Eaves gutters rainwater systems

In cold climates, snow retention systems should be installed to prevent snow slipping onto the gutters from the roof. This can quickly overload the brackets and damage the gutter – local regulations may apply. If this is not possible for any reason then the gutter’s front edge should not be higher than the projected line of the roof.

Universal outlets. There are various standard dimensions to provide a number of gutter / outlet combinations. The outlet is hooked around the gutter and is free to move so it does not limit thermal movement. Running (spigot) outlets are soldered to the gutter, so they do limit thermal movement and therefore an expansion joint must be placed a maximum of 7,5m from them. It is good practice to provide an outlet next to internal angles to deal with the extra flow at that point from the valley gutter. Depending on the size of the roof, a corner hopper may be beneficial.

The drainage capacity of the rainwater system is affected by the capacity of the gutter to carry rainwater to the outlet, and the capacity of the outlet and rain water pipe to drain that water. In normalised eaves gutter systems, outlets, downpipes and gutters are designed to create free discharge conditions, meaning that only the gutter run needs to be calculated. Using EN 12056-3, which assumes free discharge conditions, the following tables giving gutter flow capacity and the effective roof area able to be drained by a gutter run is shown. These figures assume nominally level gutters and no wind effect on the effective catchment area. It should be noted that for each corner within the run with a change in direction greater than 10º, both the discharge capacity of the gutter and the roof area it can drain must be reduced by 15%. Further reductions are needed if the outlet is fitted with a leave guard. For more information on the dimensioning of hanging gutters, please consult our technical department.

Gutters lengths are joined end to end and connected to corners and expansion joints using soft soldered joints.

Eaves gutters should be installed to a slight fall to aid their self-cleaning. Ideally 3 – 5mm / m but at least 1mm / m. This also gives them added flow capacity.

Gutter brackets should be fixed at centres varying from 700mm to 900mm according to the expected snow loads, or can be fixed to line up with standing seam centres (more expensive than the former but generally it looks much better). Two main types of bracket exist – roof fitted or fascia fitted. Roof fitted brackets must be rebated into the substrate to fit flush with the surface. They should be securely fitted, which means they should be either nailed or screw fixed through to the rafters (which in turn means they will not line up with standing seam centres) or alternatively fitted to an eaves board made of solid softwood which allows the brackets to be fixed independently of rafter positions and thus to line up with seam centres – see drawings.

Gutters are installed to allow for thermal movement and the entire system is designed taking this into account. The gutter brackets allow the gutter to slide over them and expansion joints are placed every 15m maximum (7,5m maximum from corners or running outlets) to keep expansion within limits.

Downpipes are fixed to the wall at centres not exceeding 3m using downpipe brackets. These are positioned at the top of each pipe, just below the sleeved end to end downpipe joint (which is slightly wider) and therefore cannot slip through the bracket. The downpipes should be lapped 50mm within each sleeved joint. The pipes should be fixed at least 20mm away from the wall.