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.

Important information regarding sawn-faced profiles or board on board arrangements

Siberian Larch is imported to the UK in board form. Depending on which mill it came from it will have variety of surface finishes. For example, circular sawn marks, twin arbour lines, paint marks, grease marks or compression marks from steel securing bands. To avoid an unsightly surface finish, Russwood skim the face of each board to provide a clean, unblemished fine sawn finish. See a short video of our skimming process below. 

Grades and specification

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® grade which presents an ideal combination of durability with a clean, relatively knot free look and is ideal for design led projects. 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 up to 6.0m
• 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 produces a limited quantity of A+ grade. This is virtually a clear grade timber, providing a clean, consistent, almost knot-free look combined with excellent durability. At times these boards are in limited supply. 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 up to 6.0m
• 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; the majority of boards will be sap free on one face and knots have a maximum 35mm diameter
• Kiln-dried to moisture content of 16-18% (+/- 2%)
• Lengths up to 6.0m
• 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.

Stability

The tightness of the growth rings and the high proportion of late wood enables a smoother machine finish and enhanced dimensional stability.

Additionally, Russwood's SILA is kiln-dried to 16-18% (+/-2%), the optimal moisture content for external cladding. This moisture level is retained until delivery to site and your cladding can then be installed immediately upon delivery.

Enhanced performance of dimensional stability can be achieved by using narrower widths, for example 120mm, and 95mm.

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

Optimal performance is always achieved with sawn faced finishes.

SILA can be vacuum coated in SiOO:X, a breakthrough water based 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 consistent tone which provides a solution to differential weathering whilst strengthening the timber's surface and creating a water repellent layer. SiOO:X is also available in a mid-grey colour. 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 HR Prof as an on-site applicant. 

Fixings

How timber is fixed is fundamental to its long term performance in relation to both appearance and durability.

We offer a range of fixings and systems designed by Austrian Timber Engineers to make cladding look better and last longer. There are a number of options when considering cladding fixings. Sihga's Fasseden Clip offers secret fixing giving a modern clean finish where no fixings are visible. Also available from Russwood is Sihga's F-Bohr Fix screw for effective secret fixing of tongue and groove profiles or RW115 secret fix profile. For face fixings L-Go Fix screws combined with Kompefix offer a superior look and performance to alternative face fixing arrangements. 

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 up to 6m. 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. 

The standard trade board measurement is 150mm wide traditionally this is the most commonly purchased cladding board. However, at Russwood we also offer a range of board widths including 225, 200, 175, 125, 100, and 75mm. The narrower board widths (75, 100, 125mm) offer a number of advantages including more choice in design arrangements and improved dimensional stability. As an additional benefit narrower width boards are generally graded well in excess of their specification. 

For large-scale projects we also have the ability to finger-joint and edge-glue SILA. This process allows the customisation of lenghts, which could be particularly desirable to create a design look whilst eliminating on site waste. Seamlessly joining shorter boards together can create a cleaner, 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 £32 per m² excluding VAT 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