Moving or sealing a manhole

onlyroz

I would like to build a conservatory over my patio but there is a manhole cover in the middle. I think that the drain is a shared one for the whole row of terraces and it does occasionally flood.

Does anybody know the options for moving or sealing the manhole, including an idea of cost? Also, would it be the council or the water board who would have to move it for us?

I understand that manhole covers can be sealed so that the conservatory could be built over the top of this - however I'm not sure if this would be allowed for a shared drain and I don't know how good a solution this would be if the drain flooded. Obviously I don't want my conservatory filling with sewage.

I think the best solution would be to move the manhole so that it was either down the side of the house, or somewhere in the lawn area. But I imagine this would be expensive and I have no idea of the procedure for doing this.

Any advice?

keystone

If its a shared drain then the water/sewerage company are responsible for it. Moving it all around is substantial work because it involves resiting other peoples drains and your own as well as the inspection chamber.

The sewerage company might not feel inclined to do it whatever your motivation.

You will have to get build-over consent from them anyway.

Even if they agree to move it all about to accommodate you its likely to cost an arm and a leg. You are entirely at their mercy.

I would suggest (particularly if its prone to flooding) that a double sealed lid is the way to go. However, that requires access to be maintained to it in the event of maintenance or blockage clearance so you can't just fill over the top and forget it. Your BCO should pass a double sealed cover but you still need to talk to the sewerage company anyway for buildover permission..

Cheers

onlyroz

How does a double-sealed lid work in event of a blockage? Would we end up with sewage in the conservatory's foundations?

There is currently a manhole on the back patio and another in the front garden, with a pipe running between the two. When we have had blockages in the past they have been able to deal with it by shoving their stick thingies down the front manhole cover, but we have still had to deal with sewage on our patio.

keystone

onlyroz wrote: »

How does a double-sealed lid work in event of a blockage? Would we end up with sewage in the conservatory's foundations?

No thats the point. Its sealed so it can't lift if the pressure underneath gets too high.

Cheers

onlyroz

keystone wrote: »

No thats the point. Its sealed so it can't lift if the pressure underneath gets too high.

Cheers

Presumably the water has to go somewhere though? I guess if it couldn't get out to the drain at the front then it would back up the pipes leading to mess in the source kitchen/bathroom? :eek:

Hintza

Just to give you an indication. A wooden electricity pole moved 20 feet will be about £3.5k!

keystone

Its got to come out somewhere but very unlikely to climb the stack.

Cheers

onlyroz

Well when the pipe blocks it is always in the section that runs from the back of the house to the front, which causes the water to back up and leak out onto the patio. If the patio cover was sealed then either the pressure would have to force the blockage away or it would have to back up the pipes into the houses - which I don't think would be too popular.

Rovver125

What Keystone says! If water co responsibility, shared, then there will likely be considerable expense involved.

If the manhole only has connecting pipes for your property and there is no feasible way to divert it, the water co may allow an upgrade to a stronger material like ductile iron. Expensive.

If the water co really don't want you to build over the drain, it's on a change of direction, or it's needed for access to other drains, then they are likely to request a diversion. This will usually involve laying a minimum of three new pipe runs and building three new manholes/inspection chambers. Again, expensive.

In my area, the water co would request their contractor do a survey before any work. An upgrade or diversion would have to be completed by an authorised contractor and then re-surveyed on completion.

Sealed manhole covers do a good job of preventing sewage surcharge, but it will continue to backup until it finds its first escape point. This will usually be the next gully or un-sealed cover upstream of the blockage. Defective pipework could also leak under pressure.

Approach your water co for advice. They will tell you what would likely be needed. Just make sure you're sitting down when they give you the cost!