Moonshine

Excavation cost / benefit?

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Posted (edited)

I am looking to develop a plot on a sloping site, with the rear garden level a level (first) above the entrance at the front (ground), so about 3m difference.

Working on a hypothetical depth of the house being 8 metres, I am trying to work out it it's worth excavating the full 8m back or going a fixed distance in at ground level, e.g. 4-5m.

 

The pros being that it increases the habitable space and may make the construction more straight forward, with the retaining wall tying up with the line of the rear external wall.

 

The con's are the cost increases in excavation, retaining wall and build cost

The site will need a fair bit of excavating anyway so it's may only be a relatively small increase in cost.

 

Based on a 8 m wide house it would be about 96m3 extra to excavate, but an increase in floor area of 32m2.

 

I can sketch the levels and change a bit later

Edited by Moonshine

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What’s 4m down? If it’s all soil, then xcavation should be straightforward, if it’s rock, it could become costly. What you going to do with the excavated material? The best is to retain it on site. If you have to get it removed it’ll be costly

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Shouldn't be rock, but everything is going to have to be taken off site. 

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You can double that 93 cubic meters, by the time you pull it out of the ground. It will defo add some considerable costs, but you only have to do it once.

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23 minutes ago, Big Jimbo said:

You can double that 93 cubic meters, by the time you pull it out of the ground. It will defo add some considerable costs, but you only have to do it once.

 

Yup, or better/worse  - depends what it is.

 

For our basement (11m x 13m x 4m) we had clay, gravel and chalk. That required around 75 x 20t truck visits to remove over 3 days. 

 

I needed to have the spoil WAC classified (i.e tested) to confirm it was inert - this happened as part of a planning condition for contamination and was included in the ground investigation works.

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Thanks, i am aware of the increase in volume once its un-compacted. @Bitpipe are you willing to share what the associated cost involved were, to use as a yard stick?

 

The existing site level is the red in the top figure below, and area i am thinking about is red in the bottom one

1634543156_proposedcross-section.thumb.jpg.91f58ceda5d24e8bee141496b9d90f17.jpg

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In 2015 it was about £35/m3 for the muck away - some gave a volume calc as it was in the ground and some used the out of ground value (x2)

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I've been paying about £12 per m3 for muckaway recently - however the lorry has been dropping off aggregate at the same time, so having the lorry onsite for a delivery no doubt drops the cost down. Can you tie in aggregate deliveries with muckaway?

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2 years ago I paid £21k for the combined excavation and muck away of 3000 tons of largely chalk.

This was pretty much the price of most of the other muckaway quotes without the dig.

The exceptional advantage of my chosen contractor was his yard being only 3 miles/8 minutes away versus the next closest at 20 minutes.

..... so geography will likely be a big factor in your price.   Go make friends with your local farmer or anyone else with land where they could lose your muck.

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Look for an aggregate recycler .

Basically he will dig out the rock ; clean / grind it into chippings . So should work out cheaper . This is what I did .

Edited by pocster

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