Hi this is my first post so be gentle
I am planning an extension to my property, a 1950’s brick / brick cavity wall house.
My question relates to the best way of abutting the new and old foundation.
The old foundation is a concrete slab approx 150mm thick at a depth of around 500mm with brick up to DPC blues.
The new foundation is to be a trench fill and will need to be 1000mm (we are on clay).
I have been given conflicting advice from engineers and BCOs in the past re the way they should meet
One take on this is: Step down slowly to the new depth (maintaining a sort of 45 degree step of sorts under the old foundation until the new depth is reached then fill the trench (with an optional bit of rebar at the top where the new foundation will be more ‘shallow’ (Pic B)
The other take is to effectively mass fill undermine / cut straight down and underpin the existing foundation at the junction (Pic C x 2).
My concern RE the second option is that if any settlement occurs the cracks will spread into the existing house and not just be taken up by a wall starter kit etc.
I was hoping some of you may be able to give your experience and take on this
Thanks in advance
I am planning an extension to my property, a 1950’s brick / brick cavity wall house.
My question relates to the best way of abutting the new and old foundation.
The old foundation is a concrete slab approx 150mm thick at a depth of around 500mm with brick up to DPC blues.
The new foundation is to be a trench fill and will need to be 1000mm (we are on clay).
I have been given conflicting advice from engineers and BCOs in the past re the way they should meet
One take on this is: Step down slowly to the new depth (maintaining a sort of 45 degree step of sorts under the old foundation until the new depth is reached then fill the trench (with an optional bit of rebar at the top where the new foundation will be more ‘shallow’ (Pic B)
The other take is to effectively mass fill undermine / cut straight down and underpin the existing foundation at the junction (Pic C x 2).
My concern RE the second option is that if any settlement occurs the cracks will spread into the existing house and not just be taken up by a wall starter kit etc.
I was hoping some of you may be able to give your experience and take on this
Thanks in advance