What is the difference between seasoned and unseasoned timber?

Unseasoned timber means timber than has not yet dried to a moisture content matched to its intended environment (this could be 12% for indoor flooring in Victoria and around 16% for outdoor decking in June in Victoria). This does not mean unseasoned timber is unsuitable for any use – it just means you need to be aware of, and maybe detail for, any shrinkage that may occur. Once timber has dried to the moisture content of its environment (called its EMC) it can and will of course continue to swell and shrink as it’s environment changes.

Complicated? A little. What’s important to know is that flooring in particular should always be supplied ‘seasoned’ to an appropriate EMC (usually around 12% for Victoria). Decking on the other hand can be supplied unseasoned but you need to be aware how unseasoned timber shrinks and that is in three ways – 2 ways across the grain (radially and tangentially) and also longitudinally (along the grain). Across the grain Golden Cypress shrinks remarkably little (the average of the radial and the tangential is an extremely low 2.5% from wet green to 12% MC), but like all timbers it can shrink in length. The best way to deal with this is to arriss (plane off the edges) of the cuts that make any butt joins (i.e. accentuating the join). For unseasoned claddings you can mitre the laps or use cover straps. In fact there are many ways to detail a job to use unseasoned material rather than seasoned material.

Structural F7 timber is supplied unseasoned and presents very few problems. In fact Golden Cypress F7 Structural timber is the grade and species of choice for traditional timber framers and mud-brick builders using post and beam frames (e.g. exposed rafters, cathedral ceilings and even load-bearing window frames!), due to its very low shrinkage and stable nature.

Seasoning is often performed in kilns (‘kiln dried’) which in most cases are heated by fossil fuels. Here at Golden Cypress we see no reason to burn fossil fuels when air-drying is a better and more sustainable method – though it can take longer. Despite this, Golden Cypress is actually a very quick drying species in the air; if done correctly a 150 x 25 length of Golden Cypress can dry from green to 12% MC in as little as 6 weeks.