Is a 'fall' needed for a gravel/mot area

[ken300]

Hi

I live in an old terraced house with a long garden and a 4m x 2m area paved in blue bricks next to the house. This bricked area seems to be very old indeed - the bricks have settled so they're very uneven & difficult to walk on and at least 50% of them are damaged so the area needs something doing with it. It will be light pedestrian traffic (me & my wife) and the occasional wheelbarrow - nothing heavy duty.

My chosen solution is gravel in a Nidagravel 130 hexagon stabiliser.

The layer thicknesses will be as follows:

Sub-base: MOT Type 1 - 50mm
Sand - 10mm
Gravel (containing the Nidagravel stabiliser) - 45mm (10mm diameter angular gravel)

They recommend a membrane below the sub-base too, i assume to stabilise things and stop the sub-base & sub-grade mixing.

The stabiliser is 30mm thick so the 45mm gravel depth means that it will be filled with gravel + an extra 15mm or so to hide the hexagons, they recommend the 10mm thick sand layer on top of the MOT to prevent damage to the bottom of the stabiliser.

My question is simply do i need to take drainage & run-off into account??

If it was a less permiable patio of flag stones etc i'd need to slope it away from the house by a certain amount so that rainwater ran off towards the garden but would i need to do this with what i'm proposing or would any rainwater simply drain straight down through the layers to the soil below (particularly would it drain through the MOT)?

If i do need to allow a 'fall' how much would you suggest, 1:80??

Thanks in advance for your replies!

[GB_Groundworks]

If it's permeable all the way ie not concrete below etc then no you don't

[ken300]

Thanks Giles,

I thought that I’d better check with someone who knew what they were talking about rather than doing it wrong!

So you'd consider compacted MOT type 1 to be permeable??

[Dave_L]

.......to a degree, yes.

[ken300]

.......to a degree, yes.

I'm guessing then it's still important not to have the area sloping towards the house in case the water takes time to seep through & there is a bit of run off?

Does it sound like having the area either sloping away from the house a bit or otherwise level is the way to go??

[Dave_L]

Ideally install some simple drainage adjacent to the house to stop an accumulation of groundwater.

[seanandruby]

Are you sure it is not fine grit specified, not sand for bedding ?

[GB_Groundworks]

they specify gritsand for the gravel grids as they assume ppl can't level mot/subbase out well enough a 6mm angular grit would work just as well

[ken300]

Ideally install some simple drainage adjacent to the house to stop an accumulation of groundwater.

Dave_L - what kind of thing have you got in mind?

seanandruby - i've seen a video from nidagravel where they just specify a coarse gravel base and a finer gravel between that and the nidagravel to stop the coarse gravel puncturing the membrane that is bonded to the underside of the stabiliser but the uk nidagravel people recommend MOT type 1 & sand between that & the stabiliser. My thought was that the MOT/sand would probably give a sturdier base than the coarse/fine gravel - does that sound like a fair assumption??

[seanandruby]

But not building send.

[ken300]

I was planning on using sharp sand.

Am i right in thinking that sharp sand with it's more angular grains will drain better than the more rounded grains of builders sand?

[seanandruby]

Building sand just turns liquid then everything sinks, floats and fails.