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Side Laps: Curved Roofs

The minimum pitch for curved roofs may differ from that otherwise recommended for the profile.

For barrel curved roofs, the lap sealed section over the apex is exempt from minimum pitch requirements, provided that the required minimum pitch is achieved at the eaves. For mono-pitch curved roofs terminating at a transverse apron or head barge, the minimum pitch at the apex is 5° for corrugate or 3° for other profiles. Where this is less than the normal recommended for the profile, flashing cover must be increased to the next higher category in accordance with guidelines in Flashing Cover.
This limitation does not apply to roofs outside of the building envelope, such as curved verandah roofs, provided any spill-over is unable to penetrate the structure.

Select your profile, then enter either the height or desired radius in the calculator below to determine the length of the seal.

Spring Curving Calculator

 
 
Definitions
Width = w=w
Height = h=h
Radius of curvature = r=r
Minimum pitch = p=p°
Sheet length = l=l
Length of seal = s=s

N.B. The length of seal is to reach both sides of the crest.

The Code of Practice Online provides an interactive tool for these calculations. This tool is only available online at www.metalroofing.org.nz/cop/other-products/curved-roofs#spring-curving-calculator


Enter profile and width, then select either radius or required height to calculate:
Width and Height or Radius not valid - please re-enter 


Full Calculation Details and Example
 
Formula
Example
 
Start with : w = Width of roof
w  
=  12
 
Start with : h = Height of roof
h  
=  5
 
To find r the radius of curvature
r  =  
4h²+ w² 8h
=  
(4 x 25) + 400) 40
=  12.5
To find l the sheet length
 
 
 
Find the length y
y = r - h
=  12.5 - 5
=  12.5
Find the length x
x  =  
w 2
=  
20 2
=  10
To find the tangent of angle A
tan A  =  
x y
=  
10 7.5
=  1.33
To find angle A
A  =  aTan(
x y
)
=  aTan(1.33)
=  53°
Find the arc length c b
c b  =  
2 π r A° 360
=  
2 x 3.1412 x 12.5 x 53 360
=  11.56
Find the sheet length l
l  =  cb x 2
=  cb 23.12 + 100mm
 =  23.12
To find the length of seal
p = Min Pitch for corrugate = 8°
s  =  r x (tan 8°)
=  12.5 x 0.1405
=  1.76

Curved Roof: Sealed Lap Pitch

Minimum pitch below which vertical laps should be sealed
ProfilePitch
Corrugate8°
Symmetrical Low Trapezoidal4°
Asymmetrical Low Trapezoidal3°
Secret-fix Tray3°
 

 

 

 

 

 

Clause: 
015_001_001_000_000_000_000_000_000
Clause Number: 
15.1.1
/cop/other-products/curved-roofs#side-laps-curved-roofs
Revision Category: 
2 - Editing and rearrangement
Revision Detail: 

This clause was reviewed for clarity, and the Spring Curving Calculator was updated to have improved functionality.

Draft Clause: 
014_001_002_000_000_000_000_000_000