How asphalt shingles work with underlayment and flashing

Dekoven Roofing

November 13, 2026

Shingles are visible, but underlayment and flashing are part of the weather-management assembly. A replacement estimate should explain all three.

Check the proposal for what goes below the shingle and around roof openings. Those details explain how water is managed at places where the shingle alone cannot complete the assembly.

Talk with Dekoven Roofing about which materials and installation options may fit your roof.

More than the shingle

An asphalt shingle roof is a system. The shingle is the visible layer, but underlayment, flashing, ventilation and decking together determine how well the roof sheds water.

The layers

  • Decking: the structural base.
  • Underlayment: a secondary water barrier.
  • Flashing: metal that directs water at joints and edges.
  • Shingles: the visible weather layer.
  • Ventilation: moves heat and moisture out of the attic.

Why it matters in a proposal

Two proposals naming the same shingle can differ in underlayment, flashing replacement and ventilation. Compare those lines before comparing price.

If a component is missing from the proposal, ask whether it is included, reused or excluded.

Questions to ask

Which components are included and which are reused? What underlayment is proposed and where is it used? How will flashing at walls and chimneys be handled?

Frequently asked questions

Do I need new flashing every time?

Ask whether existing flashing is reused or replaced and why.

Is ventilation part of a replacement?

It should be considered. Ask what is included.

Does underlayment matter?

Yes. It is a secondary barrier. Ask what is proposed.

Related: Ask which roofing system fits your property

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