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PVC Roof Gutters and Downpipes

Do I need Roof Gutters?

Gutters (or troughing) around the edge of your roof can be very useful. Gutters collect the water falling on your roof and manage its flow to a place where you can dispose of it sensibly.

Gutters perform several useful functions:

  • They prevent sheets of water falling from the edges of your roof make doorways accessible in heavy rain.
  • They prevent gound erosion
  • They can alleviate flooding
  • They allow you to guide the water to a place where it can soak into the ground and replenish the water table.

Here in Bali many houses don't have roof gutters and there is certain logic for this. Get the water off the roof is quickly as possible, straight onto the ground and organise for it to run away somewhere out of the way.

However, if you want an easier life, gutter can be a good idea.

PVC roof gutters and downpipes

You can get PVC (plastic) gutters and downpipes here in Bali with all the fittings you will requir . Prices are very reasonable and installation is not difficult but does need to be planned and correctly installed.

If you want to install gutters you should take care, on an island where gutters have been used very little there are a number of pitfalls that are made.

Typical mistakes are:

  • Gutters are installed without sufficient slope for them to flow properly
  • Gutters are installed with a sag in the middle allowing water to pool in the gutter.
  • Guttes are installed that are too small for large roof areas or the heavy rains we get in Bali
  • Supporting brackets are installed that are badly designed or too small for the weight of a full gutter
  • Downpipes are installed that are too small for the flow of water.
  • The PVC is joined using glue instead of PVC solvent cement and so the joints leak.

Round and square box gutters

Gutters come in 2 profiles. The first is a semi circular round section and the second are square box gutters. Two sizes are available in both the round and square section and the size you chose is dependent on the roof area that will flow into it.

Round gutters are self cleaning

A technical point. Round gutters and round pipes such as sewers are known as “self cleaning”. It works like this - as the amount of water flowing decreases it falls to a lower level and is concentrated in a smaller width in the pipe, the cross section of flow reduces so the speed of flow down the pipe or gutter is maintained thereby helping to wash things away. In a flat bottomed gutter this is not the case. As the amount of water flowing falls it still has to fill the same width of gutter so the speed of flow drops and anything being washed down falls to the bottom and is left. The Victorians understood this principle well when building sewerage systems in Britain.

Having said this I would always recommend the square box section gutter for use in Bali. Why? Because it is stronger, holds more water, is less prone to buckling and very good brackets are available.

You need good brackets

The brackets for box section gutters are good solid plastic that hold the gutter firmly in place and can take a reasonable load.

The brackets for round gutters, on the other hand,  are flimsy sheet steel. They rust immediately so they quickly look a mess. Worse they bend very easily so, during heavy rain, your gutters may sag in the middle and the water won't drain away properly.

Use plenty of brackets - water is heavy

You also need enough brackets. Contractors will often leave out most of the brackets only putting enough brackets up to hold the gutter in dry weather. Water is very heavy.

You must insist that brackets are placed as close as 60 cms apart

You must also plan the slope of a gutter along with the placement of downpipes. A slope of 1% to 2% is fine (as long as you have enough brackets to keep it firmly in place) and again enough downpipes to suit the area of roof being drained.

Drain rainwater back into the watertable

You might consider doing the island a favour by not putting your rainwater into the drains but instead returning it to the water table either through a soak pit or an old well. It is clean, fresh, sterile water after all. Believe it or not if development continues at it's present pace Bali will have a water shortage in the not too distant future.

Paint your PVC gutters and downpipes

A final word of advice, paint your plastic gutters, brackets and downpipes. Ultra violet light from the sun damages the plastic. You may see that old pipes can become faded and the plastic brittle when exposed continually to sunlight. The grey plastic has a pigment in it to protect it from UV but the sun is intense here and you will extend the life of the plastic if you paint it.

Copyright © Phil Wilson 
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