Flattening garden and laying artificial grass

[john2k]

I moved into a new build, and my back garden the builders just used it to dispose of soil and as a result the ground level is very high and uneven. I want to bring the level down to same level or below house level slightly so I can walk down onto the garden rather than walk onto the same level.

My plan is to dig out the soil so that I can lay a heavy duty driveway weed membrane then lay about 30-50mm of sub-base compacted down using a vibrator plate, then possibly another layer of cheap weed membrane and then lay about 10-20mm layer of sharp sand and compact that before adding the artificial turf on top. On one side of the garden there is a man-hole cover and opening it reveals that it seems to be rain water drains and not sewage, as my gutter seems to connect to it. What should I do about water drainage? Should I slope the ground level on laying the sub-base and lay a channel for water drainage connected to where the gutters are connected?

 

[freddiemercurystwin]

If the ground is typical of new builds it will take a year or two to settle, laying anything now will probably end up all over the place after a while and 30mm of sub base is laughable.

 

[john2k]

If the ground is typical of new builds it will take a year or two to settle, laying anything now will probably end up all over the place after a while and 30mm of sub base is laughable.

It's been a year, what would be reasonable thickness of sub base to apply 50mm?

 

[r896neo]

Firstly there is no such thing as 'heavy duty driveway weed fabric' anyone who lays a weed membrane on a driveway is a moron.

What you want to use is terram 1000 or equivalent geotextile. These will be much more water permeable which is what you need. As for drainage how does the ground drain at present? If its a new build im guessing very poorly. Artificial turf will not solve a drainage problem.

The usual spec would be 50-75mm of sub base and then terram then 25mm of grit sand compacted and screeded flat then your turf. The sand is not strictly necessary but it is very hard to level sub base to exact flatness, the sand will also give a slightly softer feeling. Its essential to have terram between sand and sub base but optional to have it between earth and sub base. If your soil is clay or heavy then you should use it under the sub base too. If its sandy or chalk then you can omit it.

 

[john2k]

Firstly there is no such thing as 'heavy duty driveway weed fabric' anyone who lays a weed membrane on a driveway is a moron.

What you want to use is terram 1000 or equivalent geotextile. These will be much more water permeable which is what you need. As for drainage how does the ground drain at present? If its a new build im guessing very poorly. Artificial turf will not solve a drainage problem.

The usual spec would be 50-75mm of sub base and then terram then 25mm of grit sand compacted and screeded flat then your turf. The sand is not strictly necessary but it is very hard to level sub base to exact flatness, the sand will also give a slightly softer feeling. Its essential to have terram between sand and sub base but optional to have it between earth and sub base. If your soil is clay or heavy then you should use it under the sub base too. If its sandy or chalk then you can omit it.

Thanks for a very informative reply, much appreciated. The heavy duty weed fabric i was referring to was the apollo one pictured below. I've seen these used at my previous property where there used to be serious weed issues and it really worked:

In regards to the drainage, currently I dont see any drainage. The soil is just uneven and high, there is rainwater drainage pipes running underneath the middle of the garden connected to an inspection chamber on the side of the garden. On one side of the garden my garage gutter drains into pip that connects to that same drainage link. So I think the drainage is currently just left to the soil to soak the water. One option is that I could slightly slope the level of the ground when doing the sub-base towards the gutter drain and then install one of those inground channel drains like below, what do you think?: or what else can one recommend for drainage?

 

[bobsuerita]

think whatt he means is weeds dont grow up through drive contruction they grow in it the textile is so subbase and sub layer dont mix plus it needs to be permable

weed membrane is only good for under stone borders and decking

 

[Ian H]

I think any water would pass through the artificial grass before it got into the channel drain.

 

[r896neo]

Putting a fall on the grass wont really help, its not like a paving surface where you fall water towards a drain and collect it. As 1990 says rainwater will soak into the ground not run off so the question is can your soil cope and not get hugely waterlogged? How is it currently?

 

[john2k]

Putting a fall on the grass wont really help, its not like a paving surface where you fall water towards a drain and collect it. As 1990 says rainwater will soak into the ground not run off so the question is can your soil cope and not get hugely waterlogged? How is it currently?

Currently the soil seems to soak rainwater perfectly fine. Will putting 50-75mm sub-base followed by 20mm sand then the grass effect the drainage?

 

[r896neo]

Not really no. If it drains ok at present i wouldnt worry.

 

[john2k]

I'm having 5x 1 tonne bags of sub-base MOT Type One delivered this week. Planning to lay it to a thickness of approximately 60mm. To compact it down I am looking to hire the vibrator wacker plate from HSS (https://www.hss.com/hire/p/light-vibrating-plate-flat-base).

They do two versions, a medium one and a light one. The light one is very reasonably priced compared to the medium one but wondering it it will do the job of compacting 60-70mm of sub-base? I need it to do the job properly so if the light one isn't going to do the job properly then I need to get the medium one.

The difference between the two is that the medium one has a compaction force of 16.5kN whereas the light one has a compaction force of 11kN. The medium one is 4hp/3kW and light one is 3hp/2.2kW

 

[r896neo]

The light one will be fine. Just give it Plenty of passes

 

[john2k]

The light one will be fine. Just give it Plenty of passes

Thanks. Weather is very unpredictable these days, does the sub-base have to be dry when compacting it? I will lay it and level it when its dry but not sure what the weather will be like over the weekend and if it gets wet is it ok to compact still?

 

[r896neo]

The sub base will compact better if its damp. It can sit and get soaked while its in a bag or in decent sized piles, DO NOT spread it out in a thin layer until your ready to compact it.

If you spread it and it gets saturated it will turn into a slop that is uncompatable.

Likewise dont spread it if there is standing water or the ground is totally saturated.

 

[john2k]

The sub base will compact better if its damp. It can sit and get soaked while its in a bag or in decent sized piles, DO NOT spread it out in a thin layer until your ready to compact it.

If you spread it and it gets saturated it will turn into a slop that is uncompatable.

Likewise dont spread it if there is standing water or the ground is totally saturated.

I have placed the geotextile material on the soil and will be spreading out the sub-base this weekend. After I have compacted the sub-base I am planning to put approx 20mm of sharp sand also compacted down before laying the artificial turf. Is sharp sand suitable for this? Also, should I put another geotextile layer between the sub-base and the sharp sand?