Building over sewer

[Daveo119]

Hey,

I'd like some advise on building over the four sewer to the rear of our 1920s semi. The foul sewer (appears to be 150mm) runs behind our row of houses in a straight run, approx 75cm from the rear wall of the house. The sewer serves approx 10 houses further up the row.

We have an existing kitchen extension (we guess 25-30 years old), a small utility (non-habitable) extension of unknown age, and a conservatory dating from 2000. All structures already bridge the sewer.

We are beginning the conversion of the conservatory to a single story extension. We are using the existing footings (already agreed with inspector following inspection holes) and side wall. Effectively we are only replacing the front of the conservatory, adding a roof structure, and replacing the existing concrete floor in the conservatory with a new insulated slab. The slab must be replaced as the conservatory has blocked cross ventilation of the suspended timber floor in the main part of the house (despite the air bricks on the front of the conservatory apparently not connected to anything!). The new slab will incorporate 4 drain pipes connected to air brick at the front.

There is currently a double sealed inspection chamber in the conservatory and utility. We would like to remove the chamber in the conservatory. My thinking being an overflowing sewer would be better in the utility rather than our soon to be open plan kitchen diner. Is there any way we can do this without re-routing all the branches to the first IC? Adding a rodding eye to the vertical section of the the soil pipe seems fairly easy. We had a CCTV survey today and there are no issues with the sewer but there were no other ICs within 25m upstream and 10m downstream.

I need to decide on the best way forward before making a build over submission to Severn Trent. For info, advise received on the phone suggested a internal IC would be permissible if other solutions were not practical, and in this case the structures already exist.

Any help appreciated.

 

[^woody^]

The manhole position is not really ST's concern (or rather not a significant concern to them), they are more interested in protection of the pipe where you build over it.

Building regulations deal with the manhole and will dictate the requirement for a sealed cover, and access for unblocking etc.

Sealed manholes don't overflow do it won't matter what room it's in.

Building control will want you to avoid new drains being laid under the building, it's not clear from your drawing what's new and proposed.

 

[Daveo119]

None of the external walls of the conservatory will be replaced apart from the front of the conservatory. Everything shown already exists. The only new building around the sewer will be ripping up the concrete floor in the conservatory and replacement, then new roof structure to be added.

On the subject of overflowing manholes, would i be right in thinking that if the sewer blocked downstream and went undiscovered for a while, therefore allowing the sewer to fill up beyond my IC. When the IC in the utility was opened to allow water jetting, the head from the full sewer upstream would cause the IC to overflow?

Do you think it would be a stupid idea to keep the IC in the conservatory if the intention was to never open it (expensive wooden floor to be installed above)? Can the IC be permanently sealed and concreted over?

Thanks.

 

[Hugh Jaleak]

You cannot permanently seal the chamber, access must be maintained for future needs. Suitable covers can be obtained, that will, if the flooring is laid properly, give a pretty disguised join where the cover is situated, reducing the visual impact considerably.

If your stack blocks, I'd rather be trying to clear it from the chamber than a rodding eye at floor level! If the sewer is blocked then ideally it needs to be jetted upstream towards the blockage from the first empty chamber. If yours is, (or assumed to be), full then I'd want to be working from the downstream chamber.

 

[^woody^]

You are not permitted to permanently cover an inspection chamber.

Sealed manholes don't overflow. Any blockage will come out of ground floor toilets or other drain gullies instead, and those will be the ones downstream towards the blockage.

There is rarely an intention to open up manholes, but there may be a necessity. Having said that most people go a whole lifetime without needing to lift a manhole cover.

 

[Daveo119]

What would you do if it were your house: remove the IC in the conservatory and move the existing branch pipes to the first IC, risk it and install a wood floor over the sealed double cover (not keen on the 'floor in' covers), or divert the sewer to an IC in the garden?

 

[noseall]

Is this feasible...

Img036

• noseall
• 9 Aug 2015

The SVP connection will be roddable from either end, so may not need an IC. Or, it can be extended to the proposed new external IC.

 

[Daveo119]

Unfortunately the external walls of the utility and conservatory are on our plot boundary. The footings for the conservatory have also been passed by the building inspector as suitable for our single story extension. So if at all possible i'd like to avoid a new pipe passing the conservatory boundary.

noseall i didn't realise that it was an option to not have an IC for the SVP. That suggests two possible ways forward:

1. Divert the gully to the IC in the utility and replace the IC in the conservatory with a branch piece for the SVP. Soakaway doesn't seem to be an option for the gully as we have solid clay ground and a high water table - happy to be corrected on that though.

2. Keep the IC in the conservatory and add a rodding eye on the vertical section of the SVP behind some kind of decorative cover. Then make sure that one of the gully runs into the IC is rod-able. Then keep everything as is and argue with Severn Trent that it's impractical to divert the sewer and we need to keep both ICs. In the event of a blockage it seems as though we should get away with not opening the IC in the conservatory (rod-able from SVP, gully and IC in utility). Then any floor covering installed over the IC is seemingly at low risk of having a power saw introduced to it.

Thoughts? Cost is a consideration since our contingency has already taken a battering after discovering lack of foundations in the dining room (simple RSJ upgraded to a box frame designed by a structural engineer.).