Waterproofing to BCA – doesn’t apply to me!
Regional variances, quirks and differences in waterproofing application are evidence of isolation and parochial trends – but BCA compliance still applies to everyone, writes Andrew Gollé.
Regional trends and practices regarding waterproofing application seem to vary throughout Australia – even to the point of the language and terminology used. Ask a Tasmanian to ‘bed a bathroom floor’, and he’ll address you with a look of bewilderment. Tasmanians will render a floor, and often only the shower floor. Main bathroom floor areas outside of the shower are often built up with three layers of 6mm cement sheeting, in order to raise the floor outside of the shower area.
Queenslanders will bed a floor. New South Welshmen and Victorians will screed; and it doesn’t stop there. Ask a Tasmanian to waterproof under the render/bed/screed and they’ll giggle at you with disdain. It makes sense to apply membranes to the top of the formed mortar thingy, and nowhere else.
New South Wales and Victoria, in particular, struggle with the concept. Many certifiers and council inspectors in Sydney will only approve of top-of-screed membrane application as a secondary membrane, where under-screed membranes are applied as the primary protective impermeable layer.
It goes further: plumb dinger, flexi dinger, visquene, forticon, flexi coupler, aussie adaptor, sewerside, Sydney sand, water stop, water bar, barrier angle and puddly flange are all common industry terms in their own localities. Some of you may recognise some of these products but others may look like another language. I won’t explain all of them – please head to Google if you want to make sense of any of the above phrases.
NCC (BCA) and Australian Standard AS 3740- 2010 Waterproofing of Domestic Wet Areas are the minimum requirements to be followed in wet area design and construction. These minimum mandatory requirements apply to building practitioners throughout all of Australia, and should be followed with the addition of state amendments. South Australia, for example requires that a floor waste be provided in all wet areas in Class 1 buildings, unless all fixtures and receptacles are fitted with an overflow relief, with outfall to drainage.
The excuse that AS 3740 mandatory requirements “only apply on the mainland”, or that “it’s a Sydney thing” don’t hold water. Anyone uttering such statements should be able to back them up with documentary evidence in the form of AS 3740 clauses, BCA State Amendments or specific product manufacturer’s requirements.
Two important things
As I mentioned in a previous Building Connection article, following two key principles will help building practitioners and designers to avoid waterproofing failures, and provide serviceable and usable wet area facilities.
The first thing – Keep water within the designated wet area
BCA Volume 2 (P 2.4.1) states “To protect the structure of the building and maintain the amenity of the occupants, water must be prevented from penetrating:
Behind fittings and linings or,
Into concealed spaces of sanitary facilities, bathrooms, laundries and the like.”
The second thing – Use only compliant waterproof and water resistant materials in wet areas
AS 3740 – 2010 (Section 2) lists compliant waterproof and water resistant materials to be used in wet area substrates and linings. The Standard requires that waterproof and water resistant substrate and surface materials are used in conjunction with each other. You can’t have one without the other.
One example of a breach of this requirement occurs when laminated wet area lining sheets are fitted over non-compliant, unprotected plasterboard sheeting.
Photos 2 and 3 illustrate where Lamipanel has been installed over unprotected Aquacheck water-resistant plasterboard sheeting. The correct construction should have been application of a compliant membrane system to the entire surface area of the Aquacheck, as per CSR requirements, and then installation of the Lamipanel with a compatible adhesive (i.e. a construction adhesive, suitable for wet areas and water based membranes).
Some regional trade practices are borne of previous technologies. Membrane application below screeds is common in Queensland and New South Wales, as an evolution from pre-fabricated copper, galvanised or stainless steel trays. People in Tasmania, South Australia and parts of Queensland will apply membranes to the top of screeds. In most cases, this is the preferred method by membrane manufacturers, as it prevents efflorescence defects and stress on the membrane at junctions where bond breakers require release of the membrane, unrestricted by compacted screed. This is supported by design details in AS 3740.
The practice of wire reinforcement in mortar beds is carried out in New South Wales and Victoria, as a continuance of the old school ‘floating bed’ layed over builder’s plastic. This can do more harm than good – exposed wire can penetrate the membrane and cause a breach through differential movement. Forming a bonded screed removes the need for reinforcement.
It sounds weird, but Tasmania has a high rate of leaking pre-formed shower trays because they don’t have termites. The absence of aggressive subterranean termites means that penetration collars, chemical protection or physical barriers are not required. A 300 x 300mm cavity around the shower waste is left open, without backfilling with concrete. This contravenes AS 3740, which requires baths, spas and shower trays to be fully supported.
The resultant leak occurs when trays and baths deflect under live load, separating wall linings at the tray junction. Water then travels along the tray gutter and jumps the tray from behind the wall sheeting, escaping the shower enclosure.
This is compounded by the common practice of installing the shower screen to unprotected wall linings and then tiling up to the screen. Escaping water then contacts and deteriorates adjoining timber skirtings – another no-no!
The adoption of new trends and techniques has resulted in varied forms of waterproofing design and applications.
North Queensland and Western Australia install masonry, tiled hobs to shower enclosures, however WA are still having trouble with placing the shower screen to the inside edge of the hob. Cairns, Townsville and Mackay like their step down shower bays. They have perfected the art of installing barrier stop angles to out-of-shape recessed shower bays, as left by the conkreatures.
38mm to 50mm step ups into bathrooms are common in Southern Queensland, NSW and Victoria, although walk through hobless showers are now all the rage. Tasmanians will not accept this step up, with their hobless walk through showers and will go the extra mile and recess the entire wet area floors. Victorians will religiously install compressed cement sheeting to recessed wet area floors, where Queensland and NSW install particle board sheeting, to be fully waterproofed. The better quality building practitioners will then oversheet with 6mm wet area cement sheeting, prior to full coverage waterproofing.
The Dos and Don’ts
Following are lists of common ‘dos and don’ts’, to help you comply with the BCA and AS 3740-2010. Some of these points might shock you, but they’re all non-negotiable.
Fit shower screens to substrate linings – unless they’re fitted to a barrier stop angle and connected as part of the waterproofing system, this practice doesn’t comply, because the screen fitting forms part of the shower and should be on compliant substrate and lining materials.
Use carpet, timber skirting, plaster setting, MDF mouldings or timber floor finishes – these are all non-compliant and non-water resistant materials, and shouldn’t be in bathrooms, laundries, toilets or shower recesses within the levels of designated risk areas.
Finish wall tiling at 2m with a ceiling-mounted shower head – compliant substrate and lining materials must extend to the shower height, as designated by the rose connection.
Adversely affect the health and amenity of occupants – below-screed membrane application can saturate
and become clogged with organic soap residues, body fats, salts and other nasties promoting bacterial growth. This results in high mould concentrations and poor sub-tile drainage. This is a breach of BCA performance provisions.
Dress membranes directly into waste pipes – AS 3740 requires that membranes are dressed to an approved drainage flange, or puddle flange, and that the flange is set at the lowest drainage point.
Use top-of-membrane application – this is a recognised application process, recommended by manufacturers and detailed in AS 3740. Only one application layer is required. An initial lower layer may result in trapped moisture within screeds, affecting the upper layer.
Seal all penetrations – this includes sheet fixings, tap and mixer penetrations, rose penetrations, toilet penetrations, screen fixings and any other penetrations through waterproofing systems.
Include toilets, laundries and laundrettes as ‘wet areas’ – these areas require waterproofing protection and must incorporate door angles connected to membrane applications. No timber skirtings either.
Apply full coverage to timber floors – full coatings of membranes should be applied to timber floors in wet areas. Best trade practice is to oversheet with f/c sheeting first.
Support baths and trays and provide periphery barriers – aside from support under load, water must be prevented from entering the cavity beneath baths and trays. This should take the form of barrier angle beneath the bath lip, or Type 2 connector sealant, as per AS3740 – Junctions & Flashing (see photos 9 and 10).
BCA and referenced Australian Standard AS 3740-2010 are the minimum and – more importantly – mandatory requirements. They apply to all building practitioners, as required under your particular state or territory legislation.
Don’t be tricked into believing that these requirements don’t apply to you. Those that utter these words must be brought to task, and asked to justify their claims in writing. Use AS 3740-2010 as your guide and justification to prove waterproofing application parameters.