Map the roof leak.
Fixing a leaking slate roof.
Use a roof rake to fix it and remove the first four feet of snow from the roof edge.
Then use ice melt product per manufacturer s instructions.
If the ice and water shield is missing then you will have to remove the shingles on both sides along the valley put ice and water shield in place and re shingle the roof.
Normally friction alone is enough to hold the lead bib in place.
Beware of using asphalt roof mastic on copper flashings it fixes the leak in the short run but corrodes the copper in the long run.
Lead bib slate repair if the roof hasn t got too many mistakes a good method of repair is the lead bib it s simply a section of code 3 or 4 flashing lead cut large enough to sit under the faulty slate or bad overlap to make it waterproof and the repair invisible.
Run the water over the place where you think the leak might be located.
You could make a temporary patch using stick down materials or on some roofs i ve seen roof mastic used in that application.
Only use caulk for very small holes and when flashing isn t an option as a leak stopper.
Place the shingle or plywood onto the tar and spread more of the tar around the edges of your patch.
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Let the wet areas dry and then apply the patch to the underside of the roof with a putty knife.
That means replacing or repairing existing flashing instead of using any type of sealant as a leak stopper.
Details are at slate roof leaks temporary repair.
If you don t want to wait for rain to look for the leak try bringing the garden hose up on the roof.
Consider investing in a roof heat cable to prevent future issues.
Have a helper stationed in the attic with a flashlight looking for moisture.
Use a putty knife to spread the tar into the leaking hole on the inside of your roof.
Be sure to start small.
A properly flashed roof valley should have an ice and water shield installed with roofing felt being properly secured over the ice and water.
Don t go crazy with the water.
Once you ve found the leak you can make a temporary leak patch from some plywood or shingle and some roofing tar.
Use enough of the roof patch to liberally cover the leaky area.