A roof edge trim is a capping profile that is fitted to the top of a roof upstand or roof edge to shed water, terminate the roof membrane and finish the edge neatly. It is mainly used on flat roofs and parapet details, and is typically made of aluminium, galvanised steel or plastic.
Functions of a roof edge trim
- Watertight termination — the roof membrane (bitumen, EPDM, single-ply) is dressed under the trim, so water cannot enter at the edge
- Water shedding — a slight tilt to one side keeps rainwater on the roof or directs it off the building
- Wind protection — prevents wind from getting under the membrane and lifting it
- Aesthetics — a clean horizontal line along the roof perimeter
Types of roof edge trim
- Aluminium roof edge trim — most common: lightweight, corrosion-resistant and available in many colours (powder-coated in RAL shades)
- Steel roof edge trim — coated with zinc or polyester, robust but heavier
- Plastic roof edge trim — lighter and cheaper, mainly on garden buildings and carports
- Drip-edge trim — with a pronounced drip nose for extra water shedding
Fixing and installation
A roof edge trim is normally supplied in 2- or 3-metre lengths and fixed to a plywood or timber upstand. Between the lengths comes a connection profile or expansion joint to accommodate thermal movement. The membrane is first dressed over the upstand and the trim is then screwed or clipped over it. At corners, preformed corner pieces or cut sections are used.
Points to consider
- Expansion — aluminium expands strongly with temperature; long runs need expansion joints
- Water run-off — make sure the top of the trim slopes slightly back to the roof surface
- Connection to the gutter — at the transition to a gutter or downpipe, a special corner or transition piece is needed
- Underlying material — use a stiff, compression-resistant upstand to prevent the trim from denting
Application
Roof edge trims are used on virtually all flat roofs: from garages and commercial buildings to modern houses with flat roofs or roof terraces. On pitched roofs a wall capping or lead flashing is more common.
Related terms
- Roof upstand
- Roof edge
- Flat roof
- Roof covering
- Coping
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