Mixed foundations?

Question

If a building is built on a raft foundation, must an adjoining extension also be built on a raft?

Stephen · Accepted Answer

Not necessarily as the new build extension could be a timber frame construction and it would be a much lighter option for the required foundations.   that with the new technology in the construction of timber kits the foundations could be considerably lower in price and time of the project it is always a good idea to consult with your planning department and to discuss your requirements with a certified engineer 
We hope that this will help you in the future construction and wish you all the best 
With your projects 
                  Yours Richard Hepburn for kingsknowe joinery and all trades

Dylan · Answer

Normally the engineer specifies a raft foundation because the ground is bad or high water table. If you contact building control in your area they may help

Gary · Answer

Yes you need a raft the weight isn't only  on the brickwork timber-framed or.not there's the roof windows etc

Kevin · Answer

Yes, normally because the ground around the building is on a raft would be the same so I would say definitely need a raft if you’re doing extension. Hope that’s helpful. Cheers Kevin

Shane · Answer

Yes it must . There is obviously a reason for the raft foundation on the existing building. But you could seek guidance from building inspectors/ architects first

David · Answer

The raft foundation was the instruction of a structural engineer, possibly because of ground conditions. 
This would require the input from building control who will be aware of the ground conditions in your area.

Adam · Answer

I am not a structural engineer however, I would say that if a raft foundation has already been used it would have been for a specific purpose due to poor ground conditions. I would assume an extension would follow a similar design but if your willing to pay alternative foundations can be considered.

Patrick · Answer

Generally ground conditions dictate there isn't a specific reason why you should or shouldn't given the build its going to support  a structural engineer might take the view that its required as it follows whats already in place ,in my experiences a raft foundation is far superior to strip founds for many reasons what you spend on extra concrete you save on excavation time just the depth and the fact that's is a monolithic substructure with no ground support required.

Jackie · Answer

Yes it can also be done just watch how you do it to be honest

Adam · Answer

Raft foundations are a common solution for small home extensions and conservatories, and can be tackled by a competent DIYer, providing accurate measurements are used and due care is taken. Raft foundations use slabs of reinforced concrete to cover a large surface area, often the entire footprint of the extension.

Mixed foundations?

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