The Brew Cabin

I've moved into a new house and I'm in the process of excavating subgrade for a new patio.

The previous owner decided to cut out a 'path' running across the grass, but never got round to paving or gravel etc. so the path is basically just mud. We had a lot of rain over the last 2 days and I've noticed surface water laying in the path (been there for 1+ day now). I've tried using a garden fork several times but the water is still lying. The grass adjacent to the path seems ok, but its a couple of inches higher.

Should I be worried about this? I intend to rip up all the grass and lay new turf eventually. Would the same thing happen with turf or is this just because of the mud path?

Finally, could this be a problem I could encounter with my new patio area (which will slope gently to the grass area)? I would hate to spend £800 on stone, spend weeks laying it, only to have drainage problems. Of course, the stone will have sufficient drainage slope, but I'm worried having seen this water lying on the mud path. Once I've excavated the sub-grade, is there any sort of test I could do for drainage? (maybe hose on water and see what happens etc?!)

Thanks in advance.

It could be that, with the path cut into the lawn, the surface- and groundwater are simply pooling at a convenient low point. I'd keep my eye on this for a few more days, and see how it behaves when we've gone, say, 48 hours with no rain.

If there is a problem with saturated ground or a heavy clay that takes a considerable period of time to drain, then when you come to lay your patio, draining it onto the lawned area might not be as successful as you'd hoped. It's quite possible that the surface water will hang about at the patio/lawn edge, slowly percolating away, but leaving a significant part of your patio submerged for hours after each downpour.

It migh be worth putting in a land drain at the patio edge to help dispose of any surface water from the paved area and, in the process, help drain the lawn/graden.

The test you ought to carry out is detailed on the Soakaways page. This will give you some indication of the ground structure and what steps need to be taken to ensure your patio isn't submerged for long periods.

Thanks for the prompt reply Tony.

The water has now gone from the path area - so it stayed for about 16 hours or so. I guess this is a good sign. I will read up on land drains to see how they could be used at the patio edge. I don't think a fall towards the house is a good idea as there is only 1 gulley in the centre of the house (where the kitchen downpipe goes into).

Given that the water has now gone, do you think it's still necessary to dig a 1.2m+ test whole as detailed on your soakaway page? If so, where should this test be carried out... where the patio will be laid, near the grass/patio border or on the grass area?

The total patio area will be about 45 sqm forming an L shape around the house. I've tried to knock up a simple diagram showing layout and existing gullies :



I think I'm in a catch 22 situation. I could forget about doing any draining work (apart from patio fall to grass) and everything may be ok... or... I could spend a lot of time and extra effort & money and add a line drain and/or soakaway(s). Of course, all of that could be unnecssary, but you don't really know that until it all goes wrong and floods! If it works, you don't really know if it was necessary!

Any advice on the above site layout is appreciated. Is 45 sqm too much to drain onto a lawn area 8 metres wide?

Thanks again for all your help.

In your scenario, I would install a new gully in the position shown, connect it up to the existing SW system and then create falls within the planned block paving to drain all of the patio area into that new gully. The paving down the side of the house can be graded to fall towards the other existing gully near the gate.



If you use a back inlet gully, you can connect up land drainage as you feel is necessary, or you could pipe-up a spur to collect the water from the land drain after it's passed through a catch-pit.

Installing the gully/spur gives you the option of leaving out the land drainage for a season or two and see how the garden behaves once it's re-turfed and the patio has been laid. Then, a couple of years down the line, if you think there's still a problem, you can drop in a couple of lengths of land drainage without having to rip up the patio.

Draining all of that patio onto the grass is just going to exacerbate the current problem, so installing a new gully, or a length of linear drain, along that outside edge is, I would suggest, an essential requirement. There is a method of draining the patio back towards the house, as shown on the Draining a Pavement page. This may be more suitable for your project, but I can't see from here, so I'm guessing. Either way, the spur to provide a pick-up for any eventual land drainage is relatively cheap to install and won't be wasted, even if you never connect it to a garden land drain, as it will function to ensure the sub-base and bedding layer of your new block paving stays really well drained, which is no bad thing. :)

Thanks once again for your reply Tony, your help is really appreciated.

Ok, I've now accepted that I need some sort of drainage at the patio/grass edge - as you say, it can only be a good thing. I will look at your pages on fitting/laying new gully's and also on linear drainage as this may be better (more work to lay, but would mean I wouldn't have to create falls in patio and rely on 1 gully).

The only problem I can foresee is that the distance between the existing gully and the proposed gully/drain is about 6 metres. Depending on the depth of the existing gully connections, I may not have enough vertical drop to connect the new gully and have adequate fall. I will inspect the existing gully to see how deep it goes. I don't think I could replace the existing gully with a deeper one, as the main sewer actually runs under the house (extension), so I couldn't modify the connection to it.

My house is pre '37 and I have a combined system. Do I need any planning permission or similar from the local council before I make draining changes as discussed above?

As your house is pre-37, I reckon it's a safe bet that the drains will be roughly 1 metre deep. They did things properly back in those days - none of the lazy, 300mm deep, "Friday Afternoon" drains we have to cope with nowadays.

The good news is that you don't need PP or a licence from your LA to install additional or amend existing drainage, as long as it's on your own property. :)

Let us know what you decide.

Ahhh, just realised that although the house is pre '37, the extension where the gully is was built circa 2000. Let's hope the gully is a decent depth and not a 'Friday Afternoon' drain!

I will have lots of fun digging at the weekend and will let you know how I get on ;)

Tony, one more thing, completely off topic... what CAD software do you use for your patio plans etc. I've got a copy of Autocad 2000 which I'm just learning to use. Seems to open you .dxf files no problem so I think I'll use it to plan out the patio.

(Edited by InfAddict at 9:28 am on April 23, 2004)

I use TurboCAD for most of my design work, as it's roughly 10 million times faster and simpler than AutoCAD, although I do use AutoCAD for more complex site drawings. If you think of TurboCAD as a Mondeo and the AutoCAD as a Bentley - they both get you from A to B, but one does it simply with no fuss and no hassle with minimal fuel consumption, while the other gets you there with loads of style and oomph and uses a deal more fuel on the way.