Treating rising damp in a brick and flint house

[MarkJ]

We are in the process of buying a brick and flint house, which was built around 1820. We instructed a building surveyor who is familiar with buildings of this type.

We just got his report back and it says that there is evidence of rising damp in the ground floor and basement, but no visible signs. I guess this means that he picked up the damp using instruments, but as we already knew there are no marks on the walls or musty smell.

When we asked him about it, he said that there is definitely some rising damp, but this is the case in all flint stone houses as it is not possible to use chemical damp proof courses. Given the general good state of the house he does not see this as a particular problem and would still recommend that we buy the house.

My question is, what are people's experience of rising damp in this type of building? I am very wary of buying a house with damp as I have always lived in Victorian houses with damp proof courses fitted. However, I don't want to walk away from a beautiful house if this is normal and not a problem. Also, is there risk to the integrity of the joists if they are sat in walls which are damp (a question for the surveyor I know, but might as well ask it here!).

Any thoughts, words of comfort or advice????

Thanks

Mark

 

[Nemesis]

If there is no visible sign of damp - I wouldn't worry! Keeping the place heated and ventilated and indeed 'breathing' will do the trick. If there is no sign of joist end rot now it's not likely there will be in future.

Sounds as though your surveyor has some sense and understands period buildings and the fact a chemical DPC is a waste of cash.

However - if there is a basement, how come there is supposed to be 'rising' damp in a floor above?

 

[MdB]

Two prong style of damp meters (as used by most surveyors) do not measure damp. They measure electrical conductivity. They only give accurate readings of damp if they have been calibrated for the surface they are measuring. This is very unlikely to have been done. So I would say you may or may not have damp.

However, if you have a basement with flint walls then it is very likely that moisture will be coming through those walls. The question is, what is happening to this moisture? If the basement is well sealed with little or no airflow through it, then the moisture has no where to go and you will see the effects. If the moisture can evaporate easily and then escape via ventilation then you will have fewer problems. However, if the water table rises, you will have a pond without question.

Most people who talk about rising damp, actually mean penetrating damp. What are the ground levels like outside the property compared to inside? They should be 150mm below inside floor level if at all possible. If not, then can this issue be sorted out?

What are the walls rendered with? Is it lime (good) or is it cement (bad)?

Damp + beams means rot. No rot suggests no damp...

Lack of signs of damp is a good sign but it could have been covered up (like in my house) before sale so look carefully.

Try reading the Damp FAQ http://periodpropertyshop.co.uk/phpBB2/viewtopic.php?t=6777&start=0

 

[MarkJ]

Thanks for that. The basement isn't currently tanked. That's a job we'll be doing straight away given there are four full size rooms with 8 foot of head height down there, but the rooms are currently not ususable. The basement company we are using uses a system which draws water away from the basement walls and pumps it away, rather than sealing the walls.

 

[MarkJ]

Oops! Posted my last message before realising there was another reply.

I think the ground floor floors should be well clear of the outside ground level as you climb several steps when entering the house. Clearly, this isn't the case with the basement.

The exterior walls are not rendered at all, just flint stone, with brick work around the doors, windows and corners.

I understand that the current owner may have had some of the ground floor windows sealed to prevent heat loss. This is because the local planning officer (the house is in a conservation area) wouldn't allow him to install double glazing. I think this is something we intend to change asap - I much prefer a house with lots of fresh air, even if the heating needs to be on a few notches higher.

Will definitely check out the link - thanks.

 

[MdB]

What exactly is this company proposing to do? A pump + not sealing the walls sounds good but I would be interested in the details.

 

[MarkJ]

I'll dig out a link that explains it better, but basically the company applies a textured membrane to the interior basement wall which funnels any moisture downwards to a channel that is dug around the bottom of the walls. The channel slopes slightly towards one corner and a pump is used to take the water away from the house.

This is supposed to be better than applying a water proof render which in time is likely to fail as water pressure builds up.

 

[NT]

There will always be a little water in a porous wall resting against damp earth. But this is not a problem in itself: if there are no symptoms, there is no damp problem.

Tanking would be a good way to create a damp problem, and is not recommended for such properties. It also tends to damage the stonework: when the cement eventually fails, it often pulls part of the stone away with it.


NT

 

[Nemesis]

Yes - this is exactly the thing to do with a damp basement - presumably Newton type membrane behind a lining - but is it really so damp that a pump is required?

Avoid cement tanking! Totally not good!

And if damp rises (an arguable point!) it isn't usually very far.

As far as windows go - some air is good, howling draughts not so good. Do you also have chimneys which can be used?

 

[MarkJ]

[quote Tanking would be a good way to create a damp problem, and is not recommended for such properties. It also tends to damage the stonework: when the cement eventually fails, it often pulls part of the stone away with it. [/quote]

I would agree with this where the tanking uses a waterproof cement render, but what about the membrance system I described, which still allows the walls to breath but carries the water away?

 

[Nemesis]

We are cross posting here - the membrane system is the one to go for!

However - unless it's really wet then a pump may not be required.

 

[stickybeak]

.

 

[Nemesis]

I suspect retro fitting a physical DPC in a flint wall would not be the simplest of tasks really.

 

[stickybeak]

If we all wanted a simple life, we would not be working with/ living in/ writing about historic buildings that need a very special kind of care.
If it was simplicity we were all after, we'd go the cement route every time. :wink:

 

[Nemesis]

Well, I've spent much of this morning baling out a small flood in the living room, helping dig up a path, and re-doing a patch of lime mortar.

No thought of retrofit of a slate DPC in walls two feet thick made of stone with a rubble core.

Ease doesn't come into it. Impossible and not required. I doubt that flint will be a great deal easier. The disruption and disturbance to the fabric of the building would be huge.

We don't have a physical DPC, we have a 200 plus year old breathing building though!

 

[Gervase]

If it was a pointless and possible destructive task I was after I'd be retrofitting a physcal DPC to a solid wall!
To quite Richard Oxley (to whom I'm happy to defer on most issues): "the successful installation of a physical damp-proof course is...extremely difficult or impossible and can also cause problems of settlement."

Taken from his 'Survey and Repair of Traditional Buildings," (Donhead, 2003) which I can't recommend highly enough.

 

[Nemesis]

Quite.

 

[NT]

AIUI lack of dpc has more or less nothing to do with the cause of damp problems generally, and insertion of dpcs more or less nothing to do with curing damp problems.

One could possibly go further and say the requirement for wall dpcs on new builds was of questionable value.


NT

 

[Nemesis]

It wouldn't have helped my damp problem yesterday either, which now seems to be cured (crossed fingers).

It's amazing how much water can run in via a small gap in the mortar!