Full fill trench foundation question

[Ruggers]

I've had some plans approved for a detached self build house with foundation & ground floor make up open to change.

Q: If using full fill trench foundations, How do you install ground a floor toilet foul pipe that exists through the floor and then passes through the cavity wall to outside. The rest bend would have to pass through the concrete foundation and without the house set out you wouldn't know where to install it before the pour? I'm sure theres a simple way to do this but I can't picture it.

I'm just working out the price of breaking ground for blocks/sand/cement/labour for a 225mm x 750mm strip foundation with minimum 600mm ground coverage required. I had a thought to work out what it would cost for a full fill foundation brought up to within 150mm of ground level. So assuming 750mm wide, 750mm deep, the price would be 3.5x more concrete, but after deducting blocks/sand/cement & labour time, I'm working it out as on par or slightly cheaper plus much quicker.

 

[noseall]

I've had some plans approved for a detached self build house with foundation & ground floor make up open to change.

Q: If using full fill trench foundations, How do you install ground a floor toilet foul pipe that exists through the floor and then passes through the cavity wall to outside. The rest bend would have to pass through the concrete foundation and without the house set out you wouldn't know where to install it before the pour? I'm sure theres a simple way to do this but I can't picture it.

I'm just working out the price of breaking ground for blocks/sand/cement/labour for a 225mm x 750mm strip foundation with minimum 600mm ground coverage required. I had a thought to work out what it would cost for a full fill foundation brought up to within 150mm of ground level. So assuming 750mm wide, 750mm deep, the price would be 3.5x more concrete, but after deducting blocks/sand/cement & labour time, I'm working it out as on par or slightly cheaper plus much quicker.

The concrete fill level does not usually end up at ground level, even 'full fill'. Rather you would fill to say 525mm (seven metric brick courses) below DPC or there abouts. If the concrete was still too high, one would hack away at the green conc' say the following morning or even later the same day, if a few inches needed scrabbling away to form a channel. Deeper set pipes are either pre-shuttered or the concrete is kept deliberately lower to accommodate more complex drainage.

 

[Ruggers]

I didn't realise that low below DPC, when I had a read into it it said bring the full fill up to within 150mm of ground level so i took that as 4 metric brick courses and thinking I'd get around 750mm deep of foundation. If the full fill had to go much deeper than 750/900mm then it would become more expensive again than strip.

I thought with full fill the setting out of the build could be more accurate too that squaring something up from so many courses down.

 

[noseall]

I didn't realise that low below DPC, when I had a read into it it said bring the full fill up to within 150mm of ground level so i took that as 4 metric brick courses and thinking I'd get around 750mm deep of foundation. If the full fill had to go much deeper than 750/900mm then it would become more expensive again than strip.

I thought with full fill the setting out of the build could be more accurate too that squaring something up from so many courses down.

Full fill still needs to accommodate things like gullies (usually about 5 courses deep) and changes in ground levels. Common sense tells us to fill to a level that is appropriate for the site.

 

[opps]

The concrete fill level does not usually end up at ground level, even 'full fill'. Rather you would fill to say 525mm (seven metric brick courses) below DPC or there abouts. If the concrete was still too high, one would hack away at the green conc' say the following morning or even later the same day, if a few inches needed scrabbling away to form a channel. Deeper set pipes are either pre-shuttered or the concrete is kept deliberately lower to accommodate more complex drainage.

I have to admit that when I built my garage, I filled to soil level and 215mm thermolite blocks from there upwards.

From memory, you aren't supposed to because of potential ground swell. Hasn't been an issue over the last 15 years though.

 

[Ruggers]

Thanks guys, I suppose a warranty company will make the final decision but it was worth me getting some info. on incase it's an option to consider. I suppose full fill benefits founds that need to be deeper than 0.9m but not deeper than 1.5 - 2m to bring it within a few courses of ground level saving the lads hassle of working within. Based on test hole dug and surrounding builds they never exceeded 1m.

It was more to consider the sites removal of some large trees that could cause heave. I was told it shouldn't be an issue but shouldn't doesn't sound 100%.