In either situation the leaking roof valley can be fixed by removing affected shingles and structural elements and upgrading your roof s flashing.
Roof gully leaking.
The roofing nails are fine so long as the lead of the roof valley is intact but once it starts to crack or fracture due to water pressure corrosion or other damage the nail provides a space for water to run into the home.
This method of lead valley repair is proven to not only be fast and safe wit.
The reason why the roof valley is such a sensitive area has to do with all the rainwater and or melting snow that accumulates and flows through the valley on its way into the gutters.
There will be a damming effect during very heavy rain especially after a long dry spell and a large amount of water can then pour into the roof cavity.
You should always attempt a mechanical leaky roof fix whenever possible.
A roof valley is very prone to leaks especially if you have an older roof.
This is where two parts of the roof join.
This video shows the traditional and best way to repair a lead valley on a roof.
A flashing is a transitional roofing material that connects the roof material to some other building material or to another part of the roof.
Rarely will caulk or roof cement cure a leaky roof at least for very long.
That means replacing or repairing existing flashing instead of using any type of sealant as a leak stopper.
This video shows the full repair from removing leaded va.
Check your lay boards are ok first and no rot lay building paper with new lead valleys retile back both sides if your tiles are bedded in cement in your valleys i tend to fit some asbestos free board cut to size dependent on overlap up the lead valley with the tiles bedded on this.
So roof valleys are important elements on a roof to be maintained properly.
If you have a roof leak it may well be through the valley.
There are times when roof valleys in good condition gets blocked with leaves and debris.