The Brew Cabin

Posted: **Wed Mar 27, 2013 5:57 pm**

Hi All

Great site, quality advice.

I was wandering if I could pick a brain or two concerning patio drainage. I'm about to terrace my rear garden to create 2

levels (currently sloping away from the house). The higher level will be a block paved patio (measuring 5.6m x 18.1m), the

lower level (approx 500mm lower) will be a levelled lawn.

A retaining wall will be constructed with the mid section (approx 10m in length) rising 450mm above the upper terrace level

- for seating/planting/directing footfall (I've attached a diagram for reference).

The patio will fall away from the house towards the retaining wall and I would like to add a linear drain running the entire length of the patio against the retaining wall (from the bottom of the pic to the top) and discharge into the SW network. I understand that using the SW network isn't ideal, but the soil I have is firm clay.

What I'm having trouble with is: if the linear drain has a fall of 1:60 then after 18m one end will be 300mm lower than the other. And lower (by 100mm) than the existing SW network.

Is there a minimum fall I could get away with? Or am I missing a trick - is there a simpler, more elegant way?

Many thanks in advance.

Andy

Posted: **Wed Mar 27, 2013 8:34 pm**

you could drop the fall of linear drain to 1:100 or even level, but the risk with level and a lack of experience in install linear drains is there may be a chance of backfall. by the sounds of it I think you fall will be determined by your starting height and as low as you can go to make a connection to the storm drain.

ps. there is nowt wrong with connecting to the sw. does the downpipe nearest the the fw come all the way over to sw or does it go elsewhere?

Posted: **Wed Mar 27, 2013 8:44 pm**

the linear drain can go in level
the drain is 100mm deep internally so if there is a hole at 1 end water will flow down it
ps you only need the linear drain where the raised wall is
on the other sections water can run down the steps
LLL

Posted: **Wed Mar 27, 2013 9:56 pm**

Mikey_C wrote:ps. there is nowt wrong with connecting to the sw. does the downpipe nearest the the fw come all the way over to sw or does it go elsewhere?

Mikey_C - the downpipe closest the FW connects to the SW at the other end. Backfall was something that crossed my mind when I thought about installing the drain level - any tips on minimising the risk?

LLL - if I lay the drain along the retaining wall only, the fall will be much reduced and I suppose as long as there is a slight fall (or none: hole at one end) water will travel the path of least resistance. Is there a danger that water coming off the steps will pool at the bottom? Would it be overkill to put in a filter drain at the bottom of the steps?

Thanks for the quick replies guys

Andy

Posted: **Wed Mar 27, 2013 10:50 pm**

you can over engineer it if you like andy but its wasting money really
the main thing is you dont want water laying against walls
LLL

The Brew Cabin

Patio drainage - Minimum fall for linear drainage?