Dave Osborne, Technical Manager at Swish Building Products, highlights the importance of correct guttering system installation and offers advice on achieving the best results for both new and replacement projects.
The importance of ensuring a correctly installed guttering system on domestic properties and buildings should never be underestimated, as poorly fitted or maintained materials can lead to damage that is costly to repair.
An effective and correctly installed guttering system, fitted around the roof perimeter and securely fastened to the fascias, can be a property’s first line of defence during a heavy downpour, helping to guard against leaks and standing water issues.
By understanding how to choose a system with the appropriate flow-rate and fitting both the guttering and downpipe so the system works cohesively, you’ll be rewarded with a smart installation that will serve to prevent building damage and last for many years to come.
Preparation is key
For both new and refurbishment projects, preparation is key to achieving a successful installation.
For new projects, you should select a gutter system that meets the design flow-rate or area of the relevant roof. As well as normal levels of rainfall, a domestic or light commercial eaves gutter system must be able to cope with intense rainfall lasting at least two minutes. To help you chose the best solution for your project, the British Standard BS12056 shows how to work out the amount of rainwater (in litres per second) that could run off a roof.
With regards to replacement projects, it is a natural decision to replace guttering ‘like for like’. However, you should consider the greater frequency of storms and increased rainfall we now experience and modify the gutter system’s capacity as a positive precautionary measure.”
Planning makes for the perfect project
Start by planning your installation using specific component diagrams that can assist you in selecting the correct materials from the very beginning. Arming yourself with the knowledge of how to correctly install guttering is also key to a successful installation. The below offers a clear and concise overview of how to get started.
Gutter installation guidelines
- Position the running outlet accurately by holding a plumb line against the fascia directly over the drain. Mark the position on the fascia with a pencil. Fit the outlet no more than 50mm below the level of the roof tiles, then fix with 2 x 25mm x 5mm round-head stainless steel screws (do not use countersunk screws as these can be over torqued with cordless drivers, consequently damaging mouldings).
- Fit a fascia bracket just below the top of the fascia board at one end of the run of guttering (opposite end of the outlet).
- Tie a plumb line (string) around the base of the bracket and stretch from the bracket along the fascia board before tying it to the outlet.
- Check that there is a fall towards the outlet (1:350 is recommended) to encourage water to drain efficiently.
- Mark the position of the fascia brackets, spacing them according to the gutter system chosen (see table below) but no more than 150mm from any corner, union, running outlet or stopend.
- In locations where heavy snowfall is prevalent, we recommend that fixing centres for fascia brackets be reduced to 600mm.
- Fix the fascia brackets with 25mm x 5mm stainless steel screws – we would recommend using all available fixing holes.
- Starting at the outlet, fit the first length of gutter by tilting the gutter to fit under the back clip, and clip in at the front edge.
- Fit a union bracket at the other end of the first length and screw it into the fascia using all available fixing holes - then fit the next length of gutter into it. Continue joining lengths ensuring all joints line up with the “fit to here” depth marked in the fittings.
- Cut the last section of gutter to fit using a hacksaw and fit a stopend.
- Use lubricant/silicone spray on all gutter seals for ease of fitting and for improved in-service performance.
Downpipe Installation Guidelines
- Using a plumb line, mark a vertical line on the wall from the running outlet to the drain.
- Place an offset bend onto the base of the running outlet. Place a second offset bend on a length of downpipe and measure the section length required to join the two offset bends, cut a suitable length of downpipe – the “swan neck”.
- Hold a downpipe clip centrally over the plumb line and mark the fixing holes on the wall with a pencil. Repeat down the wall, spacing pipe clips no more than 1.8m apart.
- Drill the fixing holes.
- Working from the top downwards, install the downpipe. If additional lengths of downpipe are required, join using a socket and pipe clip.
- Leave a 10mm gap between the end of the pipe and the bottom of the pipe socket to allow for expansion. Fix a pipe clip over the joint.
- Use wall plugs suitable for the substrate and when fitting pipe clip screws to ensure that the application is secure. Fix pipe/socket clips with 2 x 32mm x 6.5mm round head stainless steel screws.
- Where required, fit a shoe at the bottom of the downpipe so that it directs water into the drain, if required. Fix the joint with a pipe clip.
The installation of guttering may appear to be a straightforward task, but by considering the style and shape of the building on which you are installing the guttering, and the increase in inclement weather we now experience in this country - as well as preparing and planning in advance - you will ensure you deliver a first-class project, first time.