R0700 Flat Metal Roof with Plasterboard Ceiling (concealed rafters)

Structure

ICANZ system reference for this roof is R0700 - Flat metal roof of between 0 and five degrees of pitch with foil draped over or under roof battens providing 40mm air space with antiglare of foil facing the metal roof. Rafter size to allow minimum 190mm air space with 10mm plasterboard fixed directly to base of rafters or on battens to rafters (no thermal gain allowed for by plaster batten space). Above foil 40mm air space, below foil 190mm air space.

Installation

• Option 1: Foil faced blanket (R1.3 blanket) draped over battens or under batten with foil facing downwards. Assume foil faced blanket example sagged but no air space above bulk. Assume minimum 25mm air space below foil prior to batt surface. In all cases R3.0 batt positioned between joists or plaster ceiling.
• Option 2: Where R3.0 batts are used they are placed between rafters on ceiling lining. R3.0 batts installed with 25mm airspace between foil above and top of batts.
• Option 3: For 30mm reflective EPS board: 40mm air space above double sided antiglare foil, antiglare side facing metal, 30mm reflective EPS board positioned to span between rafters and located at mid height of air space providing 80mm air space above and below reflective polystyrene.
• Option 4: Polyweave or double sided antiglare or bubble foil draped foil over or under roof battens providing 40mm airspace (bright side of foil facing down) between cladding and foil.

NOTE: Total R-Values can be increased by substituting bulk insulation products of higher Material R-Value.

A. Calculations assumptions in accordance with AS/NZS 4859.1:2002.  Amendment 1. 2006. Amendment 1. 2006 on the path of the insulation, as required by the BCA Vol 1. Part J and Vol 2. Section 3.12.

B. Temperatures and parameters are based on Australian climate assumptions. Air temperature difference 12oC (36oC less 24oC) for summer conditions and 6oC difference (18oC less 12oC) for winter.

C. Thermal resistance of air films and attic spaces based on values obtained from Section K5 and K6 of AS 4859.1:2006.

D. Building material elements based on 2000 AIRAH Handbook and attic thermal value based on AS4859.1 app K6 table K2.

E. Where reflective insulation is installed, a simple addition of R-values is not possible. Care must be taken to ensure the performance of reflective air spaces is not “double-counted”.

F. The emittance of the reflective surfaces are dependent on tested values and the conditions of the installation, as specified by AS/NZS 4859.1. Amendment 1. 2006.