Different Parts of a Roof Explained

Tips & Advice
Different Parts of a Roof Explained

When you look up at your roof, what do you see? You may be thinking, well… roof tiles, shingles, a chimney or maybe even a few pigeons here and there. And you are right, a roof is made up of all of these things (minus the pigeons), however, there are far more layers to your home’s roof structure than you may think. 

Each part of the complex roof system contributes to the protection and structural support of your home. It’s important to recognise and understand the importance of each to ensure you never overlook any potential problems and won’t be left in the dark should you ever need to hire a roofing contractor down the line.

In this post, we’ll take you on a tour of your roof, giving you valuable insight into all the inner workings, layer by layer.

Pitched roof cross section1. Framework

The first step to creating a safe & stable roof structure is to start with the skeleton. By this, we mean the basic framework, comprised of rafters, joists, beams and trusses. The purpose of framing is to provide durable support for the load of your roof and walls, whilst offering a practical area for installing insulation and vents.  


Rafters are a conventional structural component, found in many traditional roofs with a pitch steeper than 10°. Each rafter is spaced evenly apart and laid parallel, joining where the slopes of the roof meet at the apex. Some rafters are visible from the space below whereas others are concealed within the roof structure. Most rafters are made from timber or, less commonly, steel and concrete.


The joist is a horizontal structural member, again made from timber and occasionally steel or concrete. Joists are integrated to join walls and support the mass of the roof structure, transferring the weight to the building’s vertical beams down into the foundations. Depending on the design of the roof, the joists may lay flat or run pitched and can be either concealed or exposed.


Integral to the strength and stability of the building, the roof beam is a load-bearing element that supports the roof whilst enhancing the cohesion of the walls to prevent spreading or leaning. Generally, beams are the thickest part of the roof frame and often span the entire length of the roof space. Wood beams are the most popular, but steel & concrete are potential alternatives also.


A roof truss is an engineered structure, comprised of straight pieces that form sturdy triangles to support the roof load. The elements of the triangle are positioned under tension and compression but are resistant to bending for optimal strength. Trusses are a pre-fabricated element, often made using a lighter timber.

2. Vapour Control Layer (VCL)

The warm air within your home contains moisture in the form of water vapour. When this warm air meets the cold surfaces within your roof, the process of condensation occurs which can be pretty damaging to your roofing materials long-term. By installing a vapour control layer onto the inner side of your insulation, this water vapour transfer is reduced and you can even improve the efficiency of the insulating material.

3. Insulation

Insulation is a dedicated material, designed to minimise the degree of heat lost from your roof by creating a barrier between the inside of your home and the exterior temperature. Fitting  roof insulation is one of the most efficient ways to save energy and money, with the potential to cut bills by approximately 20% whilst significantly reducing your carbon footprint. In fact, insulation will often end up paying for itself many times over an average 40-year lifespan when fitted correctly.

There are multiple varieties available, the style of which will depend on your specific roof type. Fibreglass is one of the most popular options out there as well as insulation boards, rock wool and even spray foam insulation. Natural insulators such as sheep’s wool have also become increasingly prevalent over recent years as a safer & more sustainable alternative. 

Did You Know? An uninsulated roof accounts for nearly 25% of the total volume of heat lost from your property.

4. Breather Membrane

The breathable membrane layer contributes to the protection and weather-proofing of the structure, whilst maintaining good ventilation through the material. It forms a moisture-resistant barrier that shields against water infiltration, commonly caused by melting ice dams or heavy downpours. Most modern membranes are very lightweight and versatile with many also offering a fire rating for extra endurance against flame exposure.   

5. Lap Tape

Lap tapes are used to overlap the point of two membrane sheets, securing the upper sheet to the lower whilst preventing ingress of water, air, and other damaging elements. These tapes are incredibly robust against external elements, offering fantastic temperature and tear resistance. Many are also double-sided for very quick and easy application.

6. Decking

Roof decking is installed atop the framing and is typically comprised of plywood sheets. This layer basically acts as the foundation of your roofing system, adding structure by covering the framework and supporting the weight of the roofing material installed above. You can typically spot the underside of your roof’s decking if you look up whilst in the loft or attic.

7. Flashing

The main purpose of roof flashing is to create & maintain a watertight roof structure by sealing exposed elements and intersections. Lead flashing is one of the most popular flashing materials available, favoured for its hardy durability, minimal maintenance and malleable nature.

There are three main flashing styles used in roofing installations:

Apron flashing is a versatile option used on the front & back of chimneys, abutting flat roof brickwork or at any point where the roof meets the brickwork of another house or outbuilding. It’s also used to seal bay windows and on slate & tile roofs where a wall or porch is met.

Step flashing is used to abutt brickwork in situations where a low height roof runs into a wall, a roof meets a chimney, or a conservatory roof meets the wall of a house.

As the name implies, chimney flashing prevents water from entering at the point at which the chimney meets the roof.

8. Underlayment

Underlayment is fitted as an extra layer of protection between the roof deck and the final roofing material. Roofing felt is the traditional choice, popular amongst DIYers, however, synthetic underlayment’s are a modern alternative that are now preferred amongst most roofing professionals.

Installing underlayment is a valuable step that benefits your roof structure by:

  • Reducing the effect of wind loading
  • Creating a waterproof barrier whilst safely disposing of water collected on the upper surface of the underlay
  • Acting as an additional layer of insulation
  • Preventing rot & mould

9. Roofing Material

Whether shingles, sheets, slate or tiles, your chosen roofing material should provide a fundamental layer of weather-proof protection whilst adding unique character to your home.

From classic concrete to contemporary composite, stylish slate to charming clay, there is an extensive selection of roof tiles on the market, each offering a distinctive look and durable finish for your roof. Most tiles deliver a lifespan in excess of 50 years, with some even reaching the 100 mark when properly maintained. There are multiple styles available including plain, pantile and double roman with dimensions to suit a wide range of structures.

Shingles are another versatile option, manufactured in shapes and sizes to suit every kind of property. Common shingle materials consist of felt, cedar, metal, plastic and composite materials including fibre cement. The square shape is the traditional preference for classic homes, however hexagonal and abstract shingles are quickly growing in popularity for the futuristic and eye-catching roof designs they can create.

Made from many different materials including metal, bitumen, fibre cement, PVC & polycarbonate, roof sheets are a reliable, lightweight & cost-effective option. As well as the standard corrugated style, box profile sheets are another sturdy and easy-to-install alternative that creates a professional and resilient finish for your roof.

10. Ventilation

When excess heat and moisture become trapped within a roof space, the framing, insulation, and roofing materials are left vulnerable to damage which can lead to some dangerous (and expensive) repairs. Roof vents are installed to maintain a consistent air flow, moderating the internal temperature, and reducing the risk of condensation. There are numerous forms of ventilation available, including tile vents, fascia vents, through-wall vents and more.

11. Ridge Caps

Ridge caps are the final element of the roof, installed along the ridgeline where two sloped sides meet to form the apex. The ridge cap fits securely over this exposed joint to protect your home from rain and snow ingress whilst fashioning a sealed, professional finish. Whilst typically made from the same material as your shingles or tiles, ridge caps are often thicker, smaller and pre-bent for easy installation.

Taking on Your Own Exciting Roofing Project?

Are you feeling inspired to embark on your very own roofing repair or construction project? Luckily, you’re in exactly the right place to find the best and most affordable roofing supplies for the job. Here at Roofing Megastore, we supply a fantastic selection of industry-leading brands including Novia, Marley, Kingspan, Velux, Tapco and many more. From sheets, shingles and tiles to flashing, insulation and guttering, we’ve got over 40,000 roofing products for you to explore.

If you need any help in finding the right product for the job, don’t hesitate to contact our award-winning customer service team on 01295 565565 or leave a message in our handy live chat.

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