inverted roof

A protected membrane or inverted roof is where the thermal insulation is installed above the waterproofing membrane of a roof deck and then secured by a ballast. Most inverted roof thermal insulation solutions in Southern Africa are for concrete-decked residential and commercial applications, including homes, hospitals, blocks of flats and offices.

These are primarily designed as suitable for foot traffic, planting for roof gardens or access to roof-top building services such as HVAC, elevators and solar systems, even helicopter landing pads. 


Inverted roofs protect the waterproofing membrane from the effects of weather and ultraviolet (UV) radiation. This maintains the membrane’s integrity, as well as thermally insulating the mass of the roof slab.

By maintaining a relatively constant temperature, the internal temperature of the building below is moderated. 

inverted roof

An inverted roof is helpful when roof greening, as the waterproofing membrane is protected.

The standard density XPS manufactured in South Africa is 36kg/m³ and has proven itself suitable for use as an inverted roof for light-vehicle traffic. It can also be retrofitted to an existing roof, as the board and ballast are comparatively lightweight. Higher board densities and compressive strengths are available for heavy-vehicle traffic, but this is the design province of an engineer. 

Moisture ingress is the downfall of thermally insulated buildings, but XPS has the lowest water absorption and will therefore have the longest durability. 

inverted roof

IsoBoard XPS has a proven track record for inverted roofs, with thousands of squares metres installed across the country.

Proven performance 

Over the past 28 years, XPS has been supplied to thermally insulate the concrete decks of many prestigious building projects. IsoBoard has the South African Board of Agre’ment assessment for the inverted roof or protected membrane application, certifying IsoBoard as “fit for purpose”.  

 Inverted roofs protect waterproofing membranes, aid thermal efficiency, and are helpful for roof greening or when making best use of the available space. 

 For more information, contact IsoBoard: 

Tel: +27 21 347 0186 




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