The Parts of a Roofing System: What’s Getting Replaced
12/30/2025
When most homeowners think about a roof replacement, they usually think of the same thing: new shingles. But a properly installed roof is made up of several components that all work together to protect your home.
If you’re getting quotes or planning a replacement, it helps to know what’s actually being removed and what should be going back on. Here’s a breakdown of the main parts of a modern roofing system.
1. Shingles
Shingles are the most visible part of your roof and your first defense against the elements. They come in a variety of materials, but asphalt shingles are the most common for most of the residential homes across the country.
During a replacement, the old shingles are completely removed, exposing the wood decking underneath. New shingles are then installed according to the pattern and specs of your chosen product. They provide the top layer of water resistance and give your roof its appearance.
2. Underlayment
Underlayment is a layer of protective material installed directly on top of the roof decking, underneath the shingles. It acts as a secondary barrier against moisture, especially during storms or if shingles become damaged.
Most modern roofs use synthetic underlayment, which is more durable than traditional felt paper. Ice and water shield, which is a special type of underlayment, is often added around valleys, edges, and other leak-prone areas.
3. Roof Decking (Sheathing)
Decking is the wood base layer that all other roofing materials are attached to. It’s typically made of plywood or OSB panels.
During a roof replacement, the decking is inspected once the old materials are removed. If it’s solid and dry, it can stay. If there are signs of rot, sagging, or water damage, sections of it may need to be replaced.
4. Flashing
Flashing is thin metal (usually aluminum or galvanized steel) that’s installed anywhere the roof meets a wall, chimney, valley, or pipe. Its job is to prevent water from seeping into vulnerable joints.
On some jobs, flashing is reused, but best practice is to install new flashing during a roof replacement, especially if the old material is rusted or bent.
5. Ventilation Components
Proper airflow in the attic is essential to roof health. During a replacement, the roofer may update or add:
- Ridge vents
- Soffit vents
- Box vents or gable vents
These help prevent moisture buildup, reduce attic heat in the summer, and protect the life of the shingles.
6. Drip Edge
Drip edge is a metal strip installed along the edges of the roof. It guides water into the gutters and prevents it from getting under the shingles or rotting the fascia.
It’s a small detail, but skipping it or reusing old pieces, can lead to long-term problems. Most modern building codes require drip edge on all new roofs.
7. Starter Strips and Ridge Cap Shingles
Starter strips are special shingles installed at the edges of your roof to help the rest of the shingles lay flat and seal correctly.
Ridge caps are thicker, pre-formed shingles installed along the peak of the roof. Both are important for wind resistance and a clean, finished look.
8. Fasteners and Sealants
A new roofing system also includes nails, sealant, adhesives, and other materials you may not see but are essential for keeping everything in place and water-tight.
Final Thoughts
A quality roof replacement involves more than just swapping out shingles. From the underlayment to the flashing to the ventilation, each part of the system works together to protect your home for decades to come.
If you're comparing quotes, make sure you’re getting a full system, not just a cosmetic update. A good roofing contractor will explain what’s included and why it matters.