AS/NZS 2785:2020 - Suspended Ceilings Design and Installation was updated in 2020. This article talks specifically about a fresh approach to full plasterboard ceilings. Here are some key points: 

The Standard now aligns with the AS/NZS 1170 series loading Standards, includes serviceability limit state (SLS) and ultimate limit state (ULS) drift and strength considerations, and terminology has been updated with terms like “action” replacing “load” to align with the AS/NZS 1170.0 definitions. 

Changes aim to improve the design, compliance, and performance of suspended ceilings. However, the Standard does not make clear distinction between simple buildings and more complex commercial high-rise type construction, nor does it acknowledge performance differences between full plasterboard and grid-and-tile suspended ceilings. This means there is a requirement at consent stage to provide full seismic design for something as simple as a residential bedroom or even a bathroom ceiling.  

Industry representatives worked with the Association of Wall and Ceiling Industries (AWCI) to include guidance for the non-specific design of full plasterboard ceilings in the newly updated AWCI Code of Practice (CoP).  

Full plasterboard suspended ceilings do not behave like grid-and-tile, and fixed-and-floating edge design is often not appropriate as seismic forces are transferred via inherent diaphragm action to perimeter fixings and walls. Full ceiling perimeter fixing is preferred and sometimes required for noise attenuation, air tightness, hygiene, and fire-resistance. 

The AWCI CoP permits full perimeter fixing of suspended ceilings lined with sheet material, without the need for specific engineering design (SED), provided these conditions are met. 

• The ceiling is installed is in a IL1 or IL2 building, and  

• incorporates ceiling lining(s) not exceeding 25 kg/m2 in mass, and   

• does not exceed 144 m2 in area and 12 m in length or width, and 

• the suspension drop does not exceed 1.0 m measured from the supporting structure above to the back of the ceiling lining, and  

• the suspension framing is designed and installed correctly to support imposed vertical loads, and 

• the sheet material linings are installed to the suspension grid in accordance with the lining manufacturer or supplier’s installation instructions, and 

• the ceiling is level, with no height variations along the ceiling plane, and 

• the perimeter detailing can transfer seismic forces to boundary walls, and   

• perimeter walls can accept and transfer these forces. 

Outside these parameters SED is required and can consider fully fixed or free edge options. 

This does not mean that 144 m2 suspended ceilings lined with plasterboard do not require SED anywhere. The last two bullet points are key. Seismic actions depend on aspects such as geographic location, building height, and ceiling size. The ability of perimeter walls to resist associated forces depends on their length and type of construction.  

We are currently working with our industry partners on non-specific design tables that align with the AWCI CoP guidelines. Watch this space!   

MasterSpec now links suspended ceiling design to the AWCI CoP as a compliance pathway. 

View the AWCI CoP here.