Western Red Cedar

Western red cedar (Thuja plicata) is a large conifer native to the Pacific Northwest of North America. Its heartwood is light, aromatic, straight-grained and naturally resistant to decay, which has made it the dominant species for wood roofing shingles and shakes in North America.

Range

The tree grows from central south-east Alaska to northern California, mainly between the Cascade Range and Coast Mountains and the Pacific Ocean. It needs moist sites and occurs only where annual precipitation exceeds about 71 cm (28 in). An inland population grows in south-eastern British Columbia and the Idaho Panhandle.

Why it suits roofing

• Natural decay resistance: the heartwood contains thujaplicins, natural fungicides that inhibit rot. The protective effect is reported to last about a century after felling. Young trees do not produce thujaplicins, so durability depends on harvesting mature, older-growth wood.
• Light weight: dried wood weighs roughly 390-400 kg/m³ (24-25 lb/ft³), so a cedar roof is light compared with tile or slate.
• Stability and grain: tight, straight grain with few knots allows clean splitting and sawing and reduces warping.

Weathering

Freshly installed cedar is reddish to tan; exposed to sun and rain it weathers to silver-grey. Many owners apply treatments to slow this colour change, while others leave it to weather naturally.

Supply and certification

The Cedar Shake & Shingle Bureau, founded in 1915, sets grading rules for certified products made by its member mills.

Limitations

The wood is fairly strong for its weight but can be brittle. Despite its natural resistance, cedar roofing still decays if it is kept wet by debris, moss or poor ventilation.