Green Building Forum - What is the maximum gradient for a foul drain? Mon, 25 May 2026 22:12:19 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211227#Comment_211227 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211227#Comment_211227 Tue, 14 Oct 2014 10:52:52 +0100 Triassic
The ground slopes and the gradient is around 1:21 over the first 40m and 1:100 over the rest.

What is the maximum gradient I should be looking at to meet building regs ? Also are there any rules on manhole size as I want to keep them a small as possible as they will be in lawned areas. Do I have to use any special bedding materials when installing the pipe?]]> What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211230#Comment_211230 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211230#Comment_211230 Tue, 14 Oct 2014 11:37:43 +0100 Jamster What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211234#Comment_211234 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211234#Comment_211234 Tue, 14 Oct 2014 12:01:43 +0100 PaulJ What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211239#Comment_211239 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211239#Comment_211239 Tue, 14 Oct 2014 12:58:42 +0100 nigelm
"If a gradient is too steep i.e. steeper than 1 in 40, the liquid may run faster than the solids in the sloping foul water pipe thus leaving the solids stranded, which could then block the pipe.
If the gradient is not steep enough, i.e. less than 1 in 110, then the pipe could still block if the solids slow down and become stranded."]]> What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211241#Comment_211241 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211241#Comment_211241 Tue, 14 Oct 2014 13:20:18 +0100 jamesingram
pipe diameter divides by 2.5

so 100mm/2.5=40 so 1:40 gradient ( self cleaning gradient for intermittent or low flow rates)

see part H as mentioned for exact info.]]> What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211254#Comment_211254 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211254#Comment_211254 Tue, 14 Oct 2014 15:53:19 +0100 borpin
For the 1:21 you may need a backdrop drain (google it).]]> What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211258#Comment_211258 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211258#Comment_211258 Tue, 14 Oct 2014 18:04:37 +0100 Triassic
Goggles backdrop - yep, can do that.]]> What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211264#Comment_211264 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211264#Comment_211264 Tue, 14 Oct 2014 20:43:51 +0100 borpin Posted By: TriassicAny idea how much pea gravel for a 63m run of pipe?Depends how much you use!! Seriously, few people put 100mm on top, depends what your backfill is like.

Oh and do not gravel to top of pipe and leave exposed if likely to rain. If the trench fills with water the pipe floats to the top and all the gravel along the sides ends up under the pipes. Had to re-lay 30M of pipe on my first build Grrrrr.]]> What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211265#Comment_211265 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211265#Comment_211265 Tue, 14 Oct 2014 20:55:14 +0100 PaulJ What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211281#Comment_211281 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211281#Comment_211281 Wed, 15 Oct 2014 09:56:43 +0100 ringi What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211412#Comment_211412 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211412#Comment_211412 Fri, 17 Oct 2014 21:01:47 +0100 Triassic http://www.pavingexpert.com/gradient_01.htm]]> What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211414#Comment_211414 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211414#Comment_211414 Fri, 17 Oct 2014 21:24:47 +0100 PaulJ What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211895#Comment_211895 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211895#Comment_211895 Sun, 26 Oct 2014 10:43:56 +0000 Triassic What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211900#Comment_211900 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=211900#Comment_211900 Sun, 26 Oct 2014 11:41:35 +0000 PaulJ What is the maximum gradient for a foul drain? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=214703#Comment_214703 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12674&Focus=214703#Comment_214703 Fri, 05 Dec 2014 07:09:38 +0000 Triassic