Timber Grades, Treatment and Terminology

  Always check

Before you put hammer to nail it always pays to check, measure twice cut once right! We have put together this page with a view to answer some of our commonly asked questions. Please note this is a guide only and if in doubt a call to your council is the best way of seeking further clarity.

Making sure you use the right grade

Building consent authorities (Councils) are likely to require consent documents which include details of the timber grade used. If the timber actually used in construction is different to that specified in design, major remedial work might be required. Because the properties of visually graded timber are identical to the equivalent machine grade, you can substitute between them — for example, VSG8 can be substituted for MSG 8 and vice versa. Likewise, you can substitute a higher grade than specified. However, it would pay to check with the Council prior to making any substitution.

What about timber treatment?

Of course, it is very important to ensure that when treated timber is required, the appropriate level of timber treatment is used.

NZS 3602:2003 (Timber and wood based products for buildings) specifies the requirements for timber treatment in buildings. It is important to refer to NZS 3602 for the full requirements.

Call size /Rough Sawn size versus Machine Gauged size 

Call size/Rough Sawn            Machine Gauged/ Finished size

         25mm                                              19mm                                                                                                            

        40mm                                               35mm                 

        50mm                                               45mm         

        75mm                                                70mm

        100mm                                              90mm               

        150mm                                              140mm

        200mm                                              190mm

        250mm                                              240mm

        300mm                                              290mm                                     

Timber Terminology

Finishes

  • R/S (Rough Sawn) – As it comes straight of the saw
  • B/S (Band Sawn) – Vertical saw cut
  • D4S (Dressed For Sides) – Dressed smooth. Suitable for joinery
  • M/G (Machine Gauged) – Machined to a uniform size
  • PP (Pre-Primed) – Undercoat sealer applied

Treatment

  • H1.2 – Boron treated for protection against borer
  • H3.2 – Exterior treated for exposure to weather, but suitable for in ground use
  • H4 – Ground treated for ground contact
  • H5 – Treated for ground contact near fresh water or soggy ground
  • H6 – Treated ground for near salt water immersion

Grades – Structural/Framing 

  •  No.1 Framing – Visually graded timber that has not had its properties checked (its assumed average stiffness is 6 GPa)
  •  MSG 6 – Machine graded timber that has also had its properties checked (average stiffness of at least 6 GPa)
  • VSG 8 – Visually graded timber that has also had its properties checked (average stiffness of at least 8 GPa)
  • MSG 8 – Machine graded timber that has also had its properties checked (average stiffness of at least 8 GPa)
  •  G8 – Visually graded timber that has been graded in the green state, and has also had its properties checked. This grade is allowed for deck joists, piles etc. where the timber is likely to remain wet in service.
  • VSG 10 – Visually graded timber that has also had its properties checked (average stiffness of at least 10 GPa)
  • MSG 10 – Machine graded timber that has also had its properties checked (average stiffness of at least 10 GPa)
  • No. 2 Framing is still allowed in non load-bearing internal walls.

Grades – Decking

  • Merchant – bark encased knots and pith are allowed
  • Number one – knots up to 1/3 of the area ratio allowed
  • Premium – very small tight knot allowed

Round-wood

  • S.E.D (Small End Diameter) – Round wood with a tapered finish
  • Lager Log – Uniformed diameter overall