Roof valleys are precisely what their name implies: valleys (of sorts) where two edges of a roof meet. Roofing tiles and mortar by themselves are not enough to protect your roof. You need to make sure you also touch up the corners of your roof with properly-made roof valleys, which help rainwater run off the roof-top by gathering the rain into a downward stream. A roof valley must be strongly constructed because leakage is highly possible depending on how much rain they take.
Roof valleys can be open or closed, and fixing roof problems is easier with an open valley. An open roof valley sheds water and ice more smoothly than a closed one, preventing granule loss from the shingles. A metal lining protects the valley from moisture.
At Buildworld, we have various types of roof valleys and other products, open valley, closed valley, and related products. The Timloc Wet Fix GRP Valley Trough, for instance, creates a waterproof channel down each valley. Similarly, the Cromar Dry Fix Valley Trough is light and easy to install and is backed by a 30-year life expectancy.