Conservatory Foundations

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Lancashire
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Hi All,

I'm having a conservatory built and the company has just dug the foundations. There is a plastic drain that runs along the back of the house and they have dug down about 2ft just exposing the top half of the drain. The company now wants to pour concrete directly onto the drain. I told them this was unacceptable and the drain need protecting from the weight of the foundations/wall. So all they did then was put up a flimsy shuttering - see photo:

//www.diynot.com/network/crooky/albums/

If they pour the concrete now the foundation will not be continuous. It will have a gap at either side of the conservatory.

Any advice would be greatly appreciated. This is quite urgent as they due to pour the concrete later this afternoon.

Many thanks
 
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They should not pour concrete over this.

The foundation must be lower than the bottom of the drain so they have to dig deeper.

The drain must be protected using similar methods to these

http://co-uk.wavin.com/master/maste...7157&middleTemplateName=oc_middle_service_sub

If not you risk it breaking and having to take the conservatory down to fix it.

Edit - You can bridge the drain but the foundation must still go lower than the lowest part.
 
Many thanks for your reply.

I thought this was the case. Everything I've looked at on the internet says just what you're saying.

The company has said if the build was subject to building regs they would do it the way you've stated. Howver, regs don't apply and a deeper foundation isn't required because the structure is comparatively light. This just sounds like a cop out.

What they've now proposed to do is to dig down each side of the pipe, but only about a foot deep and a foot wide either side of the pipe. Am I correct in thinking that the whole trench should be dug deeper? and how deep below the pipe would you recommend they should dig?

Many thanks.
 
Not an expert but as far as I am aware you can step foundations but don't know what the rules are.

As for depth the base of the foundation must be at least as deep as the invert (bottom) of the drain.

They also need to make provision for movement if they are bridging, this is normally done by surrounding the pipe with granular fill and sliding boards at each side of the concrete allowing the drain to move within the fill if the concrete moves.
 
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What they've now proposed to do is to dig down each side of the pipe, but only about a foot deep and a foot wide either side of the pipe. Am I correct in thinking that the whole trench should be dug deeper? and how deep below the pipe would you recommend they should dig?

Many thanks.

the foundation does not need to be deeper than the invert over its entire length, only locally to the pipe. 1m either side.

what they have done is rudimentary but acceptable. so long as there is no weight directly upon the pipe and you have moderate distance from footing to pipe then you should encounter no problems.

in the real world the footing bottom would be a lot lower and the pipe would end up being exposed leaving you with the option to surround the pipe with 'compressible material'.
 
Hi All,

Many thanks for your replies.

I've finally got the company to see sense.

What they are now going to do is dig the entire trench about 15 inches deeper. This will take the overall depth of the trench to about 1 metre. They are then going to pour the concrete about 12 inches deep so that the top of the strip is about 2 to 3 inches below the invert of the pipe.

They'll then come up in brick/block to above the pipe and set lintels in the brickwork, and continue with the brick work. This will leave a void of 2 to 3 inches all around the pipe.

Now, why couldn't they just do that in the first place!!
 

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