• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer
The DIY Doctor's Blog
MENUMENU
  • DIY Doctor menu logo
  • Home
  • Projects
    • All Projects
    • Brick, Block, Marsonary and Concrete
    • Damp, Condensation, Rot and Woodworm
    • Doors, Windows and Conservatories
    • Electrical
    • Fencing, Decking, Paving and Patios
    • Floors, Walls, Ceilings and Lofts
    • Garages, Sheds and Outbuildings
    • Gardening and Landscaping
    • General Building, Self Build and Renovation
    • General Repairs and Cleaning
    • Green Living and Eco DIY
    • Ground work, Foundations and Drainage
    • Heating, Central Heating and Boilers
    • Joinery and Carpentry
    • Materials, Fixings and Fixing
    • Painting, Decorating and Finishing
    • Planning Regs, Project Management and Safety
    • Plastering, Plasterboard and Rendering
    • Plumbing
    • Roofing and Gutters
    • Tiling and Tiles
    • Tools, Appliances and Access
    • DIY Tips
  • UK DIY Forums
  • DIY Videos
    • Bathroom DIY Videos
    • Building Foundation Videos
    • Building Videos
    • Carpentry and Woodworking Videos
    • Damp and Damproofing Videos
    • Decorating Videos
    • Electrical Videos
    • Fitting Blinds Videos
    • Flooring Videos
    • Gardening Videos
    • Green and Eco Friendly Videos
    • Hand and Power Tools Videos
    • Heating and Central Heating Videos
    • Kitchen Videos
    • Plastering and Drylining Videos
    • Plumbing Videos
    • Security Videos
  • Find Tradesmen
    • Find a Tradesman
    • Contract Download
    • Working With Tradesmen - Ultimate Guide
    • Home Improver Protection
    • Price Doctor
  • Tool Store
    • Tool Store
    • Bookstore
    • Tool Reviews and Product Reviews
  • Blog
    • Blog
    • DIY Competitions
  • About us
    • About DIY Doctor
    • What we do
    • Trade Shows and Exhibitions
    • Master Classes
    • Contact Us

Home > Blog Home >  DIY and Home Improvement >  How to Calculate Your Roof Area for Sizing your Guttering

How to Calculate Your Roof Area for Sizing your Guttering

Posted on November 1, 2018 by DIY Doctor

It is worth making sure that your gutters can cope with the amount of water that will come off your roof!

There are complicated and accurate techniques that take into account where your house is and the expected rainfall to work out the size of the guttering you need. However we feel that this is generally ‘overkill’ and sometimes a simpler solution is better, or at least as good.

The simple Way to Calculate Gutter Sizes

There are two things you need to know:

  1. The effective roof area that will collect the rain which will need to be removed by the guttering. As most roofs are not flat this needs to be calculated – we’ll show you a simple way.
  2. The area that your chosen guttering system can cope with. Thankfully the manufacturers will be able to provide this information through your merchant or online. In fact it is not going to vary much (if at all) between manufacturers as the common styles are very similar.

So to step 1:

To calculate the Effective Roof Area you should use this formula:

Roof Length   X   Half Roof Width   X   Roof Height ÷ 2 = Roof Area

Calculating the area of a roof
Calculate the area of a roof to work out how much guttering is required

So for a roof that is 5 m long, with a height of 4 m and the roof width is 8 m (which makes the half roof width 4m) we can calculate the effective roof area like this.

5m x 4m x (4/2) = 40 square metres

Note that this is not the true roof area but just an approximation to get you a number that is close enough to work with for our purposes.

The next step is to compare this calculate roof area against the stated roof areas that each style of guttering can deal with. Here is a table for the Floplast gutter systems compiled by gutteringsupplies.co.uk:

Floplast guide to roof sizes
Floplast guide to guttering and roof area

As you can see with an effective area of 40m2 there will be no issue using any of these systems and configurations. However if our effective roof area were 50 m2 then we would not be able to use a level Half Round gutter with a stop end outlet (ie, the downpipe at one end of the gutter, rather than in the middle).

To increase the capacity of the gutter, we would have to add a fall, which we would always recommend doing as a matter of course, or moving the outlet to the centre of the gutter but using a Running Outlet (which allows you to position the downpipe in the middle of the gutter).

If none on this makes sense, we have a project all about how to fit gutters which explains everything here.

Increasing the Capacity of your Gutter System

As you can see from the table there are a number of things that you can do to increase the capacity of your guttering system to remove water from your roof:

  1. Add a fall to the gutters, which we recommend you do anyway
  2. Move the outlet (downpipe) from the end of the gutter to the middle
  3. Change the style of gutters to one with a greater capacity.

Most merchants and online suppliers will assist you with sizing your guttering so it is not a big problem, but it is something you can do yourself if you want to double check their measurements. They do this so that they can then calculate how much guttering you will need.

For more information about actually fitting your gutting yourself, have a look at our project about fitting plastic guttering.


Signup for the DIY Doctor Newsletter

<< Next Post

Cutting Timber and Other Materials to Fit Odd and Uneven Surfaces Perfectly
Cutting Timber and Other Materials to Fit Odd and Uneven Surfaces Perfectly

Previous Post >>

Don’t Waste Time With the Wrong Waste Pipes
Don’t Waste Time With the Wrong Waste Pipes

Primary Sidebar

DIY Doctor deal of the week

DIY Utility Kit:

Build your own work bench!

RRP Price: £49.99

Special Price: £39.95

Get it here now

See our other deals now!

Advert

Signup for our Newsletter

Keep up to date with our DIY projects, tips and latest deals

Sign Me Up!

Follow DIY Doctor

Follow DIY Doctor on Facebook
Follow DIY Doctor on Twitter
Follow DIY Doctor on YouTube
Follow DIY Doctor on Pinterest
Follow DIY Doctor on Tumblr

Blog Categories

Footer

DIY Doctor

Site Menu

  • About Us
  • Contact Us
  • Blog
  • Media/Press
  • Community Work
  • DIY Projects
  • DIY Videos
  • Superstore
  • DIY Tips
  • DIY Suppliers
  • UK DIY Forum
  • DIY Webinars

Other Stuff

  • Advertise
  • Competitions
  • T and C’s
  • Privacy Policy
  • Cookies
  • NHIC
  • Sitemap

DIY Doctor Social Channels

Follow us on Facebook
Follow us on Twitter
Follow us on YouTube
Follow us on Pinterest
Follow us on Tumblr

DIY Doctor are members of:

© DIY Doctor Ltd 2021 All Rights Reserved