Overview of Over Roofing Existing Metal Roofs

MRC Groups Over Roofing or Over Cladding solution provides the opportunity to upgrade / refurbish an existing building envelope without having to remove the existing metal roof or cladding system. The system is generally considered when the existing roof is either leaking or coming to the end of its operational life.

The patented AshGrid™ System is installed in the troughs of the existing steel profiled roof sheets roof sheeting, with the brackets fixed directly to the underlying steel or timber purlins, thus creating an engineered, structurally defined cavity between the old and new roof coverings. When insulated this cavity dramatically improves the overall energy efficiency of the entire building.

MRC Groups installed over roofing system, is backed with the unrivalled single source ‘Guardian’ System Warranty which covers materials, installation & maintenance for the term of the roofing and cladding system.

Key Features of Over Roofing Systems

  • No requirements to remove the existing asbestos or metal roof system therefore the property can continue to operate while works are undertaken
  • Full range of aluminium and steel ‘Secret’ & Pierce Fix roof and cladding systems
  • Option of increasing the R-Value performance up to 10 (m2.K/W)
  • Minimum disturbance to the use within the building
  • Avoids the costs of stripping and disposing of existing materials
  • Excellent sound reduction & anti-rain drumming performance
  • Opportunity to increase the roof pitch with differing bracket sizes
  • Backed with the up to 20 year ‘Guardian’ System Warranty

Applications of Over Roofing Systems

Over Roofing Systems have been used throughout the world for over 20 years providing roofing & cladding retrofitting and refurbishment solutions for leaking roofs or property envelopes that have come to the end of their operational life.

Whether the existing roof system is constructed from metal or asbestos, or the structure is steel or timber, over roofing & over cladding provide the perfect solution to the refurbishment of operational property.

If the original design of the roof system has been designed too low, then the over roofing system provides the perfect opportunity to increase the pitch of the roof slope minimising wind driven water ingress.

  • Industrial applications such as Workshops, Factories, Food Processing Facilities and Automobile Assembly Property that require the building to operate while the over roofing system is being installed.
  • Commercial and Retail space such as Shopping Malls and Offices that are always trading and are looking to upgrade their failed roof system energy efficiency to reduce heating or cooling costs.
  • Governmental, Educational, Prison & Transportation Property such as Airports, Schools, Universities, Train Stations and High Security Property that is requires an upgrade in acoustic and thermal performance of their existing leaking roof and cladding system.

Technical Data of Over Roofing Systems


ASHGRID™ Over Roofing Spacer Support System

  • Brackets with thermal pads – standard height range from 60 – 280mm (Deeper brackets available on request)
  • Standard Bar lengths from 1.2 / 2.4 / 3.6 Metres
  • 2 No. Self-Driller Fixings per Bracket – AshFix Mild Steel 5/16 Hexagonal Head LS25 (Steel Purlins) or TF45 (Timber Battens) Self Driller Fixings, with an integrated 16mm washer flange, fixed through the existing roof sheet into the structure

Optional Insulation for Over Roofing Systems

  • Full range of insulation types & thicknesses available
  • Fire Classification Class 1 (non-combustible)

Please note that insulation compressed between purlins & roof sheets will lose at least 35% of the proclaimed R-Value, a constant cavity thickness does NOT compromise the R-Value.

The table below provides the R-Values that can be achieved using an over roofing system.

Weight of a Typical Over Roofing System based on existing purlins at 1800mm centres

  • 2 No. 135mm Bracket per Ln Metre                      1.0 kg / m2
  • 135mm roll out insulation                                 1.7 kg / m2
  • 55mm Secret Fix / Pierced Fix Roof                   6.0 kg / m2

                                                        Total Weight  8.7 kg / m2

Acoustic Data – Sound Reduction

  • 0.55mm Steel Roof System 40dB +
  • 0.8mm Aluminium Roof System 42dB +

Alternative Over Roofing Roof Sheet Options to Consider

  • 0.8mm Aluminum Roof System                             4.0 kg / m2
  • 0.8mm Steel Roof System                                    9.0 kg / m2

Over Roofing System Warranty

Up to 20 year, single source ‘Guardian’ System Warranty covers Materials, Workmanship & Maintenance

Guarantees & Warranties of an Over Roofing System

MRC Group’s up to 20 year ‘Guardian’ System Warranty cuts through the myth & mystic of product guarantees and workmanship warranties issued by the construction industry.

Traditionally a product guarantee would be issued by the manufacturer and the workmanship warranty would be issued by the installer of the over roofing system. Two separate pieces of paper, with differing length of terms and when put alongside each other, never answered the question of who will pay for the materials and works such the over roofing system fail.

‘Guardian’ System Warranty is an unrivalled new era of warranty that covers Materials, Workmanship & Maintenance. The length of term for each element matches and is issued as a single source, transferrable warranty for the life of the guarantee of the over roofing system.

MRC Group challenges the construction industry to ensure that the workmanship warranty issued by contractors matches the length of term of the supplied over roofing system, thereby ensuring high quality installations with designed and tested over roofing and over-cladding systems.