Flat Roof Insulation.

A flat roof or deck is composed of several elements: the support, the roof slope, the vapor barrier, the insulation, the seal, the apertures and protection or roof covering.

roof terrace insulation

Insulation for the flat roof or terrace is an essential requirement to:

  • ensure thermal comfort during winter and summer
  • avoid maximum energy losses
  • protect the roof support and the structure of the house against strong temperature changes

Heat rises naturally, making the roof one of the hotspots of the house. In a poorly insulated home, 30% of energy loss is through the roof.

Insulation materials for the roof

A flat roof can be insulated with different materials:

  • expanded polystyrene (EPS)
  • mineral wool, rock wool and glass wool
  • expanded perlite
  • cellular glass
  • rigid polyurethane foam

Choosing the right insulation for a flat roof or terraced roof

The choice of insulation depends on the characteristics of the roof. It is important to consider the type of roof terrace:

  • accessible or inaccessible.
  • The construction material:
  • masonry
  • steel sheet
  • wood 

Also to consider : the protection (exterior covering) that will be applied finally (the cover).

In addition, another constraint must be taken into account when selecting insulation for flat roofs: the compressive strength rating in psi, and local building and fire code regulations.



Wood fiber




Extruded polystyrene


Cellular glass


Gypsum board


It is important to be aware of relevant local building and fire codes which can be checked at the local authority planning office or town hall.

Unlike pitched roofs, it is not normally possible to insulate a flat roof from the inside. Therefore, it is necessary to insulate from the outside. The insulation is located above the vapor barrier.

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