Build over permission from water company.

[Green chef]

I have a shared sewer running parallel to the back of the house (about 0.5 metre away from the house) it runs to properties both sides of me, in a staight line.

I would like to build an extension on the rear of the house, full width of my land, so will be totally over the top of this sewer, manhole covers are not an issue, as neither neighbour has an extension, so there are manholes both properties either side of me.

On the water companies(thames) build over specs..it states..

"Top of pipe to be at least 300mm from the underside of the slab."

My sewer is close....

If the floor is not to be a slab, but instead will be a block and beam, surely this rule above isnt relevent? As the block and beam means its doesnt touch the ground(put weight on the ground and then onto the pipe?) floor its suspended above the pipe...

Or does the word 'slab' on their site also mean block and beam?

Thank.

 

[Green chef]

fyi, i asked them this question23/mar.... but they have basically shut down for all but essential work
with the virus...

 

[DevilDamo]

A slab means a structural floor so a B&B floor would also come under that ‘slab’ definition. A suspended slab that is supported on at least two sides could be argued as not increasing weight over the sewer but is still a slab and therefore a structural floor. As the pipe is public and under Thames Water’s ownership, they want to make sure nothing is within 300mm of their sewer.

What is the depth (invert level) of the sewer?

 

[^woody^]

You can design a floor slab within 300mm of a pipe to deal with any loading, and so satisfy the water company.

 

[Green chef]

the sewer is very shallow. Currently the TOP of the existing floor is only 350mm from the top of the sewer pipe, by the time you add in B&B depth, insulation, screed, tile you are way under the 300mm neede. So the extension floor would need to be higher than the existing ground floor, would have to have a step up withing the house..... not a terrible idea as the garden slopes up from the back of the house, but i think would mean the existing openings out of the back of house would need new lintels(set higher), so you didnt step up into them with your head...

 

[DevilDamo]

You can design a floor slab within 300mm of a pipe to deal with any loading, and so satisfy the water company.

Within 300mm but their guidance states at least 300mm?