Should a dam develop then water may back up under the tile or shingles and end up creating a leak.
Tile roof valley flashing.
The reason that many roofers like an open valley is that they feel that tree leaves and needles will more easily slide down or wash down an open valley when it rains.
Drip edge metal valley flashing dormer chimney and kick out flashing shed water away from the connections between roofs walls chimneys and other building assemblies this collection of 18 articles animations and videos identifies the critical roof flashing areas illustrates durable roof flashing details and shows how to flash roofs.
To understand what makes a valley either closed or open it is important to understand how a valley is constructed.
According to the international residential code irc valley flashing in tile roofs should extend at least 11 inches each way from the valley centerline and the flashing should have a formed splash diverter at the center at least one inch high.
Make sure to cover the gap at the bottom of the raised ridge to keep bugs and ice out.
Using clips permits movement in the valley as temperatures change.
Use roof valley cleats at intervals of 24 o c.
A flat tile installed directly onto standard valley flashing in a closed method restricts water in the valley flashing during heavy rains and may cause it to overflow.
Extend entire width of flashing completely to the bottom of the roof valley.
W type valley flashing is more rigid for handling so it stays straight and it stops waler rushing down one side of a roof from rushing back up the other side.
One of the details that varies between homes is the method of flashing the valley areas of the roof.
There are two common methods for completing the flashing of a valley in a shingle roof system.
Double ribs elevate tile battens above water flow area.
Cut the bottom edge and fold it down over the drip edge.
There is less of a chance for leaves to gather in a spot in the valley and form a small water dam.
Cut bottom of flashing so the entire width of the valley flashing extends approximately 1 2 to 3 4 over the fascia trim board along eaves the following photos illustrate removal and replacement of a closed cut valley with new open metal valley.
This can speed degradation of the underlayment and may cause rot in the battens and decking.
The installer fabricates simple clips or valley flashing cleats whose bent edge interlocks with the folded over or hemmed edges of the metal roof valley flashing to secure the valley to the roof deck.
