Side Laps: Curved Roofs

Where a barrel curved roof is below the specified minimum roof pitch recommended for the profile, side laps should be sealed over the crest of the arch with lap tape or silicone sealant until the minimum pitch is reached. Avoid double lapping because condensation can become trapped in the lap, which can cause accelerated corrosion with all metal products.

If the width and height of the roof are known, this information can be used to obtain the radius of curvature and subsequently the sheet length and the length of seal required for any profile.

IMPORTANT NOTE: The seal length (s) is required on each side of the crest (b).

Spring Curving Calculator



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

The Code of Practice Online provides an interactive tool for these calculations. This tool is only available online at

Enter width and height to calculate:
Width and Height not valid - please re-enter 



Full Calculation Details and Example
Start with : w = Width of roof
=  12
Start with : h = Height of roof
=  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

N.B. This length of seal is required on each side of the crest.


Curved Roof: Sealed Lap Pitch

Minimum pitch below which vertical laps should be sealed
Symmetrical Low Trapezoidal
Asymmetrical Low Trapezoidal
Secret-fix Tray






Clause Number: 
Revision Category: 
3 - Substantial change to recommendation
Revision Detail: 

This clause has been comprehensively revised during the overall review of Curved Roofs.

Draft Clause: