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Technical Guidance: Y' Junctions in Drains Under Buildings

A 'Y' junction connecting drains under a building is generally unacceptable according to building standards. Standards require that each drain segment under a building can be rodded for maintenance without entering the building. An exception is that a 'Y' junction connecting a wash hand basin drain to another drain is acceptable due to the low risk of blockages from wash hand basins. Drains serving fixtures like toilets, sinks, and utility sinks should each have their own access point outside of the building.

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3K views1 page

Technical Guidance: Y' Junctions in Drains Under Buildings

A 'Y' junction connecting drains under a building is generally unacceptable according to building standards. Standards require that each drain segment under a building can be rodded for maintenance without entering the building. An exception is that a 'Y' junction connecting a wash hand basin drain to another drain is acceptable due to the low risk of blockages from wash hand basins. Drains serving fixtures like toilets, sinks, and utility sinks should each have their own access point outside of the building.

Uploaded by

n67250
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
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TECHNICAL GUIDANCE

Y JUNCTIONS IN DRAINS UNDER BUILDINGS


5.3/04 March 2013 (Second issue - supersedes Dec 2008)

QUESTION
Is it acceptable to have a Y junction on a drain under a building?

CONSIDERATIONS
NHBC Standards clause 5.3 - D3(a) refers to BS EN 752 for guidance on drainage design. BS EN 752 : 3 Drains and sewer systems outside buildings - planning, says Every drain and sewer length should be accessible for maintenance and cleaning without the need to enter the building. Access to Y branches from upstream may be difficult or impossible to achieve and it is generally unacceptable to require the removal of plumbing fittings within the building to clear a blockage. Experience has shown that the risk of a blockage occurring in a drain run serving solely a wash hand basin is low.

ANSWER
With the exception given below, a drain serving a foul appliance should not be connected into another drain under the building using a Y junction. Each drain should run to an access point outside the building. This access point will enable each length of the drain under the building to be rodded without the need to enter the building. Where installed, a drain serving a wash hand basin (WHB) that connects via a Y junction under the building into another drain should not result in a reportable item being raised.
WC, Kitchen Sink or Utility WHB
WHB ANY

WHB

WC, Kitchen Sink or Utility

WC, Kitchen Sink or Utility

Amended

No Access Point For Rodding

NHBC NHBC House, Davy Avenue, Knowlhill, Milton Keynes, Bucks Tel: 0844 633 1000 Fax: 0844 633 0022 www.nhbc.co.uk

MK5 8FP

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HB1674 06/11

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