The Brew Cabin

Hello

We have just bought a house (built 1887) that has damp. The house has thick stone walls but doesn't have a DPC. It has tarmac paths on all sides which, for most of the house, are higher than the floors - along the back walls, by about 12"! :(

My first question is:
Given that we clearly have to get the outside levels lower than the inside, what would be the best drainage technique? Some people have suggested building a French Drain that sounds like "the Dry Area arrangement" on the DPC page. However I quite like the idea of having a land-drain at the bottom ( "Drained channel arrangement" ) so that I know I'm getting the water away. I assume I would need at least 6" below the floor level before the gravel starts, and then does a depth of about 8" for the gravel sound enough? Or is this still a bad idea (the section calls it a last-resort)?

Second question:
At the front of the house a central valley roof drains into a soakway by the front door. The floor behind the door is very wet and rotten. According to the vendor he cleared out the soakaway because it had silted up but I am worried it's still not working well. The valley roof covers about 37m2, so by the soakaway calc it should be 0.6m2, but I've no idea how big it is yet (although I do know it's full of gravel, rubble etc). Do you think I should bite the bullet and dig a new empty soakaway for it away from the house? Would you also recommend a catch pit too (we don't have lots of trees, although there's quite a lot of moss on the roof though).

This site has been very helpful. There's a whole new world out there I didn't know about and meal time conversations will never be the same again :)

Simon

A French drain is, basically, a gravel-filled trench. They are rarely used nowadays (except by DIYers and the odd buioder that's not up-to-date with things) but the terminology persists.

A Dry Channel sounds a good option for your project. Although it's less than ideal, it's better than what you have at the moment and can't make matters any worse.

As for the soakaway, I reckon you should backfill the old one and start afresh, a good way away from the building (10m, if you can manage it, but 5m minimum) and then you know you're in with a chance. I'm not certain you need a catch-pit. They are a good idea when you have a project with a lot of silt, but for a 37m² roof, it's a touch of overkill.

Thanks Tony.

When you say "Dry Channel" do you mean forget the gravel and perforated pipe at the bottom and just have the concrete channel? Does say 200mm below the inside floor level and 200mm wide sound enough? I'm slightly worried about stray people, animals, etc falling down it (!) so will consider decorative edging as you suggest.

Are there any other alternatives I could consider? (A specialist damp report I had done suggested a silicone DPC at ground level and then tanking the inner walls for 12"! Doh!).

As for the soakaway, I'm sure you're right. Not sure I'll be able to stretch to much more than 5m away though since that will almost be on the pavement (the gardens are what the e&#36tate agent calls "manageable"!). Saying that maybe a 5m pipe and a hole in the hedge would work very effectively ;) ...except it might be a bit obvious when it froze!

Thanks again!

Simon

The exact spec for a dry channel depends on the layout you have. Firstly, you need somewhere to outfall, and I suppose this is going to be the soakaway that is mentioned in the second part of your post.

So, you need to outfall to the soakaway, and because said soakaway has been constructed at sufficient depth to give all the fall you'd ever need, the dry channel can be constructed as shown in any of the options on the DPCs page.

If you use a plain channel arrangement, then you are at least exposing the external brickwork which may be useful if a surveyor's report states that an injected dpc is desirable, and, to be honest, I think this is the option I would choose. However, if you wanted to use a linear drain, I'd be a little concerned, a sthat may not reduce external ground levels sufficiently, unless you used a extra deep channel rather than the standard 100-125mm channel that is sold at most BMs.

If you use a dry channel, you can use an edging to privide 'check' at the upper surface to warn pedestrians etc of the fall hazard, or you could get a local light engineering co to knock up a grille.

As I said, when I can't see the actual site, it can be difficult to say what would be best, but the above should give you more idea. :)

Thanks Tony.

I think I'll go for the plain channel and see how it looks. Even if it collects litter/leaves it should be easy to sweep out with a thin brush. I could always put a little gravel in later, although I don't think you'll really see it and it's just something to get in the way.

I'll post again once I've done it (don't hold your breath though!)... better go and hire a kango...

Sorry, just got back off a training course so am catching up with posts.

We built a "moat" around our house using 600mm square paving slabs with a slab on end as the upstand. This leaves about a 50mm edge for people to trip over as they fall in, and retains the tarmac.

Many older houses had a "stone drain" at the foot of the walls, sometimes both inside and outside. These comprise a line of stones laid a few inches in (or out) from the wall and then covered by stone slabs, or the flooring. Eventually these stone drains get choked with silt, or someone lays a pipe or foundation across them, and they cease draining the footings.

Don't have anything to do with injected DPCs. Rising damp is a myth. If the water table is so high that capillary action is drawing water up your walls, then a damp course is the least of your worries. For more on this see
http://www.onthelevel.in-uk.com/damp-proofing.htm

For many older houses the application of a little heat and some good ventilation will reduce damp considerably - though it may take anything up to a year. You also need to avoid using gypsum plaster and cement, as the older materials such as lime plaster and mortar allow walls to dry out, which the more "modern" products do not.

Well that's very interesting. As I mentioned, I was not very impressed by the damp company's recommendation to tank the walls since it didn't appear to tackle the cause of the problem. That's why I thought if I sorted out the levels and the soakaway I could see what the damp was like in 6 months or so.

One thing I haven't been able to explain though is the damp in the cupboard under the stairs which is in the middle of the house and away from any outside walls. If that's not rising up through the floor where's it coming from? Just condensation in the air? Could it be travelling 12" or so under the floor (stone flags on one side) from the outside wall?


Simon
PS. I checked out the "onthelevel" website which was useful. Spookily enough our Timber-Damp report also suggested we spend £600 or so getting all the floors treated for woodworm! I have to admit I'd already ignored that advice :)

I wish I'd known seven years ago what I now know about timber and damp. As far as I can see as long as you get rid of the water where it comes in (and that's usually leaking gutters) and increase the ventialtion most of these things will go away on their own. I've been amazed at the way even dry rot, which I'd always been led to believe was the HIV of the timber world, goes away with a little heat and ventilation.

Funnily enough we have a similar situation with raised levels outside and damp appearing on internal walls. The previous owner installed a CDPC and tanked the walls and yet the damp is still present. Before I discovered this website I had a 'Damp-Surveyor' visit and he suggested another DPC be installed - I'm not sure how he thought that would help!

I have also been advised to line the walls with a polystyrene lining paper to insulate the cold tanked walls and to prevent condensation which is now thought to be the problem.

I would like to go a step further and increase the ventilation - would an airbrick do this for me? The next question is where would the ventilation be best placed?

Once again thanks for your help and keep up the good work on an ace website.

Mark

Mark

If you increase the ventilation you'll cool the air near the walls but whether you'll be able to get rid of the condensation I don't know - the room will be colder but then there will be a temptation to turn the heating up :(


Simon

Funnily enough I was in our cellar yesterday, looking at the spring under the house. The cellar itself is lower than the sub-room voids, but because the coal seams slant upwards the water appears about hafway across the "floor".

I've dug the rubble away from the side walls (taking care not to get as deep as the footings!) and I noticed that the damp has only risen about six inches up the wall, despite having its feet in water and wet earth behind it. Where I have installed a radiator the wall has dried out completely. I have also constructed a duct in front of the airbrick, partly to ensure the warm air from the radiator doesn't go straight out through the wall, and partly to ensure the cold air entering through the airbrick is directed down to the damp floor first. This has been remarkably effective in drying out a damp wall.

[Loads of caveats about drying out clay soil and causing your house to collapse, etc]

Just thought I'd post an update of progress so far...

I hired a pavement cutter machine (not sure what its technical name was) - it had a 8" disc/blade at the front, a Honda engine and you pushed it along. Hewdens advised that instead of a Skilsaw and it was definitely a good choice - it easily cut the slot to 4-5" deep and we did right round the house in a short day. It cost about £35 for the day plus <£35 for the wear on the blade (I think they charge £35/mm).

The next day we hired a Kango and just broke up the top 2 or 3 layers of tarmac - under that it was mostly clay and stones.

The final stage for now has been digging out the trench with a pickaxe, spade and trowel. This has probably been the most time consuming job, however, in the process I have found an airbrick or two, doubled the size of the existing ones... and found a slate DPC! This is 3" below the old ground level at the front of the house and more like 9" at the rear.

So far, so good. The stone can hopefully start to dry out in the air. The trench is just that at the moment - proper gullies etc will have to wait. However there doesn't seem to be water collecting in them so I'm not so worried yet.

Soakaway update:
Well, I couldn't resist having a closer inspection of the supposedly recently redone soakway by the front door. I scooped out about 2-3" of gravel and there was the bottom of the drainpipe (higher than the slate DPC). There was then about another foot of gravel, about the size of a domestic bucket! That was it.

I went out to look at it when there was a bit of a downpour the other week and, given that this pipe is about 6" diameter, you can imagine house much water was pouring out (and not really going anywhere fast)! Cue hacksaw, 2 bricks and long piece of guttering to get the water out onto the lawn - just hope no-one trips over it!

If anyone has any tips/suggestions please post them!

All good fun...


Simon

I'll try and take a photo of our "moat". It is floored with 2ft square paving slabs, and has slightly sloping slabs as the supstand. These project a couple of inches above the tarmac. so provide something for people to trip over as they fall into the moat. The moat has gullies to drain it, connected to our main drains, so we don't have oyur problems with soakaways. However at the front of the house (the downhill side) I will have to put a drain across the front path to enable the moat to drain down into the front garden, but I haven't got that far yet!