How to Install Gutter & Downpipe

Modern surface coatings have dramatically improved the life potential of steel guttering and downpipe. ZINCALUME® & COLORBOND® finishes have virtually replaced galvanized steel in Australia. Both finishes carry a 12 year BHP warranty against perforation while galvanized steel does not. A vital advantage that the modern materials possess over galvanized steel for gutters and downpipes is the resistance to "drip-spot corrosion". For more information on this subject see "DRIP-SPOT CORROSION" explanation at the end of this paper.

Which Gutter ?

Although there are several shapes or profiles available, the common ones are:
The choice is simply a matter of preference on the part of the customer.

Most gutter profiles can be supplied with optional overflow slots in the front.

Size will depend on the known rainfall intensity for a given location but customers can be guided by past and present experience. Typical quad. gutter size in Sydney, which has a very high intensity is 415 millimetre. Square profiles usually have a slightly larger capacity than quad. The size number and location of downpipes are very much a factor in the level of efficiency of gutters.

Lengths of gutter are available up to 9.6 metres and this saves both time and effort by reducing the number of joints to be made. Long lengths also reduce the number of potential leaks, however runs of steel gutter should not exceed 20 metres without provision for expansion.

While traditional external support brackets are still available there has been an increasing trend to internal brackets which give a clean uninterrupted gutter line. On the downside is the tendency for leaves to be trapped by such brackets. Some form of leaf protection is advised in such cases.

For the purposes of this paper, we will assume that the gutter job is a renewal of an existing installation. The fascia board is most likely timber and we will address the installation from that angle. During the past few years timber has been challenged for this task by steel and aluminium both of which tend to use complete systems for their use. This paper will refer to such systems following the section on conventional installation.

Fall: The life of guttering depends heavily on the length of time water is retained within it and it should ideally drain completely. Establish the position of the downpipes and set your falls so that there is a relatively even load on each downpipe. The fall is normally about 1 in 500 but the important point is that there must be a continuous fall to the downpipe with no low spots.

Beginning at the high point of the fall, fit a bracket then place another at the lowest point of the fall which would be at the downpipe.

Run a string line between these two brackets and place brackets at about 1200 millimetre centres using the string as a guide.

Place the length of gutter into the brackets and, using a pair of multi-grips or pliers pull the tab of the bracket back over the bead or front of the gutter.

Drive a nail or clout into the fascia, just above the back of the gutter and bend it forward and down to restrain the gutter from falling forward while allowing it to move with temperature changes. Do not drive nails or clouts through the back of the gutter itself as thermal movement will be restrained and joints will be stressed to possible failure.

Difficulty may be experienced when hacksawing steel gutter, particularly if the steel is high-tensile. The task will be made much easier if you use a very fine hacksaw blade with 32 teeth to the inch and put it into the frame BACKWARDS which means that the teeth wil be pointing back towards the handle. Cut on the "away" stroke and ease up on the back stroke. Sounds silly—but it works!!

These should be lapped in the direction of flow and not be less than 25 millimetres. They should be sealed with neutral-cure silicone rubber sealant sandwiched within the lap and fastened with sealed or waterproof aluminium rivets.

Gutter installations usually have both internal and external corners to negotiate and angles have to be fabricated or purchased.

The gutter needs an outlet nozzle of some sort at the dowpipes and these are usually a short tapered item which will fit easilly into the top of the downpipe.

When fitting these avoid using excessive sealant as it can act as a weir, preventing the total drainage of water.

These come in two basic shapes, round and rectangular or square. Round downpipe has lost much of its favour due to the skill needed to fabricate angles but they are still called up for restoration work and heritage style buildings. Rectangular downpipe is relatively easy to fabricate into angles because it is a matter of basic geometry.

The use of plastic fittings at the bottom of the steel downpipe removes much of the hassle for the "do-it-yourselfer" when guiding the downpipe to the stormwater drain.

ZINCALUME® or COLORBOND® items with gutter and downpipe made of those materials. See "Drip-spot corrosion"

The downpipe should be sealed into the stormwater drain using a 3 sand/1 cement composition mix for earthenware drains or solvent cement for un-plactised PVC. plastic.

If the installation is plain ZINCALUME® gutter and downpipe, painting is a simple matter of cleaning the surface and applying two coats of 100% water based acrylic paint. NO ETCH-PRIMING IS NEEDED. Where solvent based decorative paints are to be used or heavier corrosion protection is required, it is recommended that preparation and priming be to the paint manufacturer’s recommendations.

There is a strong trend to complete systems in which the installation becomes a matter of assembling the parts. These systems are produced in a range of finishes such as-

Plain ZINCALUME® steel

Pre-primed ZINCALUME® steel and

COLORBOND® steel.

The components consist of:

Fascia and the necessary attachment brackets

Internal & external corners, straight joiners and stop ends

Gutter and innovative concealed brackets

Corners angles, both internal & external.

Drip spot corrosion

This occurs when water from an "inert" catchment drips onto a galvanized(zinc-coated) steel surface such as a gutter. An inert catchment or roof has a surface that is very stable with the result that rainwater flowing down it doesn’t take any of the surface material in solution. This means that the water is virtually pure and has no minerals in it to react with the galvanized surface to form a hard erosion resistant protective film. As the water drips into the gutter it gradually removes the zinc surface until it is totally consumed and rust spots appear.

Water flowing rather than dripping, from an inert catchment will also cause downstream corrosion but the effect takes a little longer.

Typical inert roof materials are:

Aluminium slate ZINCALUME® steel terra-cotta
COLORBOND® steel fibre-glass acrylic
glass polycarbonate

The only materials which can provide the galvanized steel surface with a hard erosion-resistant film are either a galvanized roof which provides zinc or an unglazed cement based material to provide calcium.

ZINCALUME® & COLORBOND® gutters and downpipes are not effected by inert catchment and are therefore the recommended materials.