Specifying Insulation for Inverted Flat Roofing


When specifying insulation for inverted Flat roofing, Extruded Polystrene (XPS) brand Dow STYROFOAM™ is perfect as the flat roof is among the most exposed part of a building. So proper structural composition is a determining factor for the life expectancy of the roof.

In flat roofs with conventional build-up, the thermal insulation is placed above the structural deck but below the water-proofing membrane.

The membrane is thermally isolated from the rest of the roof construction, thus exposed to wide temperature inconsistencies would increase risk of premature failure. When applying the “inverted” roof concept, the risk of the failure is reduced. The thermal insulation boards placed on top of the roofing membrane provide protection against a number of damaging factors:

Positives for using insulation for Inverted Roofing:

  • Excessive Temperature: with inverted roofs the temperature of the membrane stays within a narrow interval
  • Climate impacts and UV-radiation,
  • Mechanical impacts during the construction period, use and maintenance
  • blistering of the membrane: the waterproofing membrane on the warm side of the thermal insulation acts also as a vapor barrier

A closed cell structured board is the basis of the excellent physical and thermal property which meets the requirements for the insulation material of an inverted flat roof:

  • no capillarity,
  • negligible water absorption,
  • resistance to freeze-thaw cycles,
  • High mechanical resistance.

The inverted flat roofing insulation system has been proven successful for more than 35 years in Europe. The life-term and long-term behaviour of the system have been examined by building experts several times. Need less to say that compared to a conventional roof the expectancy of the membrane is greater, the risk of failure is reduced, due to the effective and permanent protection of for the membrane.


The inverted insulation system is suitable for all types of flat roofs. The standard build-up is the non-accessible roof with gravel ballast on the top. The inverted roof system also works in utilized roof areas such as terraces, roof gardens and parking decks. Since the insulation is placed on the roofing membrane, an energy saving and cost efficient solution for renovation of flat roofs is possible by installing an inverted roof over the existing roof build-up.

The inverted roof concept provides the following advantages:

  • Protected waterproofing-membrane
  • The roofing membrane is installed on the roof-deck (concrete deck),
  • Simple build-up without additional vapour barrier,
  • The installation of the layers above the membrane is independent from weather
  • Easy and fast installation.
styro Foam