Maximum Area Above Penetration Calculator
A responsive online tool for calculating Maximum Area Above Penetrations is available at https://www.metalroofing.org.nz/maximum-area-above-penetration-calculator.
Before using this calculator, please read Roof Drainage Design.
Penetrations concentrate runoff from above into a single trough. Use this calculator to get the maximum allowable area above penetrations by entering the values in the designated fields.
For an explanation of each element, please click on the corresponding question mark.
For rainfall intensities, refer to NIWA’s HIRDS tool or the Rainfall Intensity Maps.
Note that this site address is used only for convenience if printing calculations to attach to documentation.
This address is not factored into calculations - you must determine intensity from Rainfall Intensity Maps or NIWA's HIRDS tool.
The address is not recorded or shared with any other parties.
This address is not factored into calculations - you must determine intensity from Rainfall Intensity Maps or NIWA's HIRDS tool.
The address is not recorded or shared with any other parties.
Select the appropriate Intensity from the Rainfall Intensity Maps, or use the Hirds-tool from NIWA.
mm/hr
Select the appropriate Intensity from the Rainfall Intensity Maps, or use the Hirds-tool from NIWA.
mm/hr
Select relevant options, which will determine the minimum Short-Term Intensity Multiplication Factor
The minimium Short-Term Intensity Multiplication Factor determined by the application type.
You can increase this manually for critical applications.
You can increase this manually for critical applications.
Enter 1:X or mm per metre- the calculator will automatically convert
Minimum Fall 1:500, Maximum Fall 1:100
Minimum Fall 1:500, Maximum Fall 1:100
1: = mm per metre
rads
bends
m
Minimum 1°, Maximum 60°
°
rads
Secondary pitch only needs to be entered manually if it is different to the main Roof Pitch
°
rads
m
Select whether runoff will drain on both sides of penetration or just 1;
m
each
For rectangular gutters you can supply custom dimensions, or use pre-supplied manufacturer data
You can select Standard Corrugate, input profile dimensions for Trapezoidal, or use pre-supplied manufacturer data
Illustration is for explanatory purposes only and is not to shape or scale.
Illustration is for explanatory purposes only and is not to shape or scale.
Illustration is for explanatory purposes only and is not to shape or scale.
Describe the product: this does not control the calculation which relies on you entering accurate data
mm
mm
Data provided by a manufacturer, especially for non-rectangular profiles. Must be nett of freeboard
mm²
Data provided by a manufacturer, especially for non-rectangular profiles. Must be nett of freeboard
mm
°
rads
°
rads
°
rads
mm
mm
Must be less than the upstand, D
mm
°
rads
= max ( RS , RS2 )
°
rads
= min ( RS , RS2 )
Using Martindales Formula:
°
rads
= atan ( tan ( A1 ) / tan ( A2 ) )
°
rads
= asin ( cos ( A1 ) * cos ( A2 ) ) + pi()/2
= cos ( A2 ) * cos ( A1 )
°
rads
= asin ( sC7 )
= tan ( A2 ) * sin ( aD )
°
rads
= atan ( tR1 )
= tan ( aD ) * csc ( R1 )
°
rads
= atan ( tC6 )
= tan ( pi()/2 - aD ) * csc ( R1 )
°
rads
= atan ( tC6' )
°
rads
= pi()/2 - C6'
°
rads
= pi() - C6 - C6' - C5'
°
rads
= C6 + C6'
Using WSP Sketch:
=W * sin ( C5' )
=D * cos ( C5' ) - FB
=IF ( ( h1max + h3 ) < h1max , h1max + h3, h1max )
=W * sin ( C5' )
=IF ( ( h1max + h3 ) < h2c,h1max + h3,h2max )
=IF ( ( h1max + h3 ) < h2max,0,h1max + h3 - h2max )
=0.5 * h1 * tan ( PI()/2 - C5 ) * h1
=0.5 * h2 * tan ( Beta - PI()/2 + C5; ) * h2
=IF ( ( h3 > 0) , ( W * cos ( C5; ) - 0.5 * h3 * tan ( C5; ) ) * h3 , 0 )
=( W * cos ( C5' ) - 0.5 * h4 * tan ( C5' ) ) * h4
=A1 + A2 + A3 + A4
=h1 / sin ( C5 )
=h2 / sin ( C5' )
=IF ( ( h3 > 0 ) , h3 / cos ( C5 ) , 0 )
=h4 / cos ( C5' )
=WP1 + WP2 + WP3 + WP4
=h2 * tan ( PI()/2 - C5 ) - IF ( ( h3 > 0 ), h3 * tan ( C5 ) , 0 )
=h2 * tan ( Beta - PI()/2 + C5 ) - h4 * tan ( C5')
=FWSW13 + FWSW24
mm
x mm
mm
Select Manufacturer (if applicable) and Profile
Describe the product: this does not control the calculation which relies on you entering accurate data
Pitch, or centre-to-centre measurement. Can also be calculated by (Effective Cover Data) ÷ (Number of Pans).
mm
Width of the pan.
mm
Calculated result from (Pitch) - (Crest).
mm
Width of the crest (top of rib).
mm
Total depth of profile.
mm
Depth of profile from the pan to the height of the capillary tube.
mm
Data provided by a manufacturer, especially for irregular profiles.
mm²
Data provided by a manufacturer, especially for irregular profiles.
mm
Data provided by a manufacturer, especially for irregular profiles.
mm
Data provided by a manufacturer, especially for irregular profiles.
mm
m²
m²
m²
m
m
mm
m
mm
mm
mm
mm
mm
mm
mm
m/s
m³/s
mm
This result is the maximum capacity that can be drained by an element of your selected configuration.
Be sure to consider all relevant elements when assessing a roof area.
Be sure to consider all relevant elements when assessing a roof area.
m²
This result is the maximum length of roof that can be drained by your selected configuration.
Be sure to consider all relevant elements when assessing a roof area.
Be sure to consider all relevant elements when assessing a roof area.
m
This result is the maximum area that can be drained above a penetration by your selected configuration.
Be sure to consider all relevant elements when assessing a roof area.
Be sure to consider all relevant elements when assessing a roof area.
This result is the maximum area that an upper roof area can drain using a spreader of your selected configuration.
Be sure to consider all relevant elements when assessing a roof area.
Be sure to consider all relevant elements when assessing a roof area.
m²
Conditions and assumptions for flat gutters:
- Mannings n assumed to be 0.014 to represent long term friction conditions.
- Equations valid for gutters with min gradient 1:500, max gradient 1:100.
- Bends are accounted for by local loss coefficients (0.5 for each 90° bend).
Conditions and assumptions for downpipes:
- Mannings n assumed to be 0.014 to represent long term friction conditions
- Any grates must not restrict flow or site-specific design is to be completed - typically double the number of outlets
- Gutters must have fall for downpipe sizing to be valid
- Calculations consider weir, orifice and friction effects
- Orifice discharge coefficient of 0.61 assumed
- Weir coefficient of 0.65 and 75% of outlet perimeter assumed available for weir flow
- Minimum pipe gradient of 20% assumed for friction conditions
Conditions and assumptions for valleys:
- Mannings n assumed to be 0.014 to represent long term friction conditions
- Minimum height of Type A valley returns to be 16 mm
- Minimum freeboard of 20mm mm for valleys below 8°
- Minimum freeboard of 15mm for valleys 8° and steeper
Conditions and assumptions for maximum run:
- Mannings n assumed to be 0.014 to represent long term friction conditions
- Only valid for supercritical flow (most roofs)
Conditions and assumptions for penetrations:
- Mannings n assumed to be 0.014 to represent long term friction conditions
- Only valid for supercritical flow (most roofs)
- Where Both Sides selected, assumes an even split of flow to either side of penetration
Conditions and assumptions for level spreaders:
- Mannings n assumed to be 0.014 to represent long term friction conditions
- Only valid for supercritical flow (most roofs)
- Corrugate Profiles
- No discharge to lap row
- One discharge hole per second trough
- Assumes flow to top of profile (no freeboard)
- Trapezoidal or Trough Profiles
- May discharge to lap row
- One discharge hole per trough
- Assumes flow to capillary groove of profile
Clause:
009_004_004_000_000_000_000_000_000
Clause Number:
9.4.4
/cop/penetrations/penetration-design#maximum-area-above-penetration-calculator
Revision Category:
2 - Editing and rearrangement
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