Making the most of rainwater run-off from a flat roof

The baffling weather of recent years has done plenty to reinvigorate interest in rainwater harvesting systems in the UK, but there is often an assumption that flat roofs will not be suitable. This is not true.

For those that are unsure: rainwater harvesting is the process of recycling the water that falls on a property. British homes certainly see their fair share of rain and for once this can be a positive thing! By catching, filtering and reusing this water, homeowners know they are part of the water management solution, rather than contributing to the problem.

So what can you do to make the most of your home’s rainwater if you have a flat roof or are considering installing one?

Flat roof rainwater harvesting

A 2011 study supported by the European Social Fund found that the two most important factors when it comes to efficacy of rainwater harvesting are the slope of the roof and the smoothness of the roofing material. Despite the name, flat roofs tend to have a slight tilt to them, so you then need to do your best to find a nice smooth material for your roof.

The problem with gravel or asphalt options is that they do not encourage the water to run off the roof as quickly as metal, rubber or plastic – some water will then inevitably be lost to evaporation. The difference in efficacy between these materials is especially marked when there is not much rain.

Another issue with gravel is that you may find that some weeds or plants find a way to grow up there, which can impact the amount of water harvested as well as the purity. It goes without saying that your rainwater harvesting will also be negatively impacted if your flat roof is damaged and allows water to go elsewhere, rather than being channelled into the system you have in place.

There are all sorts of different systems available – your preferred option will likely depend on the space you have available and the type of property you are dealing with.

Harvested water uses

You can actually drink harvested rainwater once you have treated it and there are plenty of experts out there who laud the purity of this water. While you may not go to the trouble of doing this, you can at the very least collect rainwater to use in the garden or find another usage that will save you money.

For example, Free Water UK (a rainwater harvesting system specialist) notes that one third of water in the home gets flushed down the toilet – if you can find a way of replacing some of this paid-for water with your harvested alternative, then one of your utility bills could be about to get a little cheaper.

There are suggestions that water management policies will come under closer scrutiny in the coming years, which brings innovations like rainwater harvesting systems into sharper focus. It is comforting to know that your flat roof can benefit from it too.