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General fixing requirements for ceiling diaphragms

General fixing requirements for ceiling diaphragms
  • Linings shall be installed over the entire area of the diaphragm.
  • Fastening shall be no less than 12mm from sheet edges.
  • Sheets shall be supported by framing members (eg, ceiling battens) spaced at no more than 450mm centres for 10mm GIB plasterboard and at no more than 600mm centres for 13mm GIB plasterboard.
  • Sheets within the diaphragm area may be fastened and finished conventionally in accordance with methods described on page 79 of the GIB Site Guide. All joints shall be paper tape reinforced and stopped. It is recommended that sheet butt joints are formed off framing and back-blocked.
  • When installing a ceiling diaphragm, it is important that the sheet sizes comply with Figure 1. This may require cutting the first sheet to ensure that the final sheet is 600mm or greater in width.
  • Use full width sheets where possible. At least 900mm wide sheets with a length not less than 1800mm shall be used. Sheets less than 900mm wide but no less than 600mm may be used provided all joints with adjacent sheets are back- blocked (Refer Figure 1).
  • Openings are allowed within the middle third of the diaphragm’s length and width. Fixing of sheet material to opening trimmers shall be at 150mm centres. Neither opening dimension shall exceed a third of the diaphragm width. Larger openings, or openings in other locations, require specific engineering design.
  • Fasteners are placed at 150mm centres around the ceiling diaphragm starting at 50mm and 150mm from the sheet corners.
  • GIB ceiling diaphragms are strong and stiff horizontal bracing elements which effectively transfer loads over large distances. They are used to space bracing lines further apart than 5 metres (single top plate), or 6 metres (double top plate). A ceiling diaphragm shall be square or rectangular. Its length shall not exceed twice its width — the width being measured horizontally between supporting walls. Ceiling diaphragms under light and heavy roofs are required to comply with NZS3604:1999.


Figure 1


Figure 2


For more information and full installation instructions see the GIB Site Guide.


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