The Materials

A guide to roof shape

01 Materials Customising your self-build

02 Product guides Choosing your materials

Which type of roof should you choose for your Self-Build?

Pitched, flat, trussed, curved, green – there are a number of roofs to choose from but where do you start?

Choosing the right roof can create the overall look of your home and the options are only limited by your imagination and budget. Anything can be achieved from a gable to gable roof covered in concrete interlocking roof tiles; to a lead covered dome or even a quirky hyperbolic paraboloid shape with plenty of curves and swoops.

In reality, the choice between shape and covering are interlinked. The shape will be determined by the aesthetics or look you are trying to achieve while there are limitations on the roof angle or pitch that some finishes can be laid. In extreme cases, some local planning authorities will want a say regarding both shape and finish.

Many architects will refer back to the golden ratio when considering the roof pitch on a property. This can be seen on the Egyptian pyramids, classical and modern architecture, as well as nature. All are considered pleasing to the eye. Conversely, architects will avoid a pitch of 45° especially on a gable end. It may also be appropriate to build on the local character or to reinforce the local identity through alignment with existing local vernacular within and surrounding the site.

Types of roof

Roofs fall into two main roof shapes; flat or pitched. Flat roofs offer the opportunity to create additional outdoor space in the form of a balcony or veranda or to create a green roof with the obvious environmental benefits. Pitched roofs create a more traditional feel to a building. The void between the rafters and ceiling joists provide valuable storage space and, if properly designed, can allow for future conversion to form additional accommodation. The pitched roof category can be further broken down into mono-pitch, duo-pitch, asymmetric, multi-pitched or even curved.

The gabled roof is the simplest form of roof structure and the easiest to cover. It provides a larger internal volume for storage in the loft. However, the peak of the gable can be a considerable distance off the ground and, unless designed to be maintenance-free, can be an issue.

The hipped roof is more complex to construct and finish with more cutting of the roof finishes at the intersections. However, the walls are all finished at a constant height and avoid the need to return to complete the gable wall once the roof is constructed. There is also a lower working height for maintenance.

Which roof would you use for a loft conversion?

Attic or room in the roof trusses are becoming increasingly popular as they offer increased living space without changing the footprint of the house.

These cleverly designed trusses include a lower member which provides a floor platform. The benefit of this is to provide more flexibility in roof and lower floor layouts as, depending on span and room size, the attic trusses can span onto external load-bearing walls.

Standard roof trusses are structurally very efficient with all members working in unison. Internal members should therefore never be removed to carry out a loft conversion without proper engineering to strengthen the remaining members. This can be very costly and time consuming and it will often be better to completely remove the existing roof and replace with attic trusses.

It is, of course, preferable to consider possible vertical extension of the living space at the initial design phase and consider using attic trusses to enable future conversion.

Pre-insulated roof cassettes can offer an alternative to attic trusses when habitable space is required. The use of metal web joists or I-joists enable longer spans to be accommodated in flat roof or low pitch situations. Again, these can be factory formed into cassettes to ease and speed up the installation process.

What is the best roof shape for extreme weather?

As long as the roof is properly designed, winds in the UK should not be an issue. Large areas of roof with lightweight roof coverings will require strapping down to avoid uplift. With large flat roofs, particularly with any parapets or other upstands, the possibility of drifting snow should be considered.

When does a roof need to be replaced?

Regular maintenance can help you save money in the long run. Without upkeep you could face growing roof costs in the future. A well-designed and maintained timber roof will not require replacing during the design life of the property. Replacement will only be required if the use changes such as the requirement to add a new storey or the desire to convert a flat roof to a pitched roof.

Roof covering

Tiles are a common covering for roofs but it’s best to speak to an architect or engineer to discuss the best solution for your roof structure.

Clay tiles have a long life span and are perfect for intricate details and come in all kinds of shapes and colours. Shingles are a sustainable as well as long-lasting roofing material, with western red cedar a typical wood. They can be left untreated to weather to a beautiful silver, or, alternatively, they can be treated for longer life.

Stone is an expensive roof covering and are often used on high specification builds in areas where it is architecturally fitting. Concrete is a popular choice of roofing material with a solid range of colours and finishes available. They are perfect for unusual designs/curves as they are adaptable.

Did you know?

Pasquill is the UK’s largest roof truss supplier. They manufacture roof trusses, I-beams, Posi-joists and spandrel panels. Pasquill works closely with customers and industry specialists such as the Centre for Timber Engineering at Napier University to help solve today’s construction problems using their expertise in design and off-site manufacture.

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