Patio Drainage

[jimmbo]

Hi

I’m starting my patio project at the moment, and I’ve come to a bit of a dilemma regarding drainage.

There is currently no paved area in the back garden - just grass/soil/mess, which all slopes down toward the house. The land is currently roughly level with the DPC with a bit of a trench around the house/garage.
The garage wraps around the back right corner of the house and there is a pathway down the left hand side which has a surface water drain running underneath it. The gutter from the garage roof runs to a down pipe on each of the rear corners into a gulley and then underground via 110mm pipe to the drain under the pathway.

My plan was to build a patio parallel with the back of the house, protruding level with the back of the garage to start with, and then at some point (maybe next year) extend the patio behind the garage right into the back right corner of the garden.

The dilemma is what to do about the drainage. I was thinking of removing the gulleys and underground pipe, and fitting an Aco/linear drain at least 75mm below DPC all around the back of the garage and house to join the drain under the path.

Am I right in thinking that I need at least 1:60 fall for drainage? The distance around the back of the garage and house is about 13m, which means a difference in height from the furthest downpipe to the path is going to be about 220mm (roughly 3 bricks).

Surely that can’t be right?
1. It would look daft
2. The end of the linear drain would be lower than the joint to the drain under the path!

Any thoughts, please?

Sorry about the essay!!

 

[cdbe]

Acco is 1:200 (5mm/meter). You could probably get away with less than 1:60 for the underground if it's just surface water.

 

[^woody^]

Rather than awful ACCO, you could form a border in pavers up against the walls and angle them ever so slightly in to that RW gully, and these will act as a gutter, albeit very shallow and hardly noticeable. Together with a slight fall on the patio surface this will be fine.

 

[jimmbo]

Hi, guys. Thanks for the quick responses.

I’m slightly confused about the correct fall - coz everything I’ve read so far says that a patio should have a 1:60 fall. Is this only the case if it’s sloping away from the house?

If I can get away with 1:200 then I’d be happy with that. But would such a shallow fall on the patio be enough to not leave standing water on the slabs?

Or, are you saying 1:200 for the aco drain but the slabs would still need a greater fall towards the drain?

Woody - I’ve got to remove the gulleys because they’re already too high and the pipe is in the way of where I’m digging out for the patio sub base.

Thanks again

 

[^woody^]

I’ve got to remove the gulleys because they’re already too high and the pipe is in the way

What? You are removing and not just lowering the gully? And installing crappy Acco grids?

 

[jimmbo]

I can’t lower the gulleys or the existing pipe coz it will be impossible to create a fall towards the surface water drain under the path. There is hardly a fall on it as it stands - and it runs under proposed patio areas (which need digging out)

 

[cdbe]

It would fall 1:60 towards the drain and 1:200 parallel to the drain. Why not just keep the gulley's/pipes, have the patio higher with a trough/french drain/stylish acco drain at a lower level around the wall - level access patios are all the rage these days.

 

[jimmbo]

Woody - Do you just not like the look of the linear drains? Or do you not think they work very well?
Do you think a sloped channel covered in gravel would be better? Or a French drain type thing?

Cheers

 

[jimmbo]

cdbe -

Ah right. That makes sense (the fall)

You mean have the patio level with the internal floor (above DPC)?

If I kept the existing pipes n built the patio over I would have to ram hardcore on top of it though. Wouldn’t that be risky?

Thanks

 

[^woody^]

Woody - Do you just not like the look of the linear drains? Or do you not think they work very well?
Do you think a sloped channel covered in gravel would be better? Or a French drain type thing?

Cheers

No. You don't design a nice patio in the garden hand have some industrial-looking grid thing around the edge.

Slope it the other way, form a deep gravel filled drainage chanel (aka french drain) and conceal it where it meets the grass.

But you have not mentioned what design or materials are to be used. It is generally better to incorporate something in to the design

If I kept the existing pipes n built the patio over I would have to ram hardcore on top of it though. Wouldn’t that be risky?

What is this talk of hardcore? Its a patio not a driveway for the cars.

 

[jimmbo]

Are you saying don’t use hardcore? Or am I getting confused what hardcore actually is (hmmm)!

If I drain the patio the other way into a French drain along the grass border, it won’t actually be draining into anything other than nextdoors’ garden! And that still doesn’t help with the gulleys at the rw down pipes.

We were thinking something like these slabs

 

[jimmbo]

The way I see it is I’ve got 3 options.

1. Do as I originally planned - remove gulleys/pipes & fit linear drains all the way from the corner down pipe round the back of the garage & house to the path - 4.5m at 1:200 along back of garage - 3m at 1:60 to back of house - 5.5m at 1:200 to path. (100mm height difference in total - roughly) So starting at 1 brick below, I would end about 2.5 bricks below.

2. Same as above but with gravel filled channel/French drain.

3. Have raised patio (level or higher than DPC) but with a trench all the way round incorporating French drain below DPC

I like the idea of having the patio the same level as the tiled floor inside, but not sure about having to step over a moat!

Cheers