Installation of tongue and groove flooring

When installing tongue and groove timber flooring, care needs to be taken to ensure a high quality, stable result.

• Check the moisture content of the flooring as the timber is removed from its wrapping. If the moisture content is outside the recommended range, the builder should contact the supplier before commencing laying.
• A 10 mm expansion gap must be left between the floor boards and any internal or external wall (See figure 1)
• For floors over 6 metres in width, a 10mm intermediate expansion joint should be provided in addition to the perimeter gaps. This joint is best located under a long wall in the case of platform construction, or across a hallway in fitted floor construction. Alternatively, smaller gaps may be used at closer spacings.
• Lay flooring in straight and parallel lines. The tongues should be fitted into grooves and cramped together. Not more than 800 mm of flooring should be cramped at any one time. Do not over cramp flooring.
• It is essential that boards be in contact with the joists at the time of nailing, particularly when machine nailing. Butt joints should be over floor joists. Joints in adjoining boards should be staggered.
• Fix boards of less than 85 mm cover width with at least one nail at each joint. Boards over 85 mm cover width should be fixed with two nails at each joist. Secret nailed flooring profiles should not be wider than 89 mm. Joists should be seasoned where secret nailing is used.
• The recommended minimum nail sizes are shown in Table 1. Use only deformed shank type nails into softwood joists. Follow the manufacturer's recommendations for nailing pattern, nail type and size.
• The minimum edge distance for nailing at butt joints or board ends is 12 mm. Pre-drill nail holes on the ends of boards to 80% of the nail diameter to avoid splitting.
• Punch all exposed nails (including machine nails) a minimum of 3 mm below the top surface.
• Use special fixings for floors with special dynamic loads or vibration criteria.

References:

• Toby Technical Bulletin TB011.
• Timber Research and Development Advisory Council of Queensland (TRADAC) Report, September 1994
• Gunns Timber. Personal communication.
• Australian Standard AS1684.4

Table 1. MINIMUM RECOMMENDED NAIL SIZE (for flooring up to 21 mm thick)

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Timber Research Unit
Department of Architecture
University of Tasmania