Introduction to the Sheet Metal Series
There is a category of material on historic facades that does not get the attention it deserves.
Not the decorative ironwork. Not the carved stone. Not the lime render or the glazed tile. The material that sits at the junctions — where roof meets wall, where water must be directed away, where a projecting cornice needs a waterproof cap, where a dormer window emerges from a slate roof and needs to be sealed against driving rain.
Sheet metal. Thin, worked, formed into profiles and lapped joints and standing seams. Doing its job invisibly, until it stops doing it — and then making its presence felt in every room below.
This series covers the five sheet metals that have shaped the appearance and the performance of historic buildings across Europe: lead, copper, zinc, tin, and aluminium. Each has its own history, its own character, its own craft tradition, and its own specific restoration challenges. This introductory post sets the stage.
What sheet metal does on a historic facade
Sheet metal on a historic building is primarily functional. It manages water — directing it away from vulnerable junctions, sealing interfaces between different building elements, providing a durable surface where other materials would fail quickly in exposed positions.
The locations where sheet metal appears on a historic facade follow a consistent logic:
Gutters and rainwater systems — collecting water from the roof and directing it to downpipes. The gutter is the most visible sheet metal element on most historic buildings, and the one most frequently compromised by inappropriate repairs.
Flashings — the strips of metal that seal the junction between a roof surface and a vertical element: a parapet wall, a chimney stack, a dormer cheek. Flashings are small,often invisible from ground level, and critically important. When they fail, water enters the wall at the exact point where it can do the most damage.
Dormer window cladding — the cheeks, aprons, and caps of dormer windows are almost always sheet metal. The zinc-clad dormer windows of Belgian and French urban housing are so characteristic of the period that they have become defining elements of the streetscape. Their distinctive profiles — the moulded zinc surrounds, the decorative caps — were produced by craftspeople with specific skills that are becoming rare.
Roof coverings — standing seam copper or zinc roofs, lead flat roofs, terne-coated steel on certain building types. The roof covering is the primary weather barrier of the building, and its condition determines the condition of everything below it.
Decorative elements — cornices capped in zinc or copper, ornamental details pressed from sheet metal, the decorative finials and crests that appear on the rooflines of quality historic buildings.
The five metals — a brief introduction
Lead is the oldest of the group. It has been used in building construction for more than two thousand years — the Romans used lead for pipes, flashings, and roof coverings. Lead is extraordinarily durable when correctly specified and installed: lead flashings on historic buildings are regularly found to be in good condition after two or three centuries of service. It is also heavy, soft, and expensive — which is why it has generally been reserved for the most critical applications where its longevity justifies the cost. In the UK particularly, the lead working tradition is extensive and highly developed, with a guild structure and training infrastructure that has maintained the craft at a high level.
Copper is the most visually distinctive of the sheet metals, for an obvious reason: it does not stay the same colour. Fresh copper is a bright, warm orange-red. Over years and decades, it develops a patina — first darkening to brown, then gradually acquiring the characteristic blue-green of verdigris. The final patinated copper surface is stable, beautiful, and extraordinarily durable. Copper roof coverings and decorative elements on historic buildings are frequently in good condition after a century or more of exposure.
Zinc is the dominant sheet metal of Belgian, French, Dutch, and German historic urban architecture. The grey-blue zinc roofs, gutters, dormers, and decorative elements of the late 19th and early 20th century townhouse are so characteristic of the period that their loss — through replacement with inappropriate materials, or through deferred maintenance leading to total failure — represents a significant erosion of historiccharacter. Zinc is less durable than lead or copper, with a typical lifespan of fifty to one hundred years depending on specification and conditions, but it is more affordable and more workable, which made it the practical choice for the volume of construction of the period.
Tin — more precisely, terne-coated steel or terne plate — was widely used for roof coverings and flashings in the 19th and early 20th century, particularly in France and in areas of North America with French building traditions. A steel sheet coated with a tinlead alloy, it offered reasonable durability at lower cost than copper or lead. It is now rare in new construction and increasingly rare in existing buildings — those that have not been replaced have often deteriorated beyond repair. The knowledge of how to work with it, and how to restore it correctly, is genuinely endangered.
Aluminium is the newest of the group, and its presence in this series requires a brief justification. Aluminium sheet cladding appeared on buildings from the mid-20th century onward — initially on modernist commercial buildings, later on residential construction as a cheaper alternative to traditional sheet metals. Buildings clad in aluminium from the 1950s, 1960s, and 1970s are now historic buildings in their own right, and their conservation raises specific questions about material authenticity and appropriate repair that the restoration community is only beginning to address.
What they have in common
Despite their differences in appearance, cost, and longevity, the five sheet metals share several characteristics that are fundamental to understanding how they work and how they fail.
They are all sacrificial to varying degrees. Sheet metal elements are not permanent — they have lifespans measured in decades, not centuries. Their function is to protect the building fabric beneath them for that lifespan, and then to be renewed. Maintenance — regular inspection, minor repairs, and timely replacement — is what makes this system work. Deferred maintenance is what causes it to fail catastrophically.
They are all vulnerable to galvanic corrosion. When two dissimilar metals are in contact in the presence of moisture, an electrochemical reaction occurs that accelerates the corrosion of the less noble metal. Zinc and copper in contact is a classic problem — the zinc corrodes rapidly where it touches copper. Lead and aluminium in contact causes similar issues. Correct detailing — ensuring that different metals do not come into direct contact — is essential for the longevity of any sheet metal installation.
They all require specific craft skills to work correctly. Sheet metal work is not asingle trade. The zinkwerker, the plumber working in lead, the coppersmith, the tinsmith — each works with different tools, different techniques, and different joining methods appropriate to their specific material. The craftsperson who can work competently in one metal may not have the skills for another. This matters for restoration: the right material requires the right craftsperson.
They all fail in specific, recognisable ways. Zinc develops pinhole corrosion and eventually full-thickness perforation. Lead cracks through thermal fatigue and crystallisation. Copper develops pitting corrosion in polluted urban environments. Tin loses its protective coating and the steel beneath rusts. Aluminium develops surface oxidation and, in the wrong conditions, pitting. Each failure mode has a characteristic appearance that an experienced eye can read — and that tells you something about the cause of the failure, not just the fact of it.
The craftsperson behind the material
Each of the sheet metals in this series has its own craft tradition, its own training pathway, and its own community of practitioners.
The zinkwerker — the zinc roofer — is perhaps the most visible specialist in Belgian and French historic building restoration. The zinc dormer window surrounds, gutters, and decorative elements that characterise the late 19th century urban streetscape require specific skills that are distinct from general roofing work.
The plumber working in lead — the word plumber comes from plumbum, the Latin for lead — carries a craft tradition that goes back further than almost any other building trade. In the UK, the lead working tradition has maintained a level of institutional support through the Lead Contractors Association and apprenticeship programmes that has kept the craft alive at a high standard.
The coppersmith working on architectural elements — the standing seam roofs, the decorative dormers, the ornamental copperwork of quality historic buildings — combines metalworking skills with an understanding of how copper behaves over time and how its patination can be managed.
These are not interchangeable skills. A building that needs its zinc gutters replaced, its lead flashings renewed, and its copper dormer caps restored may need three different specialists — or one highly experienced sheet metal craftsperson with genuine competence across all three materials, which is rarer.
What goes wrong in restoration
The most common errors in sheet metal restoration on historic buildings follow predictable patterns.
Mixing metals without understanding galvanic consequences. Replacing a zinc element with copper, or fixing a new lead flashing with copper nails — apparently minor decisions that create long-term corrosion problems at the point of contact.
Using cement or silicone as a repair material. The torch-applied roofing felt patch over a failing zinc gutter — discussed in the gutters post elsewhere in this series — is the most common version of this error. Roofing felt is not a substitute for zinc repair. It traps moisture, accelerates corrosion beneath it, and creates worse problems than the ones it covers.
Incorrect lap and seam dimensions. Sheet metal joints rely on specific overlaps and seam geometries to shed water correctly. A joint that is too short, or a seam that is not correctly formed, will leak — sometimes immediately, sometimes after years of apparently satisfactory performance.
Failure to allow for thermal movement. Sheet metal expands and contracts significantly with temperature. Fixings and joints that do not allow for this movement will be stressed with every thermal cycle, eventually failing at the most constrained points.
A question to the Guild
Which of the five metals in this series do you encounter most frequently in your restoration work? And which do you find least well supported — in terms of available materials, training, and specialist knowledge within your region?
The answers will vary considerably across Europe. A craftsperson in Belgium will have a different experience from one in the UK or Portugal. That variation is itself interesting, and the Guild is a good place to map it.
The series continues with each metal in turn — lead first, as the oldest and in many ways the most instructive.
RestoreFacade Guild — for the craftspeople who understand that the junction between roof and wall is where buildings are won or lost.