Typical Gutter & Downpipe Analysis

Note: that for the same discharge rate, arrangement b only requires half the capacity of arrangement a. This shows that outlets at stop ends can be less efficient

Gutter Design

Eaves Gutters Flow capacities for individual shapes and lengths for gutters, outlet sizes and downpipe arrangement can be calculated by designers or Kingspan’s Technical Design Bureau.

As eaves gutters are outside the building envelope the design is less critical than for a valley, hip, parapet or boundary wall gutter, for this reason freeboard is not usually calculated in eaves gutter designs.

Valley, Hip, Parapet and Boundary Wall Gutters

These are effectively part of the roof construction and the consequences of overflow or leakage are serious, so their correct design and installation are very important.

As they are part of the roof they must also be insulated to comply with Parts L2 and J with respect to avoiding excess heat loss, thermal bridging and the risk of condensation.

Kingspan manufacture a range of insulated gutters for which the Psi Value (Y) and condensation risk f-factor values have been calculated as illustrated in the relevant product sections of this guide. Gutters should be wide enough and sufficiently strong to allow foot traffic during installation and maintenance and comply with CDM Regulations.

Industry guides to good practice recommend minimum sole widths of 500mm for valleys, and 300mm for parapet and boundary wall gutters.

In general the shape of these gutters will be dictated by roof slope, design flow rate and the dimension between downpipes.

An additional ‘freeboard’ over the maximum water level is recommended to allow for splashing and waves (up to 75mm).

Gutters and outlets have to be dimensionally integrated into the building’s structural/secondary steelwork.