What cap sheet lasts longest over an old smooth hot roof?
Figuring out the right materials for a flat roof is tricky, even for DIYers who have successfully installed shingles before. Online tutorial videos often fail to clarify exactly what to use for the underlayment or which roll-on cap sheet is the most durable option to apply.
What the numbers show
Counted from the threads quoted below. How we count
- People have been saying this in most months since September 2026.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Using standard shingles anyway because they are familiar with the process.Did this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“What cap sheet lasts longest over old smooth hot roof ?”source ↗
“Ive been looking online for information on how to use flat roof roll on cap but out of the 100 videos I've watched I still don't understand what I need to use for underlayment and how or what exactly to use as cap.”source ↗
“I usually take on small DIY projects but this one is tricky. Hell. I've done shingles before but flat roof is very new to me.”source ↗
Where this came up
People with this problem also raised
- 7How to install drip edge on an existing roof
- 7How to patch a gouged EPDM rubber roof
- 5Is a gap in roof sheathing at the ridge okay before shingling?
- 21How to temporarily waterproof a damaged roof until replacement
- 21Uneven shingles and bulges after new roof replacement
- 3How to replace a roof pipe boot with a cap