The four most common roof areas catered for are 'Single', ' Hipped', 'Valley' and 'Double Valley' as illustrated below.

The grey area denotes the area of roof that is calculated. For a standard semi or detached house, with a 'Single' roof design, two calculations, one for each side, are required. Other roof areas can be accommodated, by using a combination of these four modules.

Click on the link to the desired roof style, a calculator will appear on your screen, enter the dimensions, and the number of downpipe outlets as required. Once this has been completed click the calculate button. The dimensions or number of outlets can be altered by clicking back into the calculator boxes. For a new calculation or to clear the information already entered click the reset button.

The results appear, which give three scenarios, 'Outlet with no angles', 'Angle further than two metres from outlet' and 'Angle nearer that two metres from outlet'. In each case the result will also give you the gutter suitable to each scenario if the outlet(s) are placed at the end or the centre of each gutter run. The results page is printable by clicking on the 'Print' button on the calculator.

N.B. This has been calculated using the maximum achievable flow rates for each system. If however the flow rate in litres per second comes near to the maximum for the suggested system, as in the table on the flow rate main page, then FloPlast advise that the next largest system is used, or an additional downpipe is added to the system.

For further assistance in sizing roof areas and gutter flow rates please contact FloPlast Technical Advisory Service on (01795) 431731.