Compliance & Comparison of Limited Combustability Sarking
We often asked to provide a vapour permeable sarking membrane that is non-combustible and vapour permeable. We are still not aware of such a product that exists in Australia.
Sarking products can be used in Type A or Type B wall constructions since NCC2019 not because they are “non-combustible” but because there is an exemption that permits their use wherever a non-combustible material is required. [NCC 2022 C2D10 or NCC 2019 C1.9]
NCC 2019 Volume 1
Part C1.9
(e) The following materials may be used wherever a non-combustible material is required:
(vi) Sarking-type materials that do not exceed 1 mm in thickness and have a Flammability Index not greater than 5.
(vii) Bonded laminated materials where—
(A) each lamina, including any core, is non-combustible; and
(B) each adhesive layer does not exceed 1 mm in thickness and the total thickness of the adhesive layers does not exceed 2 mm; and
(C) the Spread-of-Flame Index and the Smoke-Developed Index of the bonded laminated material as a whole do not exceed 0 and 3 respectively.
NCC 2022 Volume 1
PART C2D10
(6)The following materials may be used wherever a non-combustible material is required:
(f) Sarking-type materials that do not exceed 1 mm in thickness and have a Flammability Index not greater than 5.
(g) Bonded laminated materials where—
(i) each lamina, including any core, is non-combustible; and
(ii) each adhesive layer does not exceed 1 mm in thickness and the total thickness of the adhesive layers does not exceed 2 mm; and
(iii) the Spread-of-Flame Index and the Smoke-Developed Index of the bonded laminated material as a whole do not exceed 0 and 3 respectively; and
(iv) when located externally, are fixed in accordance with C2D15
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Our Solution: ProctorPassive PyroPerm A2
We have taken a position since NCC 2016 not to supply a product based purely on historic compliance as a bonded laminate with exclusions for use in non-combustible applications. If the material does not provide any functionality we did not wish to offer a material that could have negative consequences for moisture control.
ProctorPassive PyroPerm A2 includes a thin combustible polyolefin film. The addition of the film does however mean that it can function as a water and air barrier with Class 4 vapour permeance. The functional film is protected by the highly perforated mesh on one side, and heavy-weight woven glass textile on the other.
What functionality is provided by perforated sarking products ?
Sarking type materials that have small perforations at 10mm centres have been marketed in Australia for several years as “NON-COMBUSTIBLE SARKING-BREATHABLE” Such a products do not provide functionality as per AS4200.1:2017
Water Barrier
The perforations provide pathway for water to pass through the membrane. The performance solution being offered by this supplier accepts that is leaks water. We suggest thar users review this document.
Class 4 Vapour Permeance
There are insufficient perforations for the membrane to be sufficiently vapour permeable in a large number of applications and in temperate and cool climates of Australia when used to the exterior of porous insulation.
Air Barrier
The perforations provide pathway for air to pass through the membrane under pressure.
You can read the rest of this document, including a comparison between limited combustability sarking materials, by downloading the PDF here.
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