Russwood’s Siberian Larch (SILA®) is the cladding of choice for many architects, contractors and self-builders, due to the fact that it is extremely versatile - being suitable for most external timber cladding applications - has excellent durability properties and displays attractive figuring. 

Appearance

Russwood’s SILA boards come in a warm mix of colours, from light reddish brown through to golden browns. When weathered the colour changes to a muted grey tone, which is desirable in many cladding projects. 

With clearly marked annual growth rings, straight grain and relatively few knots the overall look displays attractive figuring with a contemporary look.

Grades and specification

In order to ensure that our in-house grading criteria are met, we offer three grades; A/B, A+ and B/C, with the specifications being as stated below.

Russwood SILA A/B®

Russwood offers SILA A/B®, the highest grade of Siberian Larch cladding commercially available in the UK, which provides a clean and relatively knot-free look combined with excellent durability. The specification for SILA A/B® is as follows:

• Graded to BS1186-3 Part 4 Class 1; each board is practically centre free, one face will be sap free, tight live knots have a maximum 25mm diameter. Maximum of two knots per metre on average over the total length of board, pin knots below 12mm will be discounted
• Kiln-dried to moisture content of 16-18% (+/- 2%)
• Lengths of 1.8 – 6.0m with 95% of your boards being over 2.4m
• Resin pockets permitted on exposed surfaces
• We select from the best available grades in Europe and guarantee that your order will not contain any commonly available, lower quality GOST grades
• FSC® - certified product sourced from sustainable forests, certification no - FSC-C017490

Russwood SILA A+

Russwood also hand-selects boards from the A/B grade to meet stringent internal criteria for the supply of SILA A+. This is almost a clear grade timber, providing a clean, consistent, virtually knot-free look combined with excellent durability. The specification for SILA A+ is as follows;

• Graded to BS1186-3 Part 4 Class 1; each board is practically centre free, one face will be sap free
• Further hand-selection of clearest grade boards which meet the following criteria; tight live knots with a maximum 12mm diameter. Maximum of two knots per metre on average over the total length of board
• Kiln-dried to moisture content of 16-18% (+/- 2%)
• Resin pockets permitted on exposed surfaces
• Lengths of 1.8 – 6.0m with 95% of your boards being over 2.4m
• We select from the best available grades in the UK and guarantee that your order will not contain any commonly available, lower quality GOST grades
• FSC® certified product sourced from sustainable forests

Russwood SILA B/C®

Additionally, Russwood offers SILA B/C®, a more rustic grade of Siberian Larch than our A/B and A+ grades. It gives a more knotty, less uniform look, without compromising its excellent durability properties. The specification for SILA B/C is as follows;

• Graded to BS1186-3 Part 4 Class 2/3; each board is practically centre free, one face will be sap free, knots have a maximum 35mm diameter
• Kiln-dried to moisture content of 16-18% (+/- 2%)
• Lengths of 1.8-6.0m with 95% of boards being over 2.4m
• Resin pockets permitted on exposed surfaces
• Durability class 3 (BS EN 350-2 classification) 
• High density of approximately 628 Kg/m3 at a moisture content of 18% (BS EN 350-2 classification)
• FSC® certified product sourced from sustainable forests 

NBS Specification

For advice on completing the NBS H21 for Siberian Larch cladding please get in touch with our project team.

Durability

For external cladding purposes, Siberian Larch is a naturally durable timber (Class 3 according to BS EN 350-2) due to a combination of factors;

• The presence of tannins in the wood create a high resistance to decay and rot, making Siberian Larch one of the toughest and most durable softwoods
• High density means that it is more difficult for decaying organisms to penetrate the wood

With a lifespan of 50 -100 years when correctly detailed and subject to general outdoor exposure, this is similar to Russwood’s Architect Select Western Red Cedar. Better durability properties can only be achieved with Russwood’s modified timber product: Accoya® wood.

The way a façade is fixed and detailed can have a major effect on it’s lifespan. Our range of fixings and systems are designed by Austrian Timber Engineers to make cladding look better and last longer.

Stability

Extreme continental climates in Siberia (short, hot summers and long, cold winters) produce a high proportion of late wood, which enables a smoother machine finish and enhances dimensional stability.

Additionally, Russwood’s SILA is kiln-dried to 16 – 18% (+/- 2%), the optimal moisture content for external cladding. The benefit of kiln drying Siberian Larch, as opposed to air drying it, is that the timber dries uniformly and therefore achieves optimum stability.

Once the kiln-dried Siberian Larch is received at Russwood, this enables the product to be consistently machined to a superior level of finish. It is then ensured, through the use of stringent quality control processes, that the optimal moisture level is retained until delivery to site. The cladding can then be installed immediately upon delivery.

Density

Due to its high percentage of heartwood (75-90%) and a minimum of sapwood (we guarantee that at least one face will be sap free) SILA is an extremely dense timber, classified by BS EN 350-2 as approximately 628 Kg/m³ at a moisture content of 18%. As such, it is not easily damaged and therefore is ideal for highly exposed elevations, or applications where there is the likelihood of physical damage such as knocks or scrapes (e.g. schools, shopping centres, public walkways).

Coating suitability

SILA can be vacuum coated in SiOO:X, a breakthrough silicone technology, to provide a genuine silver lustre. In effect, SiOO:X creates a weathered appearance at an accelerated rate. Following application, all areas, regardless of protection and exposure, take on a consistent tone which provides a solution to differential weathering. For further information about SiOO:X click here.

SILA can also be vaccum coated in your choice of colour from Russwood’s Teknos paint range. Due to the infrequent knots and tight grain, optimal paint adhesion can be achieved, particularly when used on sawn surfaces.

SILA can also be fire-retardant treated, using either the NON COM® process, or using HR Prof as an on-site applicant. 

Fixings

How timber is fixed is fundamental to it’s long term performance in terms of both appearance and durability. We offer a range of fixings and systems to make cladding look better and last longer. These systems can be written into the NBS H21 specification. For more information on our recommended fixings, click here.

Profiles

We can advise you on the most suitable species and profile for your project. Visit our profiles section to view some of our most popular profiles, or speak to us to discuss further options.

Sustainability

Russwood’s SILA is FSC®-certified, meaning that it is sourced from well-managed forests.

Size

SILA is available in varying lengths of 1.8m up to 6m, widths of 75, 100, 150, 200 or 225mm and thicknesses of 25, 38 and 50mm. Please note that cladding is supplied as a linear meterage based on random stock lengths at time of picking order. Other sizes may be available on request.

For large-scale projects we also have the ability to finger-joint and edge-glue SILA. This process allows the customisation of lengths, which could be particularly desirable in projects such as schools, retail units and other public buildings. Seamlessly joining shorter boards together can create a clearer, more dimensionally stable grade at longer lengths, which is often desired by architects and specifiers.

Price

SILA is one of our mid-range products, with prices starting at £28 per m² for sawn boards.

Summary

• Clean and contemporary look
• Suitable for most types of cladding application
• Excellent density and durability
• Stringent in-house grading of every board
• Sustainable

For a printable summary of the above information, click here to download our Siberian Larch Cladding Factsheet