Passive House Course Day 7 - Building Materials

5 May

This is when my ears really pricked up! Some of the common building materials that comprise or building envelope are not suited to creating a healthy indoor environment or ensuring the structural integrity of the building. We have a lot to learn about water penetration into our buildings and as a whole have little understanding of how to control it. Not surprising when some of the commonly used products on the market are not ideally suited.

Let’s look at our vapour barrier in an external wall. It is misconceived that the ‘wrap’ around the outside of the building is just to keep the moisture and dust out. More recently it has adopted a role in keeping embers out during bushfire. But it has one more role to play, to allow moisture within the wall to escape. With differing indoor and outdoor air temperatures, moisture will enter the wall build-up. It is worthwhile noting that warmer air holds more moisture.

The wall build-up should actually be allowing the moisture to either pass from the inside to the outside surface in winter - or - pass from outside to inside in summer.

A foil-based product does not allow the moisture through. A perforated foil membrane also restricts moisture from passing through, whilst creating a lack of airtightness.

For an in-depth explanation check out this BuildingScience article.

On the Passive House course, I learnt that we need to implement building membranes that are ‘diffusion open’. These products that are on the market, are specifically designed for the inside or outside surface and specifically for certain climates. With a little research, I have failed to find many examples of this terminology in Australia. Our construction code (NCC) refers to the terminology of ‘Sarking-Type Materials’

I couldn’t resist the urge to look into this further to see whether the big players in Australia are providing adequate products and also take note of their disclaimers! It was interesting to observe that they are well aware of the issues in wall build-ups, for example, read this CSR series of articles, know your cavity.

I feel it's important to consider what they claim their product does and also what cautions they are hidden in the fine print too;

Our industry needs to be educated so that the correct product is specified and implemented in our buildings, rather than choosing the cheapest ‘wrap’ available. With increased air-tightness and building improvements, incorrectly used vapour control will result in problems, quite possibly within the first year of the build. I’ll be honest and admit that I’ve seen it in the buildings we’ve designed. We are all on this learning curve, which is going to be bloody steep if we don’t correct it now! Let’s look at Canada and New Zealand who have well-publicised issues.

I cannot emphasise enough the importance of the attention required for selection and specification of building products with low toxicity to ensure healthy indoor air environments. Refer to our blog on ‘the indoor generation’ regarding indoor air quality.

Long-lasting structural integrity and healthy indoor air quality should be non-negotiable. Insist on product data and research. Do not compromise.

For further consideration on materials….

Pro Clima appears to be at the forefront of technology, providing intelligent membranes specifically suited to a particular wall or roof build-ups. They also have lots of details and educational information on this topic!

457 is a fantastic resource if you’d like to learn more on barriers, including wall build-ups and product knowledge. It’s American - please don’t hold that against me!

For future projects, I will be very insistent on our vapour barrier selection and specification, whilst also ensuring the wall or roof build-up is detailed and executed correctly.

If anyone has had any first-hand experience with the above brands or any others that we haven’t mentioned - please yell out, we’d love to learn more.

James Hardies - HardieWrap

Weather barrier

Claims to deliver a triple-shield of protection to help against external weather penetration, internal condensation build-up and external heat penetration.

Disclaimers: the building designer is responsible for performing a condensation risk analysis to ensure this product is suitable for your project. (Amongst others)

Dupont Tyvek HomeWrap

Wall Underlay & Vapour permeable membrane

Claims to be a nonwoven, This is a non-perforated sheet made by spinning extremely fine, continuous, high-density polyethylene (HDPE) fibres that are fused together to form a strong, uniform web. the high Moisture Vapour Transmission Rate (MVTR) of DuPont™ Tyvek®. HomeWrap ensures that water vapor does not linger in the walls, but passes to the outside where it belongs.

Disclaimers; For Dupont 10 year limited warranty to be valid, the installation of the wall underlay must follow the prescribed installation guidelines.

CSR Bradford Enviroseal ProctorWrap

Wall Wrap

Claims; Bradford Enviroseal ProctorWrap RW is recommended where humidity is higher inside the building than outside. It is also recommended that the higher insulation R-value used in construction that vapour permeable products are used to minimise the risk of condensation related damage. This product does not provide a reflective R-Value. Bradford Enviroseal vapour permeable wall wrap is considered a pliable building membrane that can be installed behind Brick Veneer and Lightweight Clad in BCA Climate Zones 2 to 8 and complies with NCC 2019 requirements. Bradford Enviroseal™ vapour permeable wraps can minimise the risk of condensation inside the wall that can lead to damaging mould growth. It allows water vapour to safely pass through, and condense on the outside of the wall.

Disclaimers; after installation, the selected cladding should be installed as soon as possible. If a period of 6 weeks passes without being clad, a full inspection of the Proctor Wrap to be conducted to identify damage and to repaired or replaced before cladding is installed. When this product is being used as an air barrier, to achieve airtightness, it is recommended that the building have mechanical ventilation.

Kingspan AirCell Permishield

Reflective Flexible Insulation

Claims to; manufacture with a patented closed-cell structure sandwiched by highly reflective foil surfaces and pierced with tiny, evenly-spaced breather holes, Kingspan AIR-CELL Permishield allows building professionals to do away with the traditional sarking-plus-batts combination in order to achieve thermal compliance as well as satisfy vapour permeance.

Fletchers Sisalation Vapawrap

Vapour Permeable Membrane

Claims; Features a water-proofing, a highly permeable membrane which is laminated and reinforced to a spun-bonded polymer fabric.

When overlapped and sealed with a suitable tape, Sisalation® Vapawrap™ Wall provides a secondary skin against moisture, vapour, wind and dust penetration. The effective barrier also protects the building frame by minimising the amount of rain and dust that penetrates the wall.

With a Flammability Index of ≤5 in accordance with AS 1530.2:1993, Sisalation® Vapawrap™ Wall is suitable for use in Bushfire Areas with a Bushfire Attack Level (BAL) of 0 - FZ in accordance with AS 3959-2009.

Disclaimer; it is important that the cladding manufacturer’s requirements are referred to when determining the suitability of Sisalation® Vapawrap™ Wall for a given system.