Extension Raft

pause to remember

I'm currently extending a house. The builder decided that a raft foundation was the best option due to the nature of the ground. However he has not put a step down at the edge of the raft. He intends to build directly onto the edge of the raft. Is this Ok? How will it affect the DPC? The engineer seemed to think that this was ok.. Does anyone know about this?

sydthebeat

pause to remember wrote: »

I'm currently extending a house. The builder decided that a raft foundation was the best option due to the nature of the ground. However he has not put a step down at the edge of the raft. He intends to build directly onto the edge of the raft. Is this Ok? How will it affect the DPC? The engineer seemed to think that this was ok.. Does anyone know about this?

Firstly, did the builder design the raft or did the engineer?
Is the engineer happy to certify that the raft, as designed and constructed, is suitable to take whatever loads are planned on it? Does he have PI insurance behind him to certify this?

mickdw

Sounds like a cowboy to me.

Was the Engineer recruited for you by the builder by any chance?

If this is a double wall construction, it is very odd not to have a step. The only way it could be considered acceptable that I can think of is if the raft is poured at a level very much below the finished floor level so that the dpc can be constructed in a different way to create a step in the damp course and then the inside can be built up after. All this below finished floor level.

Any pictures of the work?
Did you have a steel schedule produced by Engineer? Did the steel form a stepped cage around the outside?

Did the orignal house have a raft or strip foundation?

pause to remember

Thanks for your replies guys...

1.The engineer does have PI insurance and is certified.
2.Although the builder built/designed the raft, the engineer checked it before the mix was poured. The project manager also comes from a engineering background.
3.The engineer is happy to sign off on it and says it is fit for purpose.
4.The actual floor will be considerably higher than the current surface of
the raft mainly due to 125mm of insulation, underfloor heating and then
the actual floor.
5.The wall is going to be a double construction block built wall.
6.The original house has a strip foundation and is about 22 years
old.However the ground is well known in the area for being variable and
rocky. Indeed a house close by recently had subsidience on the back
wall after being ok for over 20 years.
I'm new to all this and finding it a steep learning curve!!!!:eek:

pause to remember

Also...I forgot to mention that the extension is a single story...

mickdw

Do you have a section drawing cutting through raft/walls/floor. that would clearly shown if the job is being done correctly.

If you have a detail showing a step in the raft and they have now gone away from that, I would request a detail of the raft in its current form including full dpc locations and showing raft/wall/floor make up and finished floor of existing building marked on it.