Apollo Homes Best Practice Guide - Roof and Ceiling Insulation

INSULATION - Roof and ceilings

NCC 2019 - VOLUME TWO
Refer to Link Below for Common colorbond color Solar Absorptance value:http://www.steel.com.au/products/coated-steel/colorbond-steel/basix-and-bca-classification

Note: When considering the reduction of insulation because of exhaust fans, flues or recessed downlights, 0.5% of the ceiling area for a 200 m2 house would permit 2 bathroom heater-light assemblies, a laundry exhaust fan, a kitchen exhaust fan and either approximately 20 recessed down-lights with 50 mm clearance to insulation, 10 recessed downlights with 100 mm clearance to insulation or only 3 recessed downlights with 200 mm clearance to insulation.

TILED ROOF

Sarking – Bradford thermoseal roof tile plus – Single sided Reflective
Ceiling - Bradford Gold™ Hi-Performance Acoustic Ceiling Glasswool Batt Insulation – R6.0

Note: Ventilated Roof space with Single sided foil and R6.0 Batts achieves R-7.1 Winter Heat Flow Out and R-7.6 Summer Heat Flow In. As the above tables 3.12.1.1e  and 3.12.1.2 show, the minimum required R Value in Perth climate zone based on Solar Absorptance of most common roof tiles being >0.6 is 5.1. 
To allow for a percentage of ceiling area uninsulated due to exhaust fans, flues and recessed downlights, the required roof system R-Value is increased to a minimum of R-6.34. In a truss roofed system where there are no ceiling support members compressing insulation, and where insulation installers have maintained minimum clearances around ceiling penetrations, this R-Value is achievable in theory. This doesn’t take into account the reduction in batt size at externall wall plates to allow manfucturers requirement of a 20mm minimum air gap between insulation and sarking membrane or roof material.
In a stick roof frame system (Most common in Perth), the insulation is compressed underneath ceiling support beams and roof support beams, therefore increasing the total uninsulated by a further 0.5-1.0%.

METAL ROOF

Sarking - Bradford Anticon™ Roofing Insulation Blanket – Medium Duty Foil – Anticon 60 – R1.3 (60mm Batt. Used In conjuction with 40/45mm Roof batten)
Ceiling - Bradford Gold™ Hi-Performance Acoustic Ceiling Glasswool Batt Insulation – R6.0

Note: Ventilated Roof space with Bradford Anticon™ Roofing Insulation Blanket R1.3 and R6.0 Batts achieves R-8.2 Winter Heat Flow Out and R-8.6 Summer Heat Flow In. As the above tables 3.12.1.1e  and 3.12.1.2 show, the minimum required R Value in Perth climate zone based on Solar Absorptance of various colorbond colours varies between R4.1 for a SA of ≤ 0.4 (eg. Classic Cream, Surfmist), R4.6 for a SA of  > 0.4 but ≤ 0.6 (eg. Paperbark, Evening Haze, Shale Grey) and R5.1 for a SA > 0.6 (eg. Jasper, Woodland Grey, Monument). To allow for a percentage of ceiling area uninsulated due to exhaust fans, flues and recessed downlights, the required roof system R-Value is increased to a minimum of R-4.84, R-5.5 and R-6.34 respectively. In a truss roofed system where there are no ceiling support members compressing insulation, and where insulation installers have maintained minimum clearances around ceiling penetrations, this R-Value is achievable in theory. This doesn’t take into account the reduction in batt size at externall wall plates to allow manfucturers requirement of a 20mm minimum air gap between insulation and sarking membrane or roof material.
In a stick roof frame system (Most common in Perth), the insulation is compressed underneath ceiling support beams and roof support beams, therefore increasing the total uninsulated by a further 0.5-1.0%.