Building a Domestic Extension in Stages

[andrew54]

I can't be happy with trench-fill using so much concrete. It might make sense economically, but environmentally it is bad. The cement for concrete uses huge amounts of energy to manufacture.

 

[limerockconstruction]

The carbon footprint of the cement content of 12m3 of concrete isn't really that worth shouting about in comparison with the additional carbon footprint of getting the the blocks there, the sand and cement and then the brickies van's to lay it, the electric for the mixer etc etc etc

Mass fill every time within reason.

 

[CHarr]

I'm surprised that no one wanted to take on the whole job. IS there something that your not telling us????

Nope, really not. One excluded the conservatory roof (but not its doors & windows), another excluded all the glazing, and the most expensive (by far) excluded doors, windows, wiring, plumbing, sanitary ware in the loo and a few other odds and ends as well. He wanted £57,500 + VAT for a shell that has cost me £12,000.

Everyone that has worked on the job so far has been a tradesman engaged directly. The 'builders' have mostly been spivs who want me to pay cash 'to avoid the VAT' (but they didn't offer to share the benefit of the evaded income tax), and they still want me to run round, pulling stuff together, doing part of the job myself, and paying a premium. No thanks.

One of the builders would have been fine: he was straightforward, helpful, quoted a sensible price, but was too busy to do the job for months (there's a connection, there, I'm sure). The rest: I wouldn't have touched with a bargepole! I'm sure that there are lots of honest builders about - perhaps I was just unlucky.

 

[bennyhedgehog]

How times have changed.

Thank the lord.

Puzzled?

I'm more puzzled that you risked a two storey extension on as little as 150mm of concrete. Very amateurish.

It is what the text books specified.
It was approved by the Building Control inspectors.

Was it not normal in those days? Is anything more just a waste of concrete?

After 22 years there are no problems.

If the Inspector was happy then presumably you have very good ground for 150mm of concrete. I am building a single storey extension at the moment and the existing founds were on 300mm of concrete, but the extension still had to go down 600mm! But at least i will get my sign off!

 

[andrew54]

If the Inspector was happy then presumably you have very good ground for 150mm of concrete.

The inspector was very fussy about the trench and what sort of clay we had come to, but no quibble at all about the specified 150mm of concrete in the bottom of a 1,000 deep trench.

 

[noseall]

I don't ever remember laying concrete as thin as 150mm and I have been building since 1982.

However, it has stood the test of time. End of story.

 

[CHarr]

Having engaged a roofer, it seems like we're on the home stretch, but of course there's lots still to do.

We've left the floor (not for idealogical reasons, but because bricklayers became available at short notice), but there are scaffold poles inside the footprint, so I still need to get them out and concrete in. I'm intending to use a mix-on-site service with a pump to pour to a level which I'll mark all around the perimeter. I don't have access to labour to barrow in ready mix, and hiring a mixer and making my own is even more expensive (and too much like hard work).

All the doors and windows are ordered, and I'm looking forward to being weatherproof (next week) and secure in a couple weeks more. By then, I'll have the floor slab laid, insulated and the screed down. I'm trying to decide whether to have a conventional screed, or a liquid screed poured in: any thoughts?

 

[limerockconstruction]

small domestic extension = traditional sand and cement I would have thought

 

[noseall]

Concur with LRC, sand/cement screed.

 

[alpcon]

erm correct me if im wrong here but I always thought the absolute minimum for a concrete footing is 225mm? and am I right in saying you have clay soil too !!!!

 

[CHarr]

erm correct me if im wrong here but I always thought the absolute minimum for a concrete footing is 225mm? and am I right in saying you have clay soil too !!!!

It depends on whether you are talking about the thickness of the concrete itself, or its depth in the ground. Part A Table 10 sets out the required dimensions of the foundation trench, but for strip foundations, the starting point is a minimum thickness of 150mm.

 

[RonnyRaygun]

erm correct me if im wrong here but I always thought the absolute minimum for a concrete footing is 225mm? and am I right in saying you have clay soil too !!!!

It depends on whether you are talking about the thickness of the concrete itself, or its depth in the ground. Part A Table 10 sets out the required dimensions of the foundation trench, but for strip foundations, the starting point is a minimum thickness of 150mm.

I'd never specify 150mm without some reinforcement in it. I'd always say a minimum of half the width of the footing to ensure the load is spread sufficiently.

 

[stuart45]

Although 150mm is the minimum in the book, in practice 225mm has always been regarded as the min.

 

[andrew54]

Although 150mm is the minimum in the book, in practice 225mm has always been regarded as the min.

So for going by the book I get called 'amateurish'.

 

[noseall]

So for going by the book I get called 'amateurish'.

You would be considered clinically insane to rely upon 150mm of concrete for a two storey extension, even way back when.

Foundations are fundamental and are extremely difficult to rectify. Adding an extra few inches in depth would not cost much.

Do you always do things to the absolute minimum?
Did i say amateurish?

I meant to say idiotic.