A roof may look like a simple structure on top of a building, which keeps out rain and other weather, but there’s far more to it than that. In this guide, we’ll teach you about the internal and external parts of a roof, what they do, and their names. Each part of a roof’s structure plays an important part in keeping it safe.

You’ll be an expert in no time, which is especially handy if you’d like a career as a roofer.

The internal structure of a roof

The part of a roof you can’t see is the internal structure, sometimes called a truss (an assembly of beams or other elements that create a rigid structure). This is the part that holds up the roof from inside the building.

We haven’t included it, but the attic or loft is the space under the roof, which is formed and protected by both the internal and external structures.

King post

A king post is a central, vertical post used to provide support for the principal rafters and has struts that extend up and out from them. When you look at older buildings with exposed roof beams, the king post is in the centre of the triangular shape that forms the roof’s shape.

Principal rafter

The principal rafters form the sides of the triangle that the king post sits in the centre of. They determine the apex or angle of the roof depending on their length.

Tie beam

The tie beam is the base of the triangle we’ve been talking about, running along the entire width of the roof to support the king post and the principal rafters.

Common rafter

Rafters are normally made from wood or metal, and they run from one end of the roof to the other to form the main framework, meeting at the apex. They support the covering and insulation for the roof.


A strut is an integral part of the load bearing aspect of a roof’s truss, providing outwards-facing support. We mentioned before that you will typically see struts extending from the king post to prevent the two principal rafters from falling in on themselves.

Purlin & purlin cleat

Purlins sit perpendicular to the rafters of the truss. They are fixed into place using cleats, which are hidden metal brackets that hold them to the rafters and help increase stability.

Ridge board

A ridge board is a horizontal piece of timber (or metal) resting at the peak of the roof over the rafters. The rafters connect to the ridge board to complete the framework of the internal structure.

Brick infill

A brick infill in a roof means that brick has been used to fill the spaces of the main structural frame. You may have seen this in older buildings where the outer walls show the exposed beams that form the roof, and brick has been used to fill the gaps and be durable.

Collar beam

These are horizontal beams connecting two rafters that intersect at the ridge of the roof. Not to be confused with the purlins.

External roof covering and features

This is the part of the roof that you can see from the outside of the building and is also what protects the property from inclement weather.

Decking or sheathing

Roof decking or sheathing is the thin wooden boards that span the entire truss and support the rest of the roof. They are covered with the underlay membrane.


These flat rectangular shapes give a roof its character as they can be made from various materials such as slate, wood, flagstone, plastic, or metal. They cover the roof by being layered to allow water runoff.

Underlay membrane

This coating, made of felt saturated with asphalt or a synthetic fabric, protects the shingles against resin released by wood decking, and protects the decking itself against bad weather.


Flashing is made of galvanised steel, aluminium, or plastic and can be flexible or rigid. It prevents water flowing near roof openings from infiltrating the roof. Flashing is found in valleys and at the bases of chimneys, walls, roof vents, and plumbing vents.


The word ‘soffit’ is from the Latin word suffixus and translates to meaning ‘something fixed underneath’. Soffit is the material between the roof’s eaves where the fascia and gutters are placed to the wall (roofs without overhangs do not have soffits). They act as a passive ventilation unit for your attic, keeping warm moisture in the air from entering the attic air, condensing, and creating mould.


This is a piece of polystyrene or cardboard inserted between two rafters to let air flow freely over the insulation near the soffits.

Roof vents

These enclosed structures made of metal or plastic feature openings and fins to properly ventilate the attic space. The most effective have four open sides and rise above the roof, allowing them to capture the wind from all directions.

Drip edge

This is moulding that covers the entire lower edge of the roof and reduces the risk of water infiltration.

Eaves membrane

This protective membrane goes under some or all the shingles to prevent water infiltration.


The valley is the connection between two pitched roofs and forms a right angle. Below the valley is a valley rafter that supports a shallow gutter to allow water and other debris to trickle down into the gutter.


This is simply the horizontal line at the top of the roof running along its entire length.


A saddle sits behind the higher side of a chimney (or something similar like a skylight) to divert rainwater around it. It resembles a triangular shape to allow water to run down either side onto the rest of the roof and, eventually, into the gutters.


The lowest point of a pitched roof is known as the eave. It’s also where the gutter is connected to the roof.


A gable is the A-shaped section of wall between two intersecting sloping sides, which can be the same size or different sizes depending on your property. Some larger properties may have numerous gables, joined together with flatter roofing styles to add more depth to the property.

Find out more about a career as a roofer

A career in roofing can be lucrative, but what qualifications might you need? This depends on the type of roofer you want to be, which is why we have three main pages dedication to the information:

From the typical hours you may work, to the ways you can get into roofing, plus a potential salary, Go Construct can help you learn everything you need to become a roofer. This includes apprenticeships and work experience opportunities that can help you on your way.