Builderers! How do I raise a round manhole?

I’m turfing our lawn and we be levelling it with 3 tons of topsoil. However in trying to get it level it’s become obvious that currently the ground dips massively to the manhole.

Can I just buy a 3 or 4 inch height extender from somewhere? Will it support the weight of a cast iron manhole cover?!

Thanks

But it’s a round cover that needs to sit on something round surely?

Just a blob of cement at each corner.

The cover and the frame it sits in are ussually sold as a single entity. Kind of depends on the system in use. It used to be simply a case of build up the manhole with bricks and mortar to the height you want and set the frame on top. In you have on of these then you can break the frame loose, add new courses and reset the frame at the new level. In the past 20-30 years (at a guess) most drainage has become more modular and based on plastic systems. If yours is this type then you will need to work out if it is modular and if it is still available and then split the cover apart, add extra rings and then stick it back together..

However, reading it is a cast iron cover would suggest it is an older system??

I think the first thing you need to do is remove the cover and find out what is under it!

Assuming it is a simple inspection chamber.

A simple solution if it is an old system. If the dimension work then buy a few rings like this…

http://www.screwfix.com/p/5-inlet-inspection-chamber-235mm-riser/57228

Drop then down inside the chamber. Block any gaps at the bottom and backfill a few inches of concrete followed by ballast/soil. Then when you are at the level you want stick an appropriate cover on top…

http://www.screwfix.com/p/5-inlet-inspection-chamber-cover-frame/78458

job done

Plenty of risers available in various sizes such as the one above. Getting one to fit tightly might be tricky but a bit of cement or sealant should sort it out. You might be better off buying a new manhole cover with frame then joining that to your existing manhole.

Alternative is to fill over it with soil. I presume you aren’t down there every day. Will look a lot nicer and if you have issues with the drains it’ll be easy to scrape off the turf. Will be very annoying for future buyers, though. Could put some kind of marker I suppose

Argh. This could all get expensive.

I’m tempted to turf over it tbh!

You could simply knock up a wooden frame with another removeable section inside it filled with soil and turf. A bit like the WW2 POWs used to do at the end of their tunnels. Then it would look pretty unobtrusive, you could mow over it, and if needed you could lift it out to get to the manhole.

Hmm, but Google says the turf will die over a man hole cover.

:-/

For you, Turf, ze war iz over.

Welshfarmer – Intersting idea but I think I’d need 6 inches of soil for the turf to survive and that would the raise the manhole too far!

The cover and frame should already be mounted on bricks so just extend by a couple of courses. Circles will sit on squares if the square is small enough!! (sorry for the sarcasm)

We used a manhole riser like these

http://www.ebay.co.uk/bhp/manhole-riser

to lift a few of ours where a path was being raised – they’re plastic so you can cut them to the height you want.

We turfed over the one in our garden!

Markie – do you reckon they’re strong enough to withstand a cast iron cover?!

How much soil did you have under your turf above the manhole?

Ta

We tarmac’d over a round manhole cover when we had our driveway done. That was 10 years ago and never needed access since. if we do need to get in there it’s only a couple of inches and I can see where it is.

I’d turf over yours RRR, you absolutely nothing to lose… just take pictures/record where it is for future reference. You could replace the cast cover with a steel or plastic one as cast is for motorised traffic which I doubt you have in your garden.

Lift the cover and see what it’s currently sat on.

What is the chamber itself made out of? If it’s a small diameter polyprop chamber, then you should just be able to use a raising piece as above. If it’s a concrete or brick chamber, then chances are the cover is sat on a few courses of brickwork. So just take the over off, and add a few more courses.

Oh, and just be aware that if the manhole also serves adjacent properties, then it should now have transferred to the sewerage undertaker as one of their assets. They probably won’t like you burying it…

if you turf over finding it to remove a blockage in the drainage becomes a challenge when you forget where it was.

lift teh cover and see what the manholes made from and how teh frame is attached.

if its on brick add another row of bricks.

if its plactic buy a raising piece.

Markie – do you reckon they’re strong enough to withstand a cast iron cover?!

How much soil did you have under your turf above the manhole?

Yes, in my utterly non-professional opinion! Ours were cast iron. All the material around it supports the side – it only has downwards pressure.

We have about a foot of soil above the manhole cover. Grass growing wonderfully, but it hasn’t had a summer yet, so don’t know how will survive full heat. I think it’ll be fine.