What makes a great roof?

Before embarking on any self-build or renovation project it’s important to understand the difference between offsite manufacturing (OSM) and traditional build roofing. Here Chris Powell from Pasquil explains the differences, and highlights the benefits of OSM

What makes a great roof is a question posed time and again by self-builders. The answer? It’s all in the truss. This wooden structure supports the structure above a home and is a popular choice due to its cost-effectiveness and design flexibility. Roof trusses, or trussed rafters as they are otherwise known, have by and large replaced traditional cut-and-fit roofs, and can save you time, effort, and money when it comes to specifying a roof for your dream home. 

Construction methods 

Offsite manufactured roof trusses are the most widely used form of roof framing in the UK, as they provide a cost-effective and flexible solution. Trusses are not only the new norm for simple roof structures but are also increasingly seen as the ideal method for turning a complex architectural vision into a working roof.

With a truss roof the structural element is constructed offsite to specific calculations. They arrive ready-made and are quickly erected, with diagonal and longitudinal bracing to avoid wind deflections. There are also plenty of different truss roof styles on the market including designs for flat roofs or vaulted ceilings.

Engineered timber roof trusses hugely reduce the amount of time spent installing the structural elements of a roof compared to traditional build methods. OSM also allows just-in-time delivery and therefore negates the need for large storage space onsite.

The more traditional cut-roof method, where the timbers of the roof are made up onsite using complex engineering and traditional joinery skills, is much more expensive, labour intensive and time consuming.

Offsite manufacturing versus traditional build 

OSM techniques have certainly gained momentum over the last few years; not only are these methods more sustainable due to waste reduction, but they have been found to minimise inefficiencies and eradicate delays on site.

Providing standardised components, offsite delivers a variety of other benefits. A repeatable manufacturing process that delivers the same component, at the same output rate to an agreed quality standard has clear advantages in terms of predictability and efficiency. Reducing the margin for error can result in a faster turnaround onsite, with less need for rework.

Speed of construction is another key area with OSM solutions drastically reducing the amount of time it takes to build a property when compared to traditional techniques. Unaffected by weather or other trades, offsite manufactured roofs are quick to construct and can be also tailored to suit any budget.

However, if you’re keen to create something more bespoke – and you’re willing to spend the extra money – then a traditional build may be more suitable. Bear in mind, though, that this option can be incredibly labour intensive, and costs must be factored in for extended scaffolding hire and waste removal.

OSM methods can also give you peace of mind that your build is manufactured to the highest standards. With traditional build, builders or joiners may not have a Quality Assurance Scheme in place to produce timber frame on site. Therefore, no independent checks will be made when it comes to build quality or adherence to design drawings.

Finally, sustainability is an area where environmentally aware self-builders are increasingly looking to make improvements. Because manufacturing in a factory can be scheduled to start as the site is being prepared, processes can run in parallel, helping to reduce waste onsite and movement of vehicles. This can also create less disruption to your new neighbours, or businesses that may be close to your construction site.

Maximising space 

When it comes to planning your self-build, maximising space is another key consideration. Have you ever thought about using your roof to create an extra bedroom, home office, or den?

Attic, or room-in-roof trusses, which include a lower chord to provide a floor platform, are becoming more popular. Depending on span and room size, attic trusses can span onto external load-bearing walls without additional support, giving you more flexibility in the roof and lower floor layouts.

The bottom chord of the truss, which becomes the floor joist of the room, can be designed and manufactured in several ways. Metal web joists, for example, offer a strong but lightweight option with the added benefit of allowing services, including mechanical ventilation and heat recovery systems, to be easily installed.

Room-in-roof trusses are becoming increasingly popular as they are an economical solution to adding rooms to your new home. They also expand living space without the need to change the footprint of your entire property and can increase its value by £15,000 to £20,000.

Other benefits include the elimination of complex labour-intensive site work, reduced build cost per square metre due to full utilisation of space, and complete roof structure provided ready for floor boarding, roof finishes and plasterboard.

The roof will be one of the most visible and important features of your new home. It therefore needs careful consideration at the planning stage.

Chris Powell is sales director at Pasquil and Saint-Gobain offsite solutions design director