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Parts of a Roof – Understanding Their Purpose

Like just about everything on a home, a roof is a fairly complex group of members that all have to work together and are essential the health and structural integrity of a home.

Here I have listed these members and giving a basic description of what they are, some of which we have full articles for you to read through should you want more information on them.

If there is anything listed below you would like more details on, and would like a full article outlining their use, please leave a comment below and we will get to it as soon as possible, and if you really like the article please do let us know in the comments section down below we would love to hear from you!

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Roof decking.

Roof decking is most commonly made of 0.5-inch plywood, located between the structural components, such as the rafters, and joists, and the weatherproofing and insulation layers, such as the shingles and roofing underlayment.

To put it simply, the roof decking is a middle ground for a large portion of roofing components to be placed. It is for this reason that your roof decking should be sturdy to hold this weight by still durable enough to cope with many external forces such as wind so that it does not just break under extreme load.

As a side note there are many more materials that roof decking can be made of such as steel or cement, however, on your standard residential home plywood seems to be the most preferred as it is cost-effective and very strong.


Shingles are the first layer when it comes to waterproofing and weatherproofing your home. Often made out of fiber cement or asphalt, they are layered together to give a watertight seal and keep you nice and dry inside.

You can expect for your fiber cement shingles to last about 25 years or so, depending on where you stay, before you should have to consider replacing them.

Roofing underlayment.

This is your next roofing component that is attributed to waterproofing. The roofing underlayment is nailed down directly to your roof decking before all other roofing materials.

The primary reason this is so important for your roof is that it is a moisture barrier as extra protection for your roof, preventing any water damage to your major roofing components such as your decking itself of your joists and beams.


This is something we have covered in great detail in a separate article all about soffits, which is the area located under the eaves. I encourage you to visit that page and give it a read by clicking here. Overhanging eaves are the very edge of your roof, which normally overhangs your exterior walls.

Eaves membrane.

This is another underlayment that is just covering the bottom-most portion of the roof, close to and extending past the eaves. The eaves membrane is added protection against water from being able to get to your roof decking or under your roof, avoiding water damage to your roofing members.

A large reason why it is necessary to have eaves and for your them to overhang your walls is to ensure that water makes it clear past the edge of your building. Without this water may be able to make it up into your roofing or attic, causing all sorts of heavy water damage.


A chimney is used to ventilate the smoke or exhaust gasses from the fireplace or boiler up through your roof and out far enough from your roof so as not to affect the house. They are usually made out of clay bricks, masonry or metal, but there are some other types, depending on the size and aesthetic you are looking for.

Saddle / Cricket.

A saddle or cricket is a ridge that is built on the highest side of a chimney used to divert water away from the chimney and around both sides of the structure.

A Cricket can also be used to transition from one area of the roof to another.

If the saddle covers quite a small area it is primarily made out of metal flashing, however, if it is larger and covers more area contractors will usually cover it with the same material as your roof such as asphalt shingles.

Ridge and Ridge Board.

The ridge is the topmost apex of any sloped roof. The ridge board is the horizontal timber board below this that joins the rafter and trusses.

Plumbing vent.

The plumbing vent is a pipe that extends out of the top of the roof. Its function is to allow air to flow into the plumbing system so that wastewater is allowed to flow freely into the sewer or the septic tank system.

Without this, it would create a vacuum and not allow waste to escape. It is worthwhile to note as well, that the plumbing vent is also protected by flashing to ensure a watertight fit, similar to the chimney.


Where two sloped roofs meet, a joint is needed to be made, flashing or a joint cover is fitted here to ensure a watertight seal so that no water is held here for an extended period.

Without this, the building would be at serious risk of water damage to the roof, but rather expels it as soon as possible away from the roof into the gutters or out off the roof entirely.

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Roof vents.

We have done several articles on EZPZRoofing about different roofing vents that I encourage you to take a look at, such as the ridge vent or the gable vent. These are used to expel hot and humid air out of the roof or attic and bring in cooler, dryer air.

The reason you want to do this is so that it keeps as much moisture out of the roof as possible so that it avoids a mildew buildup. Without these crucial members, the house is at serious risk of moisture damage.


A skylight is very much like a window for a roof. Its purpose is to allow daylight into the house. This will reduce energy costs, and the need to keep lights on in the area you would install a skylight.

These are very useful in areas of the home that does not have access to a window such as a passageway or a stairway that is in the center of a home.

Drip edge.

We have an entire article dedicated to describing what a drip edge is and what it is used for, I encourage you to click here and read up a bit more so that you can more fully understand what they are.

To put simply, the drip edge is flashing or molding that is installed on the edge of your roof, this is added protection against water from getting into your roof by water splashing back under your roof decking and causing damage to your roof.


The attic is the space under the roof and above ceiling boards. This space is usually used for storage or sometimes a loft bedroom. This space must be well ventilated as it is susceptible to high amounts of heat and thus moisture.


Trusses include all of the main members of the roof that makes up the framework consisting of the rafters, joists and collar beams. It should be known that trusses are not limited to these but can also include posts and struts as well.


These are the diagonal members of the truss that meet at the apex of the roof into the ridge board. The rafters are the main member that support the roof deck and everything on top of it.


Joists are parallel running members, typically made of timber or metal, that are used to support the roof and its weight and transfer it to your walls evenly ensuring the walls do not shift. I have done a full guide on joists, check it out if you want to learn more details.

Collar Beam.

The collar beams are horizontal members connecting to the rafters. These are used to support the rafters and take the strain off the rafters that are causing them from wanting to separate from the force exerted from the roof.


Only installed on a pitched roof, gutters are a duct or trough that is installed along the lower ends of the roof. They are used to collect rainwater that flows off your roof into them and divert them down a downspout and into a drain.


This is a channel that takes rainwater from the gutter and allows it to drain down a pipe and into a drain.

And that concludes our list. Did we miss anything? Did you love the article? Let us know in the comments section down below, I would love any and all feedback!


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