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Help with the new rainwater drainage flow calculator


We’ve been providing customers with high-quality metal guttering for nearly 20 years now. In that time our friendly, knowledgeable team has been offering technical advice, free quotations, and a ‘take off’ and flow calculation services to customers.

We can help with selecting, costing and buying the right rainwater system for your build or home improvement project.

For new builds and extensions we offer a free ‘take-off’ from your architect’s drawings to ensure you have a list of all the components you need. Then using a rainwater drainage flow calculator, we work out what size guttering and downpipes will be required on your project in your particular geographic location.

Anthony Hitchman – MD

With this information, we can then let you know the cost of buying all the guttering components from us with a free, no-obligation quote.

N.B. If you need a special colour or a bespoke item fabricated for your home renovation or self build project, we can help with that too.

And we have installation guides and installation videos available if you are installing your guttering and downpipes yourself but, if you prefer, we can put you in touch with an experienced local rainwater system installer.

Anthony Hitchman – MD
Installing the wrong size gutters and downpipes will lead to rainwater overflowing in the worst of the British weather.
Installing the wrong size gutters and downpipes will lead to rainwater overflowing in the worst of the British weather.

What’s a ‘take off’?

Our take-off service means using the architect’s drawings from your project (whether it’s a new build, refurb or extension) to make a list of everything you need for your new rainwater system.

Decorative image of somebody using an architect's plan to work out lengths of gutters and downpipes needed

That includes all the gutter lengths, downpipe lengths, fittings (corners and outlets) and fixtures (screws, nuts, bolts, and sealant) that you or your builder will need to complete the project.

Often the architect will recommend the material and profile to match the guttering already in place; in a conservation area they might have to specify cast iron guttering in order to comply with a conservation officer.

So for Rainclear to undertake a take-off you simply need to send your architect drawings to us, and (if not specified by the architect) select the metal and profile you prefer from the huge range of Cast Iron, Cast Aluminium,  Modern Aluminium or contemporary Galvanised Steel or Copper available on the website www.rainclear.co.uk.

Upload a drawing now

Our expert team perform the take-offs ourselves in-house, printing off your emailed plans on our plotter, so you know you can discuss your project with somebody who has seen and shares your vision.

We can then send you a free quotation for your rainwater system, based on the information you have supplied and the material and gutter profile you have selected.

  • Some profiles are more suitable for areas of the UK with high rainfall, like the contemporary Aluminium D-flow and Half-Round Galvanised Steel – using the flow rate calculation will help you work out which gutter profile you need.
  • Others, like the Cast Iron Victorian Ogee, may be specified by your conservation officer if you live in a designated conservation area.

What’s a rainwater flow calculation?

The width of your gutters and the diameter of your downpipes need to be able to cope with the worst the British weather can throw at them. A rainwater drainage flow calculation can help you make sure your guttering and downpipes can reliably protect your home from rainwater – and the damage it can do if it isn’t consistently directed away from your bricks, wood, and plasterboard.

The flow calculation depends on several things:

  • The size of the roof area to be cleared of rain and the pitch of the roof. The deeper the angle of the roof, the faster the water will be carried to the gutters and need to be swiftly cleared away down the drops.
  • The number of drops – ie, how many suitable locations there are around the building for downpipes that lead from the roofline down to a subsurface drain. The fewer drops there are, the more capacity (ie, a larger downpipe diameter) is required in order to effectively divert rainfall away from the building into drains and water butts.
  • The usual and the worst rainfall the location or geographic area of the building experiences (and is expected to experience in the future) based on historical records. A lot of rain in a short period of time places greater demands on the system and needs a more efficient management of the rainwater to effectively protect your property and foundations.

If you are confident doing your own rainwater flow calculations, you’ll find it here: calculator.rainclear.co.uk

The calculator works on any browser, desktop or mobile, but works best on a landscape screen
The calculator works on any browser, desktop or mobile, but works best on a landscape screen

For accurate project specific advice on rainwater flow calculations contact our friendly, knowledgeable team on 0800 644 44 26, or find out how to do the flow calculations yourself with our new in-browser calculator: https://resources.rainclear.co.uk/choosing-right-size-guttering

Rainclear always do our best to offer the best system for your project and your budget. You’ll receive have an itemised quote; trade customers can apply for an account and their own terms.

We can arrange the fabrication of bespoke angles in aluminium or patterns to recast new cast iron hoppers to match the old – we enjoy the challenge!

You can find videos explaining and demonstrating the things we get asked to explain or demo most often by people installing our rainwater systems for themselves here: Rainclear Youtube Channel

If you don’t find the answers to your questions there, or would like to discuss other metal and gutter profile options, or would like help finding an experienced installer local to you, please give us a call on 0800 644 44 26 or email sales@rainclear.co.uk

Visit www.rainclear.co.uk to see the range of metal rainwater, drainage and roofline systems we offer.

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