THERE IS A COMMON ASSUMPTION amongst trades that flexible wall underlays are weatherproof and waterproof and will provide sufficient protection to allow further construction such as installing insulation, linings and painting. However, flexible wall underlays are:
- not classified as a temporary weather protection system
- not waterproof – some water will be transferred past them, and many are absorbent
- prone to damage from wind and other on-site activities – tearing is likely at fixing points, which will allow more moisture past.
Not designed as temporary cladding
In the October 2017 BRANZ Guideline, we asked, ‘Can early close-in be achieved with flexible wall underlays?’ The short answer is, ‘No’.
BRANZ first appraised a synthetic flexible wall underlay in 1984 and, since then, has tested most of the products on the market. BRANZ has also carried out research on the performance of underlay products under wind-driven rain conditions to understand how they will perform.
Flexible wall underlays are designed as air and wind barriers and a second line of defence for any rain penetration. They are not designed to be used as a temporary cladding.
Null-and-void supplier warranties
BRANZ has discussed the practice of using flexible wall underlays as temporary cladding with the suppliers of thermal insulation and wall linings such as plasterboard. These suppliers made it clear that the practice is likely to make their product warranties null and void.
In light of this, BRANZ does not believe that flexible wall underlays provide the robustness or certainty to provide temporary weather and wind resistance. Therefore, they do not comply with New Zealand Building Code clause E2.3.7 (b).
This clause states, ‘building elements must be constructed in a way that makes due allowance for the effects of uncertainties resulting from construction or from the sequence in which different aspects of construction occur’.
Moisture unseen and may be undetected
The issue with temporary weather protection is the limited ability to assess and detect how much water and dampness has entered the wall framing and insulation and onto the back of the wall lining. If not detected and the cladding is installed, any moisture that has entered is trapped, and the risk of future issues from mould and rot escalate.
The issues may not become evident until some months after occupancy. Who will be blamed? The builder? The council? The insulation and plasterboard suppliers?
Where temporary weather protection is proposed, the risk is taken initially by the builder, but ultimately problems can reach the building consent authority (BCA) and owner.
What can be used as temporary protection?
BRANZ has evaluation criteria for temporary wall cladding products used to support BRANZ Appraisals and BRANZ CodeMark certifications.
These criteria will be used to carry out further research in this area since it is critical to the performance of construction and the ongoing serviceability of the building when occupied.
Products that meet BRANZ criteria can be exposed for 90–180 days. During this time, they will act as a temporary wall cladding, resisting storm-condition wind loadings, driving rain and UV exposure and have a robustness that meets the ongoing challenges of site construction. Their performance is verified by BRANZ testing and evaluation and supported by BRANZ Appraisals and BRANZ CodeMark certificates.
Current BRANZ-Appraised temporary weather protection systems that allow the progressing of insulation and lining installation within a defined exposure timeframe are:
- CHH Ecoply® Barrier
- James Hardie Home RAB® Pre-cladding
- BGC Durabarrier™.
More inspections may be warranted
Where a temporary flexible protection is used, BCAs carrying out the prelining inspection before the wall cladding is installed must identify any areas where the temporary protection has been compromised.
A second pre-clad check may also be needed to confirm walls are dry enough.
Such inspections will probably not be required where a rigid temporary weather protection system has been used in accordance with the supplier’s instructions.
Articles are correct at the time of publication but may have since become outdated.