Foundation depth - Sewer Build Over

[JenRM]

I have seen a few posts on this topic, but nothing that seems to match our situation.
We have a current conservatory that was built with Thames Water Build Over permission based on the attached foundation design (2006).

We want to replace the conservatory with a single story extension, as well as make the room longer so it runs the entire length of the house.

The architect I spoke to today suggested that the new foundations would need to be dug to 150mm below the level of the sewer (I have seen pictures that seem to agree with this, also attached); however from looking at Building Regs (H4) it suggests that for Sewers more than 2m deep to invert and pass under the foundations, the foundations should be designed with a lintel extending 1.5m either side of the pipe.

I am struggling to find clear advice on this, so keen to understand what I might be missing.

 

[^woody^]

What matters would be what Thames Water require.

The Approved Documents are suggestions, or one way of meeting the Building Regulations, they are not the actual regulations.

 

[freddiemercurystwin]

https://www.thameswater.co.uk/media...fications-for-sewers-up-to-160mm-diameter.pdf

Any sewers where the invert level is more than 1.1 metres below ground level must run at least 500 mm
away from the foundations. If the invert level is more than 2.0 metres below finished ground level, any
proposed foundations must be at least 1.0 metre from the sewer.

 

[Deleted member 281264]

What matters would be what Thames Water require.

The Approved Documents are suggestions, or one way of meeting the Building Regulations, they are not the actual regulations.

Is what you are saying in effect that a building inspector could pass something that was not acceptable to thames water ? I thought building regs for sewers would be the same rules as thames waters so it's a bit of a murky area

 

[Nakajo]

Yes, a building inspector could pass something that wasn't in accordance with TW's stated requirements. Whether TW considered that 'unacceptable', and the consequences of that, would be a matter for TW.

 

[^woody^]

Is what you are saying in effect that a building inspector could pass something that was not acceptable to thames water ? I thought building regs for sewers would be the same rules as thames waters so it's a bit of a murky area

No.

You need the water authority's permission first. Building control won't even register an application if there is a public sewer within the influencing zone, and no formal permission granted by the by water company.

 

[freddiemercurystwin]

No.

You need the water authority's permission first. Building control won't even register an application if there is a public sewer within the influencing zone, and no formal permission granted by the by water company.

I've had many a Building Regs App registered whilst the Build Over had not yet been agreed.

 

[^woody^]

I've had many a Building Regs App registered whilst the Build Over had not yet been agreed.

By their negligence or your stealth? They wont do it around here.

 

[freddiemercurystwin]

Maybe they just trust me.

 

[^woody^]

Yeah I'm sure that's it. The whole National Building Regulations regime revolves around what you want to do.