Wall Wrap Installation: Adhering to Australian Standards

Ever looked at a house at frame stage and seen that plastic-looking sheet flapping in the breeze around the frame? That's wall wrap, and in my experience it's often installed out of sequence.

You expect your house to be built to the standards, so it's sound and energy efficient. But wall wrap is an easy place for shortcuts, and getting it wrong compromises the building envelope (the weather-tight skin of the house) and its energy efficiency.

In this article we walk through the right way to install wall wrap under AS/NZS 4200.2 (Pliable building membranes and underlays: Installation).

You'll learn the correct sequence for windows, doors and wall wrap, so you can check your builder does it right.

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Why Specifying "Reflective Foil" or "Reflective Wall Wrap" Isn't Enough under AS/NZS 4200.2 and AS/NZS 4859.1

First, many project builders don't specify wall wrap properly. Specifications often just say "reflective foil", a term AS/NZS 4200.2 doesn't use. One of the first things the Standard says is:

The design shall specify the purpose and required properties of the membrane, selected in accordance with AS4200.2

In other words, the designer is responsible for specifying what type of membrane goes into the house, and why.

Membranes are specified by function: for example air control, water control, vapour control, or as a reflective thermal layer. So when a builder says "reflective foil", which function do they mean, and have they designed for it? Each has different installation requirements, and different costs.

"Reflective foil" describes what the membrane is made of, not what it's for. Unless the designer nominates the function in the specification, how does anyone know what they're getting, why, and how it should be installed?

AS/NZS 4859.1 (Thermal insulation materials for buildings) says this on the subject:

"Reflective insulation falls into one of the following product groups:

(a) Group 1 Pliable building membranes that have at least one reflective surface. If the products within this group are installed facing an appropriate airspace, they may provide thermal insulation. If they are marketed for this property, the requirements of this Standard shall apply. NOTE: These products are often intended to have a prime function as a sarking or vapour barrier. For this application, test methods, performance classifications and installation requirements are covered by AS/NZS 4200.1 and AS/NZS 4200.2."

So what does that mean? My interpretation is that when "reflective foil" appears in a specification, it's being used as a THERMAL layer.

That means it must be installed to the AS/NZS 4200.2 requirements for that function.

For more, see our post: The Problem With "Reflective Wrap": How Ambiguity Allows Project Builders to Avoid Responsibility.

The Typical Wall Wrap, Window and Door Installation Sequence

The sequence you'll often see on site goes like this:

The windows and doors are installed in the frame openings.
The wall wrap is wrapped around the edges of the windows and doors and stapled in place.

The problem: AS/NZS 4200.2 states that "membranes shall be installed prior to the installation of windows and doors". Installing windows and doors first leaves gaps and tears in the wrap that compromise its water and air resistance.

The Correct Sequence

The correct sequence for wall wrap (whether it's specified as a water, air or vapour control membrane) is:

Install the wall wrap covering the entire wall, including over the window and door openings.
Cut an X in the wrap at each opening, from corner to corner. Fold the flaps inside and tape them in place.
Install the windows and doors in the openings, over the secured wrap.
Seal and tape around the edges of the windows and doors to the wrap to create an air- and water-tight seal.
Seal around any penetrations. Lap sheets at least 150 mm, or at least 50 mm if the lap is taped.

Under NCC 2022 (Housing Provisions Part 10.8), pliable building membranes in external walls must comply with AS/NZS 4200.1 and be installed in accordance with AS/NZS 4200.2, so this isn't optional.

This gives you an unbroken layer of wrap under and around the windows and doors.

Here's what AS/NZS 4200.2:2017 says on the subject.

For membranes around windows:

Sarking installed before the window: the membrane must be sealed to the inner face of the studs and noggings.
Sarking installed after the window: the membrane must be tucked between the window frame fin and the reveal, then taped over the fin. There is also a requirement for the membrane to be at least 1 mm thick for this method to apply.

On that second method: I've never seen a builder do the tuck-and-tape around the window fin. It just doesn't happen. So the only practical answer is to install the wrap properly before the windows and doors go in.

This is summarised in the notes near the bottom of this CSR Bradford technical sheet:

However, I believe this CSR technical bulletin is wrong where it says that, if the windows are already in, the membrane can be tucked between the window fin and reveal and taped over.

The reason: AS/NZS 4200.2 says this can only be done when the membrane is at least 1 mm thick.

Neither the Enviroseal nor the Thermoseal range is 1 mm thick. The technical data sheets below say so on the last page (less than 1.0 mm).

Enviroseal Technical Data Sheet

Thermoseal Technical Data Sheet

What the Australian Standards Say About Proper Wall Wrap Installation

So what do the Australian Standards actually say about installing wall wrap? Quite a bit.

Under AS/NZS 4200.2, wall wrap should run continuously around doors and windows, with the edges taped.

Unfortunately, many builders cut holes in the wrap for the doors and windows, then try to patch around them. That leaves gaps for air and moisture to get into the wall.

Done properly, wall wrap sheds any water that gets past the cladding and reduces draughts, which helps keep the frame dry and the house comfortable.

Here's what the Standard requires for each type of membrane, as specified:

Vapour control membranes: where a membrane is installed as a vapour barrier (Class 1 or Class 2), it must be continuously sealed at all discontinuities, end laps, joints and penetrations, using heat- and moisture-resistant tape, mechanical fixing with adhesive sealant, or an adhesive bond.

Air control membranes: the membrane must be taped or sealed at overlaps, end laps, discontinuities and penetrations (the same way as above).

Water control membranes: upper sheets must lap over lower sheets so water is shed to the outside of the frame.

A few more installation details from AS/NZS 4200.2:

Wall laps of no less than 150 mm,
or laps of no less than 50 mm, jointed and taped,
or butt jointed and taped, where the material is thicker than 5 mm (uncompressed) and overlapping would affect the cladding installation.
All end laps fixed to a stud to form a continuous membrane.
On timber frames, the membrane must be fixed with mechanical fixings at 150 mm centres before the cladding goes on.

It takes a bit more time and care, but it pays off in a drier frame, fewer draughts and lower energy bills.

Here's the CSR Bradford document showing the correct installation sequence:

as42002-membrane-installation-mandatory-requirements-for-walls-technical-bulletin

as42002-membrane-installation-mandatory-requirements-for-walls-technical-bulletin.pdf

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Conclusion

Doing it right the first time saves time, money and headaches. Wall wrap is checked at frame stage, before the cladding hides it, so that's when to look. Don't be afraid to ask your builder to show you the sequence they're using.