Gutter Outlets

The correct number, positioning, size and type of outlets are all factors that affect the drainage performance of the rainwater system. As a general rule it is good practice to allow at least two outlets in any one length of gutter. Outlets are designed to achieve the required discharge rate based on the head of water in the gutter. In order to optimise the design of the system 4 types of outlet may be used.

Straight outlets are normally used for eaves, valley and boundary wall conditions where design conditions are not onerous.

Tapered outlets offer best performance and economy for most valley and boundary wall gutters. The opening in the sole of the gutter tapers into a standard diameter downpipe of 100 or 150 mm.

Box receivers are used for demanding flow conditions where practical conditions such as restrictions to downpipe position may otherwise restrict system performance.

Syphonic outlets employ design methods outside of that described in BS6367 and are usually designed and supplied by specialists. They operate on the principle that the drain pipes flow full of water by not allowing air to enter the system. Syphonic outlets are easily incorporated into the Ward gutter range.

Weir overflow outlets positioned at the ends of the gutter cannot prevent flooding of the gutter profile but are recommended, since they can provide warning of blocked outlets or other problems with the gutter system. Gratings or wire balloons to protect the rainwater pipe are a potential source of blockage and are not recommended for conventional systems.

Rainwater Pipes

Rainwater pipes are normally circular in section and made of PVC or Aluminium and supported by brackets to the structure typically at 2.0 m centres. Bends and joints should be kept to a minimum and horizontal pipe runs should have falls and be designed to normal hydraulic principles.

Syphonic systems involve greater design pressures and require special considerations.

Typical Applications

Materials

Gutters are normally fabricated from pregalvanised steel to BS EN 10142. Two galvanising thicknesses are available namely Z275 and Z600, indicating the coating weight, including both sides, in grams per square metre.

Specification of the galvanising weight is dependant on the exposure conditions and required life span of the building. In certain cases post galvanised gutters may be specified, this finish, due to the coating process, will require a minimum thickness of 3mm.

Steel gutters of normal design dimensions require a minimum recommended thickness of 2mm. Experience has shown that gutters with sole dimensions in excess of 450 mm will require 3mm minimum thickness.

Durability

The cost and probability of maintenance will influence the choice of material and the galvanising thickness. Black bitumen coatings or similar are required on all steel gutters. These should be applied after about 12 months weathering of the new galvanised steel and will require regular re-application to remain effective. To minimise on site painting, the gutters can be supplied with a factory applied protective coating which includes manufacturer's performance warranty. Advice on periods to first maintenance and environmental conditions is outlined in Corus' Galvatite technical manual.

Gutter Accessories

Gutter accessories such as weir outlets, stop ends, jointing mastics and joint connectors are supplied using materials that are the same as or complimentary to the gutter profile used. Custom made accessories can be made to suit each unique building application.

The following should be incorporated into the maintenance program:-

Gutters, rainwater pipes, outlets and gratings should be inspected and thoroughly cleaned at least once a year. This should occur more frequently if :-

. The building is in an industrial area with significant discharge of airborne waste (paper, packaging etc) . The building is near trees. . The building is in an area subject to extremes of temperature. . The gutter is equipped with high performance outlets.

Maintenance

Maintenance of a rainwater system is vitally important, almost as important as the initial design. All work must be carried out by qualified operatives complying with all current legislative safety requirements.

A responsible person should be delegated within the building owner's organisation to monitor and ensure that the above processes occur. Failing this an external contractor or consultant should be appointed.

The system should be inspected every five years by a specialist contractor or consultant, to check for component decay, damage or unauthorised alteration to the original specification.

All maintenance works must be carried out by complying to all current safety legislation.

Installation

Installation must be carried out by qualified operatives complying with all current legislative safety requirements.

Gutters are assembled so there is a joggle at the leading end. Seals must be fitted with care, in clean dry conditions avoiding any tendency to stretch the seal over bends in the profile. Prior to tightening the bolts correct alignment and seating of the gutter on its supports are checked. All bolts are tightened, starting from the centre of the sole working outwards to each side of the profile. Outlet positions, where possible, should be factory installed however if they are cut on site all burrs should be removed to avoid corrosion and ensure adequate surface for sealing. Damage to the gutter surface must be treated and all debris removed from the gutter prior to progressing with other roofing works.

Insulation

It is normally recommended that gutters have less insulation than the roof to enable prior melting of snow and ice. In practical terms this can be achieved by lowering the overall insulation 'U' value compared with the roof, for example use 0.6 'U' value for the gutter insulation where the roof has 0.45 'U' value.