Cedar shingles #3
Identifying and preventing damage

Cedar shingles are potentially a very durable roofing product for garden buildings as long as they are given a little care and attention every few years. That means undertaking regular maintenance such as cleaning (see previous post: Cedar Shingles – How to clean and restore them) and checking for potential problems so you can fix them before things get worse. The photos below show various damage found on one of my own garden buildings which I had foolishly neglected for seventeen years. Consequently, it had begun to deteriorate. In this post I am going to look at the kinds of damage that can arise and share what I learned about how and why they arise, and, importantly, how good design and some regular maintenance can prevent them in the first place. I learned the this the hard way, but now that I have understood the problems and their causes I am sure that I can extend the service life of my cedar roof by decades.

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Kinds of damage to watch out for

Cupping

Shingles can cup in either direction. Cupping is not usually a problem, unless it is sufficient to expose a joint beneath tiles in the row it is supposed to be covering, in which case it may allow water into the building below, in which case it should be replaced. The one in the picture above is fine, as there is a solid shingle beneath it, so can be left.

Splitting

It is relatively common for some shingles to split along the grain, producing a vertical crack like the one above. Splits like this need to be assessed for their leak risk. The one above is very close to the joint in below it, making a short path for water to get under the roof. It should be replaced.

Erosion

The lower edges of shingles are the most vulnerable and are the places where rot is likely to set in. Small amounts of erosion are unlikely to be a problem in themselves as long as the tile beneath is sound. However, the causes of the erosion need to be identified and remedied. If it is abrasion from an overhanging branch, cut it back. If it is the start of rot a more extensive assessment and remedy should be undertaken, which might include cleaning, preservative treatment and sealing the tiles. The affected shingle may need to be replaced.

Rotting

Rot is the most serious problem and needs dealing with promptly. Rotten shingles will let water through to the lower layers, setting up conditions for adjacent shingles to be infected and rot too. The cause of the rot needs to be identified and remedied, then all the rotten tiles need to be removed and replaced. It may turn out that as you investigate the area affected proves to be much larger than it initially looked. Fortunately, replacing cedar shingles is a relatively straightforward DIY job (see next post)

Prevention is better than cure

Cedar is a remarkably durable wood because it contain natural oils that act as preservatives repelling the insects and fungi that attack less durable timber. However, cedar is not entirely impervious to decay, especially when it is allowed to remain wet. To extend the working life of cedar shingles, therefore, they must not remain wet for long periods of time. This means two things:

1. Reducing the amount of water absorbed by the shingles, and
2. Allowing them to dry out quickly afterwards

These conditions can be achieved through good design, construction and maintenance. Appreciating the reasons behind such design and maintenance can help you stay ahead of potential problems.

Keeping the water out

• A well-planned and constructed cedar roof will help shed water efficiently.
• The steeper the pitch of a cedar roof, the easier it is for water to run off quickly. Cedar roofs should be at least 30 degrees. Mine are 40 to 45 degrees.
• Shingles can be sealed or sprayed with suitable water repelling coatings that help them shed water and reduce the amount that is absorbed into the shingle.
• A build up of lichens and moss on the shingles will tend to hold on to water.

Allowing cedar shingles to dry quickly

• Sunshine and good ventilation will help a cedar shingle roof dry quickly.
• When designing a cedar roof, think about sun and ventilation: avoid north-facing pitches and overhanging trees for example.
• Cedar roofs need to dry from below as well as from above, so should be designed with a well ventilated cavity under the tiles.
• To improve sunlight and air reaching the roof, cut back overhanging trees and vegetation regularly.
• Moss, lichen and algae will hold water in the shingles for longer and trap debris that will do the same. Remove them regularly.
• Clean shingles to remove dirt and organic matter which trap moisture and provide nutrients for mosses.
• A build up of leaves in gutters can wick water back up into the cedar shingles. Keep gutters and downpipes clear and free-flowing.
• Ensure gutters are placed well below the shingle drip line wherever practicable, and have a steep run so that water runs away quickly.

Summary of conditions that ensure a long-lived cedar shingle roof