A Guide to Pitched Roof Details

The following post includes excerpts from our book Understanding Architectural Details – Residential, 4th Edition.

01 UAD Resi Banner

Understanding Pitched Roofs

The roof is a key element of the building structure, providing protection from the elements and has a vital role 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

Pitched Roof Elements

The majority of residential houses in the UK are constructed with pitched roofs. These pitched roofs are often constructed as a symmetrical roof 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.

02 Pitched Roof elements

Single Pitched Roofs 

 

Mono Pitch Roof – the simplest form of pitched roof, sometimes referred to as the lean-to. The foot of the rafters generally sit on a timber wall plate that is fixed to the top of the supporting wall. The top of the rafters are supported on a timber plate that is fixed to the supporting wall. The mono pitched roof has a limited span, therefore the double pitched roof is a more popular option.

Double Pitched Roofs 

 

Couple Roof – 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. 

The maximum span of this type of roof is 3.5m, wider spans than this can cause the foot of the rafters to push the supporting walls outwards. The addition of a ring beam and other strengthening features such as ties can help increase this span. 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, usually 32mm 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 tends to be 100x75mm, 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.

03 Couple roof

Close Couple Roof – construction 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 5.5m. 

04 Close couple roof

Collar Roof – similar to the close couple roof, rafters are framed by collars one third up the height 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. 

Guidance of rafter spacing, spans and sizes can be found in the Building Regulations Approved Document Part A and also the TRADA document “Eurocode span tables for solid timber members in floors, ceilings and roofs for dwellings”.

05 Traditional purlin roof

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.

06 Trussed rafter roof

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. 

A closed eaves provides soffit boards with ventilation gaps or channels to allow air into the roof space, to be expelled at ridge level.

08 hidden gutter detail

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 specify a minimum U-value for the insulation of roofs of new dwellings to be 0.11W/m²K target [Part L – Conservation of Fuel and Power: Dwellings 2021 edition incorporating 2023 amendments].

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.

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 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, ie, 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 it’s own detailing requirements and specifications that will need to be considered. 

 

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. 

 

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.

Pitched Roof Detail Examples

The following images provide examples of pitched roof details from the book Understanding Architectural Details – Residential [4th Edition].

09 MR1 Pitched Roof Detail Insulation at ceiling level

Roof Eaves Detail – Masonry cavity wall, insulation between and over ceiling joists (MR1)

10 MR1 Pitched Roof Detail Insulation at ceiling level 3D

Roof Eaves Detail – Masonry cavity wall, insulation between and over ceiling joists (MR1)

11 MR3 Pitched Roof Detail Insulation at rafter level

Roof eaves detail – Masonry cavity wall, insulation between and under rafters (MR3)

12 MR3 Pitched Roof Detail Insulation at rafter level 3d

Roof eaves detail – Masonry cavity wall, insulation between and under rafters (MR3)

13 MR4 Pitched Roof Gable Detail Insulation at rafter level

Roof gable detail – Masonry cavity wall, insulation between and under rafters (MR4)

14 MR4 Pitched Roof Gable Detail Insulation at rafter level 3d

Roof gable detail – Masonry cavity wall, insulation between and under rafters (MR4)

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.

 

Fire Safety

Pitched roofs must incorporate fire-resistant materials and detailing to minimise the risk of fire spread between buildings. Intumescent coatings, fire-retardant treatments, and proper ventilation are essential considerations in fire safety planning.

 

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.

Get the book today!

Understanding Architectural Details – Residential, is dedicated to residential construction. The book is packed full of over 120 construction details in 2D, and 120 construction details in 3D.   We look at the principles behind construction detailing, and delve deep into each area of the building to make sure you have a full understanding of construction design.

More Pitched Roof Detail Examples

If you are looking for reference details to use as a starting point in your own projects, our sister website Detail Library has a huge database of details ready for you to download and use. 

Below we share a few pitched roof detail examples from the Detail Library.

15 Typical party wall masonry cavity wall to lean-to abutment detail - traditional slate roof - insulation at ceiling level DL304
16 DL304 - Party wall lean to abutment detail traditional slate roof 3D copy

Typical party wall / masonry cavity wall to lean-to abutment detail – traditional slate roof, insulation at ceiling level (DL304)

17 Typical mono-pitch ridge to cavity wall detail - traditional slate roof - insulation at ceiling level DL310
18 DL310 - Mono pitch slate roof ridge to cavity wall detail 3D copy

Typical mono-pitch ridge to cavity wall detail – traditional slate roof, insulation at ceiling level (DL310)

19 Back gutter party wall cavity wall to pitched roof detail - traditional slate roof - insulation at ceiling level DL312
19 DL312 - Back gutter party wall to pitched slate roof detail 3D copy

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.

The Detail Library provides hundreds of construction details for you to download and use adjust for your own projects. The details are available in 2D Revit, CAD dwg, and 3D SketchUp. You can start downloading straight away and build your own detail reference library. Not like other BIM libraries, the Detail Library contains fully resolved details rather than individual components.

Summary

To sum up, mastering pitched roof detailing is both an art and a science that requires a deep understanding of architectural principles, construction techniques, and regulatory requirements. We have just scraped the surface in this article, but as indicated above can direct you to further resources to assist with your learning both at beginner level Understanding Architectural Details Residential and beyond Detail Library.

By paying careful attention to the key components of pitched roof design and detailing, you can create buildings that not only stand the test of time but also contribute to the rich tapestry of UK architecture. 

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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3 Comments

  1. Outstanding details and description at all levels. Would just like to clarify if updates to regulations come as a free publication to download.

    Reply
    • 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

      Reply
  2. Details for flat roofs, with associated details for roof lights, lanterns etc would be a good one.

    Reply

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