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Architectural Sheet Metal by the Numbers

Profiles, mitres, raking mitres, flashings, copings and curved work for building facades and roofs, worked through one warehouse front

Develop building sheet metal by numbers: profile girth, square, angled and raking mitres, penetration and wall flashings, copings with movement and wind, and curved and gored work.

8 chapters · About 80 minutes · Free to read · Intermediate sheet metal drafting and fabrication

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About this book

Buildings carry a great deal of folded sheet metal that is not roofing: copings on parapets, fascias on canopies, barge cappings on gables, flashings where roofs meet walls and pipes pass through roofs, and the occasional curved fascia or domed finial. Each is a profile, a shape folded from a flat strip, and each has to turn corners, meet other profiles, keep water out and move with the seasons. A century ago, architectural sheet metal workers developed these shapes on the drawing board with dividers and straight-edges. Today most of the same geometry can be done with a calculator, which is faster, checkable and easy to record.

This book develops architectural sheet metal by numbers. It starts with a profile’s girth and stretch-out, develops square mitres, mitres at other angles and raking mitres where a horizontal profile meets an inclined one, then turns to flashings at penetrations and walls, copings with their falls, joints, movement and fixings, and finally segmented curved work and gored domes. Every chapter works one problem through the running case, shows how an error is caught and ends with an exercise and its worked answer.

It assumes basic trigonometry and some folding experience. Sheet Metal Patterns by the Numbers covers pipes, elbows, branches and cones, and Sheet Metal Parts by the Numbers covers bend allowances in detail; this book links to them rather than repeating them.

The running case

The book follows the street front of a fictional light industrial warehouse, W-40. Its 40 m front parapet, 200 mm thick, carries a folded steel coping. Over the entrance, a canopy 6 m wide projects from the facade, finished with a profiled fascia that turns the canopy’s front corners and rises up the canopy’s 15° gable ends as a raking barge. A 900 mm square roof hatch and a 150 mm flue pass through the main roof, and the canopy roof meets the facade wall under an apron flashing. A domed finial, 300 mm in diameter, caps a flagpole base on the parapet, and a curved version of the canopy is considered in the last chapter.

All dimensions, profiles, loads, prices and results are invented for teaching. This is an illustration. None of it describes a KEVOS® client, supplier or project. Material is 0.55 mm prepainted metallic-coated steel unless stated, and money is in Australian dollars, excluding GST.

How to use the book

Chapters 1 to 4 build the geometry of profiles and their mitres, each depending on the one before. Chapters 5 and 6 cover flashings, Chapter 7 copings and cappings, and Chapter 8 curved and gored work. Each method is set out as a table of numbers that can be checked, cut and kept.

Source limits and professional responsibility

The supplied 1922 treatise informed the range of subjects. The methods here are expressed in modern terms with original examples. Weatherproofing details, fixings and wind resistance for real buildings must follow the National Construction Code, the roofing and cladding makers’ instructions, the installation code and the wind loading standard, and be checked by a competent person. Roof and facade work is work at height and must be planned under the work health and safety law that applies.

Who this book is for

Sheet metal fabricators, roof plumbers, facade and cladding detailers, drafters and building designers who draw, cut and fold profiled flashings, fascias, cappings and copings for buildings.

What you will learn

Calculate the girth of a folded profile and set out its stretch-out for cutting.
Develop square, angled and raking mitres for any profile from its projections, with every cut ordinate calculated.
Detail penetration, apron and step flashings so water is always lapped and turned the right way.
Design copings and cappings for falls, thermal movement and wind, with joints and fixings that allow both.
Set out segmented curved work and gored domes, and record each pattern for repeat use.

Inside this book

Chapters

Figure 2The ordinate factor and the coping's largest ordinates, by corner angle

	Factor k	Ordinate at d = 240	Ordinate at d = 255
60°, an acute corner	1.732	415.7 mm	441.7 mm
90°, square	1.000	240.0 mm	255.0 mm
91.5°, W-40's western corner	0.974	233.8 mm	248.4 mm
120°, a hexagon	0.577	138.6 mm	147.2 mm
135°, a splay or octagon	0.414	99.4 mm	105.6 mm
150°, a twelve-sided figure	0.268	64.3 mm	68.3 mm

This is an illustration. Each ordinate is d × k, measured back from the corner line. At 60°, ordinates exceed the profile's own projection, so the mitre runs far along the blank.

Mitres at any angleDevelop a profile mitre for any corner angle with the factor 1 ÷ tan(φ/2), measure a real corner on site, handle splays and polygons, and see what a square cut does on a corner that is not square.

Figure 2W-40's fascia profile, horizontal and raking at 15°

	Horizontal d, h	Raking d, h′	Raking segment length
A	0, 250	0, 241.5	start
B	40, 250	40, 251.8	AB 41.3 mm, now rising 10.3 mm
C	40, 210	40, 213.2	BC 38.6 mm
D	90, 160	90, 177.8	CD 61.3 mm
E	90, 30	90, 52.3	DE 125.5 mm
F	70, 0	70, 18.1	EF 39.6 mm; girth 306.3 mm

This is an illustration. Projections are unchanged; heights change. The raking profile's girth is 306.3 mm against the horizontal profile's 316.8 mm, so the two are cut from different blanks and folded to different drawings.

Raking mitres: a horizontal profile meets an inclined oneDevelop the raking mitre where a horizontal fascia turns a corner and climbs a gable: why the raking profile must differ, its new points and girth, the cut ordinates on both pieces and the apex joint.

Figure 2Two ways to flash W-40's 150 mm flue

	Fabricated tray, upstand and storm collar	Proprietary flexible pipe flashing
Material	prepainted steel, same as the roof	moulded polymer with a metal-reinforced base
Temperature	suits a hot flue with clearance	limited by its rating, which must suit the flue
Fit to the sheet profile	base tray folded or dressed to the ribs	base dressed by hand onto the ribs
Movement	upstand and pipe slide freely under the storm collar	boot flexes with the pipe
Choice for the W-40 flue	yes	no

This is an illustration. The fabricated option was chosen because the flue's surface temperature was above the rating of the flexible flashing available, and because it matched the coping's material.

Flashings at roof penetrationsFlash pipes and kerbed openings through a metal roof: lap every piece with the water, set upstands, divert upslope water with a cricket developed from true lengths, and allow for movement.

Figure 1A quarter circle of 6 m radius in straight segments

	Chord of each segment	Sagitta, gap at mid-segment	Mitre angle between segments
4 segments	2,341.1 mm	115.3 mm	157.5°
8 segments	1,176.2 mm	28.9 mm	168.75°
12 segments	784.8 mm	12.8 mm	172.5°
16 segments	588.8 mm	7.2 mm	174.4°

This is an illustration. The sagitta is how far each straight segment stands off the true curve at its middle. At 8 segments the fascia deviates about 29 mm, which reads as a curve from the street; at 4 it deviates over 100 mm and reads as a polygon.

Curved work and gored domesMake profiles follow curves by segmenting them, choosing the number of segments from the sagitta and cutting small-angle mitres, then develop a domed finial from flat gores with calculated widths.

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References and source notes

The manuscript and worked examples are original KEVOS® writing. References inform particular concepts; their authors do not endorse this book. Web references were consulted on 26 October 2026.

William Neubecker, The Sheet Metal Publication Company, New York. The Universal Sheet Metal Pattern Cutter, Volume II: Architectural Sheet Metal Work (1922). Supplied source, read as a subject map of the cornices, mitres, raking mouldings, flashings, copings, finials and circular work that architectural sheet metal shops developed by hand. Its engravings, imperial examples and prose are not reproduced; this book's methods are expressed as calculations in SI units, with its own case, figures and exercises.
The Engineering ToolBox. Linear Thermal Expansion Coefficients of Materials (current web page). Source for the expansion coefficient of steel used for the coping movement in Chapter 7.
Standards Australia and Standards New Zealand. AS/NZS 1170.2, Structural design actions, Part 2: Wind actions, and SA HB 39, Installation code for metal roof and wall cladding (current editions). Named by number and scope only. AS/NZS 1170.2 sets the wind pressures that copings and their fixings must resist, and SA HB 39 is the industry installation code for metal roofing, flashings and cappings. No values or requirements are quoted from either; the wind pressure and clip capacity in Chapter 7 are labelled teaching values.
Safe Work Australia. Model Code of Practice: Managing the risk of falls at workplaces (2018). Background for the note on site measurement and installation at height in Chapters 1 and 8.

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