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Derbigum Built-Up Torch-Applied Bituminous Warm Roof When to Specify Derbigum built-up, torch applied, high performance warm roof systems offer the highest levels of thermal insulation, durability and waterproof integrity for new flat roofs.

Key Features Lifespan In the Derbigum BBA Certificate 86/1593C, the BBA say ‘All available evidence suggests that the product will have a life in excess of 30 years.’

Durability Derbigum has a high softening point ensuring stability of the membrane in the hottest weather, high tensile strength and excellent puncture resistance. Derbigum can be installed without any surfacing, regardless of the method of application due to the unique blend of polymers which make Derbigum resistant to UV degradation.

Derbigum Cap Sheet (Black or Mineral) Hi-Ten Universal Underlay Type 3G Perforated Layer

Performance Derbigum is a range of dual-reinforced, APP (Atactic Polypropylene) modified bitumen, high performance roofing and waterproofing membranes with a life expectancy of 30-35 years according to independent assessment. Enhanced performance properties include low temperature flexibility, excellent fire ratings, stronger reinforcement and ease of application.

Alumasc GTF PIR Insulation

Installation Derbigum Built-Up Roofing Systems combine proven durability and performance with traditional methods of application.

Quality Alumasc operates a quality assurance management system which is independently audited to BS EN ISO 9001:2008. Alumasc extends this quality management to their network of approved installers, for single source accountability and peace of mind.

Nilperm Vapour Barrier


WBP Plywood Deck (primed)


Warranties Alumasc offers a comprehensive range of warranty options. The typical warranty period for Derbigum is 20 years. Installed exclusively by Derbigum Approved Contractors and underpinned by Alumasc’s extensive project support service, Alumasc warranties cover both product and installation. Independent insurance backed latent product defect warranties are also available through FSA licensed brokers.through licensed brokers.



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Alumasc actively pursues sustainability in the full range of products and systems the company offers through its accreditation to the ISO 14001:2004 Environmental Management Standard. Alumasc, its partners and its suppliers are committed to putting consideration for the built and wider environment at the core of all aspects of their current business and future development. Derbigum membranes are 100% recyclable.

Derbigum Built-Up Torch-Applied Bituminous Warm Roof System Components Application 1. Prime the WBP plywood deck with Alumasc Bitumen Primer and allow to fully dry. 2. Apply the Nilperm vapour barrier, fully bonded in hot bitumen, providing edge protection to the insulation board at all perimeters, openings and projections, with 100mm side laps and 150mm end laps. 3. Install Alumasc GTF Polyisocyanurate insulation, fully bonded in hot bitumen (including Alumasc BGT Polyisocyanurate at upstands, where appropriate – method of attachment dependent on nature of substrate). Boards must be tightly butt jointed and staggered. 4. Install Type 3G (to BS 8747) perforated layer, loose laid, with mineral surface down, with 50mm side and end laps. Terminate the 3G layer 300-500mm from upstands and penetrations. 5. Install Hi-Ten Universal underlay, fully bonded in hot bitumen, with 100mm side and 150mm end laps. 6. Install Derbigum Black or Mineral Cap Sheet, fully bonded by torching, with 100mm side laps and 150mm end laps. A small (approx 5-10mm) continuous bead of compound must always visible at the joint. 7. Note: Pre-cut the lower corner of the end of each roll at 45º where it will be overlapped by the end lap of the next roll.

n Derbigum Black or Mineral Cap Sheet is a high performance, APP modified bituminous membrane, with dual glass/polyester reinforcement, suitable for application by torch application. n Hi-Ten Universal is a polyester based underlay, suitable for torch application (or by bonding in hot bitumen where appropriate). n Type 3G perforated layer is a sanded faced isolating layer with a mineral underside, which facilitates a partial bond of the Hi-Ten Universal to the insulation below. n Alumasc GTF is a CFC- and HCFC-free polyisocyanurate thermal insulation with plain glass-fibre tissue to both faces and is supplied in 600 by 1200mm boards and a range of thicknesses to suit the required thermal value. n Nilperm is a polyester based high performance vapour barrier with an aluminium core, and is completely resistant to the passage of water vapour. n Alumasc Bitumen Primer is a low viscosity, solvent-based bitumen primer intended to maximise the adhesion of bituminous membranes to metal and porous substrates.

8. All detail work to be executed in two layers, the first layer being Hi-Ten Universal, followed by the cap sheet of Derbigum, both fully bonded by torching. At all upstands install a 100 x 100mm reinforcement strip of Derbigum Black into the angle. The main sheet area must overlap onto the reinforcing strip by the full 100mm. Install a final flashing piece of Derbigum, fully bonded to the upstand and overlapping onto the main horizontal sheet area by a minimum of 100mm. NB: Derbigum waterproofing systems are exclusively installed by a nationwide network of Derbigum Approved Contractors.

Technical Support Alumasc Technical Services provide an extensive project support service that includes site surveys, project specifications, performance calculations (e.g. U-values, condensation risk analysis), CAD detail drawings and general technical advice. Contact Alumasc Technical Services via:  +44 (0) 1744 648400  Online resources are available on our website or via the embedded links below: Web Links  Brochures & Datasheets  NBS Specifications

The company pursues a policy of constant product development and information contained in this publication is therefore subject to change without notice. The customer is responsible for ensuring that each product is fit for its intended purpose and that the conditions for use are suitable. All quoted data is nominal and subject to production tolerances.



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 CAD Drawings for typical details