The selection of air cavities within Wall Systems and the impact on design need more significant consideration within NCC 2019 – Vol 1, particularly in reference to Condensation Management.
While there are several Standards for Wall Systems covering air cavity selection, there is no established design process that is used to decide on the ventilation provisions that will work best with all wall claddings or non-standard systems. Via the introduction of AS/NZS 4859.2:2018 - Thermal insulation materials for buildings - air cavities within Wall Systems are identified by the following categories:
(a) in which there is no express provision for airflow through it; and
(b) having no insulation between it and the external environment, but with small openings to the external environment where the openings are arranged so as not to permit airflow through the layer and such openings do not exceed—
(i) 500 mm2 per metre of length (in the horizontal direction) for vertical airspaces; or
(ii) 500 mm2 per square metre of surface area for horizontal airspaces.
An airspace in which there is provision for limited airflow through it from the external environment by limited openings of area (Av) within the following ranges:
(a) For vertical airspaces: >500 mm2 but <1500 mm2 per metre of length (in the horizontal direction).
(b) For horizontal airspaces: >500 mm2 but <1500 mm2 per square metre of surface area.
An airspace in which the openings between the airspace and the external environment are equal to or exceed—
(a) 1500 mm2 per metre of length (in the horizontal direction) for vertical airspaces; and
(b) 1500 mm2 per square metre of surface area for horizontal airspaces.
Via the nomination of either an unventilated, slightly-ventilated or well-ventilated cavity, Speckel enables a quick review of ventilation options alongside other factors that may impact the Total R-value assessment, such as the nomination of reflective membranes.
Step 1 – Let’s first reuse the Lightweight Cladding (Cavity fixed to 92mm steel frame) Wall System we created in Wall Systems Tutorial 1 – Getting Started.
Step 2 – Adjusting a Walls ventilation elements could not be easier. Simply navigate to the air layer. Here you will find access to different ventilation options, that enable you to change the properties of your wall in line with AS/NZS 4859.2:2018 calculation requirements.
Step 3 – If you would like to change the ventilation options entirely, simply click on the ventilation name, and you will be provided with three ventilation options as per the definitions above.
Step 4 - When your happy, simply click Performance Solution and download your Report.