what percentage of fall for a new sewer pipe

CamperMan

Hi,

I am about to lay a new sewer pipe outside, it's 1 metre below ground and approx. 5 metres long (150 mm pipes)..

the pipe will start at the house, go along 3 metres, then take a 45 degree bend down to the IC chamber next to the public sewer pipe

what is the fall rate that I should lay the pipes at?

Thanks

kay 9

1:40 is the ratio we were told back in the good old days of plumbing college. I generally just go off level and its A1 tbh. Just don't have too much of a fall;)

headmaster

kay 9 wrote: »

1:40 is the ratio we were told back in the good old days of plumbing college. I generally just go off level and its A1 tbh. Just don't have too much of a fall;)

Kay,
when you say 1;40, are you saying that for every 40ft of piping, you should allow 1 ft of a fall? I'm asking, because it seems like a pretty steep fall, or maybe i'm missing something?

cabledude

I built my house in 2007 and the reg's then were 1:60. I'd imagine they've not changed since.

heinbloed

For a standard household situation 2.5%. In site terms that is between 2-3%. As kay 9 said already.

headmaster

J'sus lads, can ye just tell us in very plain english what the fall is. These %ages and ratios are a bit beyond some of us.

Outkast_IRE

1:40
As in for every 40 feet fall 1
as in for every 40 meters fall 1
as in for every 40 cm fall 1
as in for every 40 mm fall 1

1:40 is 1:40 no matter what system your measuring with.

DoneDL

I thought 1 in 40 applied to 4 inch pipe but isn`t 150 mm a 6 inch pipe?

headmaster

Outkast_IRE wrote: »

1:40
As in for every 40 feet fall 1
as in for every 40 meters fall 1
as in for every 40 cm fall 1
as in for every 40 mm fall 1

1:40 is 1:40 no matter what system your measuring with.

Outkast,
do you mean 1 ft in 40 ft?

heinbloed

1:40 = 2.5% or 25mm per 1,000 mm of pipe

Curly Judge

For every 40 foot of pipe length it should fall 1[one] foot.
For every 40 metres pipe length it should fall 1 [one] metre.
For every 40 light years of pipe length it should fall 1[one] light year.

More seriously, the theory behind this is to have a gentle, leisurely fall so that the waste will sail along gently on the water and keep the pipe clear.
Steeper falls tend to cause the water to rush away leaving the waste behind thus leading to blockages.
This applies to 4 inch[100mm]plastic sewer pipe. Not salt glazed clay pipes .
You are unlikely to come across anything else on the average household site.

Outkast_IRE

headmaster wrote: »

Outkast,
do you mean 1 ft in 40 ft?

same thing, 1ft fall in every 40 ft of pipelength is the same as saying
for every 40ft of pipe length fall 1 ft.

sullzz

Outkast_IRE wrote: »

same thing, 1ft fall in every 40 ft of pipelength is the same as saying
for every 40ft of pipe length fall 1 ft.

Sweet jesus , just go and lay the pipe for him , youve the patience of a saint , id be chewng the key board

headmaster

Thanks fellas, appreciate the trouble in helping me. Sorry if i sounded a bit of a booby, but just wanted to be sure. Going to start on a sewer run tomorrow.

Carlow52

before you do, have a look here
http://www.boards.ie/vbulletin/showthread.php?t=2056431637

This link suggests that as pipe size goes up the required fall goes down so 1: 40 for a 6" pipe may be 2 steep.

Flow rate is also an issue

The regs are here
see page 10 http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,1649,en.pdf

CamperMan

I settled on a fall of quarter of an inch per foot of pipe..

hope this works

heinbloed

To little for a normal situation.

Curly Judge

CamperMan wrote: »

I settled on a fall of quarter of an inch per foot of pipe..

hope this works

I think it will be okay for a domestic situation.
More important is that the rate of fall be consistent without any humps or hollows in the pipe.
To this end I would advocate the use of a 6 foot long, high quality spirit level.
Better still, use a theodolite if you can get a loan of one.
Another important point to remember is that the consistency of the soil under the pipe must be,...well... consistent!
If the trench is dug in virgin soil then it will probably be okay but if the soil is a mixture of old and new,[what we call backfilling], then the new soil could shrink and compact under the pipe leading to the fall becoming undulating in nature.
Some builders use pea gravel under the pipe to help grade out the fall.
Some indeed back fill over the pipe with the same gravel. The theory behind this is that if the earth under the pipe does collapse in any way the pea shape consistancy of the gravel will run around and under the pipe to prop it up and keep it level.
I don't intend to make all this sound like rocket science, it isn't!
But it is the kind of a weekend job that a highly qualified engineer could make a balls of whereas a good builders laborer could fly it.

CamperMan

hope it will be OK, I laid the pipes and backfilled it now.

total length of pipe from the house to the manhole is 7 metres, at about half way, the pipe goes off 45 degrees.. I also used 150mm pipe.. I know I know.. it's big for normal house use.. but that's what we had.. I also added a rodding point...

The ground was "virgin", I graded it to the angle required, then laid sand down, compacted it, laid the pipes, then added more sand, compacted it, then backfilled it...

Curly Judge

CamperMan wrote: »

hope it will be OK, I laid the pipes and backfilled it now.

total length of pipe from the house to the manhole is 7 metres, at about half way, the pipe goes off 45 degrees.. I also used 150mm pipe.. I know I know.. it's big for normal house use.. but that's what we had.. I also added a rodding point...

The ground was "virgin", I graded it to the angle required, then laid sand down, compacted it, laid the pipes, then added more sand, compacted it, then backfilled it...

If the pipe ever does block, which seems unlikely, it will probable be at the 45% bend.
In an ideal world all changes in direction or junctions should have inspection manholes.
Best of luck with your enterprise.

CamperMan

Hello Curly Judge.

the pipes are big 150mm ;-)... I put a rodding point close to the house and about 2 metres from the 45 degree bend, so any blockage will be easy to clear.. that is the idea anyway..

from the 45 degree bend, it's a straight run to the manhole..