BUILDING REGULATIONS
Brett Martin Rainwater installations should be designed to comply with the following:

The Building Regulations 2002, Approved Document H, Section H3.
Building Standards (Scotland) Regulations 1990, Technical Standard M2.6-M2.7.
The Building Regulations (Northern Ireland) 1990, Section N7, Technical Booklet N:1990: Section 3.

Comprehensive guidance on the design and installation of rainwater systems is given in BS EN 12056-3.2000 Roof Drainage Layout and Calculation.

UNDERGROUND DRAINAGE
It is necessary to dispose of the runoff collected by Brett Martin Rainwater systems in an efficiently designed underground drainage system. A Local Authority may permit the runoff to be conveyed in a combined sewer and rainwater system, or in a separate rainwater only system. Complete Brett Martin Drain and Surface Water systems are available for these applications - see Brett Martin Drainage Handbook.

SNOW LOADING
Heavy snow falls can create hazards on steep roof pitches and on smooth roof surface finishes when the accumulated snow slips down and off the roof. Additional support brackets (maximum 600mm centres) can cope with some extra snow load. Where 160mm industrial gutter is fitted, the multi fix fascia bracket (BR60) must be used.
However, the combination of heavy load and the slip likely to be encountered on roofs of all pitches in mountainous and northerly regions of the UK necessitate the fitting of snow boards close to eaves to prevent damage to the installation. Wherever fixing holes are provided in any gutter fittings, these must be utilised during installation

RAINFALL INTENSITY
Rainfall intensity in the UK varies with location and surrounding topography: a rainfall intensity of 75mm / hour is usually taken as the UK maximum when calculating the discharge requirements for gutter, downpipe and underground drainage systems.


ROOF DRAINAGE REQUIREMENTS
The amount of rainwater collected by a given roof area largely determines the choice of gutter system to be used and the number and positioning of the outlets. It is necessary to calculate the effective area of a roof and to relate this to the draining capabilities of the Brett Martin Rainwater systems.

GUTTER FLOW CAPACITY
The draining capacity of a gutter system is determined by the gutter gradient and the size and positioning of the outlets.

112mm ROUNDSTYLE RAINWATER SYSTEM 1:600 FALL OUTLET AT CENTRE OUTLET AT END FLOW CAPACITY 2.43 l/sec 1.31 l/sec MAX ROOF AREA 116mˆ 2 62mˆ 2

114mm SQUARESTYLE RAINWATER SYSTEM 1:600 FALL OUTLET AT CENTRE OUTLET AT END FLOW CAPACITY 3.03 l/sec 1.52 l/sec MAX ROOF AREA 144mˆ 2 72mˆ 2

115mm DEEPSTYLE RAINWATER SYSTEM 1:600 FALL OUTLET AT CENTRE OUTLET AT END FLOW CAPACITY 4.58 l/sec 2.31 l/sec MAX ROOF AREA 220mˆ 2 110mˆ 2

160mm HALF ROUND RAINWATER SYSTEM 1:600 FALL OUTLET AT CENTRE OUTLET AT END FLOW CAPACITY 6.47 l/sec 3.23 l/sec MAX ROOF AREA 310mˆ 2 155mˆ 2

INFLUENCE OF GUTTER ANGLES
When there is a gutter angle closer than 2m to the outlet, reduce the effective roof area that can be drained by 10%. When there is a gutter angle more than 2m from the outlet, reduce the area that can be drained by 5%.

CALCULATION OF EFFECTIVE ROOF AREA

FLAT ROOF
For a flat roof the effective roof area is simply the plan area of the roof.

SLOPING ROOF
For complex roof structures involving several or unequal slopes, a method of calculation is given in BS EN 12056 - 3: 2000. In the case of simple roof slopes, as illustrated below, the effective roof area is derived from the formula E= (B+C/2) x L where
B= half roof span (m)

C= ridge to eaves height (m) L= slope length (m) E= effective roof area (sq. m)

EFFECTIVE AREA OF WALLS
Walls above abutting roofs drain on to the roofs below, adding to the amount of water which the rainwater system fitted to the roof has to convey.

For a single wall the effective catchment area is taken to be half the area of the elevation. E=1 /2 (L1 x H1)mˆ 2

RAINWATER RUNOFF
The amount of rainwater runoff R from a calculated effective roof area E is given by the formula:
R=0.021 x E Litres/sec