The Brew Cabin

Posted: **Tue Jul 14, 2009 9:31 am**

Hi all new to this site and wish I had a looksee prior to starting my project.... I am putting in a indian stone patio on the back of my house I have removed 8 tonnes of soil and wonder if it was necessary! Looking at this site it appears you don't always need a base! I have gone for 100mm of DTP1 45mm of bedding mix and 40mm of slab approx which gives a depth of 185mm below dpc. Is that OTT for a patio?
Also should I be using DTP1?
My concern is that I am surrounded by big trees Acers conifers etc and so when I dug the soil out I cut off roots and removed as thick as my arm. The base soil is now quite hard but was powdery on the surface so felt the need to go down 185. Anyway, do I need to stop the roots coming back by putting a membrane? My plan was to put a line of vertical slabs below patio next to tree roots then a membrane on the soil base then stone?
Should I whack plate the soil prior to the stone or membrane then stone and just whac the stone? Will this damage the root preventing membrane?
Sorry for all the questions but also the patio is 10 x 25 the lawn is 150 below dpc and where I would like my slabs to finish but if I put a 1 in 50 fall my slabs will be below lawn level I am not sure which way to put the fall or if I need one at all?
Thanks Just

Posted: **Tue Jul 14, 2009 3:16 pm**

If it is topsoil that you've removed, then you were right to do so. It's sometimes ok to rely on the sub-soil to act as a base as long as it is firm and reliable: if there is any doubt, then use a sub-base.

Cutting off tree roots as thick as you describe is likely to seriously harm the trees. Those roots are better left alone and accept there will be some slight amount of heave to the patio over the years, but that it's easier to lift-and-relay a few flags than to compromise the health of a much-loved tree.

Not sure what the membrane would achieve. Without a membrane, roots will expand and result in heave. With a membrane, roots will expand beneath the membrane and result in heave.

If the sub-grade is loose, it should be compacted prior to placing the sub-base.

Posted: **Tue Jul 14, 2009 3:48 pm**

Thanks for your prompt reply, Phew, for a minute thought I'd had 11 yards out for nothing! Down to a hard clay base now. Re trees, the roots were from a very unloved conifer and the Acer had much smaller roots inch or so section so I hope they will be fine.
I know that I need to sort out my crossfall or endfall at the base level, the patio is 3.5m x 5m adjacent to and level with the lawn. I think 5 or 6 cm crossfall will look odd to the dpc and also one side would be 150mm below dpc and t'other would be 210mm revealing blocks? Otherway of course would not be 150 below dpc? Must I therefore use a 60:1 endfall running away from the house which would mean the end of the patio is buried 10cm below the lawn? There is a shed going on the patio and I wonder what the minmum Indian stone slab fall is I could get away with? ???

Posted: **Tue Jul 14, 2009 4:52 pm**

Where I can I always run away from the house, looks odd when it runs against the house imo. Why not have a small retaining wall at the end of the patio?

Posted: **Tue Jul 14, 2009 5:05 pm**

Yep I think it will always look odd to the brickwork so agree run away. Trouble is not so much the end as at the end is a hedge but to the side is the lawn at 150 below DPC and so the same height as the slabs(by the house) so If I run away my flat lawn will make my patio look very odd so I was hoping I could get away with next to no fall? Just measured it and it is 7.5m x 3m so 2cm /M would be over a foot deep at the one end at an angle to the lawn? Plus my shed will be at an angle... at least I won't have to put any fall on the gutters.

The Brew Cabin

Indian sandstone base - Tree roots and base