How far can damp rise?

[GMM]

I was looking at a house yesterday that had a clear problem with damp getting into the plaster in a small extension (Victorian house but a quite recent extension ie in the last few years). The agent didn't try to hide it (which would have been difficult!) but said it was rising. Now, the garden of this house falls away so at the point where the damp was most apparent, the floor was about 10 courses of bricks above ground level. The wall was covered by a raised deck, so I couldn't see whether it had a dpc, but could count approximately the brick courses through the gaps between the boards. I couldn't see any obvious accumulation of soil/debris down there that would form a bridge for damp to rise. The worst of the damage to the plaster was just above skirting level, so it looked like it could be rising and there was no obvious source of a leak that would affect the one wall specifically.

So, the questions (!): I thought I had read somewhere that damp could only rise 3 - 4 feet in a wall. Is this the case or am I mis- remembering ? (if there is a limit then it could be coming from somewhere else).

Secondly, if it is rising damp, what's the best remedy? I know chemical dpcs are often mis-sold but are they effective or is there another strategy that doesn't involve demolishing the whole thing and starting again?

It goes without saying that a problem like this would be a good justification for a low offer on the place, but I'd like to have some feel for how low I have to make it to cover resolving the problem: Apart from the damp and a couple of other small issues it's a good place, which I might well buy.

Cheers chaps

[dom]

I wouldn't trust an estate agent to know the difference between rising, penetrating, and arrived-on-a-bus damp.

Four common causes of damp are condensation, penetration, leaks and rising.

Causes off the top of my head:

Condensation - poor ventilation, poor insulation, inappropriate use of the building

Penetration, damaged pointing, ivy, wrong building materials

Leaks - pipes (water and drainage), gutters.

Rising damp - bridged damp courses, cavities full of junk

(or combinations of)

In most cases, the building once worked ok, but something went wrong - you find something, you fix it.

I might investigate if installing that deck has damaged a drain.

[GMM]

I suspect there could easily be something in this: Clearly the deck was installed after the built, so i reckon there's a connection....

[GMM]

In this case, it's just a bare undecorated wall (I suspect it was re- plastered as an attempt at a 'fix' and never decorated), so no big job, although I suspect there could be trouble in the floor. Having said that, there didn't seem to be any bounce in the floor.

[The Natural Philosopher]

Even that is pushing it. Mostly three to four bricks unless its stopped from escaping outwards

Injection works if the injectant (sp?) gets everywere it needs to.

Tanking the inside with a waterproof render works as well Or both together

I'd say there is another problem.

[Tabby]

Its never going to rise beyond that

First things first. So far there's no evidence that its rising damp. Most such cases are condensation, not rising.

Identify the cause first. More heating, more insulation, more ventilation, or a dehumidifier all can improve or resolve condensation.

Hopefully the sellers have more sense.

the cost of the usual misdiangnosis of rising damp, replacement of plaster, injecting water/cream/etc.

NT

[Phil L]

a metre is the recognised maximum height of rising damp, so ten courses is easily within this measurement. Also, although you can see ten courses outside, there could be earth inside underneath the wooden beams

DPC cream is the preferred method now and yes, it does work

Then don't let something minor like this put you off, people often run away screaming at the thought of dampness of any kind, yet it is one of the easiest things to put right - the major thing that people have an aversion to is the length of time damp walls can take to dry out, often months, even after treatment

[Dave Liquorice]

Which way do the deck boards drain, into the wall? Check by pouring water onto it. Even if it drains the right way there will be splash up from the deck onto the wall, is the level of the deck the same as the floor (skirting) inside?

Having said all that I'd be surprised if an extension only a few years old doesn't have cavity walls so how is the damp on the outer leaf getting through to the inner one...

[The Natural Philosopher]

Ah. I missed the deck..

Watersplash off a deck can soak the wall immediately above. It its only single brick that will show up.

[GMM]

Good point Dave

The deck level is higher than the skirting (about halfway from there to the bottom of the window), so water coming off the deck would be in the right place. The reason I hadn't really considered this is the cavity issue - I wouldn't expect it to get through to the inner leaf. I wonder if that means the construction of the wall is wrong (even if the damp could be solved by modifying the deck somehow)?

[The Natural Philosopher]

depends how much mortar was put in the gap. Or indeed batts. They carry water too

[Mike Tomlinson]

En el artículo , GMM escribió:

Sounds as if the extension might be open on three sides, so will be cold in winter, which would cause condensation. Something to consider anyway.

I'm in a similar property to that you describe - Victorian with a single-brick-depth extension on the back which is open on three sides. Needless to say, this is the bathroom, so it was very damp. Had to have the floor relaid with a new DPC, the walls drilled and re-injected then covered with a DPC membrane, then dotted-and-dabbed, then tiled. Now OK.

[The Medway Handyman]

Any timber ledger plate fixed to the wall should be spaced 10m away to prevent water pooling there, deck should have a slight fall away from wall.

What way are the boards laid? Parallel to the wall or at right angles?

[Dave Liquorice]

What bolts do you use to get that spacing?

[Dave Liquorice]

there

That's always assuming it is a cavity wall. I'd expect it to be but might not be.

Aye, and with the deck so far up unless there is really good ventilation underneath the outer wall below the deck won't dry particulary quickly. Are the vertical edges of the deck blocked or "decked" over?

Maybe removing an outer brick in the affected area to see what is in the cavity would be a good idea? Below deck level so the new mortar when it's replaced isn't so obvious.

[stuart noble]

I was looking at a house last night where, although the board supports were at right angles to the wall, the front "facing board" (or whatever you call the one that covers the gap) would clearly prevent a free flow of air. That and the sunken air brick out front was enough for me to give it a thumbs down.

I've seen a lot of these Victorian terraced houses where paving and successive layers of concrete at the front have created a new ground level, and adjoining houses have followed suit. Then the council pavement is laid to that level and before long you have a whole sunken terrace. Then sometimes solid floors are put in and a whole set of new problems arise.

[Nightjar]

A bit of reading that you might find useful:

Bignell

[The Medway Handyman]

Very long ones :-(

I meant 10mm :-)

[GMM]

They're kind of oblique, so I suppose that counts as end-on - I suppose that could lead to water channelling to the wall if the fall was wrong. I didn't look at the ledger but my recollection was that there was no free space immediately against the wall. I sort of hope it is a decking defect if we end up with the place as it would be a lot simpler to adjust a deck than to rebuild the wall!

[GMM]

Now that really is testing my memory - I think it was decked rather than brick, so I guess it would allow reasonable ventilation. Not that it would be sufficient if the deck is channelling water directly to the wall whenever it rains, as TMH suggests.

A bit tricky to take a brick out of a house when viewing but I think that might be an early job if we end up buying it.