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Any homeowner or child, if asked what is the roof made of (or its roofing layers)? Will answer, it’s the part with the shingles on it, that helps the rain to run down it. They aren’t wrong, but a roof has many roofing layers that together allow it to work properly.

From experience, roofing mission (a.k.a "BulletpRoof") agrees with homeowners to an extent, except shingles are only a single layer of the entire picture. Let us elaborate further for you.

We’ll be discussing the roof’s layers in this article, from the roof deck up to the shingles. While the anatomy of a roof provides an in-depth look at how the roof forms a system with all of its roof components.

Table of Contents

Purpose of having Roofing Layers

The roof’s layers are meant to help insulate and protect your home; Done by providing proper drainage, ventilation and durability against debris or weather-related damage. By doing so, this helps the water to run-off instead of accumulate and provide enough fresh air to dry areas with moisture quickly. As an added benefit, this cools the home in the summer and keeps the home warm in the winter.

As a homeowner, it’s worth understanding that each roof layer performs one function really well and when it doesn’t there will most likely be a leaky roof in the future.

A Roof’s 12 Layers

A roof is made up of 12 layers from the roof deck up to the roof’s shingles that make up the entire roof’s surface. See them listed from the bottom to the top layer below:

  1. Split-Sheathing; These are equally distanced wood planks that support the roof and provide room for added insulation foam if a roof’s shingles permit it; Specifically cedar shingles don’t allow for insulation foam because they require additional ventilation. The spacing allows it to help ventilate the roof (along with the attic space below it), preventing the growth of mold and rot due to moisture build-up. 
  2. Roof Deck; Plywood base of the roof, that supports the roof covering above it and protects against water passing through to the home below it. Only cedar shingles don’t allow for a roof deck to be installed because they require additional ventilation from the attic to remain viable.   
  3. Battens; Wood planks installed on top of the wood deck to hold concrete, clay or slate tiles stay in place, not used for any other type of shingles. Proper installation allows the tiles to be staggered in a way that allows the water to run from one tile to the next preventing pooling, which requires a skilled roofer to complete. 
  4. Underlayment; A felt paper, tar paper or synthetic material that forms a protective water barrier on top of the roof deck. The material used depends on the location, environment and weather conditions of a region or area where the home is located. An essential waterproofing layer that is both durable to falling debris and assists with insulating the roof. Incorrect installation exposes the roof deck to water, which can result in water-damage, plumbing-damage and/or electrical damage from leaks in the roof deck.  
  5. Ice and Water Shield; An ice-proof and waterproof membrane installed in sensitive roof valleys and around roof penetrations (skylights, air vents, solar panels, etc.). Preventing water from entering these vulnerable joints in the roof’s decking. Incorrect installation exposes the attic space to water, which can result in water-damage, plumbing-damage and/or electrical damage from leaks in the home.
  6. Flashing; Sturdy materials or metal sheets installed on top of the underlayment and under the roof coverings to protect sensitive joints between the roof deck and any roof penetrations (skylights, air vents, solar panels, plumbing, etc.). Incorrect installation exposes the attic space to water, which can result in water-damage, plumbing-damage and/or electrical damage from leaks in the home.
  7. Drip Edge; A metal flashing installed along the roof’s edge, on a roof’s eaves and rakes to form an L-shaped protective cover. Preventing water from reaching the fascia behind the gutters and getting under the roof’s waterproofing to directly damage the interior of a home (severe damage to plumbing, electrical, hvac and the roof are all possible). Required by-law (International Residential Code) and shouldn’t be overlooked due to cost concerns.   
  8. Starter Shingles; A pre-cut row of roofing materials installed at the roof’s edge, on top of the drip edge to add to its existing protection. It has an adhesive seal that helps it to stay in place during high winds and doesn’t allow water to drip anywhere else but the gutters. Incorrect installation allows water to reach the fascia behind the gutters and get under the roof’s waterproofing to directly damage the interior of a home (severe damage to plumbing, electrical, hvac and the roof are all possible).   
  9. Ridge Capping; Pre-bent thicker trim material installed at the roof’s peak where two slopes meet, it easily covers the roof’s ridge. This provides protection at the roof’s peak joints where two sloped roof decks meet. Incorrect installation would mean installing 3-tab shingles in their place because they are not designed to protect that joint and offer many areas for water to leak through into the attic and home.   
  10. Roof Shingles; These are the square and rectangular pieces that cover the middle portion of any roof deck. They are overlapped in such a way to form a tight waterproof membrane that helps water to run-off the roof and into the gutter. While helping to create a sun, water, ice, fire and debris protection that faces the outside elements on your home’s behalf. Its built-in coating on top, is responsible for making it UV-proof and durable against falling debris (making it spring back from impact). Installed incorrectly it allows water to accumulate by blocking it or directing it towards sensitive areas it shouldn’t go.     
  11. Fasteners; These help attach the roof shingles to the underlayment and roof deck that help it to stay tight to the roof deck, preventing water from getting underneath the waterproofing below it. Normally, roofing nails are used for asphalt shingles, and metal fasteners are used for tiles and panels; Other fasteners include bonding, blue tar or adhesive paper. Installed incorrectly, these fasteners can create small holes or gaps in between the shingles, allowing for water to go directly into the attic at times. 
  12. Coatings; A polymer that can be applied on top of the roof shingles and fasteners to restore the UV-protection, water-resistance, fire-resistance and impact-resistance of the roof.

By having all of these roofing layers, it helps to increase the longevity of a roof and by extension the home from getting damaged. For homes in wetter climates, or when it rains there may be noticeable changes with the home that show that these roofing layers are not working as they should.

Commonly, a homeowner will notice these changes in the form of a higher energy bill due to the lack of insulation, dark streaks on ceilings, bulging walls, shingles with moss growing on them, etc. These are signs for a homeowner to keep an eye out for so that they can repair the roof before it takes any major damage in the future.  

The roof, normally associated with the shingled part of the roof, is one part of the entire roof system that together protects and insulates your home; Keeping it’s occupants safe from weather, debris and comfortable no matter whether it is hot or cold outside of the home.

At roofing mission (a.k.a "BulletpRoof") it's important to realize what the entire roof system is capable of when built correctly for both the roof and the entire home it protects. Absorb what you can from this article for a better roof-related experience.

This explanation of the anatomy of a roof will help the homeowner understand what each part of the roof is and their functions so that they can more easily speak with a roofing contractor when they need assistance from them. Otherwise, we have a simplified explanation of the roofing layers for those looking for a quick snapshot of their roof.

Table of Contents

Detailed Roof Anatomy

A roof (or roof system) has 3 main parts, it’s:

  1. Framing
  2. Covering
  3. Ventilation

Roof Framing

The roof’s framing is the architecture that supports and shapes the roof, built from beams (called trusses and rafters) and plyboard. From bottom to top:

Attic Space is the empty space under the base of the roof and is the area where the roof’s base is connected to the home, supporting the roof. It works like a layer of air-based insulation that prevents water moisture retention, keeping the roof’s base above and the home’s interior dry, and regulates the temperature of the home (not too hot or cold); With proper ventilation. 

The sloping shapes of rooftops made with the framing prevents water from accumulating and helps it to drain water easily, called a drainage allowance; Otherwise, any water accumulation, if neglected, can turn into a leaky roof one day. 

Commonly, there are two roof shapes:

  1. Gable Roof is a triangular shaped roof with an open A-shaped wall face, and is made up of the following parts:
    1. Ridge - The peak or the highest point of a roof
    2. Gable - A-shaped wall face that forms the roof’s peak
    3. Eaves - The overhanging edge of a roof
    4. Rake (or fascia) - At the edge of a roof (eave), a rake is the vertical flat end piece
  2. Hip Roof is a roof with a sloped-end, and is made up of the following parts:
    1. Hip - A sloped triangle-shaped roof face (hip end) made-up of two diagonal ridges, where each ridge (called a hip ridge) sits between two sections of roof.
    2. Hip End - The sloped roof face end with a peak at the top
  3. Combinations of these shapes are used to make more complex roofs
    1. Dormers - Raised roof sections containing a vertical window in the roof’s slope
    2. Valley - V-shaped area where two slopes meet

At the top, where the home makes contact with the base of the roof, are made up of the split-sheathing and roof deck:

Roofing Material Conditions:

When it’s time to re roof or perform a cedar/tile conversion, during the tear-off step is when the roofer will find rotten or soft (compromised) split-sheathing or roof deck sections that should be replaced immediately. At least, “BulletpRoofers” do it this way to increase the longevity of the roof, while some roofers choose to ignore this and layer new roofing materials on top to decrease the lifespan of your new roof. 

How many layers of shingles are allowed depends on where your home is located, generally accepted as 2 layers but we recommend no more than 1 layer.

Above this all is the roof covering.

Roof Covering

The roof covering is the protective layer that prevents the outside elements, weather and/or debris, from getting into the home. These outside elements include fire, water and ice when installed correctly.

Roof coverings can be broken into 5 main areas:

  1. Waterproofing
  2. Gutters
  3. Covering
  4. Fasteners
  5. Coating

As waterproofing entails, it’s meant to prevent water and ice from reaching the roof deck. Used for every roofing material, except cedar shakes which do not have a roof deck. It includes the following from the surface of the roof deck up to the roof coverings:

The gutters catch the water that runs off the roof and channels it away from the home’s foundation, attached to fascia at the roof’s edge. Improper installation of the gutters onto the fascia of a home or to downspouts (vertical gutters) onto the home’s siding; Resulting in water channeling towards the home or accumulating where it shouldn’t and worse, damaging the home (leaks and flooded basements).

The gutter system has broken down into horizontal and vertical pieces below.

Horizontal Pieces of the Gutter System:

Vertical Pieces of the Gutter System:

Gutters are an independent roof system, meaning they can be installed or reinstalled without affecting the roof coverings above it.

The coverings provide sun, water, ice, fire and debris protection, and are responsible for helping water to easily run-off to be caught by the gutter system; A roof’s coverings are what gives a roof a unique look, its curb appeal, that everyone associates with what a roof is. These coverings come in many materials to choose from, including:

Expected coverings:

Asphalt shingles are most common because of its affordability, versatility in design and durability relative to other roofing materials in the Lower Mainland. 

Fasteners help attach the roof coverings to the underlayment and roof deck, installed correctly they don’t leave small holes for water to enter the roof deck. Normally, roofing nails are used for asphalt shingles, and metal fasteners are used for tiles and panels; Other fasteners include bonding, blue tar or adhesive paper.  

Together the roof coverings make a waterproof seal that prevents water, debris and UV from the sun from damaging the home. 

The coating is often built into roofing coverings to make them weather-resistant, water-resistant, fire-resistant and UV-resistant (added insulation sheds heat from the sun). Made of polymers that can help coverings to give under impact and spring back into normal shape. These coatings can be added at the end, on top of the rest of the roof coverings to help restore some of its protection back as a part of regular roof maintenance. 

Next is roof ventilation. 

Roof Ventilation

Roof ventilation is responsible for cycling water moisture out of the roof system and bringing dry fresh air in, preventing water damage to the interior of the home; Seen in the form of mold, rot, algae, moss, dark streaks on ceilings, bulging walls, leaks, etc. Shortening the lifespan of a roof drastically.

To provide this ventilation to a roof, there has to be openings to allow air to enter and exit freely between the home and the home’s exterior. These openings, more specifically roof penetrations, are extremely vulnerable when not properly waterproofed and are most likely to leak. 

Roof ventilation relies on different vents to do its job properly:

For better performance, active vents are recommended over passive vents when possible. 

Vents are not only limited to the roof, a home’s kitchen, bathrooms, dryers, plumbing (vent pipes), etc. The plumbing vent pipes need ventilation to prevent sewage smells from accumulating in the home and prevents a vacuum from happening in the pipes (noticeable through gurgling noises in a home).

Roof penetrations are anything that goes through the underlayment and roof deck, and/or stands above the roof’s coverings. Examples of roof penetrations include but are not limited to the following:

The culprit of most leaks starts at the chimney, it’s recommended to look there before searching elsewhere for the source of a leak unless a leak is seen elsewhere in the home.

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