Alternative gutter solutions?

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Dear All,

One of the less often thought about features of a domestic rain-water harvesting system is the gutters it seems. Yet when actually visiting RWH systems these are often very ill-maintained and badly designed. And contrary to areas with developed markets for PVC gutters and pipes, there is a need to come up with makeshift / "home-made" solutions in many developing countries, or those gutters that are available are simply bend corrugated iron sheets.

Another factor is that roof connected gutters are often too high to reach to easily fix and clean, and there is also the issue of small, perfect for mosquito breeding, puddles forming in them.

I found some solutions for altered roof building, that involved "L" shaped setups to capture the water without a gutter. And I could imagine that through rotating the typical cg sheets, one could probably also come up with something that requires at least a much shorter gutter.

Here in Uganda a concrete floor-gutter is also not too uncommon, e.g. there is a concrete rim extending from the walls around the houses to about the extend of the roof overhang, which has a water collection indentation approximately where the water that drips down from the roof hits the ground.

Obviously that causes a lot of splash losses and from a water quality point of view it is also probably not as good as a proper roof gutter. But it is really easy to build and clean, and makes for a nice functional (and prestigious) house upgrade.

I could also imagine that having these concrete slabs around the houses has a certain HH hygiene effect, especially if they are slightly risen and thus make for preferred sitting spaces (f.e. toddlers are going to be placed there instead of the bare ground etc.) Last but not least, a similar concrete foundation for mud-build houses is a common way to make these more durable against heavy rain and smaller flood events.

Obviously this would only work with underground storage solutions, and one has to probably include some sort of filter or larger first-flush to make up for the more dirt that is bound to collect in these, but I am really not sure if overall this couldn't be the preferred solution compared to the typical badly designed and un-maintained cg-sheet gutters.

So... I would be interested to hear about your thoughts regarding this, and maybe you have also some other good ideas or examples how to improve the gutters of a domestic RWH system.

Best regards,


Hello K,

You have me thinking about the gutters that we use in Canada to collect rainwater off of our roofs....they clog with twigs and leaves and they are a pain to clean out. My concern is what the rainwater will be used for and what kind of treatment will be necessary if the collection system is at ground level (as you say there will be more dirt and contaminants in it).

One thing that I have seen here is a linked chain that directs water from a roof gutter into a gravel bed on the ground. Perhaps a filter could be built into this gravel infiltration gallery? The chain needs to be straight down, and tight for the water to flow along it without splashing...but then I can also envision goats using the chain as a good source of water...which would add more bacteria...

Just my thoughts...


- L

Yes, gutters are the weakest part of many roofwater harvesting systems - they leak at joints, overflow near the discharge end, are sometimes laid with negative slope, fail to adequately intercept runoff, rust, go brittle in sunlight, accumulate silt etc. putting.

In Europe, where rain is less intense than the tropics, gutters are set nearly horizontal. In the tropics and with corrugated iron roofing both the run-off interception and the water conveyance are more difficult. Some of the gutter material (plastic or steel) should be used for an upstand on the outwards side to improve interception. This implies a smaller channel that should therefore slope at up to 1% at the discharge end to have enough carrying capacity (avoiding both overflow and serious overshoot) . This requirement in turn means down-pipes should be not too wide apart, certainly not at one end of long buildings but placed centrally in long gutters.

As roof edges are often not horizontal it may be necessary to inspect their slope before deciding the location of tanks.

Gutter clips should not only support gutters (and maybe roof-climbers hanging on them) but also restrain their rotation, help clamp adjacent gutters together and assist in their own alignment.Unfortunately many clips are flimsy and hard to fix. Metal gutters should ideally have about 2mm of taper to improve the nesting at junctions. As the overlap of roof edges beyond fascia boards or purlins may be large or variable, spacing blocks placed behind gutter clips allow for adjustment to minimise run-off overshoot.

Cleaning! The main problem is the invisibility of debris in gutters above eye level. Mirrors on sticks and mounting rungs sometimes work. The Australians have a number of leaf-guard designs to prevent leaves even reaching gutters - but they are expensive. For single storey buildings, it's tolerable to move a ladder along in 2m steps during cleaning, but for higher gutters this is slow and somewhat dangerous. Any means of doing so 'remotely' would be very welcome. Higher than two storeys and debris is rarely dense; moreover roof edges are then often behind parapets installed to make roof maintenance safer. With some (e.g. over 0.5%) gutter slope, it is possible to leave the blind end of gutters open, which allows debris to be swept AWAY from the gutter discharge end.

I haven't met the ground-level gutters K mentions, although they would be useful on cattle sheds to capture runoff to water the cattle with. But they need to be large (unless the roof edge is curved downwards and winds are light). Where roofs overhang (typically 600mm in Uganda) and buildings have plinths, there is considerable risk of splash causing damp in the lower part of walls. So a ground-level groove to capture runoff would need to be 150mm wide to limit such splashing. A neat solution is to plant a hedge line close to the plinth, so that most runoff is intercepted by the hedge; this is however barely 'rainwater harvesting'.

There has been talk of STORING water in oversized gutters, but the difficulty of supporting their high weight usually defeats such initiatives.

To make efficient use of downpipes, there should be a gutterbox or funnel between gutter and pipe to provide sufficient drop for the discharge water to accelerate up to pipe velocity before entering the pipe. Simple tee joints between gutter and downpipe reduce the flow capacity of the downpipe. However gutter boxes are expensive and, if rigidly attached to both elements, permit excessive leverage to be placed on the gutter during the fixing of downpipes. 'Facing' gutters, whose discharge jets impinge on each other, work without gutter-boxes, but fail to support the top of downpipes. They work best with large (e.g. 150mm dia) downpipes, sized to act as 'first flush' buffer tanks, but they might also work well with chains used as instead of downpipes as was briefly popular with architects in the 1970s (?). Since the main barrier to take-up of roofwater harvesting is the high cost of components, gutters should not be oversized and the occasional loss of water due to overshoot is acceptable.

However all this is roofwater harvesting detail, which may be unfortunately diverting the focus of our Dgroup away from 'water for production'.

- T

Dear T and L,

Thanks for those insightful inputs.

I have seen those chains also before, but they are really only for replacement of the downpipe, right?

Regarding the ground-level gutters I mentioned: There are not really used for RHW, but rather for diverting the water away from the houses right now. But in an environment like it is found in most of central/southern Uganda, where RHW systems are really only storage limited and rain is plenty, a gutter can be quite wasteful and thus much simpler.

But that idea of storing water in the gutters actually got me thinking:

How about one would make the wall of the house into a rectangular storage tank? Just build a second wall and make thus a thick "hollow" wall and use the entire top of it as the gutter directly? Some sort of flat roof like gravel (or maybe even grass?) filter (similar to what L mentioned) in that "gutter" would probably be easy to realize that way also.

As half of the "tank" is already build and no real guttering is needed, it could even lower the costs of the entire RWH system significantly. --Anyone seen something like that before or has valid concerns why something like that wouldn't work?

P.S.: I wasn't aware that this group is mainly about rainwater for production? Isn't it about all kinds of rainwater harvesting, including domestic?

Best regards,

- K

Dear All,

I have a couple of observation to add to the discussion.

One is to ask the question 'Is the design of roofs with horizontal edges always necessary?' This came to my mind when I say a church in Uganda with an architectural design that has roof edges that were not horizontal. This made it ideal for roof edge gutters although no rainwater harvesting was being attempted! Some people may not like the strange design that I saw, but maybe builders could set the rafters of normal buildings so the edges of the roof slope to suit fairly steep gutters being positioned close to the edge of the roofing sheet? Steeper gutters are less likely to hold debris and small puddles.

The second is to make people aware of the possibility of using gutters suspended by wire from bent deflection plates that sit over the edge of the roof (to deflect the water downward into the gutter). This approach, using the 'V' design of gutter. Made from bent galvanised iron sheet, has been around for some time. Pole mounted gutters are also possible, if necessary with boards between the poles to stiffen the gutter so wider pole spacing can be used.

In haste,

- B