COP v3.0:roof-drainage; gutter-installation-and-maintenance

5.5 Gutter Installation and Maintenance 

Spouting should be installed with the back lower than the fascia board or cladding to allow for draining of overflow water through the gap between the gutter back and the fascia.

A 2 mm gap between the back of the gutter and the fascia will give a discharge area equal to the diameter of a 75 mm downpipe for every 2.2 m of gutter run.

This gap is only totally effective if the spouting is correctly maintained and the gap is free of debris.  A designed outlet is preferred, either a gutter bracket creating a minimum 6 mm space stop end weir, a raised outlet above the spouting sole, a slotted front or a low fronted gutter.

A weir stop-end, or an outlet with a top edge above the sole of the gutter, can be used to increase outlet capacity.

5.5.1 Maximum Gutter Length 

All gutters are subject to expansion. Maximum gutter-length is determined by the type of metal and its colour. Where gutters have an allowance for expansion (such as an external gutter on a typical gutter bracket or an internal gutter with sliding clips), lengths should be restricted to 25 m in steel and 12 m for copper or aluminium.

An expansion joint can be either a sump, rainwater head or a saddle flashing. Gutters that are directly through-fastened to the fascia or eaves purlin will not be free to move and should be restricted to a maximum of 12 m. Through-fastened gutters are not recommended as they are difficult to replace.

5.5.2 Gutter Support Systems 

The spouting bracket system must withstand the potential weight of a gutter full of water. In snow load areas, spouting may be fitted with snow straps and brackets at a maximum of 600 mm centres to withstand the additional potential weight of any snow build-up.

Brackets should be made using compatible material or non-ferrous metal. Brackets for pre-painted external gutters should be painted or powder coated before installation.

Brackets for external gutters should be located close to all stop-ends, at both ends of sumps and rain-heads at a maximum of 750 mm spacing for gutters less than 180 mm wide, and at 600 mm for gutters 180 – 300 mm wide. Brackets must be installed to provide a 1:500 (2 mm per metre) minimum gutter gradient towards the outlets.

5.5.3 Gutter Maintenance 

Gutter or spouting blockages can cause flooding because of the build-up of debris. Regular inscpection and maintenance must be carried out to ensure that gutters are free draining, overflow outlets can also prevent damage.

The COP does not recommend permanent gutter leaf guards. Although they do prevent large pieces of debris from obstructing the outlets, they allow finer particles to collect on the sole of the guttering. Without regular maintenance, the prolonged wetting of the interface between any debris and the metal can lead to early corrosion of the roof or gutter. The decay of organic matter such as leaves can produce organic acids, which will also accelerate corrosion.

The build-up of matter on the upper surface of the leaf guard can also form a poultice, which increases the time of wetness and acidity and can accelerate corrosion of the roof sheet ends.