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Apply Roof Underlayment and Flashing

11:31
15:02
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Why patio roofs fail - and how to build them right!

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What happens here

After the roof decking is installed, begin applying the weatherproofing layers. First, install the drip edge along the lower edge of the roof. Then, apply the ice and water shield over the drip edge, ensuring it adheres well. If not code required for the entire roof, it's typically used at the eaves. Install cap nails to secure the ice and water shield. Next, lay down the felt paper (or synthetic underlayment) over the rest of the roof, overlapping the ice and water shield. For the intersection with the existing house wall, cut back the house wrap along the roofline, install apron flashing over the felt paper, and then fold the cut house wrap back over the top edge of the flashing for a watertight seal. This ensures water running down the wall will go over the flashing and onto the roof, not behind it.

Goal: Create a watertight barrier for the roof structure.

Tools and materials

  • Apron flashing — Metal flashing for the roof-to-wall intersection
  • Cap nails — Securing ice and water shield and felt paper
  • Drip edge — Protecting the eave and directing water into gutters
  • Felt paper — Secondary weather barrier over the decking
  • House wrap — Existing moisture barrier on the house wall
  • Ice and water shield — Self-adhering waterproof membrane, typically at eaves
  • Nail gun — Nailing drip edge and felt paper
  • Utility knife — Cutting house wrap and underlayment materials

What they say

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of these. Install your dripper apron. Install our ice and water. Cuz this is not a conditioned space, you don't have to use ice and water. But in some areas, you might have to use this on the whole roof. And install cap nails. This has two sides, and now you can just peel the bottom side. If this isn't adhered and nailed down, you can easily slip on this material, especially on steep pitch roofs, so be careful. And install your felt. Cut back the house wrap. Then we'll cut along the deck all the way down to the other end. We'll fold up the house wrap and tuck our ice and I slit the flashing so it can go over the top of the ice and water. And now this can fold over the other flashing and also cover this corner. And now the last piece of felt will run over this top. It's often thought that the ice and water sits on top of the paper, but it does not. It's made to protect the deck when we install an apron flashing. So now water that gets behind the siding runs down this apron and onto the top of the shingles.

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