Raft footings

[pritch]

Hi

I'm off work for a few weeks so I've decided to set out, dig out and concrete my strip footings for my new single storey extension. 

Now I've been told by building control it needs to be on a raft and now I'm at a loss what to do. 

Is this something I could possibly do myself? 

Do I now need an engineer to design a raft footing or are they straight forward? 

I haven't really got the budget to just hand over the drawings to a builder and sit back and watch so I really wanted to do as much as possible myself. 

Many thanks 

[PeterW]

A raft should be engineered - sounds like you’re on clay or similar ..?

 

Most rafts in the U.K. have a thickened edge that has an element of box reinforcement in them - I’ve seen them at 600x600, then with a slope of 45 degrees up to a slab of 150mm across a 6m span. 

 

The rebar schedule for something like that is box plus mesh - you need to also make sure it’s min 250mm below the finished floor level as unless you use an insulated foundation system, it’s near impossible to get insulation below the slab. 

[pritch]

Hi

Thanks for the reply. 

Yes it's all clay around here . 

So I'm guessing I can still do the dig out but I will need to get someone in to do the steel work. 

Will the building inspector want to see a professional drawing for the foundation or would he be happy with a builder doing a general design and install himself? 

Thanks