BUILDING CODE OF AUSTRALIA - Singleton Council

CHANGES TO THE 2019 BUILDING CODE OF AUSTRALIA

Condensation and water vapour management

C H A N G E S T O T H E B U I L D I N G C O D E O F A U S T R A L I A 2 0 1 9 C O N D E N S AT I O N A N D W AT E R VA P O U R M A N A G E M E N TS I N G L E T O N C O U N C I L

The purpose of this information is to report and advise of new requirements for Class 1a (dwellings and additions),1b (boarding houses, guest houses, hostels.), 2 (units) and 4 (caretaker units) buildings introduced by changes incorporated into the new Building Code of Australia 2019 which came into force on 1 May 2019.

BACKGROUNDThe Singleton Local Government Area (LGA) lies within Climate Zone 6 and the requirements of Part 3 of Volume 2 and Part F6 of Volume 1 of the BCA have been expanded to include requirements to mitigate the effects of condensation (Condensation Management) within residential buildings in Climate Zone 6.

This new requirement has implications to the design and construction of residential buildings and the submission of Construction Certificate and Complying Development Certificate Applications.While this document contains some important and relevant information it should not be relied on to provide a comprehensive source of information on the subject and it is highly recommended that the relevant Australian Standards are consulted for more comprehensive details and fully understand the requirements.

The relevant parts of Volume 2 of BCA 2019 have been included, below, as well as some extracts from the provisions of AS 4200.1 and AS4200.2 which are the Standards for Pliable Building Membranes and Underlays - their construction and installation. The requirements of Volume 1 of the BCA 2019 are the same.

A precis of the new requirements has been included to assist in understanding the installation and identifying complying materials.

PERFORMANCE PROVISIONS

P2.4.7 Condensation and water vapour managementRisks associated with water vapour and condensation must be managed to minimise their impact on the health of occupants. BCA 2019 - Part 3.8.7 - Condensation Management. Acceptable Construction Practice 3.8.7.1 Application Compliance with this Acceptable Construction Practice satisfies Performance Requirement P2.4.7. Explanatory information:The intent of these requirements is to assist in the mitigation of condensation within a building. The installation of a condensation management system may not prevent condensation from occurring. 3.8.7.2 Pliable building membrane (a) Where a pliable building membrane is installed in an external wall, it must— (i) comply with AS/NZS 4200.1; and (ii) be installed in accordance with AS 4200.2; and (iii) be a vapour permeable membrane for climate zones 6, 7 and 8; and (iv) be located on the exterior side of the primary insulation layer of wall assemblies that form the external envelope of a building.(b) Except for single skin masonry or

COUNCIL NOTES

BCA 2019 clearly indicates that all Class 1a,1b, 2 and 4 buildings within Singleton LGA will need to have external walls wrapped in a vapour per-meable membrane which is to be located on the exterior side of the primary insulation material and flow rates for exhaust systems and ventila-tion for roof spaces have now been specified.

It is important that these matters (vapour con-trol barriers, exhaust systems and ventilation of roof spaces) are considered while preparing any Construction Certificate (CC) or Complying De-velopment Certificate (CDC) for submission for approval as full details detailing these provisions are required to be provided in the application before assessment.

It should be noted that the incorrect installation of the pliable building membrane or the installa-tion of incorrect materials on buildings for which Applications for CCs or CDCs or amendments to Applications made after 1 May 2019 may prove very difficult if not impossible to rectify without reconstruction of the external walls of the build-ing.

An examination of the relevant Australian Stand-ards discloses the following information that will be invaluable in the assessment of an applica-tion and the inspection of the relevant portions of any building.

Some details from AS4200.2 which are provided below address framed construction, specifically, but does not address brick veneer construction.

BUILDING CODE OF AUSTRALIA 2019: CONDENSATION AND WATER VAPOUR MANAGEMENT

single skin concrete, where a pliable building membrane is not installed in an external wall, the primary water control layer must be separated from water sensitive materials by a drained cavity. 3.8.7.3 Flow rate and discharge of exhaust systems

(a) An exhaust system installed in a kitchen, bathroom, sanitary compartment or laundry must have a minimum flow rate of— (i) 25 L/s for a bathroom or sanitary compartment; and (ii) 40 L/s for a kitchen or laundry. (b) Exhaust from a bathroom, sanitary compartment, or laundry must be discharged— (i) directly or via a shaft or duct to outdoor air; or (ii) to a roof space that is ventilated in accordance with 3.8.7.4. 3.8.7.4 Ventilation of roof spaces

(a) Where an exhaust system covered by 3.8.7.3 discharges into a roof space, the roof space must be ventilated to outdoor air through evenly distributed openings. (b) Openings required by (a) must have a total unobstructed area of 1/300 of the respective ceiling area if the roof pitch is more than 22°, or 1/150 of the respective ceiling area if the roof pitch is not more than 22°. (c) 30% of the total unobstructed area required by (b) must be located not more than 900 mm below the ridge or highest point of the roof space, measured vertically, with the remaining required area provided by eave vents.


SECTION 2 – DESIGN SPECIFICATION REQUIREMENTS2.2 VAPOUR CONTROL MEMBRANESWhere a pliable building membrane is installed as a vapour barrier, Class 1 or Class 2 membranes shall be continuously sealed at all discontinuities, end laps, joints and penetrations, by oneof the following:(a) Heat and moisture resistant adhesive tape.(b) Mechanical fixing with adhesive sealant.(c) Adhesive bond.NOTE: Bulk insulation or additional ventilation may also assist in reducing the condensation risk when used in conjunction with vapour control membranes.

3.2 GENERAL REQUIREMENTSWhen installing pliable building membranes, the following requirements apply:(a) Damage or tears to the membrane shall be repaired to restore the integrity andmaintain the purpose of the membrane.(b) The membrane shall be cut to provide a neat fit around obstacles and penetrations(see Section 4).(c) Exposure of pliable building membranes to intense heat, sparks, flames or abrasivetools shall be avoided.(d) Where a pliable building membrane is installed as a vapour control membrane,Class 1 or Class 2, or as an air barrier, it shall be continuously sealed at alldiscontinuities, end laps, joints and penetrations by:(i) a pressure sensitive, heat and moisture resistant tape;(ii) adhesive of equal or greater vapour resistance


3.8 FRAMED WALLS

3.8.1 Timber frame wallsWhere a pliable building membrane is installed on a timber frame it shall be fixed to thetimber stud using mechanical fixings at 150 mm centres, prior to cladding.

3.8.2 Metal frame wallsWhere a pliable building membrane is installed onto a steel frame it shall be fixed to thesteel studs using:

(a) adhesive when cladding is directly fixed to the stud work; or(b) mechanical fixings with a broad headed washer at 300 mm centres for cavity walls,prior to cladding.

NOTE: For cavity applications, fixings should be in accordance to the manufacturersrecommendations.

than the vapour controlmembrane;(iii) heat and moisture resistant adhesive tape;(iv) mechanical fixing with adhesive sealant; or(v) adhesive bond.

NOTES:1 Installation of electrically conductive membranes increases the risk of electrocution, in particular for installations in roofs, ceilings, walls and floors where electrical wiring or equipment is present.2 Working in ceiling spaces presents a potential safety hazard.3 Guidance on installation safety considerations is provided in Appendix A.

3.7 COMMON REQUIREMENTS FOR WALLS 3.7.1 GeneralWhen installing pliable building membranes in walls, the following requirements applyInstallation of pliable building membranes in walls shall be as follows:

(a) All joints shall be: (i) lapped not less than 150 mm; (ii) lapped not less than 50 mm jointed and taped; or (iii) butt-jointed and taped where the combined uncompressed nominal material thickness is greater than 5 mm and overlapping will compromise cladding installation.(b) All end laps shall be fixed at a stud to form a continuous membrane.

EXTRACTS FROM AS4200.2 – PLIABLE BUILDING MEMBRANES AND UNDERLAYS – INSTALLATION

COUNCIL NOTES

As the installation requirements for cavity brick or brick veneer construction have not been specifically addressed the requirements of the Design Specification Requirements and General requirements will need to be addressed and observed.

The requirements specify that when installing vapour control membranes (pliable building membranes) the membrane must be installed without damage or tears and must be continuously sealed at all discontinuities, end laps, joints and penetrations by pressure sensitive, heat and moisture resistant tape or an adhesive of equal

or greater vapour resistance than the vapour control membrane or heat and moisture resistant adhesive tape or mechanical fixing with adhesive sealant or adhesive bond.

It is important to note that the jointing and methods for repair rely on the use of proprietary products that have been specifically made for the task.

Clearly, all persons engaged on residential construction will need to be familiar with these new requirements and in particular the designers, builders, bricklayers, plumbers, electricians and air conditioning installers will need to be conversant with the requirements and responsible for their component work.

It cannot be stressed enough that the work involved in the installation of the vapour control membrane must be properly considered and carefully planned as rectification work may be extremely difficult or impossible without major reconstruction as Certifiers cannot accept less than full compliance with the National Construction Code (BCA).

Careful consideration is required to address the way in which any penetrations of the membrane are treated to comply with the installation standard and specifically the way in which wall ties are attached to studs (face fixing to studs may be considered as an alternate to traditional perforation of sarking type material and side fixing to studs), the way in which perforations in the membrane are closed around pipes for plumbing, electrical and air conditioning services, etc.

At the frame work inspection (critical mandatory stage inspection) Council Certifiers expect to be presented with work that addresses this new requirement and which has been carried out in accordance with the Code (BCA), the relevant Australian Standards and the Manufacturers Installation Guides.

All structural framework is to be completed, brick veneer including sills completed, all rough-ins completed and the installation of the vapour control membrane completed prior to the framework inspection being requested.



APPENDIX BROLL LABELLING

This Appendix specifies the minimum information required for each roll of pliable buildingmembrane, in accordance with Clause 6.

Each product shall have a clear and legible label as follows:

(a) The label shall be rectangular in shape and bordered by a continuous line to define its extremities.(b) No other markings or information shall be carried within the border of the label.(c) The ‘product identifier’ expression shall be identical to that used to mark the pliablebuilding membrane (see Clause 6.1).(d) Where classified as light wall, the label shall state ‘for use in walls or gables only’(see Clause 5.3.2).(e) The format of the label shall be as shown in Figure B1.(f) If including optional material classification, the label shall include the followinginformation: (i) Surface water absorbency: High/Low. (ii) Air control classification: Air barrier/ Non-air barrier. (iii) Resistance to UV exposure: Report of test result. (iv) Surface corrosion of low emittance surfaces: Report of test result. (v) Heat shrinkage: Report of test result.

6 Product marking and roll labelling6.1 Product identifierA pliable building membrane shall be identified by an expression consisting of acombination of letters, numbers or symbols (or any combination of the three), hereinreferred to as the ‘product identifier’.

4.1 GENERALThe pliable building membrane shall be cut neatly to allow penetration by chimneys, vents,pipes, cables and other services, as required.

4.3 VAPOUR CONTROL AND AIR CONTROLWhere a pliable building membrane is installed as a vapour barrier or air barrier membrane,methods shall be used to restrict air exchange between air cavities of either side of themembrane in accordance with Clause 3.2.

Extracts from AS4200.1 – Pliable building membranes and underlays.4.7 Pliable building membraneA material that is able to be folded back on

itself without causing structural damage to theproduct that affects its material properties4.11 Vapour control membraneA pliable building membrane designed to either allow or restrict the transfer of watervapour across the membrane, as classified in Table 1 – Note reference to Table 1 is incorrect and Table 4 should be used.5.3.4 Vapour control classificationThe vapour control classification shall be determined in accordance with ASTM E96,Procedure B (wet-cup test). Vapour control properties shall be classified in accordance withTable 4 and results expressed as vapour permeance μg/N.s.

SECTION 4 - PENETRATIONS

6.2 MarkingPliable building membranes shall be marked with the product identifier in a manner thatallows identification after installation. The marking shall be:(a) on at least one face of the pliable building membrane;(b) repeated at distances not more than 3.0 m in the machine direction; and(c) within the central section of the width of the roll, excluding the first 150 mm at eachedge.

6.3 Roll labellingRolls of pliable building membranes shall bear an indelibly marked label in a manner thatallows identification prior to installation. The roll label shall:(a) be located on the outer curved surface of the roll, either outside any roll packaging orunderneath any transparent roll packaging; and(b) bear the format and wording specified in Appendix B.

T 02 6578 7290 E [email protected] W singleton.nsw.gov.au 12 - 14 Queen Street Singleton NSW 2330

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BUILDING CODE OF AUSTRALIA - Singleton Council