Height of soil vent above connection.

[Sparkgap]

The soil pipe from my bathroom passes through the outside wall and into the roofspace above the adjacent single storey kitchen before dropping into the ground at the end of the kitchen (about 4.5m out). The existing vent riser comes off outside the bathroom and rises through the roof on the outside wall to above the soffit of the first floor. This roof is being replaced and I am considering doing away with the vent stack by the bathroom and fitting it where the pipe exits the kitchen roofspace and drops into the IC which would only need to be about 900mm above the connection. I'm looking for clarification on what height I need to consider for the outlet of the vent and whether it needs to be above the overflow point of the WC (about 450mm above FF level) or the overflow point of the basin (about 900mm above FF level) bearing in mind any blockage in the pipe with result in the WC overflowing first. Part H doesn't seem to say anything.

 

[Last Plumber]

I'm not sure I follow but the vent needs to be 3' above an opening into a building.
Hope that helps.

 

[Sparkgap]

I'm not sure I follow but the vent needs to be 3' above an opening into a building.
Hope that helps.

I think a sketch will help. The new vent would be 900mm above the branch, well above the nearest window.

 

[snowhead]

It needs to be 900mm higher than any opening within 3mtrs of the vent to prevent smells entering a property and that would inlcude any adjacent properties.

More importantly it needs to be above the highest inlet to the stack so that in the event of a blockage lower down the stack you don't get a (possibly unnoticed) waterfall of sewage coming out the top of the vent.
The sketch looks like it shows it might just make the height.

 

[Sparkgap]

It needs to be 900mm higher than any opening within 3mtrs of the vent to prevent smells entering a property and that would inlcude any adjacent properties.

More importantly it needs to be above the highest inlet to the stack so that in the event of a blockage lower down the stack you don't get a (possibly unnoticed) waterfall of sewage coming out the top of the vent.
The sketch looks like it shows it might just make the height.

No problem with the 900mm from openings as it will be well clear. When you say highest inlet would that be where the WC connection would connect to the outside stack, or where the basin connects into the pipe within the roof or even where the WC or basin exits through the bathroom wall? I want to ideally do away with the soil pipe rising on the outside of the house and have a lower vent on the outside of the kitchen, but as the IC is at the top of the sewer run it should be vented to atmosphere otherwise I would have just put in a Durgo or similar.
As for an unnoticed waterfall of sewage, it's beside the back door so reckon it would be noticed pretty quickly!