Perimeters and vegetation barriers


The minimum required upstand height for the waterproofing at abutments, parapets or pipe work penetrations etc, is 150 mm above the completed landscape surface. The only exceptions are at perimeter kerbs where the waterproofing extends fully to the outer edge finishing in a traditional welted drip, edge trim or at access doorways, where a linear drain is incorporated. Flush threshold access doorways can normally be accommodated, and the design of the waterproofing detail at the threshold will vary dependent upon the components to be sealed to.

Vegetation barriers

These are created with round washed pebbles and provide several important functions in a green roof:

  • As a fire break, a minimum of a 300mm border around all upstands and penetrations. The border must be 500mm around upstands with openings (doors, windows, opening roof lights, etc.)
  • Prevent vegetation from encroaching on roof elements such as rainwater outlets
  • Protection of the vegetation layer from water running down vertical upstand surfaces or from higher level rainwater downpipes.
  • Provide rapid surface drainage during heavy rainfall.
  • Reduce and ease routine maintenance.
  • Protection of the waterproofing from mechanical damage during maintenance.
  • Wind uplift resistance by increasing the imposed load at roof perimeters

  • Pebble barriers
    Round washed pebbles, graded 20-40mm should be used on all borders to a recommended width of 300mm to provide a vegetation free edging around upstand abutments, rooflights, rainwater outlets and all other penetration points.

    The pebble barrier installed on this project also prevents erosion of the XF301 sedum blanket vegetation from water draining onto the roof from the roof area above via a downpipe.