Edwardian Footings and DPC

[Kensby]

Hi, my first posting here so please go gently.....
I have an Edwardian 4-bed semi with a long-term damp problem in the front ground floor room. Belatedly, I have started to investigate this and as a first step removed a hedge which previous owners had planted directly under the windows. This revealed a small blocked air grille which I cleared. No sign of the expected damp-proof course though. Digging down in the narrow strip of soil between wall and paving however, I soon found it, about an inch below ground level! What I also found though, only two bricks further down, was the top of the footings, where the brickwork starts to step out. This seems very shallow, is it normal in a house of this age?
So, my question is, would it be structurally unwise to expose the whole length of the wall down to the top of the footings? If so, how can I maintain the DPC at a suitable height above ground? Indeed, is a DPC of this age likely to be actually doing anything anyway? How about a French drain right up against the wall? Or would it be better to lower the height of the whole front yard?
I have already arranged to have the rotten wall-plate (sole plate?) and joist-ends replaced but am anxious that the underlying damp problem which has caused this should be remedied first. Any advice would be very gratefully received.
Thanks.

 

[chuckey]

In my Edwardian house the footings were only a couple of bricks below the soil level. Ideally the soil level should be in the order of 6-9" below the damp course to stop any splash-back from dripping water, however a couple of inches would be a mile better then your present system As a cheap start I would remove the soil, back ,say 6" from the wall and give yourself 2" of clearance and see how things go. As it seems that you are having the floorboards up check that the internal soil level is OK. Despite what other people say on this forum, I have had success with silicone injection to cure a faulty slate damp course in a Victorian house. A french drain is very tricky as its the pressure of the earth that is keeping you front and back walls in line with your neighbours. So digging trenches could lead to the walls moving outwards.
Frank

 

[Feltwell]

What you describe there in terms of foundations is perfectly normal, don't worry! My house is only slightly older than yours - 1899 - and is much the same.

Are you absolutely sure the DPC is that far down? Generally, it will be level with the bottom of the wall plate internally (so all timber is in the "dry" part), but there are no hard & fast rules and it could be lower. There is no problem at all with digging down to the top of the footings. The ground level does need to be below the DPC, 9" ideally but 6" at least - in a perfect world your yard is below this level, but even making a narrow trench against the wall filled with gravel (kept at least 6" below the DPC) would be an improvement, although you'll need to keep it clear of debris. Removing the hedge and unblocking that air brick is a good start. Can you see more air bricks? There should be some - you need a flow of air under the floor. Have you access from inside to look under the floor? They won't all necessarily go outside - I have some in internal walls and some going into my cellar, which is only under the hallway of my house. They all need to be clear.

Your DPC should be fine. They were usually made of slate and do not degrade - lots of people inject silicone compound, 99% of the time it's a complete waste of time and money and any damp is due to something else. Bear in mind that most "damp specialists" are nothing more than salesmen, it is in their financial interest to get you to spend out on injected DPC's from their company.

Is the house rendered? If so, is it lime or cement render and what condition is it in? If exposed brick, what condition is the pointing in? Ideally the pointing should be in lime mortar (and certainly use that for any new work) which allows the wall to "breathe". If it's been repointed with cement based mortar then that can trap damp in the wall, but frankly on a house of this age it doesn't always cause a problem - much of my house has been repointed in cement by a past owner and the walls are dry.

Lastly, look up! Are there rainwater goods above the problem area? What condition are they in? Bear in mind that cast iron guttering can look fine on the front but be totally rotten at the back, where no one ever paints it. Get out there in the next heavy downpour!

And lastly, have a look through the forum for old posts on damp. There are plenty! But my advice would be get your wall plate / joist end work done, clear any vegetation from against the wall, make sure all the airbricks are all clear, get the ground level below the DPC - and then give it a while and see if the problem persists or not. Don't rush into any snap decisions, and if anyone suggests injecting DPC's or stripping internal plaster back to 1m high and replastering in a "waterproof mix" then show them the door....

Have a look at this impartial article, but bear in mind that the author is covering pretty much all ages of buildings up to & including yours.

http://www.spab.org.uk/advice/technical-qas/technical-qa-20-rising-damp/

 

[Feltwell]

Forgot to say - others on here, far nosier than me you understand, do like pictures of old houses :wink:

 

[Flyfisher]

But my advice would be get your wall plate / joist end work done, clear any vegetation from against the wall, make sure all the airbricks are all clear, get the ground level below the DPC - and then give it a while and see if the problem persists or not. Don't rush into any snap decisions,

I'd go along with all of that. A long term damp problem will inevitably take some time to sort itself out once the underlying causes have been found. The encouraging thing in this case is that there are some definite problems found, i.e. blocked airbricks and too-high outside ground levels. Fixing these can only be a good thing and the coming summer can do its thing and help dry out the residual dampness.

 

[Kensby]

Thanks for those helpful replies (although a bit contradictory regarding the dangers of digging a trench down to the footings!) No, there is definitely only the one airbrick but the renovation company doing the joists etc are going to install two larger ones. There is a bit of an airflow since there are two more airbricks at the back of the house.
Looking at it from inside, the DPC is definitely a couple of courses down from the wallplate and appears to be some sort of thin flexible material (can't be plastic though, unless it's been replaced before!). Seen from under the floor, the brickwork is very crusty and covered in crystal growths. To their credit, the renovation company didn't suggest injecting a chemical DPC. I wouldn't have agreed to that anyway. (As an aside, does anybody know if Jeff Howell's book 'The Rising Damp Myth' which I read avidly, is generally considered to be correct or has it, as somebody suggested to me, been discredited? As a technician I admired his experimental no-nonsense approach.)
The house is not rendered at the front and is going to be repointed in the damp area. I have insisted on lime mortar for this. If they refuse I will do it myself.
Feltwell, I don't need to look up, I did that last August when water started to run down the internal walls, upstairs and down! A roof valley had been leaking and I hadn't spotted it due to the water being redirected by the under-slate felt. Another story. Suffice it to say that the roof has been fixed, the house has dried out and the aforementioned renovation company will be doing a lot more than just the work I have mentioned (including raising the roof in order to replace wallplates and ceiling joists!)
Finally, I have attached a couple of photographs as requested. One shows some of the upstairs damage revealed when I eventually realised the roof was leaking. The wallplate had the consistency of a very soft spongecake. The other shows the front of the house with the roof being repaired.
Kensby.

 

[Kensby]

Oops, sorry, got those photo headings the wrong way round!
Kensby.

 

[Feltwell]

Digging down to the top of your footings is fine - it's below that where you need to be careful. The force pushing down from the weight of your walls is spread out at base by the masonry, and then acts at around a 45 degree angle into the ground below there.

So digging down to the top of your footings is fine. Digging down to the bottom of your footings should not be a problem either, but you don't need to do that. Digging below the level of the bottom of your footings, you do not dig within the zone that spreads out at 45 degrees from the wall - and frankly, if you're not sure what you're doing you just don't dig that far at all!

What I think Chuckey was referring to was the lateral pressure on a wall caused by having soil at different heights on each side, i.e. outside and under your floor. Unless the difference is huge then this is no concern. A proper french drain would go down quite a way, quite likely below your footings - you don't need to do that, just making sure that you're clear 6" below DPC will do just fine to start with. If the problems persist you may need to look at more extreme options.

Your "crusty and covered in crystal growths" brickwork is just because it's been damp - the moisture dissolves salts within the brickwork that then get deposited when it evaporates off the surface of the brick. Just brush them off with a dry brush if it bothers you. Extra airbricks is a good idea - they definitely won't do any harm, just have a look to check you're OK with the appearance of them as there are some quite nasty plastic ones in a lot of merchants. You can still buy clay airbricks which will weather in much better. Sounds like your company has made some sensible suggestions if they are talking about increasing airflow and not injecting DPC's.

Very naughty that your roof valley leaked like that, especially when from the look of the tiles the roof dates from the 1970's at the earliest. The valley shouldn't leak in the first place, but if it did then the felt should have caught the water and deposited it in the guttering, so whoever did that valley originally didn't do a very good job!