What is an inverted roof?

In this type of construction the principal thermal insulation material is applied on top of the weatherproof covering so that the complete roof construction including roof covering is kept at warm temperatures during the winter months and at moderate temperatures during the summer months; the system is also referred to as a ‘protected membrane’, or ‘upside down’ roof.


Liquid applied waterproofing systems are used as the waterproofing layer below the insulation layer, usually directly over the structural deck where their seamless nature is a great advantage over sheet systems.

Sika Liquid Plastics Solution

A roof was once seen only as a means of protecting a building from the elements, but now it is increasingly being seen as a valuable space that can be utilised. Roofs may be used to house plant and machinery that service the building, or provide a terrace that can be used by inhabitants. Both scenarios would require safe general access and may lend themselves to a ballasted, inverted or green roof design.


A ballasted roof is one where the roofing membrane is protected by means of either gravel or paving slabs. As the waterproofing is protected from mechanical damage, UV degradation, and temperature extremes the system can be expected to have a life in excess of that obtained in an exposed situation. The main way that an inverted roof differs to a ballasted is that the insulation sits on top of the waterproofing, but in both scenarios the waterproofing is essentially never exposed.


Green roofs can also classed as ballasted roofs because the waterproofing system is protected by sedum or other vegetation which can be aesthetically pleasing. There are many additional advantages to specifying a green roof which include reducing storm water run-off, replacing the bio-diverse footprint that construction destroys, improving the thermal performance of the building and reducing pollution to name but a few.


All of the afore mentioned roofing systems use the completely seamless Decothane® Root Resistant Waterproofing membrane, which is proven to resist penetration by aggressive roots. Traditional systems can be subject to failure because the waterproof layer allows water ingress through joints, seams, and detail areas. It is therefore particularly important to avoid this scenario in the roof situations where the waterproof layer is below the surface and not easily reachable should problems occur.


Sika Liquid Plastics also specify a number of accessories to accompany the waterproofing membrane that include filtration layers, separation layers, drainage layers and insulation that can be included in the Product Guarantee.

The System Build Up

Bonded Preparatory Layer

Our system includes a bonded preparatory layer, which ensures a sound surface for the application of Decothane Root Resistant Waterproofing Membrane.

Liquid Waterproofing Membrane

Decothane Root Resistant Waterproofing Membrane is a high performance polyurethane coating, which rapidly becomes resistant to rain damage. It cures to form a completely seamless, elastomeric membrane. The system is fully reinforced with Sika Reemat Premium glass fibre matting.

DecoDrainage Composite Mat

When used in an inverted roof construction, it will reduce soil ingress into the void space of the drainage and protect the waterproofing layer from abrasion and puncturing during installation. It has also been engineered to allow good water flow under high loading.

Eco-Inverted Roof Board

Insulation is provided by Sika Liquid Plastics Eco-Inverted Roof Board, an extruded polystyrene board that is manufactured using CO2 as the blowing agent and has zero Ozone Depletion Potential (ODP) and low Global Warming Potential (GWP).

S-Felt VS140

The main function of this layer is to stop fines from blocking the drainage outlets and can be used in both an inverted or ballasted system.


Ballast or Pavers

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