The Most Suitable Thickness
For many decades, the traditional mantra for timber facing products has revolved around 19(18)mm for external use (cladding and the like) and 12mm for internal panelling, ceilings & soffits. While the theory influencing that still dominates today, the break to tradition through the utilisation of thinner profiles for hardwood cladding (under suitable circumstances) provides a very viable (and economical) alternative.
The Decision to Specify 12mm or 18mm Hardwood Cladding.
Traditionally, milled timber products in Australia have been produced from 25mm and thicker hardwood sawn boards, which after drying and machining, produced a finished profiled product of 19(18)mm thickness. Until very recently the 19(18)mm product has been used for external AND internal applications, however the advent of improved wood machining technology in particular has resulted in a 12mm product becoming a viable option for both these areas – internal AND external.
Building Code & Standards Requirements.
Codes - The NCC and BCA are both ‘performance based’ codes – beyond performance criteria, there are no specific requirements regarding the thickness of external timber claddings.
Standards – A.S. 2796 (Milled Hardwood Products) contains reference to a minimum effective board overlap of 13mm for products with a moisture content up to 18% (see point 5 below regarding this).
Fundamentally, except for resistance to impact, 12mm cladding will perform identically to its thicker counterparts. Dimensional stability, shrinkage and expansion are primarily due to moisture related issues – initial moisture content (and gradient) coating and maintenance. Where these are the same for products of both thicknesses, similar performance can be expected.
Properly seasoned products which are appropriately fixed, coated and maintained can be expected to provide stellar performance whether 12mm thick or thicker (see web content on ‘Fixing’ and ‘Finishing’).
TIMBECK architectural - Range of 12mm Cladding.
TIMBECK architectural has developed a new range of 12mm hardwood claddings to complement their 18mm profiles. Product attributes are :-
1. Structural performance for cyclonic & non-cyclonic applications has been certified (see web site for certification statement - also refer to note 1 below).
2. Profile design incorporates tongue and groove projections the same as on 18mm cladding.
3. Production sequencing ensures the same strict moisture content controls as achieved on all other TIMBECK machined profiles.
4. Products provide a profile face which matches 18mm cladding for cases where both thicknesses are required and adjacent to each other.
5. An effective board overlap of 14mm on both 12mm and 18mm Cladding exceeds the A.S. requirement.
Benefits of 12mm Over 18mm Hardwood Cladding.
Price - 12mm cladding is about 20% less than 18mm.
Weight - 12mm cladding is about 30% less in weight – savings in freight and on-site handling.
Where To Use And NOT Use.
Three aspects closely related to the performance of timber cladding are Fixing, Finishing and Maintenance. The TIMBECK architectural web site provides wide coverage and guidance on these topics and their relevance also applies to 12mm hardwood cladding.
As with Fixing, Finishing and Maintenance, the decision to nominate an 18mm OR 12mm cladding rests with the specifier. Location, orientation, degree of exposure to the elements, fixing type & size, selected finish and likely maintenance programme should all be objectively considered. Selecting a 12mm cladding product for the right reasons is as important as choosing an 18mm option for the right reasons, and there are any number of situations where the 12mm option will perform equally as well as the traditionally chosen thicker option.
Note 1 – performance certification for 12mm hardwood cladding is based on withdrawal of fixing from sub-framing and pull-through of head of fixing through the cladding. Impact resistance to flying debris has not been included.