New patio - Drains and manhole cover

[buz1500]

Hi,
Ive started work on patio that covers 13m wide by 4m deep in the main area. The patio will stretch the fill width of the rear of the house plus extend to a path around the conservatory which has been built on the side of the property.

I have two queries:

1. I'm planning to install a liner drain across the full width (13m) and I'm planning to install it 450mm from the rear house wall using a linear drain that has a built in fall. I've chosen 450mm as this allows me to neatly lay a full flag between the wall and the drain and doesn't place the drain in middle of the patio. The ground rises away form the house which has required me to dig out to a depth of 0.6 metre to attain the correct base level. I'm planning to build a retaining wall at this point.
Does this sound okay?
2. When digging out the main area I uncovered a large concrete inspection chamber. It would appear that the previous owner had knocked the brickwork off the top and just laid the metal grid on top of the concrete slab before burying the whole thing under a rockery. The problem I have is that I don't have much room to spare and I would like to fit one of those covers that allow a flag to be inserted directly onto the concrete slab.
Is this possible?

I do have photos if that helps but I'm unsure how to add them to this post.

[lutonlagerlout]

1: yes thats perfect
2: yes you need a 80mm insert cover they are about £60 for the good ones
have fun!
tony

[buz1500]

Thanks Tony,

Just one question, when you refer to 80mm I'm assuming that this is the height of the cover with flag inserted. Do these covers allow a flush fit onto the existing inspection cover or do I have to allow for a depth of cement for fixing purposes. As stated in my original post, I have very little height to play with and I don't want to have to reduce the height of the existing inspection cover. Not sure how I would do it anyway.

[lutonlagerlout]

you would noramlly remove the old one and bed the new one on some strong mortar,it must be in line with the slabs though.
if you have to reduce it farther it gets a bit trickier as you have to cut bricks off ....
regards tony

[buz1500]

Hi Tony,
Sorry, I don't think I've explained the issue very well.

All that I have is a very large (approx 4-5ft dia.) flat concrete surface with a circular hole in the middle. This appears to be the top ring of a number of concrete rings which form a very deep inspection chamber. The chamber has internal steps and is approx 10ft deep. Any brick work or construction to house a standard manhole cover has been removed by the previouse occupant to allow them to hide the drain below the surface of the garden.

Many thanks for your time thus far.

Mark

[seanandruby]

there should be a minimum of 2 maximum of 4 course of engineering bricks on top. no manhole should be hidden thats asking for trouble. use sulphate resistant cement to bed them on.

[lutonlagerlout]

sounds like you have a land drain. i take it your house is fairly new?? the chances are that you have a machine dug land drain for stormwater,
you can get concrete covers with a manhole sized hole in the top of these ,but i feel reducing it would be best left to a professional as these covers are very heavy and difficult to manhandle with a machine
all the best tony

[buz1500]

Hi Tony,
Thanks for the help thus far...

I've measured gap between the surface of the concrete cap and the DPC and it's 210mm. This leaves only 60mm to lay anything over the top without exceeding the planned patio level. I could add another 5-10 mm as the patio is draining towards the house into a linear drain set one slab away from the house.

Further info: The Concrete cap has a diameter of 147 cm and the access hole, which is set off-centre, has a diameter of 57.5 cm.

Just been to the Tobermore site at Leyland. They said that I may have to remove/replace one of the concrete rings in the chamber to reduce the height. Seemingly there are various depths of rings and I could swap an existing ring for a shallower version. This would then enable me to replace the missing brickwork etc. and still leave sufficient height to use hidden drain cover.

Regards
Mark

[lutonlagerlout]

ye i gotcha now mark, yes the rings come in different sizes i think 100 mm is the smallest, but what i am saying is they are blooming heavy so watch your back!
that would be the answer remove 1 ring and replace with a smaller 1 then brick up to new level
alternatively put the out-laws down there and concrete over the lot (tongue firmly in cheek)
regards tony

[buz1500]

Hi Tony,
Thanks for your comments. I'd best let them help me lift the darned thing before I shut them in!

Cheers.
Mark

Ps. I'll let you know how I get on....

[seanandruby]

how deep is the top ring? it may be easier to cut it down with a diamond blade then bed cover slab back on. you woldnt believe the amount of earth to be dug out (hope you have plenty of space to put it) if its say a 500 deep ring.

[Ross-Paving]

Hello Mark,
Sounds like your giving yourself too much work here, these recessed pavior covers can be anything from 47mm deep upwards, so why not just get a 47mm deep cover and bed it directly on top of the inspection chamber cover.
http://www.clark-drain.com/prod02.htm
The above will take you to a typical manufacturer, your local Builders merchant should be able to get you an alternative.

[lutonlagerlout]

i think you will find the 47 mm ones are double sealed covers intended for indoor use to cover a manhole ,we normally use these for floor screed.
i have never seen a insert cover for external use less than 65mm,also as the OP mentions he has a round hole so he needs some lintels/brickwork to get a square opening (or rectangular)
so he can bed the cover on.
a couple of years back i had an 18 ft storm drain dia.1800 under a drive that we were doing,it was a nightmare as the lid was only200mm below d.p.c so we had little to play with
better than soakaways though......

[buz1500]

Hi,
I've now ordered a 600x600 recessed cover that's only 50mm deep. I'm planning to bed this directly onto the surface of the cap that's covering the inspection chamber.

I'll let you know how I get on.

[lutonlagerlout]

post a piccy if you can
cheers tony