There are many methods to installing gutters, with each regular installer favouring a preferred method. Here is an explanation of a common method, and one that I personally favour. As an easy example that covers all the common components of a run of guttering, we will look at a return around an internal corner between 2 gable ends.  

The first step is to quickly assess the underside of the fascia for level, as we will be using this as a reference point to mark out our bracket locations. On a new roof, the fascia should be perfectly level, making it a useful reference point. On an existing roof, the fascia may have sagged. By checking the fascia we can determine if it is running out. If it is running out, we may have to use a laser level, or a spirit level to mark a level reference line around the fascia. We can also use a string level bubble to aid us in the installation if we can't reference off of the fascia. With this information in mind, we can take a bracket and determine where we want it to sit at the high end of the run in relation to the tiles. By marking the top of the inside of the bracket, we can set a combination level to this point off of the bottom of the fascia.  

In most instances, the overall profile of the unions, outlets, and brackets differ, so the important measurement in our scenario is the distance from the bottom of the gutter, or inside of the fittings, to the bottom of the fascia. With this measurement set on the combination square, we can move over to the position of the outlet to begin our installation. For most scenarios, the downpipes will be installed plumb directly down the side of a building from the outlet to a drain. As such, we can use a level to plumb up from our existing drain until we reach the fascia line. We can take the line all the way up to the underside of the soffit, and use a square to pull this line forwards to the front of the fascia. This line represents the centre of the outlet and the downpipe. By measuring the distance from the highest point of the gutter to the outlet, we can approximate the amount of fall that we will need. In this instance, we are utilising 3 standard 4m long lengths worth of gutter. The total run is approximately 12 metres. With a fall of around 3mm per metre, we can assume a fall of 36mm over the guttering will be sufficient. We can use our combination square to make reference points on the fascia either side of the centre line. We can measure down from these points 36mm to find the location of the top of the outlet. From here, we can use our registration marks to align the outlet, marking the centre of the mounting holes. Mounting these outlets in the perfect alignment can be difficult, and I find starting the screws then removing them before the install helps to align things. With the outlet mounted, we can double check that it’s in the correct location and that it's close to level.  

From here, we must install a bracket at the correct height at the furthest point away in a straight run from the outlet. This bracket will allow us to attach a string line to, that we can then use to install all of the other fittings in the run. In this scenario, the furthest bracket away is just before the internal corner, and will support the corner fitting in place. These corner fittings don’t typically have mounting holes, and must be supported by brackets that are installed nearby. By holding a corner fitting and bracket in the corner, we can see where the bracket will be seated. By making a mark of this position, we can take an approximate measurement from the outlet to the last bracelet of the run. In this instance, the distance is 6 metres, or 1 ½ 4m lengths of gutter. This means that this last bracket in the run will sit approximately half of the fall of the total run of gutter - 18mm down from our initial combination square mark. By marking and measuring down this distance, we now have both of the reference marks required to align the bracket in the correct position. With the brackets fixed in place with multiple screws, we can attach a string line between it and the outlet.  

First, remove the rubber gasket from the outlet, as this will interrupt our string line alignment. Place the loose end of the string through the hole in the outlet, and wrap it around the fitting, back into the top of the fitting, and hooked over the far clip. This will secure the string in the correct position for our intention. Pull the line out all the way to the fixed brackets, and wrap it over the bracket a few times. With the string pulled relatively tight, we can tie a half hitch or tension the string somehow to secure it in place. Note that we cant pull it as tight as we typically would for other string line tasks, as we risk snapping the relatively brittle plastic fittings. With the string line in place, we now have a straight reference from the outlet to the halfway point that rises half the distance of the fall over its length. We can use this string line to align the top side of the rest of our fittings for this run.  

Using a tape measure or metre rod, we can set out the position of the brackets off of the outlet. For regular gutters, the brackets are spaced apart by 1 metre, with three brackets supporting each length of gutter in between connecting fittings. Measure 1 metre in from the insertion line of the outlet, and 2 more marks in sequence from this mark. We can install the brackets to these marks by slowly raising them up to the string line. As the brackets are installed, we can pull them downwards slightly to ensure that they are not pushing the string line up. With the three brackets installed, a length of gutter can be loosely placed in them. With the end of the gutter lined up with the insertion mark of the outlet, we can mark the other end of the gutter to enable us to correctly locate the position of the union fitting. This fitting receives the end of the two lengths of gutter in combination with rubber gaskets, to extend the length of the total run. Using this mark in combination, we can install the union in place, making sure to remove the rubber gaskets beforehand. We can then install the remaining brackets at metre intervals from the other union insertion. This straight run is now ready for the gutter. Remove the string line, and replace the gaskets in the outlet and union. A full length of gutter can be installed, with a length being cut down to fit in the smaller section of the run. The corner fittings can be clicked onto the end of this length, and manoeuvred into place.  

From here, we can repeat the same processes to install the next straight run. Another supporting bracket is installed on the other side of the corner piece. The string line can be attached to this, and the other far bracket that is installed at the full height of the original fascia mark. The brackets and unions are installed to this line, with the appropriate lengths of gutter being installed afterwards. At the very end of the run, a stop end is installed to prevent water from running out of the wrong end of the gutter. This stop end features a gasket as well to prevent leakage. On the other side of the outlet, a small section of gutter must be installed with a supporting bracket and a stop end to finish the run. With the gutter installed completely, we can use water to check that the gutter is running correctly.  

External corners are formed in the same way, though depending on the profile of the gutter, the fitting itself may be an external specific fitting. This is also the case with stop ends for certain moulding. Outlets with integrated stop ends can also be purchased.

With the gutter installed, we’re ready for the downpipes to be installed. This is obviously subject access, as the scaffold may sometimes be in the way. A small section of downpipe is cut to allow the first swan to clear the underside of the fascia. This piece can be screwed together and into the outlet. A small section of downpipe with the other swan on it can be placed on the wall, with a bracket clipped around it to give it the correct standoff. We can use a tape to measure the distance between the two swan insertion points. By cutting length at this measurement, we now have the full swan assembly cut and ready for installation. This swan receives into a full length of downpipe that is fixed to the wall at regular intervals, typically 2 or 3 per length of pipe. The downpipe should fall directly into a pipe or drain with a gasket, or with a shoe that directs the water into the drain.