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Green oak cladding

Weathered green oak feather edge | VFE1Weathered green oak feather edge | VFE1

Weathered green oak feather edge | VFE1 Weathered green oak feather edge | VFE1

Oak grows widely across the whole of the British Isles and continental Europe and for centuries has been used in all aspects of construction. Despite the loss of much of our native woodland, there continues to be a viable supply of British oak. We make every effort to ensure that all oak logs supplied to Vastern Timber originate from either independently certified woodlands or those managed under the strict guidelines of the Forestry Commission. English oak cladding has many environmental benefits, including a reduction in carbon emissions from transport and the contributing of funds to our native forest management.

Green oak cladding when freshly cut ranges in colour from pink to pale honey. After the surface of the sawn wood has dried, the colour deepens to a golden yellow and then fades to natural silver as the wood weathers.

The knot content of British oak cladding will will contain many small pin knots. Character grade boards will contain many small pin knots, small knot clusters (cat’s paws), sound medium-sized knots (up to 25mm), and occasional larger knots, some of which may split as the wood dries. Boards may also show some tight heart splits and small fissures.

Green oak cladding is a popular choice because of its density, strength and durability. It is most suited to sawn sections such as feather-edge and waney-edge, which create a natural and quite rustic appearance. Green oak cladding is a relatively cost-effective choice when compared to dry oak.

Tannic Acid
One feature of green oak cladding that must be considered is the high tannin content. During the first few months after the cladding has been attached, tannin will exude from the boards, resulting in streaks and stains where it comes in to contact with masonry or render . Tannin also corrodes ferrous metal, so it is therefore important to use either stainless steel fixings. Additionally care should be taken to keep other ferrous metal such as scaffolding away from the cladding to avoid staining of the boards.


Technical Specification

Produced to comply with the harmonised standard for construction products regulation BSEN14915:2013 and to conform with BS8605-1:2014 External timber cladding: Method for specifying.

Trade Name Green oak (or fresh sawn oak)
Base timber English oak
Species Quercus robur
Process None
Origin Legal and well-managed forests in England and Wales.
Intended use External cladding
Other uses Decking, framing and landscaping
Appearance Green oak is often described as being a straw colour. Boards will contain regular sound knots.
Weathering As the boards weather the colour will change to a silver-grey. On shaded elevations or in areas of higher pollution the oak may weather to more of a black colouring. In semi-shaded areas such as under eaves the exuding tannin may leave unsightly stains. As the oak dries out the boards will shrink and are likely to distort to some extent, resulting in a rustic appearance.
Profiles Sawn only. Feather-edge, square-edge and waney-edge
Dimensions Various
Lengths Random. 1.8mt + longer
Moisture content Wet. Beyond measurement.
Natural durability (EN350-2) Durable Class 2 (heartwood only)
Insect attack The ambrosia beetle can attack the wet timber (30% moisture +). However, the beetle will die as soon as the wood dries to less than 30%. Re-infestation will not occur. Other dry wood will not be affected. Sapwood is commonly attacked by the powder post beetle (Lyctus spp). However, sap is normally excluded from cladding boards.
Desired service life:(BS8417) Occasionally wet 60 yrs
Frequently wet 30 yrs
Treatability class Resistant
Movement class Large (Up to 10%)
Resistance to impact Medium to high
Resistance to fixing High. Pre-drilling recommended.
Mean density 330 – 390 kg/M3
When to fix Autumn / winter only. Definitely not during summer months.
Grading Not graded to a BS standard. Generally rustic.
Working properties Green oak is generally easy to work and takes fixings satisfactorily, but becomes increasingly difficult as it dries.
Extractives Oak contains tannic acid, which will corrode ferrous metals. When the two come into contact, a blue sludge is formed that will stain the oak and anything else it comes into contact with. All fixings used in conjunction with green oak should be stainless steel. Tannic acid could also leave unsightly brown stains in the surface of the cladding and will stain any porous materials below the cladding. The reactivity of tannin makes oak cladding unsuitable for polluted areas and shaded areas.
Emission of formaldehyde (EN14915) E1 (Not significant)
Reaction to fire (EN14915) Euroclass F (Untested). D-s2, d0
Fire treatment Not suitable
CE compliant Yes
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