Having finally got several other jobs out of the way, the time has come to tackle the rainwater drainage around my house. I'm dreading it, but it has to be done.
The house itself is an 1850's blacksmith's and adjoining cottage, and there's a couple of places where dampness is showing internally.
The big problem is the rainwater drainage. Some clever soul added CI gutters and dwonpipes at some time, but ended the downpipes about 4" below the soil surface, right next to the wall. On top of that, the ground level is way too high most of the way round the house - level with the internal floor, sometimes higher.
So, to me,
1) Reduce the ground level. I had in mind 12" below internal floor level as the finished ground level. Is that enough or should I go further? (I'm a bit cautious about going too far and exposing the foundations to frost, they're probably quite shallow.)
2) Rainwater drainage. I'll have more questions as the week goes on (as this week I'm getting the tape out and trying to figure out a design).
3) French Drain. I intend to install a french drain as there is only partial chemical DPC on the building. It looks like a chemical DPC has been tried instead of sorting the levels and drainage. so,
3a - My thought is to excavate to foundation level directly against the wall, and install in this position. Sensible, or better off in a different position?
3b - Can the rainwater pipe and french drain share the same trench?
3c - can the same pipe be used for both at the same time? ie, run the rainwater into the perforated pipe. I reckon not, but I've seen some examples that look like this has been done.
4 - Soakaway. I've seen the method on here of calculating the volume required, that's fine, but what rainfall per hour is sensible for 1000ft up in Scotland? We get a lot of rain!
5 - Suppliers. Who would you use near Edinburgh that actually has a decent range of drainage stuff, and some idea of what can be done? Go into my local merchant and mention plastic "crates" for soakaways and they look at me like I'm a nutter.
Tonight, off to measure up the roof and come up with the area to be drained.
Don't go so deep, finished ground level wants to be 150 below internal floor level, chemical dpc are a waste of time never worked and a big con for the insurance industry....
Set your gully pots in, will have to trim the ends of with grinder or hack saw etc.
No to using the same pipe, you want solid pipe for your downspouts, and the perforated for your land drain.
Can share the same trench but it's not really advisable as the water
will wick along the solid pipe rather than entering
Edited By GB_Groundworks on 1283788541
Giles
Groundworks and Equestrian specialists, prestige new builds and sports pitches. High Peak, Cheshire, South Yorkshire area.
french drains are only marginally better than nothing
better to install a proper land drain to a soakaway
as for soakaways it depends mainly on your ground
dig a trial hole ,fill it with water and see how long it takes to go down
building control usually want 2 per house of 1m3 each
cheers LLL
I'm in exactly the same situation as you although I have an existing soakaway that is more than up to handling the extra water. I reduced the levels to min 150mm below IFL and installed linear channel drainage and single gullies where neccesary. Things seem to be drying up but it's gonna take a while. I had to replaster the bottom part of the external wall which is quite common to have to do on old stone houses they rarely plastered below groundlevel which could have been 2ft above IFL. If the damp turns out to be capilliary from the subsoil then I'll have to go down the drylining or Osmotic route and live with it. If there isn't an existing stormwater system and a soakaway won't work then you may have to have a collection tank that intermitantly pumps it off site to a main or a ditch/ stream.
I find it best to talk to the sales/ technical guys in the BM's not the desk staff when I'm after anything not off the shelf. They are the ones who deal with the reps and can do the sourcing and will have a greater idea of the best product for you.
Thanks for the replies so far, and apologies for the stupid questions.
Doing some measuring, I think I'll have no choice but to run the land and rainwater drains in the same trench, around most of where they need to run there's only 1-1.5m clear space to run both.
"Proper Land Drain" seems to be exactly the same as a french drain, but laid to fall and to a soakaway, right? Is it acceptable to run both rain and land drain to the same soakaway? Last thing I want is to wind up with the land drain flooding with rainwater!
Incidentally, on the "drying out" thing, a stonemason told me to allow 1 month per inch of wall thickness. Having lowered the level at one corner already, it seems pretty accurate.
a land drain has a slotted pipe wrapped in non woven geo textile,encased in shingle
a french drain is a just shingle
when i do a site inspection,one of the biggest causes of damp is leaking gutters
check and fix your gutters first
cost pennies save thousands
LLL
Yep, I'm all over them gutters! They're trad cast iron ones, so needed the odd tweak here and there.
There's been quite a few joints dripping, and it's an easy job to sort them, as long as you never waste time trying to undo the joint - cut the nut with an angle grinder, punch the bolt up into the gutter, quick squirt of
into the joint, new bolt and nut. Unfortunately, when chimp-fisted goons install gutters that fall away from the downpipes, life gets a little harder. One of them's so bad that it'll be easier to install a new downpipe rather than try to reset the fall along the building.
Funnily enough, plumber's mate is what had been used, on a 14m run every joint was leaking. Not good.
Anyway, back from hols and spent the afternoon going round with a tape measure (i'll post up a drawing later) to work out the soakaway size. Now, stupid question.
Here - http://www.pavingexpert.com/drain08.html the calculations for a soakaway are shown. Do I use the flat plan area of the building, or calculate the roof's surface area?
I've done the same as your proposing with the french drains. My property has a slab foundation and suffers from water ingress through the slab and walls below ground level.
I'm in the process of installing french drains around the perimeter with the trench being next to the wall and the depth going to the top of the foundations. So far I've done the front and side and this has proved very effective with the surface of the slab being free from damp and water. The walls have also dried out.
I've shored the trench with PCC flags on edge. Trench lined with Terram. I've used standard 110mm drainage pipe and fittings. The bottom of the pipe in the trench has been drilled to perforate it. Filled trench with pea gravel and wrapped terram over top. I opted for the rigid pipe and fittings make rodding/jetting maintenance easier
I drain to a sump which is pumped out into mixed surface/foul drains. This is because the ground is clay.
Note of caution - I presume your fondations are strip. You don't want to dig out long sections of earth against walls in one go as it may cause the wall/foundation to shift. (others please advise)
You can install the trench in sections but you'll either need to use flexible piping or use couplers as you go. Some sort of shoring on the end of the working section to separate the soil and gravel.
Also if you have clay soil it will shrink when water is extracted so take care with the depth of the trench and don't go below the foundation whatever your soil type.
Well, from what I have been told locally the foundations are likely to be lime and horsehair! Very old stone house, solid walls, suspended timber floors.
My thinking is rather than place the drain right next to the building, is to place "near" to the building, using the same trench as for the rainwater, which will be about 500mm away generally - my reckoning being it should allow the soil to drain properly and prevent it from being saturated. Most of the problem seems to be due to the lack of proper rainwater drainage, the land drainage is, as much as anything, a precaution that isn't going to cost much extra to install.
Between that and lowering the ground level to where it should be, I'm fairly optimistic. Will be doing a test for a soakaway this weekend, so will be back with pictures of a big hole soon.
One of them's so bad that it'll be easier to install a new downpipe rather than try to reset the fall along the building.