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Inverted System

Firestone TPO Inverted System


The Firestone TPO Inverted System is a variation of the conventional Ballasted System. It is ideal for roofs with regular traffic or in severe weather climates. It can be applied on any building that can accommodate the extra load of the ballast and where the roof slope does not exceed 10%.


  • Low installation cost
  • Use of large TPO panels up to 3.05 m
  • Fewer seams
  • Fast installation
  • Large choice of compatible substrates
  • Extra durability
  • Flexibility for upgrading of insulation in reroofing projects


TPO sheets are loose laid over an acceptable substrate. Adjoining sheets are overlapped a minimum of 75 mm and the seams are heat-welded. Once the seams are welded and roof perimeters and penetrations are flashed in accordance with Firestone specifications (PDF), a layer of extruded polystyrene and a geotextile are placed over the membrane. The total system is held in place using one of the following materials as ballast:

  • Gravel in form of round, smooth, river washed aggregate without broken pieces, of adequate size (nominal 16 to 32 mm).
  • Concrete pavers with smooth trowel finish (min. 50 mm thickness).
  • Crushed gravel that must be graduated.

Prior to selection of this system, the specifier should evaluate structural conditions of the building to verify its load bearing capacity. Roof slopes and wind requirements should also be investigated.