Wall position on foundations

[^woody^]

Again, I agree with geraint!

There are some theoretical reasons why you may like to load the foundation strip centrally, but in practical terms for an extension, there will be no detriment to offset walls on the foundation strip, or even walls built on the edge

TBH, the BCO will check the foundation depth and trench width. By the time the substructure walls are built up to DPC, and then the banks of the trench knocked in, then BCO wont notice any off-centre loading and he won't even care

 

[RedHerring2]

TBH, the BCO will check the foundation depth and trench width. By the time the substructure walls are built up to DPC, and then the banks of the trench knocked in, then BCO wont notice any off-centre loading and he won't even care

.................. Cannock and Stafford authorities even insist on visiting the site to check the masonry is central as part of their remit.

OP is in Staffordshire

 

[noseall]

BCO wont notice any off-centre loading and he won't even care

Try telling that to Tricky Trev (Trevor Edensor) at Stafford council.

 

[^woody^]

In which case the builder will know to splay the top of the strip, to show the BCO what he wants to see

There must be loads of failed, leaning over foundations in Staffs then which need to be prevented in future by diligent BCO's, as this does not seem to be much of a problem elsewhere.

Do they insist on cube and slump tests too - just in case?

 

[wavetrain]

TBH, the BCO will check the foundation depth and trench width. By the time the substructure walls are built up to DPC, and then the banks of the trench knocked in, then BCO wont notice any off-centre loading and he won't even care

Indeed this is the whole point, the BCO may not care less if the strip footings tilt, it is not his house. It is the home owner's responsibilty or a person he pays to take responsibilty ie a project manager, SE etc to ensure things are done correctly. No sensible person would transfer complete trust to a builder over this matter. If I was having work done on my home, I would care to ensure work was does to a standard that ensured the footings did not tilt over time.

Do they insist on cube and slump tests too - just in case?

No they do not because with residential housing the concrete strength is greatly over-specified for substructures to allow for substandard mixes, as I am sure you well know

 

[RedHerring2]

Don't forget the OP.
We're talking about a strip of trench wall, 100mm thick, perhaps 300mm deep, perhaps 7 m long. An extra 0.2m³

If there's a problem in clearing this out at this stage, I fear for the rest of the project.

 

[^woody^]

No they do not because with residential housing the concrete strength is greatly over-specified

Even when you knock it up yourself? How does the BCO know?

I've never seen problems with rotating foundations - failure is always related to something else.

IMO, it remains a theoretical possibility, with little relevance to typical domestic extensions. There are many other things to be worried out for long terms stability which are often ignored

 

[stuart45]

On most of the big sites I've worked on over the years I would say that the majority of walls sat near one edge of the concrete. For practical purposes it's much easier to build the footings when it's over to one side in the trench. In theory however the walls should normally be central.

 

[wavetrain]

Stuart is is well known that the self certifying that the large building firms do is open to falsifying. Your observations are therefore not surprising.

 

[RonnyRaygun]

We did have a BCO refuse us permission to use a designed eccentrically loaded foundation quite recently. Don't know the reason as it wasn't a job I was working on...

Definitely good practice to build centrally, but as Woody says, in practice it will probably never fail. Why take the chance though, unless someone has made a cock-up?

In theory though, a concentric footing is often eccentrically loaded as it will often have more load on the inner leaf due to floor and roof loads, especially if floors are, for example, beam and block...so you could argue that in order to load the footing concentrically, you actually
need to build the wall closer to the outer edge...

 

[wavetrain]

RR you are correct, will the OP please post the loadings/weights of the inner and outer leaves as well as the wall thickness details and 'we'will post suggested postions for the wall.

I have seen a DIY built outbuilding where the substructure consited of a raft concrete slab sitting on 300mm x 1200mm trench foundations consisting of 50% used brick and 50% concrete 6:1 mix. As long as the slab does not fracture, it does not matter, within reason, where the walls are placed. The footings and slab were built at different times to reduce the burden on the DIYer's back etc

 

[^woody^]

On most of the big sites I've worked on over the years I would say that the majority of walls sat near one edge of the concrete. For practical purposes it's much easier to build the footings when it's over to one side in the trench. In theory however the walls should normally be central.

Thats right, that is how it was when I started out as an apprentice.

Paddy in the Himac, would use whatever bucket he had on the machine at the time, and would dig the trench with a near enough level of precision. Then when you found that the external corner was off the strip, Mick would come along with his shovel to cut the trench wall, enough for us to get the corner onto the clay! If we couldn't wait, the walls were reduced by a brick or so - never mind if the doors, windows .... or cars would not quite fit later on

 

[hotrod]

Stuart is is well known that the self certifying that the large building firms do is open to falsifying.

Care to elaborate wavetrain? LABC still make inspections on all commercial projects I've been involved with. They just tend to be a little less "vocal" because they're normally accompanied with client side building professionals.

 

[theoldun]

wave train. If you had ever worked on a residential building site small or large, you would know that there is no self certifying. on foundations. They all come under inspection by either LABC, NHBC building control or independent building control. Who ever the builder has chosen.

plantroo, Listen to what noseall has told you, then just tell yer builder to get his nut, down, ar*e up and rip founds out all as Approved Document 1E2 (a) diagram 24. FOOTINGS CENTRE OF FOUNDS.
oldun

 

[RonnyRaygun]

wave train. If you had ever worked on a residential building site small or large, you would know that there is no self certifying. on foundations. They all come under inspection by either LABC, NHBC building control or independent building control. Who ever the builder has chosen.

plantroo, Listen to what noseall has told you, then just tell yer builder to get his nut, down, ar*e up and rip founds out all as Approved Document 1E2 (a) diagram 24. FOOTINGS CENTRE OF FOUNDS.
oldun

And let that be an end to it