Metal Edge Trims – Typical Use and Example
This page provides detailed technical information on metal edge trims used in concrete and roof decking applications.
Covering slab edge formwork, shape codes, closure systems, and installation guidance, it is designed to support engineers, contractors, and specifiers working with composite floor and roof decking systems.
Purpose:
Edge trims are galvanised steel formwork components used to:
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- Maintain the correct level of wet concrete at slab or roof perimeters.
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- Provide a neat, restrained edge for deck formwork.
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- Support cantilevered slabs up to the specified limit without temporary propping.
Typical Use Example:
At a perimeter beam or wall, the edge trim is fixed in the same way as the deck usually with shot-fired fixings or self-drilling screws and restrained by 25 mm wide straps at 600 mm centres. These straps fix to the top of the deck crown with rivets or screws to prevent deflection and concrete leakage.
In roofing applications (e.g. RoofDek):
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- Edge stiffeners or trims are formed from the same or thicker material as the deck.
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- They extend back one pitch from the free edge with a vertical leg of approx. 30 mm or ½ the deck height.
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- Fixed at 500 mm centres to the deck or verge structure (steel angle, timber, or masonry).
Metal Edge Trim Shape Codes and Ranges for Concrete Slabs
Shape and Codes:
Edge trims are typically right-angled sections with a return flange. Their depth is selected to match slab thickness.
Shape codes generally follow slab depth and steel thickness, for example:
| Trim / Slab Depth (mm) | Trim Thickness (mm) | Max Cantilever (mm) |
| 130 | 0.9 / 1.2 / 1.6 / 2.0 | 100–195 |
| 150 | 0.9 / 1.2 / 1.6 / 2.0 | 50–185 |
| 200 | 1.2 / 1.6 / 2.0 | 100–160 |
| 250 | 1.2 / 1.6 / 2.0 | 50–135 |
| 300 | 1.6 / 2.0 | 50–100 |
| 350 | 2.0 | 50 |
( Technical Data – serviceability limit ≈ 3 mm deflection under wet concrete weight only.)
Notes:
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- Edge trims must bear a minimum of 50 mm on steel or 75–100 mm on masonry.
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- Cantilevers greater than 150–200 mm require additional reinforcement or stub beams.
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- For non-standard projections, temporary works design may be required.
Closures and Edge Trim Systems for Concrete Decking
Closure plates and fillers are used to close any remaining gap between the last decking sheet and the edge beam or wall — typically when a full sheet does not fit exactly within a bay.
Functions:
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- Prevent concrete loss.
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- Complete the shutter for pouring.
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- Eliminate waste of cutting an additional full deck sheet.
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- Allow economical completion of irregular bays.
Types and Materials:
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- Flat or profiled closure plates: 0.9 mm–2.0 mm thick galvanized steel, up to 245 mm wide.
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- Filler blocks (foam or rockwool): used for acoustic or fire stopping and sealing ends.
Economic Benefit:
Closures reduce waste and labour by filling residual gaps precisely without requiring a full-width deck sheet.
For example:
If a bay requires 3.3 sheets of deck, installers use 3 full sheets plus a closure plate instead of cutting a fourth sheet.
This saves material and time while maintaining consistent concrete containment and alignment.
4. Summary - How Closures and Edge Trims Work Together
| Component | Primary Role | Installation Note | Economic / Structural Advantage |
| Edge Trim | Maintains concrete level and provides deck edge restraint | Fixed to support with straps @600 mm c/c | Enables clean edge, controls deflection, supports cantilever |
| Closure Plate | Fills partial bay or gap | Fixed to non-loadbearing side of decking | Reduces waste by avoiding custom sheet cuts |
| Filler / End Cap | Prevents grout loss | Fixed at deck trough ends | Maintains concrete integrity, fire/acoustic seal |
For more information on our edge trim and flashing services,
Summary
- Edge trims are essential components used in metal deck construction to form slab edges, contain wet concrete, and ensure accurate, clean finishes on both roof and floor decking.
- Often referred to as slab edge formwork, metal edge trims are used across a wide range of applications, from composite floor slabs to structural roof decking.
- Edge trims are essential components used in metal deck construction to form slab edges, contain wet concrete, and ensure accurate, clean finishes on both roof and floor decking.
- Often referred to as slab edge formwork, metal edge trims are used across a wide range of applications, from composite floor slabs to structural roof decking.
