Rising damp - advice on action please!

BB1984

Hello,
Another question about my house renovation I'm afraid...

Now, I was aware that my house had a damp problem down one side before I bought the place, but now I'm in the process of doing it up, I'm not sure quite what to do about the problem.

This is what I've learned so far:

• My thoughts are that the damp is worst on this side of the house because the external ground level is higher on this side - in fact, the path was about the same level as the internal timber floor level. I believed that the soil/path at the side is above the DPC, which has caused damp to travel up the wall.
• Also, the outside walls have been rendered, and the render goes right down to the ground - I think this is bridging the DPC.
• Inside the house, under the floorboards, the void (about 8") has been filled in places by bits of rubble etc - this potentially has enabled moisture to soak up into the bottom of some of the joists.
• There are only 2 air bricks along the whole wall on that side - about 10m. There is no ventilation at all in the corner where the damp is worst - probably because they couldn't fit an airbrick in due to the lack of difference between internal and external levels. The two airbricks that are there have been almost totally blocked by dirt, render etc.
• The footings of the wall are only about 4"-6" below ground level, and are solid concrete. I have dug down to this, and have seen how, when it rains, water puddles up on top of the footings, against the wall - probably draining straight into the cavity!
• My ideas thus far are: Dig the path down to a lower level, below the DPC (hindered somewhat by the discovery of the solid footing); cover the path with a decent layer of gravel; dig out all the rubble under the floorboards; install some air vents; remove and replace the rotten floor joists, using treated timber and putting damp-proof material around the ends of the joists.
• One builder that looked at it agreed with most of this and added that periscopic air vents would work well.
• Another builder suggested taking out the timber altogether and putting a solid concrete floor with integrated DPC, but this is not something I'm particularly keen on.
• A council surveyor (who works with my mum) went round today and his advice was that the DPC may have broken down on the inner leaf, which has enabled moisture to get at the bottom of the joists, causing them to rot. He suggested using porous ceramic tubes (www.hydrotek.co.uk) which apparently soak up moisture from the masonry, and drain it to the outside. These would work in conjunction with the periscopic air vents. He also suggested that rather than my "French drain" idea, the path could be paved and sloped away from the house, to encourage water to drain away rather than puddling. He thinks that if I just fill a trench with gravel, the water would settle at the bottom of the gravel, on the concrete wall footing.

I think that's covered everything - sorry about the lengthy post but I hope that some of you wise folk will have a some advice! We don't have much money to spend on this but equally this is something that is important and that must be sorted properly - no bodging here!

Thanks very much

BB

ps more photos on my blog www.thehouseofdoom.wordpress.com - not many illustrating the above though unfortunately, but feel free to have a nose...!

Space_Cowby

Im sorry but what is your question ?

Your plan all seems good.

I agree with sloping the paving away as the gravel will just act as a water collect point unless it is more like a land drain with pipes etc.

Never seem the ceramic things but personally im not convinced they would work. You can hire all the kit to inject your own chemcial DPC and I think I would do that.

BB1984

Thanks Space Cowboy - ok well my question is really, what should I do about the path?

Also, has anyone seen or heard of the porous tubes?

And can anyone think of anything else that I could do or not do, to make it all good?

Thanks

BB

weekendwarrior

Never heard of the porus tubes before, but I have had Electro osmosis DPC fitted in two properties and it worked a treat.

mistah

The trouble with the porous tubes is that there is no real evidence that they work. In fact the Building Research Establishment studied them in the 1930s and found that they did not lead to any reduction in rising damp.

There are a lot of systems around that claim to treat rising damp by various weird and magical means - e.g. electricity, radio waves, etc... However the only ones that have ever gained independent accreditation in the UK are physical damp courses and injected chemical damp proofing products.

If you want more info on treating damp, the best place to start is probably the website of independent consultant, Graham Coleman - http://www.buildingpreservation.com/

siocledpoeth

we had similar problems. tanking failed, lowering ground level outside failed, french drain solved the problem.

27col

You seem to have covered all the options yourself. The main problem would appear to be the levels around the outside.You are not going to solve anything until this has been fixed. More air bricks are obviously required as well.
I have never heard of the ceramic tubes, but, who knows, they may work. Not difficult to fit by the look of it. Possibly worth trying if they do not cost a fortune and if you can fit them yourself.
You say that the void is about 8". I would have thought that this is about right. If you have a very deep void, there is not going to be much air movement with just a couple of air bricks. The shallower the better, to get a good underfloor air movement. In my first house there was a 3ft drop under the floor and only a couple of air bricks, this meant that there was no way the bulk of the air was being moved. We had appalling dry rot as a result, some of the other houses in the road had the void filled so that there was just a few inches of air under the boards and thus a good air movement. You need to check out your rot, because, if it is dry rot, then replacing the rotten wood will do nothing but provide more fuel for the dry rot spores to infect. I do not know if modern timber treatments will prevent dry rot infestation, but you need to find out.. There other posts in which they say that they replaced affected timber and the rot was back within a very short period. I remember that we scorched the brick walls with blow lamps to kill the dry rot spores. Google 'dry rot' and see what comes up.
Usually you can tell if a joist has dry rot, if you feel underneath it you will feel that it is hollow. This is a sure fire fire way to detect dry rot. Also there will probably be white tendrils of spores hanging off the timber and adjacent brickwork. I had similar problem to those that you have described in my first house and had to replace the entire ground floor. We did not have the damp course problems that you have. Ours was just due to high levels of ground water and a generally damp atmosphere under the floor. I offer this post, based on my own experience. Do not try to do a bodge, make a thorough job of it.

BB1984

Thanks for the replies.

Mistah - I had a read of some BRE info this lunchtime and came to much the same conclusion! I will have a look at that other website.

27Col - I'm pretty certain we don't have dry rot. I'm a (young and fairly inexperienced!) structural engineer and I have seen dry rot in action - we don't have the signs. What we do have is damp and wet rotten joists and damaged plaster. The ceramic tubes (also known as Knapen tubes, I believe) aren't very expensive, and can be done DIY, so I might give it a go.

From everything i've read so far, I'm realising that damp, and particularly rising damp, is a minefield, and as such my current thinking is this: the room is a spare bedroom; there's no rush to decorate it. So I will dig down the path as best I can, and install a french drain of sorts. I will also install several air vents, clear out the below-floor rubble that is right up under the joists, and replace the rotten joists. I will use treated timber and use fresh DPM under the joists. I will also make sure the cavity is clear as far as I can. Then I will dry out the room for a while, and see how we go. If the damp seems to clear up, then I will decorate and keep an eye on it. If it doesn't improve, I'll have to think again and try something else - and at least I won't have wasted a fortune.

All very stressful! :rolleyes:

BB

illzlee

BB, it seems you have covered the evidence pretty conclusively and i can only echo some of the previous posts;

1. The levels are too high externally, and as you elude to the path is probably covering one or more air bricks. This is a key factor to be remedied.

2. The telescopic air bricks would be difficult to retrofit into existing walls neatly, but if you decide to do so i would recommend these:
http://www.manthorpebuildingproducts.com/building/products/throughWallVent.php

3. If you deside on a french drain, perhaps try aco drive drain or similar to make sure the water is actually divertd away from the wall (sounds like you may have issues with levels doing this anyway?)

4. The render is, in my opinion a key element. I am looking at a GP's practice currently where a section of render with 'chunky' aggregate has been patched with a more modern cement mix with minimal small aggregate and no large - although all the render bridges the DPC the only damp occurs at the point of the new render. Prognosis; the new render is much more dense and more easily allows water to 'wick' upwards more easily.

5. Sounds defo like you have wet rot - this is wet (duh!;) ) and causes longitudinal cracking of the timber which can be easily crushed. Dry rot causes cuboidal cracking of the timbers as the cellulose is drawn out.

Apologies for the lengthy reply, but eager to help - even if i am young and fairly inexperienced building surveyor!

evilgoose

Sorry if I've missed it and you've mentioned it - but have you actually checked inside the cavity of the house?

I'm doing some renovation on my semi and there are patches of damage from damp, I've removed some bricks to gain access and the cavity was blocked, bridging the (admititly old) DPC and bridging the cavity. I've cleared out the blockage and tried my best to removed the debris to a level a few bricks below the DPC.

It's not pleasant job (I keep getting images of that scene in Flash Gordon where the guy from blue peter sticks his arm in a tree trunk).
But I've got loads of 'muck' out of there and in the areas I did 1st they look drier.

If you dont want to remove bricks I think you can hire scopes to look inside the cavity.