What is a mono-pitch roof?

A mono-pitch roof has one sloping roof plane, falling from a high point to the eaves. Unlike a dual-pitch or gable roof, it does not have two opposing slopes. Where the top edge meets a wall, this is often referred to as a lean-to.

Where are mono-pitch roofs commonly used?

The simple, asymmetric form works well where space, height or appearance makes a conventional dual-pitch roof less suitable. Common applications include:

• single-storey property extensions, including kitchen extensions
• garages, carports, sheds and other outbuildings
• garden rooms and home offices
• entrance canopies and covered walkways
• small commercial or industrial buildings, and contemporary architectural projects
  
  

What are the advantages of a mono-pitch roof?

A mono-pitch design can offer several benefits when it is appropriate for the building and properly specified:

• Straightforward geometry: One, straight, roof plane eradicates the need for hips, valleys and junctions compared with a more complex roof, making mono-pitched and lean-to roofs a very good low maintenance option over their lifetime.
• Controlled rainwater drainage: Water is directed to one eaves edge, provided the covering, detailing and rainwater goods are designed for the pitch and expected rainfall.
• Useful roof area: A single, uninterrupted plane can work well for rooflights or solar PV, subject to orientation, shading, pitch and system requirements.
• Distinctive appearance: The clean, asymmetric form can complement both contemporary buildings and carefully designed additions to traditional properties.
  
  

What are the considerations of a mono-pitch roof?

The construction of a mono-pitch roof can bring some potential constraints that should be considered early in the design state of the project:

• Roof space: Headroom and usable roof void reduce towards the low edge, so a mono-pitch roof may not be suitable where generous loft space is required.
• Structure: Long spans and high supporting walls can affect the structural solution. Loads and their transfer into the building should be assessed by a competent designer.
• Rainwater concentration: All run-off reaches one eaves edge, so gutters, outlets and downpipes need to be sized and positioned accordingly.
• Low-pitch limitations: A shallow slope narrows the choice of roof coverings and makes product-specific headlap, rafter-length and exposure limits particularly important.
• Wind and fixings: Site exposure, roof zones and edge details affect wind loads and fixing requirements. A project-specific fixing specification is essential; a mono-pitch roof should not simply be treated as inherently more or less wind resistant.
  
  

What pitch should a mono-pitch roof have?

There is no single standard angle: 'mono-pitch' describes the roof's form, not its pitch. The minimum suitable pitch is determined by the selected roof covering and its technical data. Finish, headlap, rafter length, exposure and location can all change whether a product is suitable. Never install a tile or slate below its stated minimum pitch.

Which Marley roof coverings are suitable for low-pitch mono-pitch roofs?

Marley's range includes several products for low-pitch applications.

• Mendip 12.5: This concrete interlocking tile can be used down to 12.5° with a 100 mm headlap and a rafter length of up to 6 m.
• Standard Mendip: The smooth-finish tile can be used down to 15° with a 100 mm headlap; the current product data allows a rafter length of up to 10 m at 15-17.5°.
• Other low-pitch options: Wessex minimum pitch is able to go down to 15°, Edgemere and smooth-finish Modern/Duo Modern down to 17.5°, and Lincoln Clay Pantile down to 15° at a 100 mm headlap.
  
  

How is the top edge of a mono-pitch roof finished?

If the top edge meets a wall, it needs a correctly designed abutment and flashing detail. If it is free-standing, a compatible mono-ridge detail may be appropriate. For example, Marley's concrete 457 mm segmental mono ridge is intended for pitches from 15° to 50° and is compatible with the Marley ventilated mono ridge system. The clay 305 mm mono ridge is suitable for pitches from 30° to 45°. These fittings are not interchangeable across every covering or pitch, so compatibility and ventilation requirements must be checked.

Can a mono-pitch roof include solar panels?

Yes, where the roof's orientation, shading, pitch and available area are suitable. Marley SolarTile® is a roof-integrated solar PV system that replaces sections of the conventional roof covering. It is suitable for roof pitches down to 20° and compatible with its range of roof coverings. The array and electrical system must still be designed for the specific project and installed by appropriately trained contractors.

What should be checked when specifying a mono-pitch roof?

A complete specification should consider the roof pitch and dimensions; structural spans and loads; the covering's finish, headlap and rafter-length limits; site exposure and fixings; underlay and battens; ventilation and condensation control; abutments and high-edge details; and the capacity of the rainwater system. Use current manufacturer information and obtain design input from competent roofing and structural professionals where required.

Where can I get help choosing a Marley solution?

Explore Marley's low-pitch roof products and current technical literature, or contact the Marley technical team for project-specific advice on product selection, detailing and fixings.

Disclaimer - The information shared in this blog is correct at the time of publication. Guidance, standards, and best practices may change over time, so if you’d like further clarification or the latest updates, please get in touch with the Marley Technical Advisory Team, who will be happy to help.