About Co2 Larch ®

Co2 Larch <sup>®</sup> about
Co2 Larch ® is a imported Siberian Larch (Larix sibirica). Siberian larch is a very resistant (heigh levels of arabinogalactan a toxic to fungi) and durable wood and is the only conifer that is classed within the hardwood group of timbers with a Durability Class 3 rating (BS EN 350-2 classes) and is compatible in hardness to oak.

At Co2 Larch ® we only sell Unsorted I – 3 A/B Grade, which is the highest grade available in regards to quality and look. It is known as unsorted and consists of the highest three appearance qualities i.e – I-2 & 3.

Other grades are:-

Sawfalling I – 4 B/C Grade, and is made up of a mix of grades I – 4. The actual percentage of the mix is totally dependent upon the recovery of grade 1-4 at the saw mill.

Fourths = C Grade, Fourth is an economical grade that includes a higher proportion of knots and other natural characteristics. It is an excellent choice if you are looking for a more “rustic” appearance.

Co2 larch can be left to naturally age for a rustic appearance or treated please see our accessories for a range of products.


When selecting your timber type for your project it is worth taking in to consideration BS EN 350 timber durability class.

Durability is the ability of a species to resist decay either naturally or through preservatives. The Class is based on the ability of the heartwood (inner part of the tree) to resist fungal decay. The sapwood (the living outermost portion of the tree)is considered not durable and should not be used for external projects without preservative.

BS EN 350 has 5 classes of durability they are:-

Class 1 to 3 can be left as untreated timber, a natural ageing process will accrue e.g. Larch will turn a grey colour. Class 4 and 5 will need to be treated with preservatives.

For further information see www.greenspec.co.uk/building-design/cladding-durability-quality

Quality Grades According to BS 1186-3

BS 1186-3 has 3 grades applicable to external timber cladding, mostly concerned about the size and frequency of knots::-

For further information see www.greenspec.co.uk/building-design/cladding-durability-quality