Know your wood: Western Red Cedar

Weston Studio Western Red Cedar cladding

A native of North America, Western Red Cedar also grows in the UK. Both varieties are popular choices for timber exterior cladding.  

A tall, conical, evergreen tree, it typically grows to a height of between 45m and 75m, with a diameter of 1m to 2.5m. The largest of the cedars, it is pyramidal in shape, with a broad trunk and dense fern-like foliage. The bark is ridged and dark reddish-brown. Some specimens of western red cedar can live to be over a thousand years old.

Cedar shingles on the extension and renovation 'Forest Framework in southeast London', designed by District Architects; © Megan Taylor

Cedar shingles on the extension and renovation ‘Forest Framework in southeast London’, designed by District Architects; © Megan Taylor

The timber

Western Red Cedar’s wood is non-resinous, straight-grained, somewhat coarse-textured and exhibits a fairly prominent growth-ring figure. It is soft, rather brittle, aromatic (especially when wet) and light in weight, about 390 kg/m3 when dried.

It grows predominantly in Canada and North America, but also in Britain in commercial quantities. British cedar is cheaper, but there are other significant differences between the two, which are important to appreciate.

What colour is it?

The sapwood is narrow and white in colour, and the heartwood is reddish-brown. Canadian Western Red Cedar is darker in colour and will include a relative variety of colours within the batch, from a chocolate brown to an almost salmon pink. British Western Red Cedar is paler – a lighter pink – and more consistent in its colour.

↓ Cedar cladding on the holiday let Looking Glass Lodge, designed by Michael Kendrick architects; © Tom Bird

Cedar cladding on the holiday let Looking Glass Lodge, designed by Michael Kendrick architects; © Tom Bird

How does it weather?

After long exposure to weather the colour is lost, and the wood becomes silver-grey. This weathered appearance is sometimes purposely sought by architects, but one peculiarity of the wood is its ability to take and hold stain of the finest tint without discolouration.

Canadian cedar’s wider variance in colour can result in a patchy look while it is weathering. It also contains a lot of brown oil, which will leach out in the early months. That is part of what makes it durable. But this can lead to staining on the boards, or on any materials beneath the board, such as porous stone.

It reacts with ferrous materials – so any steel used should be stainless steel. In polluted areas, Canadian cedar can go nearly black. British cedar’s more even colour means it weathers to a more consistent silver colour. While it is a little less reactive to ferrous compounds, use of stainless steel is still recommended.

Timber grading

Many UK suppliers import Canadian cedar under the ‘No.2 clear and better’ grade, with 15% falling into the ‘No.4 clear’ category. This is the case currently for TDUK members Vastern Timber, for instance. “We prefer to use the BS and EN standards: BS 1186-3, which has now been superseded by BS EN 942,” says Tom Barnes, Vastern’s Managing Director. “They are more consistent across species.

But British Western Red Cedar is too knotty to use any recognized standards, so we just describe it as ‘knotty cedar’.”

Tom also points out that it is important to check whether the Canadian red cedar is “second growth”: this is faster-grown and is closer to British cedar in colour and overall properties.

A Costa Coffee branch, with Western Red Cedar cladding, supplied by International Timber. The cladding designs included lots of individual pieces of cedar, all the same size but cut at different angles.

Working with Western Red Cedar

The timber works easily with both hand and machine tools, but its relatively brittle nature can cause splintering during some operations. Its soft character can also lead to chip-bruising.

This means that care is needed in order to obtain the best results during mortising, planing and moulding. A good finish can be obtained, but cutters must be kept sharpened.

Strength

Its light weight and soft timber contributes to low strength properties and compared with European redwood (Pinus sylvestris) it is some 20 to 30 per cent inferior in bending strength, and about 1 5 per cent less stiff. It is also much less resistant to splitting and indentation on side grain than redwood. These properties are not problematic for its typical usages in the UK such as cladding, shingles, fencing and other exterior uses.

Knottiness, density and durability

Canadian cedar is relatively knot-free. It is denser and stronger than British, which can be seen in the end-grain: the Canadian’s growth rings are very close together, which is indicative of denser timber. British cedar’s growth rings are further apart. Both are classed as durable, with a service life of over 30 years.

Cedar cladding and maintenance

Maintenance requirements will vary according to whether the cladding is finished with a coating or uncoated. Uncoated systems generally require little maintenance and can be left to weather naturally.

Periodic inspections should be carried out to check that the cladding system continues to perform as required and to identify any repair work needed. To refresh the visual appearance of cladding, proprietary surface cleaners can give good results and manufacturer’s guidance should be followed.

Cedar cladding on the Weston Studio at Rambert School, designed by MICA architects;  © Andy Stagg

Cedar cladding on the Weston Studio at Rambert School, designed by MICA architects; © Andy Stagg

Biological staining (e.g. green algal growth or grey/black fungal staining) can be removed by washing the surface with a 1:4 dilution of household bleach and water. If, at a later stage, you decide to apply a coating to well weathered, bleached wood, the degraded surface layer would have to be removed.

Any surface coatings applied require maintenance and the coating manufacturer’s guidance should be followed. It is far better to maintain coatings on a proactive basis, rather than allow them to deteriorate.

Cladding: proper installation is key

Tom Barnes suggests that the need to maintain cladding is related to how well (or poorly) it has been installed. “One common mistake is installing cladding to ground level,” he says. “To prevent premature decay, be sure to leave a gap of 8-12 inches between the cladding and ground level.”

Tom Compton, owner and joint Managing Director of English Woodlands Timber, agrees.

“With cladding, the important thing is that the fitting should shed water,” he counsels. “The problem is when water gets in at corners or edges. Detail it right – that’s what we really impress on our customers. The detailing is as important as the wood.”

Cedar shingles

Blue Label cedar shingles are 100% heartwood (the durable part of the tree), 100% edge grain (less likely to cup and distort) and 100% clear (no knots or defects). Western red cedar is naturally durable and , generally. cedar shingles have a life expectancy of over 40 years untreated. However, some companies do offer a preservative treatment on the shingles for extra reassurance.

Lower grade cedar shingles (such as Red and Black label) may have reduced life expectancy as they will contain some sapwood, flat grain and possible defects in the shingle.

In general, treated cedar shingles will not need re-treating and can be left to weather naturally over time. It is good practice to carry out periodic inspections, remove any roof debris, clean gutters and if possible remove any moss build-up.

Thanks to Tom Barnes, Managing Director, Vastern Timber; and Tom Compton, Joint Managing Director, English Woodlands Timber

Further information from Vastern Timber about Western Red Cedar

Further information from English Woodlands Timber about Western Red Cedar