Downpipe installation

It is very important when installing a rainwater drainage system to a building, that it is installed correctly to prevent damage to the building structure from water ingress. If you follow manufacturers guidelines and the building regulations document (H) the installation should be spot on.

Before starting work, identify the position of the drain at ground level, run a plumb-line and fix gutter outlet above, to line up with the drain below that the rainwater pipe will be discharging into. Check that the fascia board that the gutter brackets are to be fixed to has been fitted level.

Start by fixing the gutter support brackets, with 2 corrosion resistant screws at furthest end on the fascia board. Keep the bracket as close to the underneath of the roof tiles as possible. Fit the gutter brackets to the recommended distance apart of 1 metre maximum.

Run a string-line from the gutter bracket to the outlet, wrapping it 5 or 6 times around the end gutter bracket at the bottom, repeat at the outlet keeping the line taut to prevent sagging. This can be used now to fix the remainder of the brackets to the correct fall of 1:600.

Fix the gutter brackets evenly spaced, slide each bracket up until the bottom of it just touches the string line and screw to the facia board

It is good practice to have the brackets at an equal distance apart, e.g. 4.25m of guttering gives an equal distance of 850mm when divided by 5. This also gives better support than the 1 metre maximum.

Run all the brackets around the fascia board, checking the fall is at least 1:600. This would give a fall of approximately 1.6mm every metre. Again, this is only a recommendation, on shorter runs the fall can be up to 3mm per metre.

On long runs if the fall of the gutter was too excessive, the gutter running towards the outlet end would be so low beneath the roof tiles, there would be a possibility of the rain water running off the roof and overshooting the gutter.

There is always an allowance for expansion required when installing lengths of guttering. When fitting the gutter into a joint, ensure that it is clipped it into the ‘insert to here’ line, usually giving around a 10mm gap.

This insert line can be found indicated on inside the fitting. Be sure not to push the gutter tight up against fitting stop, otherwise expansion will not be allowed for and the gutter will buckle, twist or sag, causing problems with guttering drainage and visually look like an unprofessional installation.

Where the gutter is taken around corners the corner angles need to be supported by fascia brackets positioned as close as possible to the angle. The 90° are always prone to fall on the corner of the building, unless well supported.

When all of the fittings and guttering has been installed, double check the falls to all outlets by placing the level inside the gutter.

When clipping in the gutter, use both hands on the front of the gutter either side of the front clip, and your 2 thumbs pushing up on the front clip until the gutter is in place.

At certain outside temperatures clipping the gutter into the fittings can sometimes prove difficult, apply some silicone lubricant and it should make the process a lot easier.

Never use any other lubricant especially washing up liquid as this reacts chemically with the seals and can cause them to crack or split. Never cut the profile of the gutter down, as this will cause leakage to occur on the gutter joints.

When installing the rainwater downpipes, ensure all 45° bends are fitted the correct way around and have pipe fitted inside, to prevent leakage.
Attach the swan-neck (the two 45° bends) to the outlet with a short piece of pipe connected to the spigot end. Fit a pipe clip to the pipe just below the swan-neck and grip the clip to the pipe and mark the wall with a pencil.

Use a chalk loaded plumb line from one of the clip holes that you have marked with the pencil, then drop the line until it remains vertically level. With assistance ping the line against the wall. Your clips can now be fitted vertically plumb, to maximum of 1.8m intervals. Again, it is recommended to divide your drop length into equal distances to give an aesthetically pleasing look, also more support and strength to the pipe.

Using this method is particularly useful on long drops of two storeys or more, where the scaffold is in place. On shorter drops a laser or spirit level can be used.
Always fix the rainwater downpipe clips, using non-corrosive screws. Finally check the pipes vertical using a spirit level.

By following these recommendations you should have an external rainwater drainage system that is maintenance free for many years.