What Are the Layers of a Roof, From the Wood Up?

Updated 2026-10-24 · Sources checked

"Is that 12 layers of shingles? What am i even looking at"

A commenter in r/Roofing wrote that about a roof they were looking at. If your quote is full of words you can't place, you may be asking the same thing. Here is the answer: a roof is a stack, and each word on a quote names one part of it. From the wood up: decking, underlayment, flashing and drip edge, then shingles.

The main parts on a quote map to one place on the roof and one job, so you can check them today without going near the roof. For a line that is not in this stack, such as ridge cap or pipe boots, ask the roofer what it is.

The stack, bottom to top

• Decking (the deck): the wood base that everything else is fastened to. On a quote, look for a line that says what happens if bad wood is found.
• Underlayment: also called roofing felt or tar paper, it is the secondary protection for the roof deck¹.
• Ice and water barrier: a self-adhering sheet used as underlayment¹, often at the eaves (the lower edges) and in valleys, to help minimize damage from ice dams.
• Flashing: the layer that protects the places where the roof is interrupted or meets something else.
• Drip edge: a metal flashing with an outward-projecting lower edge², meant to control the direction of dripping water.
• Shingles: the visible top layer.

Wondering what it means if the wood below turns out to be bad? What roof rot means and what to get in writing.

What do underlayment and ice and water barrier protect?

Underlayment is the backup. If water gets past the shingles, it is the sheet between them and the wood. The ice and water barrier is a stronger version of that backup for the spots where ice dams form.

Whether your roof needs it depends on the place. In Minneapolis, ice and water barrier is often used and required at the eaves and in valleys¹ because of ice dams.

Flashing and drip edge: where water is steered

Flashing goes where a roof has a hole or a joint. In Minneapolis, flashing must be installed around roof penetrations such as vent pipes and chimneys, in valleys, and at wall and roof intersections¹. In Minneapolis, existing flashing is also replaced when rusted or damaged, and roofing tar cannot stand in for approved flashing¹.

A drip edge works at the bottom edge of the roof: it sends dripping water away from the parts under it. If your quote lists neither, ask whether the job includes them or leaves the old ones in place. In Killeen, Texas, new drip edge is required³ at the re-roof inspection. Ask each roofer which parts of the stack will be new on your job and which stay.

If your flashing looks rusted or loose, what are your options? Can roof flashing be repaired, or does it need replacing.

What is the space between the ceiling and the roof?

The ceiling is the inside surface of your top-floor rooms. The roof is the outside covering and the wood that carries it. The space between them, if your house has one, is the attic.

The attic is part of how the roof works. In summer, airflow through a well-vented attic moves super-heated air and moisture out, which protects the shingles⁴. In winter, outdoor airflow helps keep the attic cold, which reduces the potential for ice damming⁴.

Do extra layers of shingles make a big difference?

They are a different thing from the stack above. An overlay means new shingles go over the old ones. A tear-off removes the old ones first.

In Minnesota, roofing materials are heavy, so multiple layers can affect the ability of a roof to hold the weight of winter snow⁵. An overlay can be the less expensive option there, but is not necessarily always the best choice⁵. A tear-off typically gives a longer roof life than an overlay, because the new roof goes over sound material and has new underlayment installed⁵.

The count is the tricky part. One r/Roofing reply put it this way: "It's not always apparent how many layers the roof has until you start tearing off." So the useful question is whether there is any mention of extra layers in the contract, and what happens if more turn up.

Reading your quote: what to look for, and what to ask before the roofing job

Go down the quote with this list. It is also what to have in hand before you call anyone.

• Decking: does the quote say what happens, and what it costs per sheet, if rotten wood is found? A reply in a roofing thread asked: "Do you have a picture of the decking before shingles went on?" Ask for photos of any bad wood before it is replaced.
• Extra layers: does the quote say what happens if additional layers are found?
• Underlayment and ice and water barrier: which is quoted, and does local code call for it?
• Flashing and drip edge: are they new, or is the old kept?

Ask each roofer to put the decking price and the approval step in writing. You can send this:

Please write in your quote the price per sheet for replacing damaged decking, and what you charge if you find extra layers of shingles. Please also send me photos and get my signed change order before any extra cost.

If a roofer pushes you to sign today or won't put this in writing, that is an answer too: weigh it against the bids that do.

Which layers should a full replacement quote name? What is included in a roof replacement.

Quick questions

Does "layers" mean the stack or layers of shingles? On a quote it can mean either. If the word appears, ask which one the roofer means and what it changes in the price.

Is the 25% rule national? No: in Florida, no more than 25 percent of a roof or section may be repaired, replaced or recovered in 12 months⁶ unless it is all replaced. In San Diego, more than 25% of the roof area replaced, altered or repaired within twelve months⁷ triggers a fire-rating requirement. Wherever you live, ask the roofer whether any such limit applies to your job.

Does a 30-year shingle really last 30 years? The name is an industry label, not a promise⁸. Homes can be only one storm away from needing a new roof cover after just 10 years⁸, a wind-performance finding. Read the shingle's warranty before you choose.

What is the most expensive part of replacing a roof? It depends on the roof and on what the roofer finds hidden under the layers of roofing. Ask for a quote that lists each part as its own line, so you can see where the money goes.

Sources

1. City of Minneapolis, Community Planning & Economic Development: Roofing at single-family and two-family dwellings

2. Insurance Institute for Business & Home Safety: Metal Flashing

3. City of Killeen, TX (Building Inspections, .gov): Re-Roof Inspection (checklist dated 9/4/2024)

4. ENERGY STAR: About Attic Ventilation

5. Minnesota Department of Labor and Industry (copy hosted by City of New Ulm): Asphalt Shingle Roofing and the 2020 Minnesota Residential Code

6. Florida Building Commission: DS 2021-007 Staff Analysis

7. City of San Diego Development Services: Information Bulletin 123

8. Insurance Institute for Business & Home Safety: 2022 Year In Review

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