Frequently Asked Questions – Trapezoidal Steel Sheets
1. What Is a Trapezoidal Steel Sheet?
A trapezoidal steel sheet is a steel or aluminium sheet with characteristic trapezoid-shaped ribs. Profiling increases the rigidity of the material and allows it to be used for roofing, façade cladding, fencing and other building applications.
Trapezoidal sheets differ in profile height, steel core thickness, protective coating and intended application.
Popular profiles include T7, T14, T18, T35 and T55. Lower profiles, such as T7, are mainly used for façades, fences and roof soffits. Higher profiles are used, among other applications, on the roofs of residential, agricultural and industrial buildings.
Trapezoidal sheets are valued for their low weight, durability, ease of fabrication and wide selection of colours and finishes.
2. What Are Trapezoidal Steel Sheets Used For?
Trapezoidal sheets are used in residential, industrial, agricultural and utility construction.
Their most common applications include:
- Roofing for garages, houses, industrial halls and warehouses.
- Building façades.
- Fences and gates.
- Roof soffit finishing.
- Cladding for shelters, gazebos and utility buildings.
- Structural elements in appropriately designed systems.
T7 trapezoidal sheets are particularly suitable for façade, fencing and decorative applications. Their low rib height creates an attractive, uniform surface.
For roofs requiring greater load-bearing capacity, profiles such as T18, T35 or T55 are more commonly used, provided they are correctly selected for the structure.
3. What Types of Trapezoidal Steel Sheets Are Available?
Trapezoidal sheets are primarily classified according to rib height, steel thickness, protective coating and intended use.
| Profile | Nominal Profile Height | Typical Application |
|---|---|---|
| T7 | 7 mm | Façades, fences, soffits |
| T14 | 14 mm | Façades, lightweight cladding and selected roofs |
| T18 | 18 mm | Garage, house and shelter roofs |
| T35 | 35 mm | Industrial hall, warehouse and industrial building roofs |
| T55 | 55 mm | Roofs and applications requiring higher load-bearing capacity |
Trapezoidal sheets can also be classified as galvanised, aluminium-zinc coated or colour-coated products, available in various RAL colours.
The choice of profile depends on the intended application, support spacing, expected loads and aesthetic requirements.
4. What Is the Difference Between T18 and T35 Trapezoidal Sheets?
T18 and T35 trapezoidal sheets differ mainly in profile height, which affects rigidity and the range of possible applications.
The T18 profile has a nominal height of approximately 18 mm and is commonly used on garage, shelter, house and utility building roofs.
The T35 profile is approximately 35 mm high. Thanks to its deeper ribs, it can provide greater load-bearing capacity and rigidity with comparable material specifications.
| Parameter | T18 | T35 |
|---|---|---|
| Profile height | 18 mm | 35 mm |
| Typical application | Garages, houses, shelters | Industrial halls, warehouses, larger roofs |
| Rigidity | Lower | Usually higher |
| Minimum roof pitch specified by Blachodach | 10° | 10° |
| Effective cover width specified by Blachodach | 1092 mm | 1050 mm |
These specifications apply to the indicated Blachodach products.
For façades, fences and soffits, a lower profile such as T7 may be an alternative, offering a different visual effect and suitability for lighter applications.
5. Which Trapezoidal Steel Sheet Is Best for a Roof?
Choosing a trapezoidal steel sheet for roofing depends on the building size, roof pitch, support spacing, and expected snow and wind loads.
T18 sheets are often selected for garages, houses and utility buildings. T35, T55 or higher profiles are also used for industrial halls and larger structures.
Important factors include steel core thickness, corrosion-resistant coating, effective cover width and the minimum roof pitch permitted by the manufacturer.
Blachodach specifies a minimum roof pitch of 10° for its T18 and T35 roofing profiles. However, this value should not automatically be applied to products from other manufacturers.
Low-profile T7 sheets are primarily intended for façade and finishing applications. Any proposed use on a roof requires confirmation of the permitted application, load-bearing capacity and installation method.
6. Which Trapezoidal Steel Sheet Is Best for a Façade?
Low-profile trapezoidal sheets, such as T7, T14 and T18, are often chosen for building façades.
T7 trapezoidal sheets are particularly popular for lightweight façade cladding because of their low rib height and attractive appearance.
They can be used to finish the façades of garages, utility buildings, industrial halls and selected elements of residential buildings.
ASPanel offers T7 façade sheets in colours and finishes including:
- RAL 7016 – graphite / anthracite.
- RAL 8017 – brown.
- RAL 9010 – white.
- Wood-effect finish.
The availability of individual colours, thicknesses and dimensions should be confirmed before purchase.
When selecting façade sheets, it is also important to consider the quality of the protective coating, environmental conditions and the method of attachment to the supporting substructure.
7. Which Trapezoidal Steel Sheet Is Best for a Garage?
The choice of trapezoidal sheet for a garage depends on whether it will be used for the roof, façade or another cladding element.
The T18 profile is commonly used for garage roofs and can provide the required load-bearing capacity when supported by a properly designed structure.
T7 trapezoidal sheets can be used for garage walls, façades and lightweight cladding. Their low profile provides an attractive appearance and allows a consistent exterior finish.
When choosing the material, consider sheet thickness, support spacing, wind and snow loads, and protective coating type.
For unheated garages, it is also worth considering solutions that reduce moisture condensation on the underside of the roof covering.
8. Which Trapezoidal Steel Sheet Is Best for a Carport or Shelter?
T18 or T35 profiles are commonly selected for carport and utility shelter roofs, depending on the structural span and expected loads.
T18 sheets may be suitable for smaller roofs, while T35 is often used where greater rigidity is required.
T7 trapezoidal sheets can be used for side walls, wind screens and decorative elements of shelters.
Their low rib height provides an attractive finish available in various colours.
For open-sided shelters, correct sheet fastening and appropriate consideration of wind uplift forces are particularly important.
9. Which Trapezoidal Steel Sheet Is Best for an Industrial Hall?
Higher trapezoidal profiles, such as T35, T55 or suitable structural decking profiles, are most commonly selected for the roofs of production halls, warehouses and industrial buildings.
Rib height, steel thickness and sheet geometry affect load-bearing capacity. Therefore, the choice of sheet should comply with the structural design and the manufacturer’s load tables.
Blachodach provides technical documentation and load tables for selected trapezoidal profiles.
Lower profiles, including T7, can also be used on industrial hall façades if they meet the design requirements.
T7 sheets may be used for lightweight cladding, screens and finishing elements of industrial buildings.
10. Are Trapezoidal Steel Sheets Suitable for Fencing?
Yes. Trapezoidal sheets are a popular material for fencing private properties, industrial sites, warehouses and construction sites.
Low profiles such as T7 are particularly suitable for this application because they provide a regular, uniform appearance.
Trapezoidal sheet fencing reduces visibility into a property, is relatively quick to install and is available in various colours.
T7 sheets offered by ASPanel are available in finishes including graphite, brown, white and wood effect.
When constructing a solid fence, posts, foundations and fasteners must be correctly selected because the sheet surface can be exposed to significant wind loads.
11. What Thickness of Trapezoidal Steel Sheet Should You Choose?
The thickness of a trapezoidal sheet should be matched to its intended use, profile height, support spacing and expected loads.
ASPanel offers T7 trapezoidal sheets in thicknesses of 0.4 mm, 0.5 mm and 0.6 mm.
| Thickness | Example Application |
|---|---|
| 0.4 mm | Lightweight screens, soffits, selected façade elements |
| 0.5 mm | Façades, fences, garage cladding |
| 0.6 mm | Cladding requiring greater rigidity with the same profile |
Thicker steel sheets generally provide greater rigidity and resistance to deformation. However, actual load-bearing capacity also depends on profile geometry and support conditions.
When purchasing, check whether the stated thickness refers to the steel core or the complete sheet including its coatings.
12. Is 0.5 mm Trapezoidal Steel Sheet Thick Enough for a Roof?
A trapezoidal sheet with a steel core thickness of 0.5 mm may be suitable for roofing, but its suitability depends on profile height, support spacing, roof pitch and climatic loads.
T18 sheets with a thickness of 0.5 mm are often used on garage, shelter and utility building roofs.
For larger roofs or longer spans, higher profiles such as T35 or T55, or other solutions specified in the structural design, may be required.
A thickness of 0.5 mm alone does not mean that every sheet is suitable for roofing. For example, the T7 profile offered by ASPanel is primarily intended for façade and finishing applications, so its use as roofing must always be verified.
13. What Do the Symbols T7, T14, T18, T35 and T55 Mean?
The symbols T7, T14, T18, T35 and T55 indicate the nominal rib height of a trapezoidal sheet in millimetres.
The higher the profile, the greater the sheet rigidity generally is, assuming comparable material specifications.
| Symbol | Profile Height | Typical Application |
|---|---|---|
| T7 | 7 mm | Façades, fences, soffits |
| T14 | 14 mm | Façades and lightweight cladding |
| T18 | 18 mm | House, garage and shelter roofs |
| T35 | 35 mm | Industrial hall and warehouse roofs |
| T55 | 55 mm | Roof structures requiring higher load-bearing capacity |
Manufacturers may use different designations for profiles of similar heights.
For example, Blachodach uses the designation E7 for its 7 mm façade profile, while a similar product category on the ASPanel website is called T7. This does not automatically mean that the two products have identical geometry.
14. What Is the Difference Between Galvanised and Colour-Coated Trapezoidal Sheets?
Galvanised trapezoidal steel sheets are protected by a zinc layer that helps prevent steel corrosion.
Colour-coated sheets have an additional organic coating, such as polyester, applied to a suitably prepared metallic substrate. This provides additional protection and gives the material its selected colour.
| Parameter | Galvanised | Colour-Coated |
|---|---|---|
| Protection | Zinc | Metallic and organic coatings |
| Colours | Metallic finish | Wide range of colours |
| Appearance | Industrial / functional | Decorative |
| Typical application | Utility and technical buildings | Roofs, façades, fences |
| Price | Usually lower | Usually higher |
Galvanised sheets can be an economical option for utility buildings and lightweight structures.
Colour-coated sheets are often chosen for façades, fences and roofs where appearance is important alongside durability.
The actual corrosion resistance depends on the specifications of the coating and the environmental conditions.
15. What Protective Coatings Are Used on Trapezoidal Steel Sheets?
Trapezoidal steel sheets are protected with metallic and organic coatings designed to protect the steel against corrosion and weather conditions.
The most common options include:
- Galvanised zinc (Z) – a zinc layer providing corrosion protection.
- Aluminium-zinc (AZ) – a metallic coating containing aluminium, zinc and silicon.
- Gloss polyester – a popular decorative coating available in many colours.
- Matt polyester – a matt-finish coating often selected for roofs, façades and fences.
- Polyurethane coatings – used on selected products requiring enhanced resistance to external factors.
- PVDF – coatings used, among other applications, where high colour durability is required.
Blachodach lists polyester coatings, galvanised zinc and aluminium-zinc coatings in the documentation for its profiles.
When choosing a coating, consider the building’s location, sun exposure, corrosive environment and the manufacturer’s warranty conditions.
