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Understand Tongue and Groove flooring

There are a number of fundamental requirements and procedures that need to be followed to ensure the long-term performance of Tongue & Groove (T&G) flooring. The following requirements are applicable where a feature floor or covered floor are placed on traditional timber bearer and joist systems.

Characteristics of timber flooring

  • Timber is a natural product that responds to changes in weather conditions. In high-humidity conditions timber will absorb moisture from the air, causing it to swell and increase in size. Conversely, in dry, low-humidity conditions, timber will shrink and reduce in size. This shrinkage can vary depending on the timber species and cutting pattern of individual boards
  • A variation in board movement can be caused where floors are exposed to the sun through unprotected windows or around fireplaces
  • It is normal for gapping to occur across a floor – gap size between individual boards will vary
  • A small amount of noise can be expected from timber floors when walked on. The level of noise will vary with weather conditions.

Ordering the right timber

When ordering flooring, the following should be provided to your timber supplier:

  • Species
  • Grade
  • Profile and end joint type
  • Cover width
  • Thickness
  • Quantity in linear metres*

You should also ask your supplier to provide the moisture content of the timber they will provide.

* To calculate linear metre quantity, the following method can be used:

Total flooring (m) = (Area of Floor (m²) X 1000) + Wastage
                                                          Cover Width (mm)

Wastage allowances should be 5% for end-matched flooring and 10% for plane and butt joined flooring.

Timber flooring products should be fully protected by your timber merchants or your timber supplier to ensure appropriate moisture content. Once delivered to site it is the contractor/installer’s responsibility to have the timber remain at that appropriate moisture content. The timber should be protected from weather and dampness while on site until the project is completed. 

Construction options for timber floors

There are two traditional construction methods when installing feature timber flooring:

  1. The preferred and strongly recommended method is a fitted or cut-in floor method, where the flooring is installed after the roof cladding and external wall cladding are in place and the house is weather tight
  2. The second method of installation, but not recommended for feature floors, is the platform method. This is where the floor is laid prior to the erection of wall and roof framing. When using this method the contractor will find it difficult to protect against the effects of sunlight and wet weather conditions and normal day-to-day work practices.

A more expensive method but often method used, for a variety reasons, includes laying a platform/structural floor over the joists and bearers or engineered floor trusses/joists using chipboard flooring, or similar and continue framing and getting the building weather tight and when near completion laying the flooring either as a traditional floor or as overlay flooring.

When constructing feature timber floors on bearers and joists it is critical to ensure the subfloor area has adequate cross-flow ventilation, whether by natural or by mechanical means. Minimum requirements for ventilation are outlined in the National Construction Code (NCC) , but the minimum subfloor ventilation recommended for feature T&G floors is 7500mm2/m of external walls, which is greater than NCC requirements.


The information above is based on information contained in Timber Queensland Limited Technical Data Sheets.

To find out more, contact HIA’s Building Services team.

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