Expert Advice
Frank DiStefano

Merbau Veranda Flooring

Timber flooring used for verandas was traditionally produced from Jarrah. Jarrah has a reasonably high durability rating and was once widely available in a range of building materials including veranda flooring. 

Today there is little Jarrah available as production is constrained. For this reason, we now stock set length Merbau flooring ideal for veranda flooring.

Older period homes often used Jarrah tongue and groove flooring in their veranda spaces. Veranda flooring is not as common in today’s new homes, as decking provides a better solution in outdoor conditions. The main issue with using a tongue and groove flooring externally is that the interlocking profile is not able to cope with excessive expansion or contraction. Decking provides a gap spacing between boards purposely to allow for this natural timber movement. Understandably, decking may not be an option sometimes when keeping to heritage specifications.

Merbau has a higher durability rating of Class 1 compared with Jarrah Class 2 above ground. Merbau is a proven durable hardwood and one of the most popular decking timber species. It has extremely high stability when faced with changing seasonal conditions. Many builders will not deviate from its use in decking applications for this reason.

“Merbau has a higher durability rating of Class 1 compared with Jarrah Class 2 above ground.”

Its colouring is an orange, brown that deepens to a darker reddish brown. Merbau is a high tannin timber and can leach a reddish, brown stain when it is wet.

Merbau flooring is available in set lengths for veranda applications, in 80×19 in set lengths of 1.8m, 2.1m, 2.4m and 2.7m. If solid timber flooring must be used externally in a veranda, then it’s important to consider the points below.

  1. Always keep the flooring board width narrow, like 80mm x 19mm rather than a wider 130mm x 19mm. The expansion and contraction rates affecting narrow boards is much less than when the boards are wider. Be aware that direct rain or high humidity will cause the flooring to expand resulting in peaking and direct sunlight and heat will cause floorboards to contract, creating gaps and possible cupping.
  2. The installation of veranda floorboards should be loose fitted and not clamped tight to help prepare for expected expansion. If the boards can’t move, the pressure can build to cause severe splitting or boards buckling.
  3. Top fixing the flooring with two nails per joist connection and a flexible adhesive is best to hold the flooring flat against the joists. A flexible adhesive still allows for movement and reduces any floor squeaking.
  4. Have a slight fall in the veranda floor allowing water to run off, avoiding any pooling of water on or under the flooring. This slope should be approx. 10mm per metre directed away from the house. The flooring tongue and groove edges need to also follow the direction of the fall.
  5. The subfloor area must be well ventilated allowing for a cross flow of air. This is very important for decking as well as all timber floors. Baseboards should not fully enclose the subfloor area. The Building Code of Australian requires subfloor ventilation for timber flooring. If the subfloor ventilation is unavoidably restricted, then mechanical ventilation should be considered.
  6. A protective oil coating or preservative should be applied to all surfaces prior to installation. This can be a factory applied as a pre coat that ensures the tongues and grooves are also protected. Importantly the end grain also needs to be sealed at installation. Topcoats need to be maintained to continue protecting the flooring from absorbing moisture.
  7. In wet or damp subfloor soils some form of drainage should installed, particularly if the flooring is also low to the ground. Installing aggie pipes and grading the ground to divert water away from the house will help to keep a stable environment for the flooring.
  8. Laying polythene sheeting over any damp soil can significantly reduce the moisture uptake by the subfloor air. Following the above points will help to lessen common expansion issue when floorboards are used externally.


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