Union Européenne

Douglas Fir

Back to summary

4 • Material

Douglas Fir has both excellent mechanical properties and remarkable capacities to resist attacks from wood-boring insects and fungi, properties which make it a sought-after building material.



Mechanical strength


The mechanical properties of the French Douglas Fir have been the subject of many research campaigns since the mid-1980s. Since 1985, the work of Nepveu (InRA – National Institute for agricultural research) and Blachon (CTBA) have also clearly demonstrated that in the case of an equal growth ring width, the Douglas Fir has a better level of mechanical performance than all of the other national softwood production and, that even with high growth, the elastic modulus (E) of the Douglas Fir is at a particularly high mechanical performance level (12,000 megapascals).


The following studies, conducted at France Douglas' initiative, have enabled Douglas Fir to fall within the French national standard since 1998 (NF B 52 001 relating to the visual grading for the structural use of the main softwood and hardwood species). Several additional studies, conducted at the start of the millennium, have meant that these results have been refined, enabling:

- large cross sections (greater than 18,000 mm²) to be incorporated (2007) into the initial text

- specific grading for lumber intended for use in glued timbers to be proposed (2009).

A special study was also launched in partnership with a North American standards body (the West Coast Lumber Inspection Bureau) to integrate (2007) French-origin Douglas Fir into the official grading standards already in force in the United States, giving it a global standing. Each of the studies highlighted the very good mechanical properties of the Douglas Fir which, in almost all cases, can claim to reach the highest European resistance classes (C24, C30 etc.), thus authorising it to be recommended for the most demanding usages.



The visual grading, however, does not perfectly reflect the mechanical properties of the Douglas Fir, which is why, in addition, France Douglas has contributed, with mechanical grading machine manufacturers, to the approval of several of these. To date, around fifteen devices are available on the market. Current investments within sawmills will thus very soon allow a higher value lumber offering to be provided which is even more reliable for the final user.
All of the standards and DTUs in force can be accessed from AFNOR (French National Standardisation Body). The studies mentioned are available from the media library for members of the Association. Summaries of the main texts can be consulted in the guide: "Douglas Fir, a natural choice for construction" available to download.





Natural durability



In addition to these mechanical resistance properties, Douglas Fir (heartwood) also has recognised natural durability properties. Depending on its use, internally or externally, each species has a greater or lesser useful life. This depends on: 

- its exposure to climatic agents (transcribed by categories of use) 

- its natural durability, namely its natural resistance to attacks from fungi and wood-boring insects. 


In France, the July 2011 instalment of the FD P 20-651 documentation governs the definition of classes of use and the natural compatibility of species with each of these. The documentation section confirms the very good durability of the Douglas Fir heartwood (the most durable softwood species along with larch and red cedar) and underlines its specific feature, being especially resistant to moisture absorption, which guarantees structures with 3.1 and 3.2 categories’ greater sustainability compared to species with the same durability but which are more sensitive to moisture absorption.



Thus demonstrated, the mechanical resistance and natural durability properties combine to give Douglas Fir a privileged position in complex architectural projects for which the timber must withstand demanding stresses: outdoor architecture, works of art, use in enclosures with high hygrometry, etc. 



Additional explanations on the definition of categories of use and Douglas Fir’s positioning are available from the Catalogue: "Douglas Fir, a natural choice for construction" accessible by download.

Compared elastic modulus of the main French commercial softwood species - Source: study by Neveu (INRA) and Blachon (CTBA) - 1985.

Compared elastic modulus of the main French commercial softwood species - Source: study by Neveu (INRA) and Blachon (CTBA) - 1985.

Breakdown of lumber by mechanical resistance classes - Source: CTBA, study by Mokuzaï - 2003.

Breakdown of lumber by mechanical resistance classes - Source: CTBA, study by Mokuzaï - 2003.

Extract from the documentation instalment FD P 20-651, confirming the very good durability of Douglas Fir heartwood.

Extract from the documentation instalment FD P 20-651, confirming the very good durability of Douglas Fir heartwood.