity. There wasn't much in there - I removed a couple of pieces of rubble, and at the bottom there seems to be some sand, which feels damp. Going back tomorrow with a trowel to see what I can rake out.

So at this stage we plan to rake anything else we can get out of the cavity, seal the Virgin Media cable inlet properly and attend to the guttering before making good inside. I plan to fit an air brick from the cavity into the built-in cupboard and a vent on the front of the cupboard as well to maximise ventilation.

The plan is to leave this for a few months and if it's still damp in the summer get chemical damp proofing done - I think of this as a last resort.

Yes, the pavement slope won't be helping - but the fact that the damp problem took 20 years to appear (and that the neighbours I've asked that also have this channel in front of their houses tell me they don't have a particular damp problem) indicates to me that this probably isn't the root cause. Wish me luck!

good that you've found the problem. Once sorted everything should dry out slowly.

good stuff

I wouldn't. First there's no point. 2nd it'll let high RH indoor air into the colder cavity where it will condense on the outer skin. 3rd it'll create heat loss.

makes no sense

You've found the cause. You don't need luck.

NT

I was in Guildford yesterday and I noticed several of those inset cast/wrought iron channels taking the downpipe of a terraced house

I also found one property with those concrete slabs with V-shaped slots doing the same thing, but also taking the water away from the house front wall and into the gutter.

What the council have done is highly dubious. What you don't know is, if that underground drain, connected to that grill under on the of downpipes is intact. It could have been cracked by the numpties who did the paving work.

Some fluorescent dye might give the game away if it is.

Was back at the house yesterday, and this was my first visit in years when there was heavy rain so I at last had the chance to see for myself what was happening.

There was some water splash on the front wall, although I didn't actually see the guttering overflowing. I've still asked the builder to check it and make sure it's clean and free-flowing.

What I did see, however, is more concerning. I now think I'm sure what's going on. When I lived in the house 20 years ago, during which time the council raised the pavement level and caused it to slope towards the house, adding the drainage channel, the channel flowed freely down the gentle slope along the pavement to the right and away from the house. What I saw was different - in heavy rain there is now a pool of water in the channel in the area where the downpipe flows out, next to the telephone pole.

Most of the channel is made up with grooved slabs, but a short section around the telephone pole was bodged with concrete, with grooves added to the concrete by the original paving contractors. This photo shows what they did - note the rougher surface of the concrete section on the right:

I'm pretty sure the gully isn't part of the problem. It's two doors down (to the right of my house) and appears to flow freely. The damp problem emanates from the left side of my house, the right side being pretty dry.

So maybe I've found the root cause, but it's going to be a hard one to crack :(

I would still suspect that dodgy cable entry shown in your photo. That plastic cable bung is not stopping anything and possibly the bodged concrete surrounding the cable/bung is also acting as a reservoir trapping any water running down the wall. In heavy rain the water level may rise just enough to channel it in through the cable hole.

In previous photos I seem to recall that other cables or similar go through the wall at a much higher level with the vertical section protected by trunking etc.

I've finally worked out a strategy for dealing with the damp problem.

1. After dismantling the cupboard where the worst of the damp was I hacked off the plaster around it and after raking the cavity and getting a bit more debris out have had the loose bricks in the cupboard made good. I've rebuilt the cupboard leaving bare brick inside and added a decent sized vent to the front of the cupboard. The area around the outside of the cupboard has been replastered.
2. The builder has cleared the guttering (in heavy rain later on I did see water from the gutter dripping and splashing the worst-affected area, so it definitely needed doing and could have been the main cause) and made good an area of render and pointing at the bottom that was crumbling.
3. I've sealed the cable and where it enters the cement around it.

My plan now is to see if the wall dries out and take the matter up with the council if it doesn't.