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Simple, clever sustainability

by Darren
Simple clever sustainability

Part 1: A site-assembled metal roof system that provides optimal thermal performance for both new builds and retrofits.

Steel is one of the ultimate building materials for sustainable buildings – it is light, very strong, long-lasting, design versatile and above all, it is 100% reusable and can therefore be fully recycled. Therefore metal roofing and cladding systems play an important role in creating better, more sustainable buildings.

A metal roof system made up of a series of everyday components can outperform almost any alternative system for bespoke and specific thermal properties. Site-assembled systems are built up from their constituent parts on the building site and critically, this system can be used for a new build as well as a retrofit over an existing metal roof.

The Safintra-warranted assembly combines best of breed components to create a system which will perform for decades.

It consists of a steel liner sheet of aluminium-zinc coated steel, a layer of insulation material, the Ashgrid bar and bracket spacer system, and an outer profiled weather sheet, also in aluminium-zinc coated steel.

Site-assembled system:
1.    Weather sheet
2.    Ashgrid Bar and bracket
3.    Insulation
4.    Liner sheet
5.    Purlin

Liner sheets
Liner sheets are simply profiled sheets of aluminium-zinc coated steel with a trapezoidal profile and a thickness of anything from 0,3mm to 0,55mm. The thickness of the liner sheet will depend on the traffic it is required to handle, spanning capability, the cladding installation method and the acoustic requirements of the cladding.

Where required, the acoustic performance of the cladding, in particular its ability to absorb internal sound and minimise reverberation, may be enhanced by the use of a perforated liner sheet.

Thinner gauge liner sheets are not strong enough to walk on, so it is essential that the insulation, spacer system and weather sheet are installed from access panels. Access panels are thicker profiled steel sheets with the same profile as the liner and can be equipped with adhesive non-slip strips. These are loose laid and nested over the liner sheet and used as a platform, shifted along the roof plane as work progresses.

Whether trafficable or not, the steel liner sheets provide an excellent, non-fragile barrier against falling once they have been fully fastened.

The spacer system
The primary function of the spacer system is to support the weather sheet at the required height above the liner sheet. The components of the system must therefore possess sufficient strength to safely transmit the required loading through to the primary purlins, without deformation.

The Ashgrid bar and bracket system consists of steel bars, which provide continuous support to the weather sheet, supported at intervals by steel brackets firmly attached to the purlins through the liner. The bracket foot must incorporate an EPDM pad, which acts as a thermal break, to minimise thermal bridging.

It is important to note that in the absence of an engineered spacer system, the structural integrity of blanket insulation or rigid insulation boards installed over purlins is entirely reliant on the roofing fasteners and packers. The design lengths of the fasteners are often exceeded whilst the insulation and packers do not offer them adequate support. This places the entire roof assembly at risk.

Insulation
Glass fibre or mineral wool blankets are favoured due to their light weight, low thermal conductivity, acoustic performance, ease of handling, cost-effectiveness and fire performance. Glass fibre and mineral wool blankets are flexible, which ensures that gaps between the insulation are eliminated during installation, preventing thermal bridging.

The outer weather sheet
The outer profiled metal sheet of a double-skin built-up cladding system is known as the weather sheet. While protecting the building by forming a weather-tight envelope, it also acts as a structural element, as it plays an important role in transferring externally applied loads, for example from wind, hail, snow and foot traffic, through to the secondary steelwork and the primary load-bearing frame.

Built-up steel systems offer savings of approximately 10% over rigid insulation board applications of equal R-values. They also offer savings by fast-tracking the critical path of the project.

Safintra supports its Built Up System with Performance Warranties. Technical advice is gladly offered at no cost at all stages of the project.

Safintra South Africa
Tel: 011 323 6300
Website: www.safintra.co.za and www.safintra.com

Benefits of built-up systems
•    Cost-effective.
•    Lightweight and fast method of construction.
•    Secure and waterproof at an early stage of the build programme.
•    Efficient R-values up to 7m².K/W, and offers consistent thermal performance for the life of the building.
•    Improved structural performance: The liner sheet and Ashgrid bar and bracket spacer system provide restraint to the steel purlins, thus ensuring rigidity of the roof structure.     
•    Glass fibre and mineral wool deliver an A/A1/1 fire rating with no restrictions.
•    The acoustic performance far exceeds that of rigid insulation boards installed over purlin and eliminates rain drumming.
•    Improved security due to a second steel skin.
•    Recyclable and reusable: As the individual components are not bonded, recycling of the materials after the building’s operational life does not present the potential ecological impact presented by foam-cored composite panels.

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