Damp problems in Victorian Townhouse

[AMole]

Hi everyone,

I'm hoping someone here can help with a couple of (possibly related) damp issues in our Victorian town house - I've consulted a few so-called professionals and they have just offered up solutions that I'm convinced won't help.

Firstly, a description of the house: it's a 3-storey townhouse, built around 1870. We're at the end of a terrace of four houses and have a gable end wall that faces roughly west. The lowest of the the three storeys is a semi-basement - floor level is around 1.2m below street level. Unusually for a house of this age, it has cavity walls but the gable end in the attic is just a single skin. There are two chimney breasts running up the end wall, each with three flues (hope I've got the terminology right!). The two chimney breasts come together at attic level, with a single stack at the apex of the roof. Of the six flues, only two remain open, the others have been sealed.

The previous owners carried out various "improvements". These included having cavity wall insulation installed (in 2009). As well as the cavity, they seem to have also filled at least one of the chimney flues. (The insulation looks a bit like cotton wool). At the bottom level they knocked two rooms into one and fitted a new kitchen (again around 2009/10). As part of this work, they had a local damp "specialist" apply a waterproof plaster to the walls, which they then painted with some kind of vinyl paint. They also had vinyl flooring laid across the whole of the basement level. We had water coming in around the chimney stack when we first moved in, so we had someone fit a lead flashing around the stack and they also refitted a couple of slipped slates. However, the quality of the job they did wasn't the best and although it solved the issue at the time, I'm not sure if it is now contributing to the second of the problems below. Finally, I suspect the floor level in the basement has been lowered (by about 10-20cm) at some point - I suspect this because we appear to have slightly more headroom at this level than our neighbours and the bottom step of the stairs down to the basement is clearly newer than the rest of the staircase.

Now to the problems.... Firstly, the basement. Unsurprisingly, the works done in 2009/10 didn't solve the damp problem. The vinyl flooring bubbled up and we removed it a few years ago, revealing an earlier (relatively modern) ceramic tiled floor. The paint also bubbled up in various locations and we were able to peel off most of the paint from the affected walls. The plaster has what looks like damp patches from floor level up to about 30cm above floor level, with evidence of salts leaching out of the plaster. However, when a surveyor put a damp meter on the walls recently, he said the walls (including the "damp" patches) were effectively dry. But, if we leave anything in the basement rooms, especially near the gable end wall, for any length of time it gets damp and eventually mould starts to form. Also, we recently left a (full) plastic bag on the floor for a couple of days and, when it was moved, there was film of moisture on the on the bag and on the floor where the bag had been. We want to re-fit the kitchen, repair the walls and put down a new floor but obviously don't want to waste money doing this if the underlying damp issue isn't resolved. We've had various solutions suggested to us over the years, including lining the basement level walls , various waterproofing treatments that could be applied to the walls and just accepting the situation and stripping the walls back to bare brick to let them breath.

The second problem is up at attic level. When we have heavy rain combined with a strong westerly wind, the inside of gable end wall in the attic becomes visibly wet in the triangle beneath where the two chimney breasts come together. This water then runs along the underside of the chimney breast and drips onto the attic floor, resulting in a damp patch forming on the bedroom ceiling below. Again, various solutions have been suggested, including rendering the gable end wall (which I'm not keen to do, especially as we're on clay and the house does move slightly with the seasons), and painting the end wall with a clear waterproofing treatment.

I'm not sure if the two problems are in some way linked - e.g. water penetrating the end wall and collecting at the bottom of the cavity? We'd really like to remedy the damp issue to make the basement level properly useable but can't afford to waste money on solutions that don't work or make matters worse. Any thought or ideas on how to resolve either of these problems would be gratefully received!

 

[Cubist]

With regard to the perceived damp in the top floor room you first need to confirm that its either penetrating damp from the buildings exterior or ifs due to condensation driven by your heating and ventilation practices. Far from coincidentally I have referred several other people to the technique of taping a sheet of either kitchen foil or clingfilm over the upper section of the damp patches. Left for 24hrs or so if the face of the sheet is wet then its condensation and if dry but the side against the wall is wet then its penetrating damp from outdoors.

The source(s) of damp in the basement though may be more difficult to nail down as will therefore the nature of any remedial measures. The poor weather over the last couple of years has led to a general increase of the levels of groundwater across the country and many people have observed increased flooding, albeit temporary, in their cellars and under-floor voids. Rising damp through floors and walls has, as a consequence, increased and is, forgive me, reaching new heights.

Before going any further though are you aware of the routes used to drain waste water from the kitchens and bathrooms and do pass drains pass through the basement? Others here are more experienced than I regarding the best strategies for cellars and basements but any likely approach would benefit from access to an effective external drainage system.

 

[AMole]

Hi Cubist,
Thanks for the reply. With regard to the basement and drainage matters, there is a passageway (big enough to get a car through) between us and next door at street level, with bedrooms (one of ours, one of next door's) over the passageway. The main drain runs through this passageway, and out to the main sewer in the road in front of the house. The basement level toilet and utility room (in an extension on the back of the house) together with the basement level kitchen drain out to this main drain (exiting the house at the side). The other bathroom is on the top floor and drains via soil pipe down the front of the house which, again, feeds in to the main drain running through the passageway. We did have a break in the connection from the soil pipe to the drain a few years ago. At the time, we had a full CCTV survey of the drains. This showed the main drain to be in good condition but revealed the break in the connection from the soil pipe, which we had lined. This cured the damp issue we had in the corner nearest the soil pipe. But there are still the problems described in my original post - which are away from the drains.

With regard to the problem on the top level, the damp patch on the bedroom ceiling is relatively small (less than 10cm diam) and coincides with where water can be seen dripping onto the top side of the ceiling (i.e. in the attic space) as described above. On one occasion after particularly bad wind and rain, we've also had damp appear at the top of the bedroom wall, close to where the damp patch on the ceiling is. Although we do get a fair bit of condensation on the (single glazed) windows in cold weather, I'm fairly sure the damp patches in the bedroom relate to what's going on in the attic rather than heating/ventilation issues within the house.

 

[Cubist]

Apologies, I misunderstood your discussion of the damp on the top floor walls. The 'usual' suspects at the root of such rainwater incursion problems around the chimney are associated with the mortar flaunchings at the top and foot of the chimney stack, failed lead flashings or failed mortar pointing of the brickwork of the stack and also movement and/or damage to the tiles and any membrane beneath them. Direct inspection is required to determine the exact nature of the problem and to prescribe an effective course of action. However, a paint on waterproofing treatment will most definitely NOT suffice. please disregard whoever suggested it.

As to the basement. It seems that the bulk of this structure is above ground level and has good access to the main waste water drains. Others here have direct experience of how best to deal with the issues there but I would urge you to also consider and examine all the exposed brickwork that forms parts of the external walls of the basement. I appreciate that some parts of these may be sheltered but if the masonry and its mortar pointing is in poor condition this could be a significant contributor to the damp problem inside.

Hopefully one or more other members will be along soon to offer additional advice.

 

[AMole]

That's great, thanks Cubist. The pointing on the end wall doesn't look to be great, especially further up the wall (to the extent I can see it clearly from ground level) - looks like there might be a couple of small gaps. So, perhaps time to consider repointing and getting someone to do a proper job on the chimney stack/roof interface. Thanks for taking the time to reply - really appreciate the guidance.