Extra Deep Foundations

[Sandy Miller]

Hi all.

 

Planning a small rear extension.  Our post code is RH12 5XQ.

Building Control have told me due to the proximity of a neighbours mature oak I will need more than the standard foundations (i.e. option B below)

I need a ball park as to how much this is likely to cost, if it's as bad I think it will kill the budget and we won't be able to afford any of it and I won't bother getting the drawings done.

Tried a few local builders with this question but they didn't even bother to reply.

 

 

A)  Standard 10 meters of trench 1m deep + 13m2 of concrete floor.

B)  Standard 10 meters of trench 2m deep + compressible material + 13m2 suspended concrete floor.

What would be most helpful to us is, if someone could say something like;

 

for just the foundations and assuming there are no snags, then for each you're looking at around

A)  ? thousand

B)  ? thousand

 

I know there are a ton of things that will affect the cost of any job.  I just need some helpful person to take a stab at it.

Any ideas on this will be so helpful, thanks.

[Steptoe]

I know it doesnt answer your question,

but, could you pour a slab?

 

[PeterW]

Hi

 

So this is a straight 4x3m rectangular extension ..? How close is the neighbour's tree to start with ..?

 

On your second option I would get rid of the concrete suspended floor - assuming BC is working on you having a clay soil then they will want something like 75mm of EPS40 on the inside of the trench and that also needs to go under the floor, however it's not worth it in this case as a suspended timber floor will be quicker and much cheaper. 

 

Back to your original query - 10m @ 600mm wide and nominal 1m for trench fill is 6 cuM, so bulked up is an 8 cuM skip (£180).

 

Clear 13m2 to 300mm ground level is 4 cuM, so let's add another skip. (£180)

 

Machine and labour about £400 to do that lot in a day, should be doable assuming no drains to move etc. 

 

Trenchfill those founds using a standard mix (and assuming no pumps etc) would be about £110 per cuM so a full load at 6cuM is £660. 

 

Labour to pour and place of another £280 for the day. 

 

Totals about £1700 plus the vat, going twice as deep will probably add about £1400 to that plus your EPS. 

 

They are ballpark numbers from rates I see around here. 

 

Hope that helps 

 

 

 

 

[Declan52]

Impossible to give you a price for that type of job without knowing lots more details. 

Can you get a digger to dig it out and what size is the way in??

How much is concrete per cubic m3???

How do you intend to get the concrete from the lorry to the founds, wheelbarrow or pump or can it get poured straight in???

What about the spoil getting removed, what are you doing with this?? 2m of digging will leave a very big pile that needs to go somewhere. 

What happens if you need to go to 2.5m/3m have you enough contingency money to cover this

What about services running across the area?? Water, electric, sewer or rainwater.

Do you have any friends or family that could help out to save on labour???

 

[Buzzfan]

SandyMiller, unless you already know, I'd dig a quick trial pit to see where any clay/sand/gravel is - and ask your building control officer if you can avoid trench foundations entirely - the small job size will probably exclude the rig hire cost of solutions such as bored piling, but an economic low tech solution near trees may be a mass concrete pier (pile) at each corner with a raised ground floor supported on beams. If building control won't help, then I'd ask a structural engineer to have a look for you - if one's local they may be willing to meet you on site without charge to assess the job & comment on any solution together with their fee quote. Look too at helical screw piles as yet another alternative.  

[Ness]

It's hard to say. We have protected trees and had to get an arborist to do a report which cost about a grand. My dad's extension had to have a 3m wall in front (and below ground) of his foundations to protect of an oak.... so if the council are only recommending a 1 or 2 m depth..... I don't think that's too bad. 

 

As a guide, in Norfolk (and it changes everywhere) to hire a digger for the day is £150 and a driver is around the same price. My hubby dug ours and we bought the digger to start. Our foundations were £83.50 per cubic metre, but we needed a stronger mix which bumped the price up and a pump at an extra £450. I rang round concrete places to get the best price.... but at least that could give you a starting price? Or ring a couple of builders and get a price from them? All in? 

 

Good luck