Large roof repair job - Proper SIDE lap of Underlayment?


Old 08-25-18, 01:31 PM
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Large roof repair job - Proper SIDE lap of Underlayment?

Here is the situation I have been presented with. It exceeds my experience level and need advice.

please see the shared photos in this icloud link: 3

All three vents you see here were done wrong by the previous roofer and a leak started between the two on the right (see pic) so all the shingles and 3 layers of old underlayment (first layer: ice and water shield, second layer: tar paper Third layer: Ice and water shield) was removed to check for plywood damage.

FUN FACT: Its a 2/10 pitch roof so local code requires ice and watershield for the whole roof. We are using GAF WeatherWatch

HERES THE QUESTION - what is the correct way to do the SIDES of the underlayment. Obviously, starting at the bottom, I lap the new underlayment over the old, (6" overlap) and then tuck it 6" under the top existing layer (which will be a total pain since the underlayment is aggressively stuck to the plywood) - but what about the sides?

Nothing in the GAF WeatherWatch installation instructions covers a situation like this other than calling for a 6" overlap on adjacent sections - but this assumes a new install for an entire roof, not patching a large section.

I might point out - re-doing the entire section of the roof isnt an option.

Thank you in advance
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Old 08-25-18, 06:56 PM
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You don't tuck anything under because it's generally impossible to separate it and still have the membrane intact. So you overlap it EVERYWHERE you have removed shingles. That means your "repair" will be the maximum width of what you have currently removed... plus at least 6" on each side. You would continue that all the way up the roof to the TOP. So you have to remove more shingles above the repair. Due to the nature of things, your repair area will get wider as you work your way up the roof toward the ridge, as the best practice would be for each course of Weatherwatch to be at least 12" longer than the previous course.

Meaning, if the first row was cut 10' long, the next row would be at least 11', the next 12' and so on in order to have 6" of endlap from one row to the next.
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