The 10 Layers of a Roof System

Do you need a roof replacement but don’t know what gets replaced? Are you wondering how many layers a roof actually has?

As you’re walking down the street and looking up at roofs, you only see the top layer. However, a roof system is a combination of different layers that fit together like puzzle pieces. 

And when getting an estimate the last thing you want is to be surprised by all the different materials (layers) you’ll pay for when getting a new roof. Even more important, you don't what any of the layers missing. 

For over 35 years, Bill Ragan Roofing has helped homeowners understand everything that goes into their roofing project. So, let’s break down all the layers of a roof system. 

By the end of this article, you’ll learn about the following layers of a roof system, what they do, and why they’re important:

• Roof decking
• Drip edge
• Underlayment
• Ice and water shield
• Starter shingles
• Main roofing material
• Roof flashing
• Ridge and hip capping
• Roof vents
• Pipe boots

1. Roof decking 

Roof decking (also called roof sheathing) is the wooden foundation (plywood or planks) and the first official roof layer. Your roof will have one of two types: plank or sheet decking.

Plank decking is made of 1x6 or 1x8 rectangular wooden boards, depending on the span of your rafters. Sheet decking (or sheathing) is made of flat sheets of wood that cover more area than planks.

There are two types of sheet decking: OSB and plywood. OSB (oriented strand board) consists of wood chips/strips compressed together to form a flat 7/16” sheet, while plywood comes in several different thicknesses (⅜”, ½”, ⅝”, and ¾”).

Just know that any rotten or compromised roof decking must be replaced before installation begins. However, your roofing contractor won’t know how much will need replacing until after the tear off process of your roof replacement.

2. Drip edge

Drip edge is metal flashing installed at the roof’s edges (eaves and rakes) to prevent water from getting underneath the roofing material and going behind your gutters. It’s such an important roof layers that it’s actually required per building codes and must be installed correctly.

Not only will your home fail an inspection without it, but your fascia board and roof decking’s edges will rot from prolonged exposure to water. So, its importance can’t be overstated.

Unfortunately, there are too many roofs without drip edge. It can be left off by laziness or lack of experience, but bad roofers knowingly exclude it from their estimates to lower prices.

3. Underlayment 

Roof underlayment is a felt or synthetic material installed directly over your roof decking before the roofing material is installed. Its purpose is to provide a layer of protection for your decking if water gets underneath your roofing material.

(Synthetic underlayment)

The two types of underlayment options are felt and synthetic.

Felt underlayment has been around the roofing industry longer than synthetic and comes in 15 lb. and 30 lb. rolls. Both types do the job, but 30 lb. felt underlayment is thicker, stronger, and less likely to tear than 15 lb.

Synthetic underlayment is made out of woven/spun polyethylene or polypropylene, which means it won’t hold moisture. It’s more durable, holds nails better, and repels water better than felt underlayment.

Felt isn’t a bad choice, but I recommend spending the extra money for the functionality and better water protection synthetic underlayment offers.

4. Ice and water shield

Like underlayment, ice and water shield is a layer of waterproof membrane that protects your roof decking from water if it gets under the roofing material. But instead of installing it over the entire roof deck, it’s installed on/around problem areas prone to leaks that need more protection. 

Ice and water shield is mainly installed in roof valleys, around penetrations, against walls, and on roof pitches below a 4/12. It does add more to a new roof’s price, but the extra protection is well worth the peace of mind.

Just know that certain areas above the snowline in the US require two rows along the edges of your roof per building codes to prevent frequent ice dam leaks. However, this is considered an upgrade in places like our service area in Middle Tennessee. 

5. Starter shingles

Starter shingles are a layer of pre-cut roofing material installed along a roof’s edges before shingles are installed. They look like shingles without the tabs but are thinner and pre-cut for easy installation.

Starter shingles also have an adhesive that seals the shingles at your roof’s edges to improve resistance to strong winds. In fact, installing them determines the wind warranty provided by the manufacturer.

While this is mainly for asphalt shingles, every roofing material has a starter component that locks or seals the roofing material at the edges.  

6. The main roofing material

The roofing material is the top layer that you actually see that makes up the bulk of a roof system. There are plenty of options, but the most popular residential roofing materials are asphalt shingles, standing seam metal roofing, cedar shake roofing, synthetic roofing, and slate roofing. 

The one you choose greatly impacts your new roof's cost, aesthetic, lifespan, and warranty options. That’s why it’s important to do the research to pick the right one for you and your budget. 

7. Roof flashing

Roof flashing is a metal material that directs water away from areas (walls, chimneys, roof valleys) where the roofing material butts up against something. It’s one of the most important roof layers, and you’ll definitely have roof leaks without it. 

(Counter flashing on a brick chimney)

Roof flashing can be any metal type, but aluminum, steel, and copper are the most common metals. Also, the specific type of roof flashing used depends on where it's installed and the building material it's installed against.

The main types of roof flashing are:

• Counter flashing
• Step flashing
• Apron flashing
• Valley flashing

While roof flashing usually outlives the other components, it's always recommend replacing it when getting a new roof if the existing metal is questionable. This is simply to prevent future problems and ensure everything installed on your roof is the same age.

8. Ridge and hip capping

Ridge capping is the layer installed where two slopes meet to completely seal your roof system at the very top. It will be made of the same material as the main roofing material, except that it’s pre-bent to form perfectly on a roof’s ridge.  

No matter which roofing material you choose, your roof needs the associated ridge capping. While ridge capping is needed on the ridge, there's also hip capping on hips.

9. Roof vents

Roof vents allow your attic and home to breathe properly by pulling fresh air through intake vents before pushing it out of exhaust vents. There are multiple vent options, but the type of ventilation system (active and passive) narrows down the choices.

(Box vents on an architectural asphalt shingle roof)

For an active ventilation system, the most common options are turbine vents, power vents, ridge vents with a baffle, or solar-powered vents. For a passive ventilation system, you’ll have static vents (box vents), ridge vents without a baffle, or gable-end vent.

While certain vents are better for certain roof styles, I recommend an active ventilation system for performance reasons. But no matter the system, it’s crucial that your attic is ventilated properly to avoid cutting your roof's life drastically short.

10. Pipe boots

A pipe boot (also called roof boot) is a type of flashing that goes around the base of the pipes coming out of your roof. Without them, water leaks down the pipes into your attic and home.

Depending on the roofing material and type of pipe, pipe boots can be synthetic rubber, plastic, lead copper, etc. While you have these options, the most common type of pipe boot used on roofs today is a synthetic rubber called neoprene.

Just know that neoprene pipe boots will need replacing every 10 years or so once cracks form. However, they’ll be cheaper than copper (or another metal), more durable than plastic, and won’t attract animals like lead.

What else do you need to know before getting a new roof?

After reading this article, you know the 10 layers of a roof and have a better understanding of what you’ll pay for when getting a replacement.

If even one roof layer is missing, I guarantee you'll have problems. So, it's crucial to make sure every estimate has a line item for each material and component.

However, this isn’t the only information you need. In fact, knowing the layers of a roof is just the beginning. It’s important to go into the roof replacement process as prepared as possible with the right mindset.

That’s why I wrote another article breaking down everything you should know before starting the roof replacement process. 

Check out 7 Things to Consider Before a Roof Replacement to learn what homeowners should consider and do before getting a new roof.