Maximum depth of concrete slab new build?

[gwebstech]

Hi all

 

Im getting ready to pour my concrete into the trench weve dug. The trench is about 1m deep, the building notes say 700mm conrete into that, then build the substructure from either 7n concrete blocks and or engineering bricks.

 

Seeing as laying the initial first courses in the superstructure is slow and time consuming (ie expensive as i cant lay bricks well)  im wondering what the maximum depth of concrete i can pour in? i know the engineering bricks/blocks have to be filled with concrete to strengthen them, but  am i determined by where the DPC will be and the concrete cavity fill has to be a certain depth below the DPC?

 

Can i put more concrete in and save a couple of courses of bricks?

 

thanks

Edited July 16, 2019 by gwebstech

[bassanclan]

I guess you mean deep trench fill concrete strip foundations.

If the build is brick/block then there's no reason not to pour the concrete to say 100mm below the top of the trench

[gwebstech]

Hi yes it is trench fill

 

But in my notes from the architect it says that its cavity filled with concrete to either 225mm below DPC or 150mm below, im not sure which is rigt and why it states 2 differing options

 

thanks

[Temp]

 NHBC say 225mm cavity below dpc. Can be reduced to 150mm if there are weep holes..

 

http://nhbccampaigns.co.uk/landingpages/techzone/previous_versions/2011/Part5/section1/sitework.htm

 

 

[Temp]

If building a brick outer, block inner cavity wall you usually arrange for both inner and outer to end up at same height at the dpc which is typically at least 150mm above ground. Bricks and blocks are different heights so some combinations achieve this and some dont (unless you cut blocks). Plan ahead and this determines the ideal height(s) to fill the trench to below dpc. 

[nod]

12 hours ago, gwebstech said:

Hi all

 

Im getting ready to pour my concrete into the trench weve dug. The trench is about 1m deep, the building notes say 700mm conrete into that, then build the substructure from either 7n concrete blocks and or engineering bricks.

 

Seeing as laying the initial first courses in the superstructure is slow and time consuming (ie expensive as i cant lay bricks well)  im wondering what the maximum depth of concrete i can pour in? i know the engineering bricks/blocks have to be filled with concrete to strengthen them, but  am i determined by where the DPC will be and the concrete cavity fill has to be a certain depth below the DPC?

 

Can i put more concrete in and save a couple of courses of bricks?

 

thanks

Our footings were between 1500 and 1800 deep 

There was a delay in starting which meant a November start

The whole site was flooded So I took the decision to full fill the trenches 

This saved me time and money 

[PeterW]

We backfill with EPS and weak mortar below DPC and use a step DPC with weeps above to close this cavity off. 

 

Only downside about bringing your trenchfill up to the top is you have to make sure that you have enough space over the top of the founds to get any drainage or other services out through the wall as you will be very high up. Alternative is you sleeve the pipework and reinforce appropriately.

 

[gwebstech]

thanks for the help guys

[joe90]

We backfilled with extruded polystyrene insulation to avoid a cold bridge (see https://www.greenbuildingstore.co.uk/golcar-passivhaus-ground-floor-foundations/.

Edited July 17, 2019 by joe90