Cedar roof shingles can last for many years, not much can ruin them, other than moss.
Moss left untreated can be damaging to a cedar roof and it can soon spread from a small patch to cover large parts of the roof. That is why it is important to take a few small steps to prevent it from forming and to remove it if it does form.
The most important thing to do is to prevent moss from forming in the first place. Moss thrives in damp, shady areas and in a slightly acidic environment. Removing these conditions will prevent moss from forming on your cedar roof.
Clear back any trees that are likely to cause shade or a build up of damp debris on the roof. Ensuring that your roof receives plenty of sunlight will really slow down the growth of moss.
It is equally as important to ensure that water can drain freely from your cedar shingle roof. After rain it must dry as quickly as possible to prevent a damp environment that encourages moss to grow. If you are having a new cedar shingle roof then the plans must incorporate plenty of drainage. If you are having trouble with moss on your existing cedar shingle roof then it may be worth looking at how your roof has been designed, to see if alterations can be made to improve water run-off.
Another great way to prevent moss from forming on cedar shingles is to use zinc or copper. A strip of zinc of copper at the top of the roof ridges is very effective at keeping moss at bay. If this is not enough then you can also use copper wire throughout the roof. When rain washes over zinc or copper it causes a mild solution that won’t harm the cedar, but will prevent moss growth.
If moss has formed after a particularly damp spell then it is important that you remove it. However, you don’t want to further damage your roof with the removal. Avoid any chemicals which will harm the shingles, no matter how tempting it is.
Pressure washing can work, but must be carried out by an expert, so as not to damage the shingles, or not to get water underneath the shingles that will then leak into the roof.
You should use a brush to knock moss off the roof. If you do this a few times and it keeps returning, wash it off with a weak bleach solution, but try to avoid this as it can cause the shingle to discolour and may reduce its lifespan. Do not use bleach and another liquid detergent as the chemicals can react with each other.