Building Construction, Renovation, Maintenance & Advice

PVC Roof Gutters and Downpipes

"The Acne Guide To Removing Cats and Dogs From Your Roof"

Have you noticed? The Balinese don't like rain, they don't drink rainwater and they certainly don't like it on their heads. It is something to do with picking up evil spirits on it's way from the sky. I picked up an evil spirit the other day, it was supposed to be gin and tonic but I suspect it was a particularly evil batch of Arak. “Arak attack” is of course the name of a condition not a drink. Arak does have it's uses though - it is very good for cleaning carburettors.

Have you also noticed, the Balinese don't have gutters. The logic is, in fact, sound. Get the water off the roof straight onto the ground and organise for it to run away somewhere out of the way. This is also good because much of it ends up back in the water table.

It is a bit of a pain though isn't it. It starts peeing down, cats and dogs turn into elephants and whales and as Mr Murphy would predict you are just about to leave for work with papers clutched under your arm. You wait with a sheet of water running off the roof in front of you, it doesn't slow so you make a dash for the car. Damn, where is the key on the key ring? Then the key just won't go into the lock. You flop, wet through, on the car seat and you stare out through the windscreen as the rain eases off. The soggy papers clutched under you arm are starting to run ink onto your shirt. The worst bit was that initial drenching as you plunged through the sheet of water coming off the roof.

A gutter can be a good idea.

PVC roof gutters and downpipes

You can get plastic gutters and downpipes here in Bali with all the fittings (apart from good brackets but we'll come to that). Prices are very reasonable and installation is not difficult but does need to be planned.

Be careful because most Indonesian people know very little about gutters. Unfortunately the fact that water does not flow uphill has never been pointed out to Indonesians. Have you noticed how much time and effort goes into building those drainage channels along the sides of the roads, and have you also noticed how the bottoms of the channels don't always flow downhill, they go up and down with the surface of the road?

I can't count the number of times I have climbed on a roof to find out why water is coming in to find a valley gutter between two roofs which is lower in the middle than at the end where the water is supposed to run out.

Round and square box gutters

Gutters come in a round semi circular section and 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. Don't underestimate how many cats and dogs will fall out of the sky in a particularly fertile wet season. You should also make sure the downpipe can take a full sized cat.

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 you can get good brackets for them.

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 one dose of cats and dogs and your gutters sag in the middle and the water doesn't drain away properly. You may be interested to know that round gutters are being heavily promoted by the “Denpasar Save The Mosquito Society”.

Use plenty of brackets - water is heavy

You also need enough brackets. The Indonesian habit of “saving a bit of money for my poor old mum” means that local contractors will agree to put up a gutter but leave out most of the brackets only putting enough brackets up to hold the thing in dry weather. Cats and dogs, and water for that matter, are very heavy. You must insist that brackets are placed as close as 60 cms apart (ok, ok, two feet to you imperialists, why don't you get a life, a metric one that is, join the real world.......  I do like the inch though. It is such well proportioned thing isn't it. Even it's name has a rather nice ring to it. I don't really like centimetres very much, in fact I hate the horrible little things but we must move on. I stopped using a bone to bang in a nail a long time ago.)

You must 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.

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.

Now where did I put that evil spirit?

Copyright © Phil Wilson 2009
This article or any part of it cannot be copied or reproduced without permission from the copyright owner.

17 July 2017 Copyright © Mr Fixit,
Jl Bypass Ngurah Rai, Gg Penyu No 1, Sanur, Bali 80228, Indonesia
Telephone: +62-361-288-789, Fax:+62-361-284-180