Currently UK Building Regulations will accept either the old British Standards of Class 1 (BS476 Part 7) and Class 0 (BS476 Parts 6 & 7) or the new Euro classes (B & C) however in a couple of years when the Construction Products Regulation becomes a Directive it will be mandatory to treat timber to be used in permanent construction to Euro classes.
To drive this transition forward Arch Timber Protection have a policy whereby they now only process material to be used in permanent construction to either Euro classes B or C (i.e. they no longer process material to Class 1 or Class 0).
Please be aware that when timber is subject to the non-com process the material must first be KILN DRIED.
Fire Treatment on claddings
Due to the rigorous nature of the pressure impregnation and re-drying processes that the material will be subjected to, which is an unavoidable part of the process to obtain either a Euro Class B (Class One or Class 'O') FR rating, you must be aware of the following.
- The material is subjected to hydration by pressure impregnated chemicals and then re-dried to original moisture content. Due to the characteristics of the particular timber species treated and grain direction of individual pieces, the material may suffer some dimensional distortion i.e. shrinkage/swelling.
- The same process can also lead to additional stresses within the timber, which may lead to some distortion (bend/twist/cup) of material.
- The process can also leave some chemical residue on the surface of the material, which although this is not detrimental to the performance of the material, it may not be acceptable aesthetically. This will need to be removed by either a damp cloth/sanding for Dricon or site cutting if Non-Com residue.
- The above effects are a by-product of the treatment process and cannot be considered as a defect and therefore you may wish to increase any wastage calculation to cover such eventualities.
- The process can also make materials more brittle and this can lead to some unavoidable breakage during transit.
Specifiers Beware of Density Specifications for Fire Retardant Treatment
Leading industry organisations have rejected the unreliable density classification system used by some fire retardant treated timber suppliers in the UK following extensive research conducted by the independent fire test house Exova Warrington fire. This system is based on the density of the timber before fire retardant treatment and assumes similar density species will require the same treatment levels. This is incorrect.
Research has shown that species specific testing must be carried. This is because in some
Cases similar density species at the same thickness require very different levels of fire
Retardant retention in the timber to achieve the correct - and safe - level of fire protection.
With some species, this difference in retention could be over double the level
Recommended using the density classification system.
Exova Warrington fire encourages specifiers and Building Control professionals to utilise a
species specific Classification Report system from independent test houses.
Lonza Wood Protection has invested in a wide range of individual independent
Classification Reports to cover timber species, timber thicknesses and end use
Applications for both of its proven fire retardant impregnation treatments - DRICON and
NON-COM Exterior. Dricon continues to be the only BBA-approved
Fire retardant for timber, celebrating over 25 years of continuous certification. NON-COM Exterior is the only National House Building Council (NHBC)
Accepted fire retardant treatment for exterior cladding timbers. For full information on these quality fire retardant treated timbers from Vincent Timber & Timber Click Cedar