Is there any legal requirement regarding the depth of 5" plastic drains in
a house's back garden? I've just acquired a property where a pipe run has
been left only partially buried in shallow trenches. I guess the owner
planned to raise the surface of the surrounding ground. I have now raised
the level of the surrounding ground using broken concrete blocks, (which
needed disposing of anyway). If I then make sure the drains (and broken
blocks are covered by 4" of crushed limestone aggregate, is that
sufficient? Is that a suitable material to cover the work with? Part of the
pipe run is for sewerage and part is for rainwater drainage which runs unto
the sewerage section.
The drain is close to the back of the house, so no vehicles are likely to
drive over them, except at one section, which is the rainwater drainage
section. Should I encase the drain in concrete at that section?
mmm legal requirements or not I'd start off investigating as quietly
as poss. if anyone (in authority) knows about this 1/2 finished work -
if they do and they are expecting and requiring it to be done properly
then they are the ones you need to please and they are the ones who
will tell you what to do...
If no-one knows or you fancy a gamble - cover it over as you see fit -
10mm pea gravel is usual for bedding and covering drains - depth I
don't know offhand but someone will be along with the "offical" line
soon. Where the vehicles "may" run then concrete encasement would
probably be a better bet.
I got to know a lot about bloody drains, building this house. And got to
like them, too.
The most overriding requirement is to get the fall right: This is
subject to building control as is the second most important thing, to
keep them straight and arrange a manhole or rodding point when they are not.
They should ideally be bedded in something that wont cut into them - pea
shingle is a good cheap solution. Limestone and rubble is not. Its OK
higher up, juts not round the pipes, if any vehicles are ever to go over
I do not believe there is a minimum depth: they are not as far as I
remember subject to protection against freezing, as half the time hot
water goes down them. This is in direct contrast to incoming mains that
do have a minimum depth for anti-freeze reasons!
The final requirements are to be moderately gas tight to ensure no leaks
of foul water into the local ground water, and to be vented againts
build up of methane and the like.
That is an entirely different reason for venting compared with the other
requirement that may be fulfilled by a vent or air admittance valve, and
that is to not have the suction of a flushed loo or emptying bath suck
traps dry, and allow noxious odours into the bathroom..
Oh and there is a minimum diameter constraint for non pumped systems as
That's about it.
no minmum depth. Heck lots of soil pipes run down the sides of buldings
from upstairs loos, and those can, and do freeze!
Many thanks for the helpful response! Yes, you confirm my suspicion: that
the work was actually approved by building control, but has just not been
covered over. I must go and buy the said pea grave...
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