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A section dedicated to help support your DIY/Installer needs.

Please click on the below sections to learn more about installing our products:

Calculator

Design and installation

Roof Area

The effective roof area can be calculated by using the following formula:

Method of calculating effective roof area

Roof pitch 10° 12.5° 15° 17.5° 20° 22.5° 25° 27.5° 30° 32.5° 35° 37.5° 40° 42.5° 45° 47.5°
Factor 1.088 1.111 1.134 1.158 1.182 1.207 1.233 1.260 1.288 1.319 1.350 1.384 1.419 1.459 1.500 1.547

For roofs of 50° or more and walls, the factor of 1,600 should be used

Gutter flow capacity

Gutter flow capacity is dependent upon system type, outlet position and whether gutter is laid level or to a specified fall. The table above gives the required information based upon a Rainfall intensity of 75mm per hour and recommendations from BS EN 12056-3:2000.

Please enter details of the Double Valley roof. All measurements should be in metres.

Please complete the fields that have gone red

Length of roof (L):

Please complete the following field

Width (Plan View):

Please complete the following field

Pitch of roof °:

Please complete the following field

Number of Outlets:

Please complete the following field

Flow Rate - Help

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.

Results

System with outlet and no angles:
System with outlets @ end :
System with outlets @ centre :
Roof Area = Square Metres : Flow Rate = Litres per second
System with angle further than 2 metres from outlet:
Angle > 2 metres from outlet (end):
Angle > 2 metres from outlet (centre):
Roof Area = Square Metres : Flow Rate = Litres per second
System with angle nearer than 2 metres from outlet:
Angle < 2 metres from outlet (end):
Angle < 2 metres from outlet (centre):
Roof Area = Square Metres : Flow Rate = Litres per second

Please enter details of the Double Valley roof. All measurements should be in metres.

Length of roof (L):

Please complete the following field

Width (Plan View):

Please complete the following field

Pitch of roof °:

Please complete the following field

Number of Outlets:

Please complete the following field

Flow Rate - Help

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.

Results

System with outlet and no angles:
System with outlets @ end :
System with outlets @ centre :
Roof Area = Square Metres : Flow Rate = Litres per second
System with angle further than 2 metres from outlet:
Angle > 2 metres from outlet (end):
Angle > 2 metres from outlet (centre):
Roof Area = Square Metres : Flow Rate = Litres per second
System with angle nearer than 2 metres from outlet:
Angle < 2 metres from outlet (end):
Angle < 2 metres from outlet (centre):
Roof Area = Square Metres : Flow Rate = Litres per second

Please enter details of the Double Valley roof. All measurements should be in metres.

Roof 1

Length of roof (L1):

Please complete the following field

Width (W1):

Please complete the following field

Pitch of roof (°1):

Please complete the following field

Roof 2

Length of roof (L2):

Please complete the following field

Width (W2):

Please complete the following field

Pitch of roof (°2):

Please complete the following field

Outlets

Number of Outlets:

Please complete the following field

Flow Rate - Help

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.

Results

System with outlet and no angles:
System with outlets @ end :
System with outlets @ centre :
Roof Area = Square Metres : Flow Rate = Litres per second
System with angle further than 2 metres from outlet:
Angle > 2 metres from outlet (end):
Angle > 2 metres from outlet (centre):
Roof Area = Square Metres : Flow Rate = Litres per second
System with angle nearer than 2 metres from outlet:
Angle < 2 metres from outlet (end):
Angle < 2 metres from outlet (centre):
Roof Area = Square Metres : Flow Rate = Litres per second

Please enter details of the Double Valley roof. All measurements should be in metres.

Roof 1

Length of roof (L1):

Please complete the following field

Width (W1):

Please complete the following field

Pitch of roof (°1):

Please complete the following field

Roof 2

Length of roof (L2):

Please complete the following field

Width (W2):

Please complete the following field

Pitch of roof (°2):

Please complete the following field

Roof 3

Length of roof (L3):

Please complete the following field

Width (W3):

Please complete the following field

Pitch of roof (°3):

Please complete the following field

Outlets

Number of Outlets:

Please complete the following field

Flow Rate - Help

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.

Results

System with outlet and no angles:
System with outlets @ end :
System with outlets @ centre :
Roof Area = Square Metres : Flow Rate = Litres per second
System with angle further than 2 metres from outlet:
Angle > 2 metres from outlet (end):
Angle > 2 metres from outlet (centre):
Roof Area = Square Metres : Flow Rate = Litres per second
System with angle nearer than 2 metres from outlet:
Angle < 2 metres from outlet (end):
Angle < 2 metres from outlet (centre):
Roof Area = Square Metres : Flow Rate = Litres per second

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