Conservatory Foundation and Soil Pipe Waste Drains and Dwarf Wall


Postby Swalla13 » Sat Jul 30, 2016 7:02 pm

I have been digging footings for a dwarf wall P shaped conservatory and across the length of the bottom of one of the trenches parallel to the house wall is a clay waste drain.
I have ask around what I should do and have been told to put a couple of inches of sand on an angle molded just over the clay waste drain or polystyrene as to keep the foundation concrete from touching the waste drain
,then adding the foundation concrete as normal.
Does any one have any views or ideas on this?

Google searches and diy forums only explain about bridging a drain with lintels that are running through the foundations ,my problem is the drain running along and underneath the foundation.
Any comments would be grateful.
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Postby welsh brickie » Sun Jul 31, 2016 9:59 am

It must be incased in concrete, you need to expose the drain, there should be 450mm of concrete around it, that incudes the area under the drain.
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Postby Swalla13 » Sun Jul 31, 2016 12:03 pm

Do you mean dig a deeper trench to expose the drain or a new 450mm trench in the trench around the drain?
Then fill with concrete to cover drain ,allow to set ,then pour foundations directly onto the encased drain?

my worry about digging all around the drain is disturbing the joints on each of the 4-5 sections of drain as they are only about 2' long. This waste drain is really wide too,maybe 200mm across, so would 125mm all-round encasement of concrete be ok?
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Postby Swalla13 » Sun Jul 31, 2016 12:31 pm

Do I dig a deeper trench to expose the drain or a new 450mm trench in the trench?
Then fill with concrete to encase the drain, when set then pour the foundations directly onto the concrete encased drain?

My worry about digging around the drain is disturbing the joints on each of the 4-5 sections of drain as they are only about 500mm long . This drain is really wide too maybe 200mm so would 125mm all round the drain of concrete encasement still be ok?
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Postby welsh brickie » Wed Aug 03, 2016 5:00 pm

No you need to expose the drain completely, it must be clear under the drain from soil/debris, the concrete foundation must be poured in one go.
No weight must be allowed over the drain, so the concrete under the drain stops this from occurring, allowing you to build on a supported foundation.
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