Introduction
Pitched roofs come up in almost every residential project and yet when you first sit down to draw one, the details can feel surprisingly hard to get right.
If you’re here because you’re trying to understand how a pitched roof actually goes together whether that’s for a university project, a crit, a placement, or to fill a gap you’ve been quietly aware of — this post is a good place to start.
We’ll cover the main types of pitched roof structure, the key elements and junctions you’ll need to know, how insulation fits into the picture, and what the Building Regulations require. We’ve also included some detail examples from our book Understanding Architectural Details – Residential so you can see how this looks in practice.
In this post:
- Key elements: ridge, eaves, verge, hips, valleys and more
- Types of pitched roof construction (mono pitch, couple, close couple, collar, purlin and truss roofs)
- Hipped and mansard roof forms
- Insulation strategies, U-values, airtightness and ventilation
- Key components of pitched roof detailing (roof coverings, underlays, eaves, ridge, valley, hip, verge and abutment detailing)
- Pitched roof detail examples
- Regulatory considerations, including the Future Homes Standard
- 2D and 3D detail examples from the book and Detail Library
Want the full set of details alongside this post?
You can download a free sample of Understanding Architectural Details – Residential to see how the construction details are set out and what the book covers in full.
Understanding Pitched Roofs
The roof is a key element of the building structure. It provides protection from the elements and has a vital role to play in reducing heat loss from the building. Roofs tend to be either pitched or flat, and typically in residential construction, timber is the most common material used.
The Building Regulations in the UK provide guidance on roof design. You can find the Building Regulations here.
Functional Requirements
The functional requirements of the roof are:
- Strength and stability
- Protection from the weather
- Durability
- Resistance to passage of sound
- Thermal insulation
- Resistance to air leakage
- Fire safety
- Security
- Aesthetics
- Condensation control
- Moisture management
- Ventilation
Pitched Roof Elements
The majority of residential houses in the UK are constructed with pitched roofs. These pitched roofs often have a symmetrical geometry with equal slopes that meet at a central ridge. Roof covering materials often determine the angle of the pitch, being the minimum slope that is necessary to prevent rain and snow ingress.
Ridge
The horizontal apex where two roof slopes meet.
Eaves
The lowest edge of the roof, where it overhangs the wall.
Verge
The edge of the roof at a gable end.
Hip
The external angle where two slopes meet on adjacent elevations.
Valley
The internal angle where two slopes meet.
Rafter
The sloping timber forming the roof structure (common, jack, hip or valley).
Purlin
Horizontal timber supporting the rafters at mid-span.
Wall plate
The timber bedded on the wall that the rafters sit on.
Batten
The timber the tiles or slates are fixed to.
Underlay
The secondary weather barrier laid beneath the battens.
Fascia
The board fixed to the rafter feet, carrying the gutter.
Soffit
The board closing the underside of the eaves overhang.
Barge board
The board that finishes the roof edge, at a verge.
Flashing
The weathering (usually lead) at junctions and abutments.
Single Pitched Roofs
Mono Pitch Roof
This is the simplest form of pitched roof, sometimes referred to as the lean-to. The foot of the rafters sits on a timber wall plate fixed to the top of the lower supporting wall, while the top of the rafters bears onto a wall plate fixed to the higher wall.
Traditional domestic mono pitch roofs generally have shorter spans when compared to double pitched roofs. However, engineered timber and steel structures can achieve much larger spans.
Double Pitched Roofs
Couple Roof
A simple pitched roof structure, consisting of timber rafters pitched up from the walls that support them, to a central ridge. A central ridge board is used to fix the rafters on each side. This form of roof is often seen in farm buildings, stores and more simple structures.
Traditional couple roofs are generally limited to approximately 3-4m spans without additional restraint or ties. Wider spans than this can cause the foot of the rafters to push the supporting walls outwards. The addition of ties or collars can help to resist this spread and increase the achievable span. A tie at ceiling level effectively turns the structure into a close couple roof. Rafters are spaced at 400-600mm intervals, sizes are calculated according to span and support required for the roof covering.
The ridge board is a continuous softwood board, commonly 32-38mm thick. The foot of each rafter is fixed to the timber wall plate, which is fixed to the top of the wall to provide a level fixing surface. The wall plate is commonly 100×75mm but varies depending on structural design. It serves to spread the load of the rafters along the wall. A notch (or bird’s mouth) is cut into the rafters at the foot, so the rafter can fit tightly onto the wall plate.
To resist wind uplift and tie the roof to the structure below, the wall plate is normally secured with galvanised steel holding-down straps, and lateral restraint straps connect the rafters and ceiling joists back to the walls. Both are requirements under Approved Document A.
Close Couple Roof
This construction is very similar to the couple roof, but in this instance horizontal ceiling joists are fixed to the foot of each pair of rafters. This serves as a tie to resist the tendency for the rafters to push the walls outwards but also serves as support for ceiling finishes.
This type of roof is seen in small houses and bungalows. The ceiling joists can be 38-50mm thick, and a depth can range from 98mm to 220mm depending on span requirements and centres of the joists. These joists can provide roof space for services storage, such as water storage cisterns, along with general attic storage. The close couple roof tends to have a maximum span of around 5-5.5m before additional support becomes necessary.
Collar Roof
A collar roof is similar to the close couple roof, here rafters are framed by collars located in the upper third of the roof. This opens up some of the roof to the first-floor rooms, whilst providing support to the rafters. This system is often integrated with dormer window arrangements in order to maximise light penetration into the room. Providing support to the rafters a third of the way up the roof, is not as structurally effective as support at the foot of the rafters as described in the close couple roof. The collar roof tends to have a maximum span of 4.5m.
Purlin Roof
Purlins are horizontal timbers that are supported by end walls or struts to internal load bearing walls, which offer support to the rafters, thus enabling a reduced rafter section. The overall clear span of the rafter is reduced by half, therefore making a large saving in required rafter size. Purlins supported by gable end walls sit on masonry corbels projecting from the wall, or on joist hangers. If there is no gable end support, the purlins can be supported by the internal load bearing walls, using support struts between the wall and the rafters.
Approved Document A sets the structural requirements for roofs, and points to the TRADA Eurocode 5 span tables for rafter spacing, spans and sizes.
Truss Rafter Roof
A truss rafter roof system is a prefabricated triangular frame of timbers tied together. As the trusses are prefabricated, predominantly mechanised, it results in a very accurate finish to the roof system. The trusses are delivered to site ready to be lifted into position. They are fixed to the timber wall plates.
The Building Regulations Approved Document Part A provides specific requirements relating to stability of trussed roofs and associated bracing. Some domestic timber trusses can span up to 15m. The disadvantage of the truss roof system is the loss of attic space for storage or additional rooms which tends to be in demand these days. It is not possible to convert a truss roof into a usable loft space without major structural works, such as new purlins, floor beams and joists.
For new builds where loft space is wanted from the outset, room-in-roof (attic) trusses are available. These are designed with a clear central space and a built-in floor, offering the speed and accuracy of trussed rafters while still providing a usable room.
Other Roof Forms
Beyond the symmetrical double-pitched forms mentioned above, two other shapes are common.
Hipped roof
A hipped roof slopes on all sides, meeting the walls on every elevation rather than finishing in a vertical gable, which sheds water and wind well but is more complex to construct.
Mansard roof
A mansard (or gambrel) roof has two pitches on each slope, the lower one much steeper, and is often used to create a full storey of habitable space within the roof. This is a popular choice for loft conversions and where height is restricted.
Eaves
The eaves of a roof can be described as the lowest courses of tiles and the timber that supports them. The eaves of a pitched roof tend to extend around 150-300mm beyond the external face of the wall, to provide protection from rain. In some cases, a closed or flush eaves can be designed, which stops the rafters and ceiling joists at the face of the external wall, where a fascia board is then fixed to the ends of the joists and the rafters.
Closed eaves provide soffit boards with ventilation gaps or channels to allow air into the roof space, to be expelled at ridge level.
As a guide, a ventilated cold roof typically needs low-level (eaves) ventilation equivalent to a continuous 10 mm gap for pitches above 15° (25 mm for shallower pitches), together with high-level ventilation equivalent to a continuous 5 mm gap at or near the ridge. Ventilation requirements are set out in Approved Document F and should be read alongside BS 5250.
Hidden gutter eaves detail – from the Detail Library
Insulating the roof
Providing sufficient roof insulation design is key to minimising heat loss through the fabric of the building. The Building Regulations set a limiting (worst-acceptable) U-value for a new pitched roof of 0.16 W/m²K, but the notional dwelling specification used in the compliance calculation is around 0.11 W/m²K. Because a U-value is a maximum rather than a minimum the lower the figure, the better the performance. In practice, roofs need to be designed towards roughly 0.11 W/m²K to pass – Approved Document Part L.
Achieving this U-value can require relatively thick insulation either at ceiling level or at rafter level. Different insulation types provide different thermal conductivities; therefore, some more high performing insulation will require a thinner layer than some insulations that have a higher thermal conductivity.
Where the insulation sits determines the type of roof, and with it the approach to ventilation and condensation control. In a cold roof, the insulation is placed at ceiling level, leaving the roof space above cold and ventilated. In a warm roof, the insulation follows the line of the rafters, keeping the roof structure within the warm envelope. This approach is used where the loft is a habitable room.
Either way, the underlying concern is the same: warm, moist air from inside the home can condense on cold surfaces in the roof, so both moisture and air leakage need to be controlled. This is managed with a vapour control layer on the warm side of the insulation, ventilation of any cold void in accordance with BS 5250 (the code of practice for managing moisture in buildings), and a continuous, well-sealed airtightness layer. Part L supports this by setting a limiting air permeability of 8 m³/(h·m²) at 50 Pa, with a notional target of around 5.
Key Components of Pitched Roof Detailing
To achieve a well-detailed pitched roof, it is important to pay attention to several critical components:
Roof Pitch
The angle of inclination of the roof surface, commonly expressed in degrees (for example 30°-45°), and sometimes as a ratio (e.g., 1:4). The pitch affects both the aesthetic appearance of the roof and its ability to shed water efficiently. This in turn may influence the choice of finish material, i.e., slates, clay tile, concrete tiles, sheet metal and so on.
Roof Coverings
Various materials can be used for roof coverings, including clay or concrete tiles, natural or synthetic slates, and thatch. Each material offers unique characteristics in terms of durability, appearance, and cost. In addition, each material will have its own detailing requirements and specifications that will need to be considered.
Since 2015, BS 5534 has required all single-lap tiles to be mechanically fixed with clips and/or nails according to a wind-uplift calculation. Mortar alone is no longer accepted as the primary fixing. This has led to the widespread use of dry-fix ridge, hip and verge systems, which fix the covering mechanically and often improve ventilation at the same time.
Underlay and Breather Membranes
Beneath the tiles or slates, a roofing underlay provides a secondary barrier against any wind-driven rain or snow that passes the covering, and it plays an important part in managing moisture within the roof. Traditional bitumen felts have largely given way to vapour-permeable (breathable) membranes, which allow moisture to escape from the roof space while resisting water from above. Whichever type is used, it must be laid to the correct drape and fixed in line with BS 5534 to prevent wind uplift and “ballooning”. The choice of underlay also interacts with the ventilation strategy, as some membranes can reduce or remove the need for separate high- and low-level ventilation.
Eaves Detailing
The section of the roof that overhangs the walls, known as the eaves, requires careful detailing to ensure proper water runoff and protection of the building’s exterior. This includes the installation of gutters, fascias, soffits, ventilation and drip edges. There are many different ways to detail a roof eaves, with many different factors to aid decision making. For instance, gutters and downpipes should be sized to suit the roof area they drain, in line with BS EN 12056-3, so that heavy rainfall is carried away without overflowing.
Ridge Detailing
At the highest point of a pitched roof, the ridge requires robust detailing to prevent water ingress and provide ventilation. Ridge tiles or ridge vents are commonly used to cap the roof and allow for air circulation within the attic space.
Valley and Hip Detailing
Where two roof slopes intersect, as in valleys and hips, special detailing is needed to direct water away from vulnerable areas and maintain the roof’s integrity. Flashing and underlays play crucial roles in waterproofing these junctions.
In construction terms, valleys are formed with a valley rafter and either a preformed liner (such as Glass Reinforced Polyester or lead) in an open valley, or interwoven tiles in a closed valley, while hips are built up over a hip rafter and finished with hip tiles or a dry-fix hip system.
Verge and Abutment Detailing
At the gable end, the verge can be finished with a mortar-bedded under cloak and barge board, or increasingly with a dry-verge system that clips mechanically in line with BS 5534. Where the roof meets a wall or chimney, abutments are weathered with flashings and soakers, typically lead with a stepped flashing following the line of the brickwork and, at a chimney, a front apron, side soakers and a back gutter.
Pitched Roof Detail Examples
The following images provide examples of pitched roof details from our book Understanding Architectural Details – Residential.
Roof Eaves Detail – Masonry cavity wall, insulation between and over ceiling joists (MR1)
Roof Eaves Detail – Masonry cavity wall, insulation between and over ceiling joists (MR1)
Roof eaves detail – Masonry cavity wall, insulation between and under rafters (MR3)
Roof eaves detail – Masonry cavity wall, insulation between and under rafters (MR3)
Roof gable detail – Masonry cavity wall, insulation between and under rafters (MR4)
Roof gable detail – Masonry cavity wall, insulation between and under rafters (MR4)
The detail examples above are taken from Understanding Architectural Details – Residential. The book covers each of these junctions in much more depth with multiple insulation strategies, full annotation, and downloadable 2D CAD and 3D SketchUp files. If you’d like to see what else is included, the free sample is a good starting point.
Regulatory Considerations for Pitched Roof Detailing
Compliance with building regulations is paramount in the design and construction of pitched roofs in the UK. Key regulatory considerations include:
Building Regulations
The Building Regulations provide requirements for structural stability, fire safety, thermal performance, and other aspects of building design and construction. It is important to ensure that pitched roofs meet these standards to obtain approval for their projects.
For pitched roofs specifically, the most relevant parts are Part A (structure), Part B (fire safety, including external fire spread and roof-covering classification), Part C (resistance to moisture), Part F (ventilation) and Part L (conservation of fuel and power).
Fire Safety
Pitched roofs must be detailed to limit the spread of fire, both within the building and from one building to another. For housing, the main concerns under Approved Document B are the roof covering’s resistance to fire spreading across its surface and from an external source. This is expressed as a reaction-to-fire classification such as BROOF(t4) and the minimum separation distance to the site boundary, which together govern what coverings can be used and how close to a boundary they can sit. Internally, cavity barriers and fire-stopping at party-wall and compartment junctions prevent fire and smoke spreading through the roof void.
Thermal Performance
With an increasing focus on energy efficiency, pitched roofs should be designed to minimise heat loss and comply with insulation requirements specified in the Building Regulations. Adequate insulation, airtightness, and ventilation strategies are integral to achieving thermal comfort and reducing energy consumption.
The Future Homes Standard
Looking ahead, the Future Homes Standard represents the most significant change to how new homes are built in England for over a decade. The final Approved Documents were published in March 2026 and will come into force on 24 March 2027, following a twelve-month transitional period. For roofs, the most notable change is a new requirement for on-site renewable electricity generation on all new dwellings. In practice, this means rooftop solar PV with an area roughly equivalent to 40% of the dwelling’s ground-floor area, alongside the move to low-carbon heating and the end of gas boilers in new homes. Designers should expect roof build-ups to work harder thermally and to accommodate integrated or mounted solar arrays from the outset.
Understanding Architectural Details – Residential (4th Edition)
If this post has been useful, the book takes everything here much further.
Understanding Architectural Details – Residential covers pitched roof construction alongside every other key area of residential building including walls, floors, foundations, windows, flat roofs, and more. It contains over 120 construction details in 2D and 120 in 3D, all updated to reflect the current Building Regulations.
It’s designed to be the kind of resource you come back to on real projects, not just read once and set aside. Students use it to build their understanding of construction junctions before crits and tutorials. Junior architects and architectural assistants use it as a practical day-to-day reference in practice.
You can download a free sample to see how it’s put together before you decide.
More Pitched Roof Detail Examples
If you are looking for pitched roof details to use directly in your projects, our sister site Detail Library has an extensive database of pitched roof details and much more. All ready to download in CAD, Revit, and SketchUp.
The Detail Library houses hundreds of details and is built specifically for architects, technologists, and designers who want a reliable starting point for technical design so that you don’t have to build every detail from scratch. Our details are fully resolved, not just component libraries, and are also updated regularly as standards and regulations change.
Typical party wall / masonry cavity wall to lean-to abutment detail – traditional slate roof, insulation at ceiling level (DL304)
Typical mono-pitch ridge to cavity wall detail – traditional slate roof, insulation at ceiling level (DL310)
Back gutter party wall / cavity wall to pitched roof detail – traditional slate roof, insulation at ceiling level (DL312)
If you are interested in joining our community, head over to the Detail Library to learn more about our platform and get yourself signed up.
What to do next
This post covers the main principles of pitched roof construction — the structural types, the key junctions, how insulation works within the build-up, and what the Building Regulations require. It’s a solid foundation.
If you want to build on it, Understanding Architectural Details – Residential is the natural next step. It’s been used by architecture students and early-career architects across the UK to develop their understanding of residential construction in a way that’s practical and easy to work from.
Author
Written by Emma Walshaw, Architectural Technologist and founder of First In Architecture and Detail Library. Emma has written a number of books about construction and architectural detailing.
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Outstanding details and description at all levels. Would just like to clarify if updates to regulations come as a free publication to download.
Hi Graham, thank you for your interest. We aim to update the books as regularly as possible. While these are not free updates, we always offer discounts to existing customers who have already purchased the book in the past. If you have any other questions please don’t hesitate to ask. Best regards, Emma
Details for flat roofs, with associated details for roof lights, lanterns etc would be a good one.
I am looking for details for Reinforced Concrete Pitched Roof and to my amazement, I found little to none on the web. How come when this is wide spread in Mauritius where we have mono pitched, gable, hip and various other types of pitched roof made with in-situ concrete. I have found a site based in UK that contains some details of pitched roof but nothing in published codes, standards, handbooks. Even looking with AI return wrong references again and again. I will greatly appreciate your input on that.