Foundation Dilemma (moved from Projects)

[chris coupe]

I am currently having a double story extension on the side of a detached 3 bed.


The existing house is an a raft foundation, and we have been advised by the council (Leeds) to put another raft foundation for the extension at the side of it.


In searching for a structural engineer, by one we were recommended to have a “pile foundation” as the raft foundation will ‘settle’ and pull away from the existing house, and by another we were recommended to stay away from Piles and to have a raft foundation.


Confused………….


Wondered if anyone could offer some assistance and experiences on here.


Thanks

Chris.

 

[London Mike 49]

I would ask each one to state the pros and cons of their recommendations, at least that way you will have a objective veiw of what is most suitable for your site.
And ask around in your area to see and ask what other people have done with their extensions, often that is the best way forward.

Good luck

 

[Footsoldier888]

Your Building Control Officer will have knowledge of what others have done locally, as London Mike said.

They are happy to talk I have heard.

 

[bernardgreen]

If the raft under the present house was on firm ground and has not sunk at all then a raft for the extension taken down to the same level will be OK.

If the present raft did sink over the years then piles down to solid ground may be necessary to prevent the extension settling and creating cracks in the join new to old.

As said the local building control will have good knowledge of ground conditions and settlement rates

 

[wessex101]

A raft is designed to move, piles are not. To combine the 2 in one building sounds like madness to me.

 

[bernardgreen]

A raft is designed to move,

True,

Some rafts do move up and down as the water table changes and clays swell and shrink. Normally only a very small movement

Some rafts are designed to sink ( slowly over a year or so ) as the ground underneath compresses under the weight of the building and stay at that level.

If the raft is one that is designed to rise and fall then piles for the extension would be wrong.

If the raft was designed to and has settled to it final and permanent level then piles could be used. To use another raft one would have to make allowances for it to settle befoe the #new is joined to the old.

I can recall a raft being built, then loaded with building materials and left for almost a year to settle before the final joining of new to old. ( it was a long time ago when money and fast build turn around was not critical, cannot do that today ).