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Opinions please on this quote for substructure & drains.


Tony L

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Hi everybody

 

This is my first post.  I’m going to demolish my approx. 100 year old bungalow & build a detached house (13.5 x 8.8M footprint) + detached double garage.  I have PP. 

 

I’m in Surrey, & my plot has a very high water table.  Due to the water table problem, if I don’t get everything in place now, so that the foundations can be dug in September, it would make sense to wait until next September, so really, I need to make some quick decisions.

 

I’ve received this quote (below) & I’m keen to know whether it seems reasonable.  I will make sure setting out is included, if I accept this quote.  The ply that’s mentioned is for the shuttering that we’ll need to use to stop the foundations caving in (due to the water that will seep in within a few hours of the trenches being dug).  I bought a job lot of reclaimed plywood boards for this purpose some time ago.

 

I’ve attached a drawing to show the substructure plan.  This was drawn by an SE about 4 years ago, before the project was put on hold.  I realise the regs have changed, so I’ll be getting a new drawing showing a 150mm or perhaps 200mm cavity, but this gives you an idea of what’s involved.  There’s around 60 linear metres of trench here.  BCO have told me I’ll need 1M trenches, 60cm wide, with 60cm concrete.

 

The site plan shows the new house & garage.  I’ve drawn the drains in, in red & the circles indicate the access chambers that are included in the quote.

 

& here’ the quote.  It’s a shame they didn’t break it down, with a price for each line.  The existing garage is a large single, made from very flimsy wood, so that will not take too much effort to demolish, although it has a corrugated concrete asbestos roof, so care will need to be taken with this.  I reckon the demolition is £5K max.  It’s an almost level site now, as the garage area was dug out some time ago, so there’s already about 3 loads of muck away to go (£1,000?) & the quote covers this too.

 

Please see below comprehensive list of works to be completed and quotation for this work.

 

Demolition of existing bungalow and garage

Dig out and remove existing foundations

Removal of hardcore and waste material from site

Dig foundations (an allowance of 1m depth by 600mm wide trenches)

Form shuttering (ply supplied by customer)

Concrete foundations (depth to be advised by building control)

Lay in ducting for gas, water, electric and NTL to receive services by others

Lay all foul and rainwater drainage including manholes

Build up block and brick footings to receive block and beam flooring

Allowance for three courses of bricks in Staffordshire blues

Lay block and beam floor

Allowance of 1.5m of hard standing around new property plus a hard stand area to the front of the cabin for storage of materials

 

No allowance

Clay master

Sheets of plywood (to be supplied by customer)

Base for new garage - awaiting designs/spec

 

Total: £59,584.00 (Net) 

 

I’m sure this would have cost a lot less if the project hadn’t been put on hold four years ago.  Do you think this seem reasonable at today’s rates?

Site plan showing my proposed drains cropped.JPG

cropped GFP with foundations.pdf

Edited by Tony L
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On the face of it I wouldn't think that price is hugely off the mark, there is a significant amount of work and materials.

Have you other quotes to compare against?

 

I'd also keep in mind that costs reliant on ground conditions should only be considered an estimate.

Be prepared for the BCO, on inspection of the dug foundations, now requiring 1.5m foundations and 1m of concrete, or such & such.

You need a contingency set aside for groundworks.

Edited by Annker
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I would get a second quote, to me it looks expensive, but have no idea if you local day rates. 

 

My foundations were twice that size, way more complex and half the cost. Done at the height of the COVID price hikes.

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Posted (edited)

Thanks for the responses.  I haven't sought other quotes.  I'm very short on time at the moment & I was hoping I'd receive a few positive or neutral comments here, & that would be enough for me to decide to go ahead with this quote.  I will make more time when I come to consider who will do the work for the next stages. I am particularly keen to go with this ground worker because I know of his very good reputation as he mostly works for a local developer who is good friends with my brother in law.  Originally (ie 4 years ago, before the project was put on hold), I was planning to pay him a day rate & pay for everything he needed, but things have moved on; he was unwell for a while, & he brought a general builder he sometimes works with to our recent meeting. The quote has come from the builder, so I'd be paying the builder, who will be doing the work together with the ground worker I'm keen to work with.

 

@Mr Punter, no, I haven't considered doing anything special under the beam & block floor.  Ideally, I'd have my B&B a little higher above ground level, but the planning department have been very insistent on a low ridge height, so I have no room to play with.  I have received permission to put all the rain water from the roof into the drain that's taking the waste water (that's what happens with the rain water from the bungalow that will be demolished), because a soakaway is not feasible.

 

 

Edited by Tony L
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1 hour ago, Mr Punter said:

Will the water table mean you need to make special provision to for drainage under the slab?  @nod had a soggy site on and laid concrete to falls under the beam and block.

Good points by both of the above 

Groundwork’s are the only unknown of The build They can only base quotes on what they have in front of them 

I would keep a 10% contingency for more concrete more muck away and more labour 

You will only No on the day when BC says Yep that fine Or give me another 600 

I had to go to 1800 and fully fully with concrete Then had to add 5 cube of concrete under the house 

No issues with the current build 

You just don’t know 

 

Quote looks fine 

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Thanks, @nod.  Sorry, I forgot to explain: I dug two test holes either side of the new house location, 2M deep, & I pumped them dry & BCO came & inspected them, so I think they're unlikely to change their minds on the 1M deep requirement.  There was a new build, next door, two or three years ago (their GL is slightly lower than mine) & they were given the same 1M instruction on their foundations.

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the house i ma inat the moment was built on strip founds etc and outsied the back door there is an area of concrete about 49sqm -- 

idecided to buiold a raised patio there as there were 3 steps down to it 

 

so when i started to look at it - i did some digging and  found the the clay under this concrete area not having being exposed to rain etc had shrunken back from it by about 3 inches over a 20year preiod 

 so this is why on clay grounds they want the founds to go right down so far to be on clay that will not be affected by rain water to keep it swelled up and wil stay moist all the time  and not shrink back 

 there is a house built on the side of the nith river  that used a different solution 

 

dug out to 1.5m below ground --then fitted 1m cubs of polystyene all linked by rebar --then a concrete raft on that 

It has neve moved in40 years and on high tides the garden is flooded its thatclose the the river  edge  and that is all clay +sand 

I would have thought that would be am uch cheaper option than mega thickness of concrete and also gives some insulation and floatation value  -- its how a boat works

they also use this system for building roads through bogs that freeze inthe winter in scandinavia 

,

 

 

 

Edited by scottishjohn
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Thanks for the advice, but there's no clay.  The quote says "no allowance clay master", but I think the builder probably just says that on all quotes where clay master hasn't been specified, to cover himself, just in case.

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10 hours ago, Tony L said:

It’s a shame they didn’t break it down, with a price for each line. 

Not really. It allows a client to pick and choose between contractors on very line.

The bottom line is what matters.

10 hours ago, Mr Punter said:

drainage under the slab? 

If it is that wet, then you should be building higher so that it doesn't become an issue.

 

8 hours ago, Tony L said:

I have received permission to put all the rain water from the roof into the drain that's taking the waste water

That is bad. The planners don't normally understand drainage, hence flooding and sewage being released into waterways and the sea.

But you could try to do 'the right thing, which is to delay rain on its way to the rivers and lakes  (and sewage works). Barrels at downpipes can do this well enough, set to a dribble to release the water slowly into the drains.

 

It seems the BCO is designing this for you for free. Well done. The builder should know this, but dig to 1m only if it is very dry at the time. otherwise it all gets muddy and mud should not be built upon. Whatever the level, the bco will ask for 100mm to be removed before concreting, so dig 900 and have a shovel ready to get the mud out in a hurry...while not making more mud.

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Re. water butts:  Good point. I heard somebody on Radio 4 a while ago explaining that if everybody who had room for water butts installed them & used them in this way, it would go a long way to alleviate the flooding that follows on from heavy rain.

 

Re. building on mud: I am not expecting the bottom of the 1M trenches to stay dry for more than a couple of hours after they've been dug.  We’ll be going straight down to 1M & shuttering as we go.  We’ll probably dig a sump & put a pump in there just to keep everything as dry as possible until we’ve finished digging.  I’ll ask BCO to come & have a look late in the day when we dig the trenches & we’ll have the concrete pour lined up for early the next morning.  I was planning to stop pumping as soon as the trenches are dug.  The theory is that if I’m pumping silty water all night long before the concrete is poured, this will be removing fine particles from the soil around the foundation trenches so this soil will become weaker & less able to support the foundations once they’re poured.  Already, there’s the minor concern of the plywood & OSB shuttering that will slowly be rotting at the sides of the concrete, so I don’t want to make the soil weak as well.

 

So unless someone persuades me otherwise, the concrete will be poured into trenches that may have up to 50cm water in them.  When they dug their foundations next door, I lent the builder my pump & he kept the trenches dry until the concrete was poured.  The BCO told him he need not have pumped the trenches.

 

Any more opinions on the £59,500 quote would be most welcome, please.  It’s looking expensive compared to @Jane W’s £30,500 quote posted yesterday, although this was for a slightly smaller (but irregular shaped footprint), & my £59,500 includes, demolition, drains, manholes, connection to main sewer & ducting for services.

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4 hours ago, Tony L said:

building on mud: I am not expecting the bottom of the 1M trenches to stay dry for more than a couple of hours after they've been dug.  We’ll be going straight down to 1M & shuttering as we go.  We’ll probably dig a sump & put a pump in there just to keep everything as dry as possible until we’ve finished digging.  I’ll ask BCO to come & have a look late in the day when we dig the trenches & we’ll have the concrete pour lined up for early the next morning.  I was planning to stop pumping as soon as the trenches are dug.

good luck with that 

If you are sure it will fillback up straight away --then you are building on a bog -

can,t see how 1meter  founds will solve that

surely they will just sink until they hit something solid 

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On 18/06/2024 at 07:28, Dave Jones said:

£60k for 3 days work is a bit tasty.

 

Have you had the foundation designed by an SE ?

Yes, an SE has designed the foundation.

 

Everyone, & that includes you, knows this is more than 3 days' work.

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19 hours ago, Tony L said:

Yes, an SE has designed the foundation.

 

Everyone, & that includes you, knows this is more than 3 days' work.

 

what makes you think that ?

 

day to dig, day to shutter, 1 hour to pour with pump.

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10 hours ago, Dave Jones said:

 

what makes you think that ?

 

day to dig, day to shutter, 1 hour to pour with pump.

If it as soft as he says and will half fill with water overn ight ,then you would have to dig a bit and shutter as you go  and that will not be quick 

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