Depth of 'chase' into breeze block.


I am currently re-modelling my bathroom. I have had a combi boiler installed and therefore have been able to remove the airing cupboard from the bathroom and am replacing it with an offset quad shower cubicle.
The bathroom is almost square and, looking with a 'bird's eye view', the soil-stack is in the lower left corner with the w.c. connecting directly into it. Along the left wall lies the bathtub and in the top right hand corner and partially down the right hand wall will be the shower cubicle. On the 'top' wall, between the shower and the bath is the wash-basin.
The waste from the shower, wash-basin and bath all link together and drain into the soil stack. Down the left wall is no problem because the drain runs under the bath and is hidden behind the bath panel. The problem is along the top wall because I will have to run the waste from the shower along the top wall, under the wash-basin where the wash-basin drain joins it, and then under the bath. I cannot run the waste below the floor because the joists run in the 'wrong' direction.
I don't particularly want to have the waste from the shower running along the bottom of the top wall to the bath and 'boxing it in', and am considering 'chasing' it into the breeze block wall. The breeze blocks in my house are like chalk - you can dig pieces out with your finger-nail, so the actual digging out of a length to bury the drain would not pose any difficulties. What I am concerned about is the depth of 'slot' that I would have to cut to bury the 40mm waste pipe.
The horizontal distance that the pipe would have to be buried in the wall would be around 800 cm but several breeze blocks would be cut into for at least half their thickness. Anyone have any comments upon how wise it would be to cut so deep into a breeze block inner wall? The wash basin is a suspended type with a stainless steel trap cover but I would also need to bury part of the down-pipe from the basin into the wall to enable it to join up with the buried horizontal drain from the shower.
Shame it isn't a stud wall!
Kev
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On Sun, 16 Mar 2008 13:31:21 -0000, a particular chimpanzee,
produced:

If it's structural, you shouldn't chase it to a depth of more than 1/6th of its thickness - for a 100mm thick wall, 16mm. Any more, and the centre of gravity of the wall lies outside its 'middle third'.
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Hugo Nebula
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randomly hit the keyboard and

Yes, that's my concern. On the other hand the deep chase will be only across a short distance, and in an upper room with no other floor above. I will see what depth of plaster I've got to play with before I start cutting into the breeze block. I may just get away with it without having to cut too far into the breeze block!
Thanks for your response.
Kev
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