Need advice - strip foundations in bays or a raft???

[Standy5050]

I'm trying to get a garage 8 x 5 metres built. I got someone to draw up plans and they have said I need to build the foundations 1200mm deep and they have to be filled in bays and tied rather than as a trench. My builder has told me that this is going to increase the cost considerably - as the concrete will have to be made by hand rather than ordered in, building inspectors will have to come out loads, etc. It's basically to protect the garages on either side from damage from making the ground unstable - they are right next to the site.

The cost has gone up so much that now I can't afford to have the garage built. Does anyone have any other ideas on how to tackle this? A friend suggested it might be possible to build it on a concrete raft. Given that the foundations have to be dug and filled in bays, does anyone think this woul be a cheaper option?

Any suggestions would be gratefully received. I'm stuck and gutted.

BTW - the garage is 8 x 5 in concrete block and render with concrete tiles on the roof - it would be a bit of a beast.

 

[RedHerring]

I'm not an expert and have very little experience but I'm having difficulty in understanding the concept of bays as a type of foundations. Unless your architect is sufficiently concerned about ground disturbance that he is suggesting that you create your foundations in sections to minimise the disturbance to the other properties.

i.e dig and create a section of foundation (strip, trench fill or raft), then continue to create a further section etc.
The depth should be determined by loading and local ground conditions.
I don't understand two comments though, a) the cost becomes inhibiitve and b) it requires a mix on site.
Unless the sectionional approach is such small sections that suggest a delivery of ready-mix to be prohibitive.
Incidentally a 8 x5 garage is by no means a bit of a beast.
I've recently completed just such a garage. I used trench fill foundations and it took two loads of readymix.

 

[Standy5050]

Your interpretation is correct - the foundations would be done in 1m sections so it doesn't disturb the neighbouring garages' foundations (which are apparently 6 inches!)

The builder has said that the cost of doing it in sections would be considerably more becuase he would have to dig a hole and then fill it and could not get a concrete company to bring a load around for such a small volume and so it would have to be mixed by hand.

 

[RedHerring]

So what is/was your budget. My estimate of costs was £15,000. Only estimate 'cos I didn't keep accurate records.

In my estimating I've always estimated readymix and mixing on site as comparable. That didn't take labour costs into equation and readymix always won the day 'cos of speed and convenience.
The depth of the foundation is really a given due to loading and ground type. I doubt if you can change this.
Some considerations for you:

A question for your builder is why is mix on-site so more expensive than readymix?

Can you provide any of the labour?

Can the amount of concrete be reduced by courses of foundation blocks?

I doubt if a raft foundation would be appropriate in this situation 'cos a raft allows the buidling to move in one which would mean it moving out of kilter to the adjoining buildings, which could cause damage.

But don't forget my opening gambit. I'm no expert.
Hopefully the situation is a little more clearer for the experts and experienced on this forum to chip in.

 

[RedHerring]

I've just discovered that you've duplicated your request, which means that you'll either be getting conflicting advice or you'll be repeating loads.

The other responders are more experienced than me so just go with the one post in the other forum.

 

[simonjay]

Hi, first post on here, although I've been reading for a while.
How unstable is the ground ?
The usual way would be to dig out half the foundations first (1m bays separated by 1m untouched ground), fill these in, then dig out the rest, so the whole process is done in 2 stages, not multiple stages. This is just two mixes. Get the mixamate type guys, who mix the amount you want on site.
You'd need trench foundations (filled nearly to ground level) in order to keep the ground stable I would have thought.
The process is like when underpinning is done.
Hope that helps,
Simon.

 

[Chukka63]

Hi, first post on here, although I've been reading for a while.
How unstable is the ground ?
The usual way would be to dig out half the foundations first (1m bays separated by 1m untouched ground), fill these in, then dig out the rest, so the whole process is done in 2 stages, not multiple stages. This is just two mixes. Get the mixamate type guys, who mix the amount you want on site.
You'd need trench foundations (filled nearly to ground level) in order to keep the ground stable I would have thought.
The process is like when underpinning is done.
Hope that helps,
Simon.

i used mixamate once.never again,was twice the price of readymixed form a different supplier.

 

[simonjay]

i used mixamate once.never again,was twice the price of readymixed form a different supplier.

I used a mix-on-site, probably not actually Mixamate.
Close to a full load from a readymix place will be cheaper, but for small loads the mixamate types can be cheaper. Thats is their market - smaller volumes. Otherwise they'd be out of business !
Simon.