Project1_Layout 1 07/05/2013 RCI TECHNICAL NOTE NUMBER 252
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Gutter and outlet sizes (half round eaves gutter laid level, sharp edge outlet at one end)
H3. Rainwater drainage
(1) Adequate provision shall be made for rainwater to be carried from the roof of the building
(2) Paved areas around the building shall be so constructed as to be adequately drained
(3) Rainwater from a system provided pursuant to sub-paragraphs (1) or (2) shall discharge to one of the
following, listed in order of priority –
(a) An adequate soakaway or some other adequate infi ltration system; or, where that is not reasonably practicable
(b) A watercourse; or, where that is not reasonably practicable
(c) A sewer.
Thermostatically controlled, air-jacketed mixers
available in 2 sizes:
• 1.5 drum, 110 volt, caster mounted with lifting point
• 3 drum, 110 volt, caster mounted with lifting point
Keith Roberts is an independent roofi ng consultant.
You can contact him at Roberts Consulting,
2 Gardiner Close, Abingdon, Oxon OX14 3YA.
Tel: 01235 529693
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a lower roof or paved area, a pipe shoe should be
fi tted to divert water away from the building.
The materials used should be of adequate
strength and durability. All gutter joints should
remain watertight under working conditions.
Pipework in siphonic roof drainage systems
should be able to resist negative pressures in
accordance with the design.
Gutters and rainwater pipes should be fi rmly
supported without restricting thermal movement.
Different metals should be separated by nonmetallic
material to prevent electrolytic corrosion.
Alternative approach and other systems
Part H3 also describes in outline, siphonic roof
drainage, eaves drop and rainwater recovery
systems. Readers are then referred onto the
principal British Standard for roof drainage,
BS EN 12056 Part 3. This standard contains
additional detailed information and is one of
the core standards that should be available and
understood by the roof design team.
This Technical Note is no more than a
summary. Readers should refer to Approved
Document H for the full details.
1. Approved Document H: ‘Drainage and waste
disposal’, 2015 edition (62 pages), freely available
roof area (m2)
6 - - -
18 75 50 0.38
37 100 63 0.78
53 115 63 1.11
65 125 75 1.37
103 150 89 2.16
2. BS EN 12056 Part 3: ‘Gravity drainage systems
inside buildings – roof drainage, layout and
calculation’, 2000 (84 pages)