Roof Diagram: See Every Part of a Roof in One Visual Guide

FROM ROOF DECKING TO SHINGLES, VENTS & MORE

Get a clear, contractor-ready breakdown of the full roofing system. This visual diagram of a roof highlights every major component—framing, sheathing, underlayment, flashing, shingles, ventilation, and more—so you can quickly identify what you’re looking at on any job. Perfect for training crews, explaining estimates, or verifying code-related details before installation. Use it alongside OneClick Code’s verified building code details report to confirm every code-related detail before installation.

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The Diagram of a Roof

Before we dive into the details, take a look at the complete roof diagram below. Each part is clearly labeled so you can see how the entire system fits together. From structural framing to protective layers and exterior finishes, this diagram serves as a reference point for all roofing projects. Pair it with OneClick Code to verify which local roofing code items apply to your project.

1. Sheathing
2. Underlayment
3. Shingles
4. Chimney Cricket
5. Ventilation
6. Insulation
7. Rafters
8. Drip Edge
9. Ice and Water Shield
10. Gutters and Downsprouts
11. Valley Liners

Sheathing (Roof Deck)

The roof sheathing (or deck) forms the foundation of the entire roofing system. Made of plywood or OSB, it’s fastened to the trusses or rafters and supports everything above it — from underlayment to shingles. Strong, code-compliant sheathing distributes load evenly and prevents sagging or leaks, making it one of the most important roof structure components to inspect on every project. Use OneClick Code for an accurate roof sheathing codes report.

Underlayment

Placed directly on top of the sheathing, underlayment provides a crucial secondary layer of protection against moisture and wind-driven rain. Modern synthetic underlayments resist tearing and offer longer durability than traditional felt. Contractors can use OneClick Code to confirm roofing manufacturer requirements as well as slope-based and climate-based underlayment requirements before installation.

Shingles

Shingles are the roof’s outer protective layer, designed to shed water and shield the home from weather and UV exposure. Installed in overlapping rows, they rely on proper underlayment, ventilation, and installation to perform effectively. In any diagram of a roof, shingles are the visible finish—but their accuracy depends on correct measurements and waste calculations to avoid delays or overages on the job.

Note: Shingle waste: Shingle waste is the extra material needed to account for trimming, overlap, and roof angles. Estimating it incorrectly can cause over-ordering or job delays.

OneClick Code’s Shingle Waste Calculator delivers property-specific waste factors based on roof geometry — eliminating guesswork and giving contractors precise, insurance-ready reports in minutes.

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Chimney Cricket

A chimney cricket, or saddle, is a small peaked structure built on the uphill side of a chimney. It diverts water and debris around the base to prevent pooling and leaks. Building codes require a cricket for chimneys wider than 30 inches. Confirming these requirements through OneClick Code ensures compliance and avoids overlooked installation details that can cause major leaks.

Ventilation

Proper ventilation extends the life of every roof. Using OneClick Code’s Vent Calculator, contractors can instantly determine the correct ratio of intake to exhaust ventilation based on attic size and slope. It’s the fastest way to confirm whether a roof meets the 1:150 or 1:300 ventilation ratio required by code — ensuring balanced airflow and energy efficiency.

Quickly verify proper roof ventilation with the OneClick Code Ventilation Calculator. Get instant guidance on balanced airflow so you can build longer-lasting, code-compliant roofs with confidence.

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Drip Edge

The drip edge is a narrow metal strip installed along roof edges to guide water off the shingles and into the gutter system. This simple piece protects fascia boards and decking from water damage. Sometimes also known as flashing, it is thin metal placed around chimneys, valleys, skylights, and vents to seal joints against water intrusion. Missing or damaged flashing is one of the leading causes of roof leaks. Though often overlooked, drip edge/flashing installation is required by code in most jurisdictions — something contractors can confirm instantly with OneClick Code’s verified jurisdiction data.

Ice and Water Shield

The Ice and Water Shield (IWS) is a self-adhering membrane that seals around nails to prevent water infiltration in vulnerable areas like eaves, valleys, and around vents. In colder climates, it’s critical for preventing ice dams. OneClick Code provides local code data that tells you exactly where IWS is required — so you install once, and install right.

Accurately calculate your IWS requirements in seconds. Try the OneClick Code Ice & Water Shield Calculator now and get precise coverage totals — stay compliant, estimate confidently, and install right.

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Valley Liners

A valley liner protects one of the most leak-prone areas of any roof — where two slopes meet. It channels heavy rain and melting snow safely down to the gutters, keeping moisture out of the decking below. Using the correct liner type for your roof system ensures long-term protection and prevents one of the most common call-back issues in roof repair.

Frequently Asked Questions

Why is drip edge required on a roof?

Drip edge protects the edges of the roof by directing water away from fascia and sheathing, reducing long-term rot and moisture problems. It's a code-required component in most areas. OneClick Code makes it easy to verify whether drip edge is mandatory for your project location.

What’s the purpose of roof underlayment?

Underlayment acts as a secondary water barrier beneath the shingles, adding essential protection against wind-driven rain and temporary exposure. It’s critical for durability and compliance. OneClick Code helps you see exactly which underlayment type is required based on slope and climate.

Why do valleys need a valley liner?

Valleys collect and channel the most water on a roof, making them one of the most leak-prone roof structure components. A valley liner reinforces this high-stress area and prevents moisture penetration. OneClick Code lets contractors verify valley liner requirements for each jurisdiction.

When do I need a chimney cricket?

A chimney cricket diverts water around the uphill side of the chimney, preventing pooling and leaks at the base. It’s required on chimneys over a certain width, depending on local code. OneClick Code makes it simple to check if your project calls for a cricket before installation.

How much shingle waste should I plan for?

Shingle waste varies with roof shape, pitch, and cut requirements, so guessing often leads to shortages or over-ordering. OneClick Code’s Shingle Waste Calculator gives you accurate, property-specific waste percentages so you can order precisely what you need.

Where should Ice and Water Shield be installed?

IWS protects vulnerable areas like eaves, valleys, and penetrations by sealing tightly around fasteners. Its placement depends on climate and code requirements. OneClick Code maps out exactly when IWS is required for your jurisdiction and roof design.

How do I know if my roof has enough ventilation?

Balanced ventilation prevents heat and moisture buildup, extends shingle life, and improves energy efficiency. Using OneClick Code’s Ventilation Calculator, contractors can instantly determine if they meet the correct intake–exhaust ratio for local code.