Extension Footings / Foundation

[si1984]

Hi all,

I should start by saying I have very little clue when it comes to anything buildings related so I apologise in advance for any stupid questions.

My wife and I are currently having an extension installed to the rear of our property, replacing our conservatory. We have appointed a contractor and work started approximately 2 1/2 weeks ago.

There is a public sewer running along the back of the property (previously under the conservatory) which we have got a build over agreement for from the water board. The agreement states that foundations must be at least 150mm below the invert level of the sewer/manhole. These have been dug to the appropriate depth which the surveyors are apparently satisfied with.

After removing the old conservatory, it exposed pipework from our kitchen and also the soil pipe from our bathroom. We noticed after a couple of days that one of the trenches started filling with water but it was difficult to know where this was coming from. The builder initially suggested it was running from the kitchen pipe and stated that this was going to be replaced anyway. However, on inspection there was a a crack in the soil pipe (again, something they said would be replaced). Nothing seemed to be done to rectify this issue until I asked the building to carry out a temporary fix until the pipes were replaced. Even then, the temporary fix seems very temporary as it looks like they have just moulded some of the clay soil that has been dug up around the pipe. Subsequently, the drain for the kitchen water was clearly blocked so this has caused even more water to pool up in the trenches, with one being about a foot deep now. The foundation is due to be laid tomorrow and my concern is that they will just pour the concrete on top of the water. This seems madness to me and from a quick internet search, my concern seems justified. However, the builders are adamant that this won't be a problem.

Who am I to question these 'experienced' builders and I don't know where to turn to seek advice or reassurance that what they are doing is correct and ultimately that I'm not going to be faced with a huge issue in the future due to their poor workmanship. Is this something that Building Control will get involved? I plan on speaking to the water boards surveyor when they come out later today but conscious that their concern will be with the drains rather than the building work itself.

Any advice will be greatly appreciated.

 

[^woody^]

What's the actual question, I can't make it out

 

[Notch7]

Hi all,

I should start by saying I have very little clue when it comes to anything buildings related so I apologise in advance for any stupid questions.

My wife and I are currently having an extension installed to the rear of our property, replacing our conservatory. We have appointed a contractor and work started approximately 2 1/2 weeks ago.

There is a public sewer running along the back of the property (previously under the conservatory) which we have got a build over agreement for from the water board. The agreement states that foundations must be at least 150mm below the invert level of the sewer/manhole. These have been dug to the appropriate depth which the surveyors are apparently satisfied with.

After removing the old conservatory, it exposed pipework from our kitchen and also the soil pipe from our bathroom. We noticed after a couple of days that one of the trenches started filling with water but it was difficult to know where this was coming from. The builder initially suggested it was running from the kitchen pipe and stated that this was going to be replaced anyway. However, on inspection there was a a crack in the soil pipe (again, something they said would be replaced). Nothing seemed to be done to rectify this issue until I asked the building to carry out a temporary fix until the pipes were replaced. Even then, the temporary fix seems very temporary as it looks like they have just moulded some of the clay soil that has been dug up around the pipe. Subsequently, the drain for the kitchen water was clearly blocked so this has caused even more water to pool up in the trenches, with one being about a foot deep now. The foundation is due to be laid tomorrow and my concern is that they will just pour the concrete on top of the water. This seems madness to me and from a quick internet search, my concern seems justified. However, the builders are adamant that this won't be a problem.

Who am I to question these 'experienced' builders and I don't know where to turn to seek advice or reassurance that what they are doing is correct and ultimately that I'm not going to be faced with a huge issue in the future due to their poor workmanship. Is this something that Building Control will get involved? I plan on speaking to the water boards surveyor when they come out later today but conscious that their concern will be with the drains rather than the building work itself.

Any advice will be greatly appreciated.

its not clear what the exact issue is however:

In general, foul drainage pipework would normally be installed and connected up if it crosses a foundation trench -before concreting the founds.


I wouldnt necessarily assume you have bad builders, we need more info - a picture showing the overall site would be helpful

 

[oldbutnotdead]

Are your old broken drains going to be buried or difficult to get at when the footings are poured? If yes then they need fixing before muck goes in the hole, if no then calm down.
Well worth verifying that the stray water is actually coming from the kitchen drain- food dye down the sink and see if the trench gets colourful used to be the trick. And different coloured dye down the loo to verify that one.
Water board inspector may get stroppy if they see sudsy greasy water just draining into the land so wld advise not running the washing machine tonight

 

[si1984]

I warned you that I was clueless.

My biggest concern is the effectiveness of the foundation if pouring concrete directly on to a puddle of 6+ inches of water (which would appear to be foul water). It could be that this is common practice but I just don’t know.

I have attached a few pictures which might help understand my question. It should be noted that some of the pipe work had been installed today and is (clearly) not finished.

I had a quick chat with the water authority chap this afternoon and he assured me that they are doing a good job so this is positive.

 

[oldbutnotdead]

Pouring concrete into a puddle isn't a problem. If it was sink water and there was a lot of sugar in it then you'd have problems.
There's an awful lot of flex connectors on that pipework, looks as if builder is only replacing where he's had to break into existing. Given it's all going to be under your extension it would be much better practise to renew the lot. Yes it's a bit more digging and a bit more cost but how old are those clay pipes?

 

[^woody^]

No foundation should be poured into water. The bottom of the trench will be soft and this will massively increase the risk of excessive initial settlement or later movement.

Water should be pumped out and the bottom scraped down to firm soil.