Pliable Building Membrane known as Sarking Exterior Wall Types • • • • Single-Leaf and Solid Wall Cavity Wall Direct Fix Cladding Wall Unique Wall Single-Leaf Wall / Solid Wall • Consists of only one layer of building material. Exterior Wall Types Cavity Wall • Consists of two or more layers of building material separated by a drained cavity. Exterior Wall Types Direct Fix Cladding Wall • Wall cladding attached directly to the wall framing without the use of a drained cavity. Exterior Wall Types Unique Wall • A wall that is neither a cavity wall nor a direct fix cladding wall. Exterior Wall Types Exterior Loadings for Building Envelope • Wind • Hail or snow • Wind-driven rain • Humidity • Solar / thermal • Air pressure Water / moisture penetration Effects of Water / Moisture Penetration • Deterioration of building elements • Loss of amenity • Unhealthy or dangerous conditions (mould and mildew) Pliable Building Membrane / Sarking • Defined as a water barrier. • Also called as weather-resistive barrier, water control barrier, and etc. • It must comply with AS/NZS 4200.1 and it should pass the tests specified in AS/NZS 4201.4 • Can act as water, air, vapor, and thermal control membrane. How Does Water Penetrate through Walls The Problem: • BCA does not clearly specify in the NCC the need for sarking / pliable building membrane in walls, especially in cavity walls. • No provisions directly stating the need for a water control layer or weather-resistive barrier. NCC 2019 Provisions for Sarking NCC Volume 1 NCC Guide to Volume 1 Facts: • Brick veneer itself is not a waterproof assembly and it is considered as reservoir claddings (porous cladding materials). • “The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a weather-resistive barrier behind the exterior veneer.” (Source: International Building Code or IBC 2018) • Cavity drainage walls anticipate that water will penetrate the cladding. And the most effective procedure in deterring water penetration in building wall is the use of cavity drainage wall system in combination with a weather-resistive barrier. (Source: ASTM E2266 –Design and Construction of Low-Rise Frame Building Wall Systems to Resist Water Intrusion) Facts: • Workmanship affects the permeability of the walls more than any other factor. The quality of the workmanship inside the walls have greater influence than the kind of surface finish on the brick joints based on experiment. (Source: Water Permeability of Masonry Walls by C. Fishburn, D. Watstein, D. Parsons) • A water-resistive barrier is not required on projects where exterior walls have concrete or masonry backing behind brick veneer, but one may be included for redundancy. (Source: The Brick Industry Association) Sarking may not be required in double brick veneer According to AS 3700 – Masonry Structures Section 4.7 – Prevention of Moisture Penetration According to AS 3700 – Masonry Structures Section 5 – Design for Durability Building Enclosure Basic function – to act as barrier against the exterior environment / weather conditions. Weather-Resistive Barrier Sarking Water Control Layer Pliable Building Membrane Water Barrier Demonstration of Compliance with FP1.4 Classification of Sarking Advantages of Sarking • Low installation cost (labor and material) • Low maintenance requirement • Multi-functional • Ease with installation • Protection during construction • Added bushfire protection Disadvantages of sarking • If wrong specification is chosen for a project, it will cost a lot for maintenance and heighten risk of condensation Notes for Sarking Installation • All sarking must have a min. of 150mm overlap when installed. • Sarking must create a continuous water control layer for the exterior wall or building envelope. • Sarking to flashing overlap must be at least 75mm. • Holes and penetrations on sarking shall be sealed with suitable sealing tape. References • https://energyeducation.ca/encyclopedia/Control_(building_envelope) • BSI-117: Rain Control: Drained, Barrier and Mass by J. Lstiburek(Building Science Corporation) • International Building Code or IBC 2018 • ASTM E2266 –Design and Construction of Low-Rise Frame Building Wall Systems to Resist Water Intrusion • The Brick Industry Association • Water Permeability of Masonry Walls by C. Fishburn, D. Watstein, D. Parsons • A Guide To Residential Installation (Australian Glass And Window Association Guide Series) • https://www.buildingscience.com/documents/digests/bsd-018-thebuildingenclosure_revised#:~:text=The%20primary%20function%20of%20the,the% 20roof%20system(s)
