Patio Drainage

[chilluk]

I'm just in the process of laying a new patio, approx 9m x 3.6m, in 600x600 concrete slabs.

On Saturday I got the 4 inches of hardcore down and whacked and have constructed what seems to be a pretty firm base with the appropriate run off.

Yesterday it rained solid for 24 hours!! Now beyond my hardcore base I have a bit if a trench which I plan to build a retaining wall out of new railway sleepers approx 2 foot high.

This trench is currently full of an inch or so of water - at least that shows the run off is OK!! The soil is clay mostly although the garden is surrounded by Oaks which normally drink most of the water!!

Should I try and install any type of drainage between the edge of the patio and the retaining wall? Some sort of gully, or just a gravel channel? I know yesterdays rain was pretty excessive but I don't want to end up with a lake where the patio should be!!

I was planning to just bed the sleepers on a couple of inches of mortar just to help level/set them - the finished wall construction will be pretty self supporting as it has a few right angles in it, and will obviously weigh an absolute ton (20 - 25 sleepers).

I don't think I could get any kind of drainage connected up to any of the house drainage that easily and was hoping some sort of "natural" soak away would be easier if it works that is.

As usual any advice gratefully received.

 

[noseall]

if the paved area is 'locked in' on all sides with no run off areas then you will need drainage to avoid ponding. light rain or drizzle, it could probably cope with, but a heavy storm will pond and attract mud, crud and mozzies.

a soakaway should be 5m from the building but clay aint to clever at draining water.

is there no way of linking into the existing storm system?

 

[chilluk]

Not without some difficulty - nearest guttering downpipe is close to house - back up the slope where the water is coming from - which is now covered in hardcore!!

I think what has made it wore this weekend is there is not a single piece of greenery in the whole garden - we "napalmed" it to start all over again and so the higher area which was turf now has nothing to soak up any moisture so I think it was draining from both sides into what is currently the lowest point.

Any value in digging a soakaway under where the sleeper steps will be do you reckon?

 

[noseall]

Any value in digging a soakaway under where the sleeper steps will be do you reckon?

absolutely. but there may be limited success in heavy prolonged downpours.

once, on an extension over north stafford we dug the soakaway at the same time as digging the foundations, to make full use of the hired digger.
once dug out, we had the most almighty summer storm.
everything filled up, foundation trench and soakaway was brimming with water. we pumped the trench out and concreted but left the soakaway alone to see how much water would actually soakaway.

about 12" in 4 weeks. maximum.

 

[chilluk]

Ouch!!

OK if I wanted to hook up to the current rainwater drainage whats involved in that?

The current downpipe is at the back right hand corner (highest point) - presume id need some sort of gully along lowest edge of patio, with a return back under the patio (against the surface fall) into the down pipe - anyone know what to expect in terms of connecting in under there? (house 10 years old)

Can you get a gully that is level at the top, but with an inbuilt fall, so it looks level with patio / sleepers?!!

Cheers.

 

[noseall]

provided you can achieve a 1:60- 1:100 fall you will be ok. it will depend how deep the storm drain pipe is.

you will need to dig around the base of the down pipe to expose the 110mm pipe below. it is this pipe that you will connect into.

all the above is only worth while if your property has a storm drainage system, that is carried away from the house. if your home drains locally onto your own land via soak-aways then you might as well dig another for the patio.

 

[chilluk]

Noseall - thanks for all your posts on this.

Do you think I should start by excavating near the drain pipe then to see how low it goes?

How would I tell if it goes off into the drains or a soakaway?

Cheers

 

[noseall]

[quote="chilluk"

Do you think I should start by excavating near the drain pipe then to see how low it goes?

yes, good idea, look to see if a connection is feasible.

How would I tell if it goes off into the drains or a soak-away?

if you live on an estate ask a neighbour or look at plans or deeds, or speak to the original developers. even the local council may have a clue.

but you can sometimes trace the lines back to inspection pots and ultimately back to the road where you will have large triangular manhole covers, indicating a storm system.
Cheers[/quote]

 

[chilluk]

I've fired off an email to Bellway but don't hold out that much hope with them!!

I have the plans that you get marking the boundary etc with the deeds - will it show up anywhere in that sort of documentation?

Neighbours have been in houses less time than us unfortunately so not sure they'll be much help!!

There is a small rodding eye type cover and also a small grate draining the driveway near the opposite corner of the house (right by the other downpipe covering the other half of the roof) - does that give any clues I wonder? There is nothing in the back garden like a drain cover but I guess it could go out under the fence to something out the front of the house.

Cheers.

 

[chilluk]

Sorry to keep posting to this thread but I just thought of something else :

If some of the water is coming from the raised area of the garden (pretty sure it is) then should I do something on that side of the sleeper retaining wall also? I am presuming when turfed it will drain through a bit slower and some of the water will actually be "used" by the grass, but if I'm going to do this I may as well do it right first time.

My concern is if I put a gully (i that is the right word) along edge of patio, that would be higher than where the water would find it's way to behind the wall - does that makes sense? I could photoshop a diagram if required!!

Cheers.

 

[noseall]

i would be inclined to backfill with gravel or loose hard core behind the sleepers, don't bother with a gulley though.