Lintel or ductile iron pipe for building over a public drain
Anonymous user 23/02/2024 - 3.32 PM
Hello, we're looking to build a two-story extension that goes 4m out from the existing house and the full width of the house. There's a public drain of 15cm diameter at 1m-1.3m depth running along the whole width of the house (from the adjoining property on its way to the main sewer). This drain is about 3m out from the existing house. Will this be possible to lintel over do you think? The sewer company has said we might need to replace the existing clay drain with a ductile iron pipe though we haven't had a formal consultation with them yet. What is the rough cost added to a project by having to lintel a drain like this VS replacing the pipe with ductile iron? Many thanks.
Are you a tradesperson and able to answer this question?
Assuming the consent to build over is in place the consultation in most cases would only explain their requirements, authorities usually provide a generic drawing or a drawing of multiple situations to which they expect the bridge over to in line with. This is usually satisfied with a concrete lintel and compliance with the depth of foundation beneath the invert of the sewer.
A concrete lintel over will be required regardless of the type of pipe used. The additional cost for the lintel is only very slight (assuming 4 or6” pipe). As it the drain serves more than your property it is the responsibility of your local water authority. A build over agreement will be required. It’s worth noting the water authority will not issue a build over agreement retrospectively.
Whilst the water authority will give you full information about what they require I would assume they will require a joint in the pipe either side of where the pipe passes through the structure known as a rocker joint and the pipe to be sleeved with a larger pipe where it passes through the new structure below ground.
Answered9 June 2020
1
Anonymous user
You will need excavate the trench to 150mm below the drain run. You will need to leave 600mm either side of the drain. Concrete trench as normal and bridge over with prestressed concrete lintels. Must be confirmed by Architect and Building Inspector prior to work commencing!
If building over an adopted sewer you must get permission to do so. They may ask to change the sewer to ductile iron as this will require far less maintenance over time and is not massively expensive at this depth. lintel over would probably not be acceptable.
