Cedar Shingle Weathering

It can be said, from a very board perspective, that WRC will weather to black and EWC will weather to a silver grey. The

blackening of the WRC is a combination of mildew infestation and natural extractives in the wood. The most prestigious homes in the

USA’s New England are often treated with bleaching oil if they choose WRC. Thus the red cedar shingles can weather naturally

and evenly while enjoying protection against discoloring mildew.

In practice the effect of aging can vary quite dramatically with EWC often mistaken for WRC and vice versa. The images taken below

are from a small town in Quebec.

I will try to describe the various effects of the elements on aging.

This modest seaside home shows how weathering can vary rather dramatically from one exposure to the next. Shingles are about 20 years young.

The Eastern Walls of this home are subject to very

strong storms (note Sea in the background) and long morning summer sun. This provides for

very even weathering and yields the traditional EWC

silver . The notable exception (shown below) is directly

beneath the small window ledge. This area would dry more slowly and mildew

develop more quickly.

The South facing walls (right side) see relatively little

summer sun and have less direct exposure to the driving snow and rain.

Staying wet longer, they will age more quickly. The top

section protected by the roof overhang shows little aging.

This small hut shows (+/- 75 years) how cedar planks will age in a similar fashion to shingles. These C Grade Cedar shingles are not used on roofs today

(see page following) although they are sometimes used (though not recommended) on garden shed roofs like roof shown here.

The exposed knots allow us to classify these shingles as grade C. The knots harboring water that promotes rot eventually become the weak point, and eventual failure. If installer was working in the right fashion, each knot will cover only a shingle area that is knot free, so leakage will NOT penetrate through to the inside.

Images that follow are from a very modest out building added adjacent main building painted below but that has since been taken down.

Note that the +/- 60 year old shingles have aged rather evenly EXCEPT (see insert) where mould is develeping behind the

tree where shade would slow the drying process.

This “boathouse” is part of a much larger estate . Shingles – left natural on the roof and stained on the walls are about 80 years old.

You will notice the opposite side of the roof has some black mildew developing in the centre. Most ROOFS, will be cleaned regularly with a light chlorine

bleach solution to preserve the silver grey appearance and discourage mould growth

This modest home and addition are clad in C grade shingles. Addition at right is about 10 years and original at left about 40 years. Insert shows close up of south face(left of house

numbers) and black mould developing . Note even weathering again of east face (left of chair)

This home was re-clad in about 3-4 years before photo was taken using grade A shingles

East exposure shows the typical uniform aging to

silver grey.

West exposure shows mildew developing where shingles stays wet longer in area protected from drying

winds.