How Is a Roof Built?
A roof is a layered system installed in a specific order, starting with the structural decking and ending with ridge ventilation. Each layer plays a role in moisture control, durability, and airflow, and skipping or misinstalling even one layer can shorten the life of the entire roof system.
- Shingle roofs are made up of 9 layers/components installed in a specific order.
- Each layer manages either water, heat, or structural integrity.
- Skipping layers or changing installation order leads to premature failure.
- Flashing failures are the #1 cause of roof leaks.
- Proper ventilation extends roof life and prevents moisture buildup.
Bottom line: A properly built roof isn't just shingles—it's a sequence of layers designed to manage water, heat, and airflow.
- Common mistake: Skipping ice & water shield in valleys and around penetrations, which leads to interior leaks.
- Quick fix: Always verify your contractor installs ice & water shield at eaves, valleys, and all penetrations.
A properly built roof isn't just shingles. It's a sequence of layers designed to manage water, heat, and airflow—especially important in Middle Tennessee, where roofs face heavy rain, summer heat, and storm activity. Below is the correct installation order, from the deck up.
The 9 layers of a complete shingle roof system are: 1) Roof Decking, 2) Drip Edge, 3) Underlayment, 4) Ice & Water Shield, 5) Starter Shingles, 6) Main Shingles, 7) Flashing, 8) Ridge Caps, and 9) Ridge Ventilation.
- Roof decking provides the structural foundation
- Drip edge directs water away from edges
- Underlayment adds secondary moisture protection
- Ice and water shield seals high-risk areas
- Starter shingles secure the roof perimeter
- Main shingles provide weather protection
- Flashing prevents leaks at transitions
- Ridge caps protect the roof peak
- Ridge ventilation controls heat and moisture
1. Roof Decking — The roof decking is the structural base of the entire system, typically plywood or OSB panels fastened to the rafters or trusses.
2. Drip Edge — Drip edge is a metal flashing installed along the eaves and rakes of the roof. It directs water away from the fascia and into the gutters.
3. Underlayment — Underlayment is a protective layer installed directly over the decking, typically synthetic felt or asphalt-saturated material.
4. Ice & Water Shield — Ice and water shield is a self-adhering waterproof membrane installed in vulnerable areas like valleys, eaves, and penetrations.
5. Starter Shingles — Starter shingles are installed along the roof edges before the main shingles. They provide a secure seal and proper wind resistance.
6. Main Roofing Material — This is the visible roofing layer—most commonly architectural asphalt shingles in Middle Tennessee.
7. Flashing — Flashing is installed around chimneys, walls, skylights, and roof transitions. These areas are the most common sources of leaks.
8. Ridge Cap Shingles — Ridge caps cover the roof peak and secure the ends of the shingle system. They protect the most exposed area of the roof.
9. Ridge Ventilation — Ridge vents allow hot, moist air to escape from the attic. Proper ventilation extends roof life and prevents moisture buildup.
Key Facts (Quick Reference)
| Number of layers | 9 distinct layers in a complete roof system |
|---|---|
| Most common failure point | Flashing at chimneys, walls, and skylights |
| What to ask your roofer | "What underlayment and ice & water shield are you using?" |
| Middle TN note | Heavy rain and summer heat make every layer critical here |
Middle Tennessee roofs face intense sun, heavy rain, and seasonal storms including hail and high winds. Every layer of a properly installed roof system works together to handle these conditions. Cutting corners on any layer can lead to premature failure in our climate.