PITCHED ROOF CEILING LEVEL
It is possible to achieve very high levels of insulation in pitched roofs where the insulation is positioned at ceiling level because the insulation thickness is largely unrestricted by construction considerations.
A major factor influencing the design of pitched roofs with insulation at ceiling level, is the type of roof tile underlay chosen.
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Pitched Roof Rafter Level
Insulation between the rafters can be designed in two ways:
• ‘Breathing’ roof with Low Resistance (LR) underlay - With this option, insulation fully fills the rafter space without an airspace between the insulation and type LR underlay.
• Ventilated design with High Resistance (HR) underlay - Insulation over the rafters provides a completely insulated external envelope to the roof construction, and allows the maximum usable space within the roof enclosure.
Flat Roof
There are two basic categories of roof design:
A warm roof has the insulation above the structural deck, which is thus kept warm. The waterproof layer is above the insulation and a vapour control layer is placed below the insulation.
A cold roof has the insulation placed below the structural deck, which thus remains cold. This construction relies on a vapour control layer working effectively, and in tandem with a continuous ventilated airspace to disperse the water vapour to atmosphere before it reaches the cold deck and condenses.
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Built Up Metal Roof
Profiled metal roofing systems typically consist of a low profile metal inner liner sheet, separated from an outer, higher profile, metal weather sheet. The cavity between them is filled with a layer of thermal insulation to provide the specified level of thermal performance.
The insulation is normally a lightweight, high performance, non-combustible glass mineral wool quilt, with a Euroclass A1 Reaction to Fire Classification. Built-up metal roofing systems are typically assembled on site with the design and components used forming part of a proprietary system.