House Extension : new sewer pipe through foundations..

[spikeuk36]

Hi there,

A couple of quick questions - any comments/advice would be greatly appreciated.

I'm currently digging my foundations to save as much money as possible before getting builders in to do the brickwork etc. and have a couple of questions...

The details below are what I have found researching online, I am a DIYer so I am not a professional - please critic/make comments/ recommendations

1) Sewer pipe through foundations:
There is to be a new sewer pipe going through the foundations, looking online is it correct to just leave a gap in the foundation concrete (pipe width to the bottom of trench), and then use 2x concrete lintel for each wall leaf above? (to support single story extension) ...either side wont move as they are not joined...?

Example I found online:

It's ok to leave a full gap to the bottom of trench for the pipe work? :/

2) Is it ok to fill trench fill concrete in stages.. i.e. do a small section at a time wait for it to set, then do next section several days later?

I watched a video where the builder filled their trench with concrete in stages, left it to dry then did the next bit over a few days- I would have thought if you did it this way to have rebar rods in the end joining the set concrete to the new bit you are laying for strength?

I was under the impression the whole length of trench would have to be laid same day?

Example - in the video the strip joining the house has just been poured, the rest is already dry from day or two previous..

 

[^woody^]

Bad example. a foundation should be continuous and done as one pour.

There are several options for shuttering or building around and over a pipe - just don't' look in the same locations as those images.

 

[SpecialK]

That's how building control told me to do mine with regards to the drain pipe.
As for laying the footings in stages....at the end of the day you only need a 300mm(?) deep footing, you then build off it. So what difference is there in laying a 300mm footing and building in blockwork to putting concrete on top?

Ideally do the pour in one go. Is there a reason why you cant?

 

[spikeuk36]

Thanks for comments, reading more online I think I will step down the foundations deeper in the section the pipe will cross over, then step back up and lintel over the top but will clear with BC.

As its my first time i'm dreading pouring the concrete, 90% of my trenches are 1 meter deep extension is approx 5m x 9m as below- (2 story), theres a lot of corners and odd angles, I have to work out volume of concrete, and getting it all level, with a couple of people... if I could split it up would be a lot easier..

 

[noseall]

What nutter drew that extension?

What an absolute nightmare to build! I'd be surprised if anyone would be interested In that combobulation.

 

[spikeuk36]

Yes, I agree, it was a good idea at the time lol., we had to have the strange shape to match the existing house to please council to get it through planning after a ton of revisions as its a old house, lucky its not listed.

 

[Londoner2]

That's how building control told me to do mine with regards to the drain pipe.
As for laying the footings in stages....at the end of the day you only need a 300mm(?) deep footing, you then build off it. So what difference is there in laying a 300mm footing and building in blockwork to putting concrete on top?

Ideally do the pour in one go. Is there a reason why you cant?

300mm?? min is 1m these days.

 

[mikeey84]

300mm?? min is 1m these days.

I'm no expert, but depth under the ground and depth of concrete are 2 separate things to my understanding.

Most people mass trench fill as its easier, but if the ground conditions are right, you can use much less concrete, and use trench blocks.

I think....

 

[RonnyRaygun]

I'm no expert, but depth under the ground and depth of concrete are 2 separate things to my understanding.

Most people mass trench fill as its easier, but if the ground conditions are right, you can use much less concrete, and use trench blocks.

I think....

Correct. Minimum 1.0m in high volume change clay, 900mm in medium, and 750mm in low volume change (from existing or proposed ground level, whichever lower).

However, if the bearing strata is non-shrinkable (sands or gravels for example) then 450mm is fine (although in practice it'll usually be deeper than that).

If you're straight onto rock, just start laying blockwork!

And yes, you can get away with 300mm (or potentially less) concrete as a strip, although most builders do trenchfill as it's easier and quicker than laying blocks in a trench. It is also less susceptible to ground movement if the depth of concrete is greater, although it's possible to install mesh reinforcement into the footing to help deal with differential movement along the length of the footing.

 

[RonnyRaygun]

Bad example. a foundation should be continuous and done as one pour.

Ideally, although NHBC do provide a couple of details for a construction joint if unavoidable.

 

[^woody^]

What nutter drew that extension?

What an absolute nightmare to build! I'd be surprised if anyone would be interested In that combobulation.

LOL, and random measurements to boot which don't work bricks or blocks if its supposed to be rendered!

The window in the bottom LH corner needs to be moved over 7mm, BTW - and someone will still need to find 11mm unless the OP loves the look of joints like Mars Bars

I think the actual drawing of it is worse than the designing of it, and just in case the OP wants a quote, I'm busy for the next three decades. Sorry.

 

[noseall]

I think the actual drawing of it is worse than the designing of it

I can't even begin to imagine the heartache and pain the brickies are going to have setting that lot out.

Bonkers design.

 

[^woody^]

I can't even begin to imagine the heartache and pain the brickies are going to have setting that lot out.

Bonkers design.

More cuts than a Tory Manifesto?

 

[noseall]

unless the OP loves the look of joints like Mars Bars

Known as 'Christmas joints'.

Everyone likes a big joint at Christmas.