Things we know and don’t know about Siberian Larch in the UK
It is always interesting to see what customers know or don’t know about Siberian larch when they select it for use in their joinery or landscaping projects either as decking, fencing and cladding.
Siberian Larch also knew as Russian Larch – Larix sibirica is a softwood which has a wide range of density depending on the country of origin – growth regions ranging from 570 kg/m3 to 650 kg/m3. The mean density 590 kg/m3.
There are other variations of larch being sold as Siberian Larch which is not really such as Dahurian larch L. gmelinii from eastern Siberia. It may not be easy for some people to tell the difference; some distinguishing factors are Dahurian Larch is lightweight, paler and more sparse growth rings.
Siberian Larch is readily available species in the UK but we have seen a lot more volume now as we see more Siberian larch arrive which is not FSC Certified and its origins are not well known. It is important to check that the timber you are using or intending to buy is legal and from sustainable sources always ask for the proof of Certification. Doing an environmental source check also helps tell if you are being supplied with real Siberian larch, not any other species as there is a chain of custody where you can trace the timber back to the source or forest. Legality is very important as timber from Russia can be a high risk of illegality, corruption etc.
Most Siberian Larch quality grades on the market tend to be supplied according to the GOST Grading Rules e.g Unsorted Grade (I-III), Sawfalling S/F IV (Fourths) etc. The bulk of the timber produced by the mills in Russia is saw falling grade and is available in a wide range of sizes and kiln dried to an average moisture content of 18% +/-2%. This moisture content is not appropriate for internal joinery especially where central heating is used but ideal for external applications. It is important to note that this is normally available from 18mm to 50mm thick and thicker sizes tend to be supplied as air dry or kiln dry to approximately the Fibre saturation point (FSP) appx 30 %.
Unsorted Grade is very limited in supply as most mills will not want to focus their resources on selecting this grade as they are high volume mills and time is very important in their production mills and will not justify the sorting time. The UK has been known to be a big consumer of U/S Unsorted Grade which is now becoming more difficult to source as the Russian mills now require customers to buy a mix of Unsorted and higher portion of Sawfalling.
It is also important to note that Unsorted grade will tend to come from the outer part of the log which tends to have higher sap content affecting its durability.
In an effort to help utilising the Sawfalling Grade further processing mills such as Puidukoda OU have resorted to regarding the timber to more utilisable grades such as A/B Grade which is more superior to the saw falling grade and selected for the durable heartwood making it ideal for use for external joinery cladding and decking above ground. This grade is equivalent to BS1186-3 Class 2/3 normally specified for timber cladding weatherboarding specification H21. The lengths we see coming in from some of these mills are more of the lengths designed for the Japanese markets 3.0mtr, 4.0mtr long and 5.1mtr long.
Siberian Larch is a moderately durable species which is sufficient for use in cladding and decking applications and expected service life in excess of 20years. It does not require any additional preservative treatment against decay.
Siberian larch machines, profiles and moulds to profile very well if you are using it for a decking and cladding application. Most common profiles include shiplap, planed square, board on board, tongue and groove for cladding and for decking smooth and reeded dual use decking.
There are some important characteristics that people need to be aware of when selecting or specifying Siberian larch these include;
Siberian Larch has a tendency to cup when not restrained/fixed e.g boards left lying for a long time, it is important to store larch away from direct sunlight. When fixing Siberian larch always face fix and use screws or annular ring shank nails stainless steel.
Siberian larch is a dense heavy species which will mover distort if used for louvres and not well supported.
Siberian larch has a tendency to split and shake when exposed to the elements, you also get resin exudation making it difficult for coating or oiling although other companies have developed particular finishes suitable for coating larch being used externally e.g with Akzo Nobel / Sikkens light Oak these are applied under factory conditions and not onsite by companies such as Puidukoda OU available in the UK.
Siberian larch has a tendency to attract surface non-wood destroying mould, fungi and this tends to blend in as the timber weathers, if larch is exposed like most timber species it will turn grey and a number of factors cause the weathering process. There are products now available on the market that give the uniform weathering look from the date of delivery to minimise the patchy, or watermark on larch decking or cladding e.g using ferrous sulphate this is applied in a factory environment and delivered to site pretreated.
It is always important to take these tips on board and order A/B Grade Heartwood larch for your project and samples are always readily available from your suppliers.