Parts of an Asphalt Roofing System Explained
Most homeowners think of a roof as simply “the shingles.”
In reality, an asphalt roofing system is made up of many different components that all work together to protect your home from water, wind, snow, heat, and Colorado’s extreme weather conditions.
When one part of the system fails, it can affect the performance of the entire roof.
Understanding the different components of a roofing system can help homeowners make better decisions during roof replacements, inspections, and insurance claims.
At Excel Roofing, one of the most common things we see is homeowners not realizing how many layers and details exist underneath the shingles themselves.
Roof Decking: The Foundation of the Roof
Roof decking, sometimes called roof sheathing, is the wooden surface installed over the roof framing.
This is the foundation that the entire roofing system is attached to.
Most residential roofs use:
- OSB (oriented strand board)
- Plywood
What Does Roof Decking Do?
The decking:
- Supports the roofing system
- Provides structural stability
- Holds nails from shingles and underlayment
- Helps distribute roof loads
If the decking becomes rotted, soft, or water-damaged, it may need to be replaced before a new roof can be installed.
Can Roof Decking Be Reused?
Often yes, if it is still structurally sound.
However, during roof replacements, damaged decking is commonly discovered after the old shingles are removed.
Underlayment: The Secondary Water Barrier
Underlayment is installed directly over the decking and underneath the shingles.
It acts as a secondary moisture barrier if water gets underneath the shingles.
Types of Underlayment
The two most common types are:
- Synthetic underlayment
- Traditional felt paper
Today, synthetic underlayments are much more common because they are:
- Stronger
- Lighter
- More tear resistant
- More water resistant
What Does Underlayment Do?
Underlayment helps protect against:
- Wind driven rain
- Ice dam backup
- Temporary exposure during installation
- Minor moisture intrusion
Even though shingles are the primary waterproofing layer, underlayment provides critical backup protection.
Ice and Water Shield: Extra Leak Protection
Ice and water shield is a self-adhering waterproof membrane installed in vulnerable areas of the roof.
In Colorado, this is especially important because of snow, freeze-thaw cycles, and ice dams.
Where Is Ice and Water Shield Installed?
Common locations include:
- Roof eaves
- Valleys
- Around chimneys
- Around skylights
- Around penetrations
- Low slope areas
What Does It Do?
Unlike standard underlayment, ice and water shield seals around nails and creates a waterproof barrier designed to prevent leaks from ice backup and standing water.
Step Flashing: One of the Most Important Leak Prevention Components
Step flashing is metal flashing installed where a roof meets a vertical wall, such as:
- Sidewalls
- Dormers
- Chimneys
This is one of the most important waterproofing details on a roof.
What Does Step Flashing Do?
Step flashing redirects water away from wall intersections and onto the shingles below.
Without proper step flashing, water can easily enter behind siding or walls and create hidden leaks.
Unfortunately, improper flashing is one of the most common roofing installation problems seen during inspections and leak investigations.
Roof Ventilation: Why Roofs Need Airflow
Roof ventilation is one of the most misunderstood parts of a roofing system.
Many homeowners do not realize roofs are designed to breathe.
Why Is Ventilation Important?
Proper ventilation helps:
- Remove heat from the attic
- Reduce moisture buildup
- Improve shingle lifespan
- Reduce condensation
- Help regulate attic temperatures
- Prevent mold and wood rot
Poor ventilation can lead to:
- Premature shingle aging
- Excessive attic heat
- Moisture damage
- Ice dam formation
What Is the Proper Roof Ventilation Ratio?
Most building codes follow a ventilation ratio of:
1:150 Ratio
1 square foot of net free ventilation area for every 150 square feet of attic floor space.
In some situations, the ratio may be reduced to:
1:300 Ratio
if certain balanced ventilation conditions are met.
Balanced Ventilation Matters
Roof systems work best when intake and exhaust ventilation are balanced.
Typically:
- Intake vents are installed lower on the roof, often in soffits
- Exhaust vents are installed higher on the roof, often at the ridge
This creates natural airflow through the attic.
Ridge Vents and Intake Vents
Ridge Vents
Ridge vents are installed at the peak of the roof and allow hot air to escape.
Soffit or Intake Vents
These vents pull cooler air into the attic near the lower portion of the roof.
Together, they create continuous airflow.
Starter Shingles: The First Row of Protection
Starter shingles are installed along roof edges before the main shingles are applied.
What Do Starter Shingles Do?
They help:
- Prevent wind uplift
- Seal roof edges
- Improve water resistance
- Provide proper first row alignment
This component is small but extremely important during high wind events.
Field Shingles: The Main Roofing Surface
Field shingles are the primary visible shingles covering the majority of the roof.
These shingles provide:
- Weather protection
- UV protection
- Impact resistance
- The overall appearance of the roof
Different shingles offer different:
- Wind ratings
- Impact ratings
- Warranty coverage
- Lifespans
Hip and Ridge Shingles
Hip and ridge shingles are specially designed shingles installed along:
- Roof peaks
- Hips
- Ridges
Why Are They Different?
These areas experience:
- Higher wind exposure
- More movement
- Greater weather stress
Hip and ridge shingles are thicker and designed to properly flex over roof transitions.
Skylights: Benefits and Challenges
Skylights can dramatically improve natural lighting inside a home.
However, they are also one of the more technically sensitive parts of a roofing system.
Why Can Skylights Be Difficult?
Skylights require:
- Proper flashing
- Waterproof integration
- Ice and water shield protection
- Correct slope considerations
Improper skylight installation is a common source of roof leaks.
Are Skylights Bad?
Not necessarily.
A properly installed high quality skylight can perform very well for years. The key is proper installation and flashing details.
Roofing Systems Work Together
One of the biggest misconceptions homeowners have is thinking shingles alone protect the home.
In reality, a roofing system is made up of many layers and components all working together.
A high quality roof depends on:
- Proper materials
- Correct installation
- Ventilation design
- Waterproofing details
- Flashing work
- Quality workmanship
Even premium shingles can fail early if the rest of the roofing system is poorly installed.
At Excel Roofing, educating homeowners about how roofing systems actually function is a major part of helping people make informed long term decisions about their homes.
