Anatomy of a Roof

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:

  • Split-Sheathing – Wood planks equally distanced apart to support the roof above it and provide room for insulation or not, depending on the roofing material’s need for ventilation above.
  • Roof Deck – Base of the roof, made up of plywood boards that are either installed or not, depending on the roofing material above.
  • Battens – Horizontal planks of wood installed on top of the roof deck to hang roofing materials, either installed or not depending on the roofing material.

Roofing Material Conditions:

  • Battens are installed only to hang tiles, concrete and clay tiles, and no other roofing material; Battens help to stagger tiles to allow water to run from one tile to the other, preventing it from accumulating and causing water damage.
  • Roof deck and split-sheathing’s insulation are both removed only for cedar shakes (or shingles), and no other material; Cedar shakes require additional ventilation underneath them to prevent moisture retention and prevent rot from setting in.
  • Normally, split-sheathing with insulation and a roof deck are installed for asphalt shingles, rubber shingles, metal panels, composite, etc.; Every other roofing material not mentioned earlier

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:

  • Underlayment – Protective water barrier made of felt paper, tar paper, or synthetic materials. Material is dependent on the location, environment and weather conditions of a region or area where the home is located. It provides insulation, waterproofing and protection from falling debris.
  • Ice and Water Shield – Ice-proof and waterproof membrane installed in roof valleys and around roof penetrations (ventilation pipes and vents, skylights, solar panels, etc.). They come in 2/12, 3/12 or 4/12 pitches depending on the area they are installed. Prevents water from entering sensitive roof joints. 
  • Flashing – Sheet metal or sturdy material installed on top of the underlayment, under the roof coverings (for example, the asphalt shingles) to protect sensitive joints around roof penetrations; Including chimneys, air vents, plumbing, etc. This helps redirect water away from roof penetrations and down to the gutters, otherwise without proper flashing protection, expect to see leaks in these areas.
  • Drip Edge – A metal flashing installed on the roof’s edge (on its eaves and rakes) to prevent water from reaching the fascia and get under the roofing’s waterproofing, directly damaging the roof deck. Required by the IRC (International Residential Code), contractors who ignore installing this will lower the quote and will result in serious water damage to a home in the Lower Mainland.

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:

  • Gutter; Half-cut metal tube on the edge of the roof that catches water running-off the shingles and channels it along its tube, each piece is called a “section”; Signs of rust, corrosion, holes, broken section(s), clogged or overflowing gutters will cause leaks in the gutter
  • Hangers; Strips of metal that support the gutter’s bottom helping the gutter stay level with the roof’s edge; Signs of uneven gutters or sagging mean these hangers are causing leaks in the gutter because water can not be channeled evenly through the gutter
  • Ferrule; Hollow shaft that encloses a “spike” or long screw and helps the gutter attach to the roof’s edge, onto the home’s fascia; Signs of the gap between the gutter and fascia means the spikes are loose causing water to drip down the house’s side 
  • End Caps; A cap (a seal) that fits at the end of a gutter “section” that prevents water from channeling out of a gutter’s edge; Signs of rust, corrosion, holes, the end cap being loose or missing causing water to drain onto the side of the house or eroding the ground near it
  • Mitered Corner; Corner piece of a gutter that helps water to channel around the corner of a roof’s edge; Signs of rust, corrosion, holes or a leak causing water to drain down the corner of a house.      

Vertical Pieces of the Gutter System:

  • Downspout; Vertical tube that runs down the side of a house, responsible getting the water caught by the gutter and moving it towards the ground; Signs of rust, corrosion, holes or a loose downspout would cause water to drain onto the side of the house
  • Downspout Elbow; The part of the downspout closest to the ground that redirects the water coming down the downspout and away from the home’s foundation; Signs of holes, rust, looseness or excessive ground erosion on the ground, or landscaping damage indicates water could be leaking into the home’s foundation.
  • Pipe Cleats; Strips of metal that attach a downspout to the side of a house, responsible for keeping the downspout secure to the wall when draining water; Signs of corrosion, rust, missing or loose pipe cleats means the downspout could shift out of place and cause water to drain onto the side of the house  

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:

  • Shingles – Asphalt, rubber and cedar (cedar shakes or shingles)
  • Tiles – Clay, concrete, slate
  • Panels – Metal
  • Synthetic (or composite) 
  • Commercial – foam, single-ply roofing, built-up roofing and modified bitumen  

Expected coverings:

  • Starter Shingles – A pre-cut row of roofing material installed at the roof’s edge which has an adhesive seal that helps it resist strong winds, added protection on top of the drip edge.
  • Ridge Capping – Pre-bent thicker trim material installed at the peak of where two roof slopes meet that is meant to easily cover and protect the ridge of a roof. Be wary of contractors who quote lower and opt to replace ridge capping with 3-tab asphalt shingles because they are not designed to protect the ridge and will result in leaks. 

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:

  • Passive vents, openings that allow air to enter and exit as it pleases. They include: Static vents (box vents), ridge vents without a baffle, gable end vents (opening beneath gable triangle point), soffits (opening under the fascia or rake board), undereave vents,  etc. 
  • Active vents, openings that continually make air enter and exit. They include: turbine vents, power vents, ridge vents with a baffle or solar-powered vents, etc.

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:

  • Chimney – Brick or stone exhaust point for indoor smoke and fire that escapes from the chimney flue, an interior lining that runs up the roof. A chimney cap is installed on top of the chimney flue to prevent rain and snow from entering the chimney.  
  • Box vents – A sturdy box covering that ventilates air through its downward or side-facing opening passively, preventing rain from entering directly from the top.
  • Turbines – A metal turbine that uses the wind to let air flow in and out of the attic, an active ventilation system.
  • Vent Pipes – Pipe that connects to plumbing and passively allows air flow in and out of the plumbing
  • Ridge Vent – A vent on the roof’s peak that passively allows hot air to escape and cool air to enter 
  • Skylights – A roof opening covered with transparent material like glass to allow daylight or moonlight into the home.
  • Satellites – Metal dish that emits signals to radio towers that are installed on the roof to increase its signal.
  • Solar Panels – Panels that can absorb the sunlight and convert it into electrical energy for the home to use

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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