Have you walked past a site one day, noticing the superstructure is about to be constructed, only to come back in a couple days’ time and see a nearly completed house? Then you have experienced at first hand one of the main advantages of offsite timber construction – speed on site.

This is a consequence of the ‘offsite’ definition – a process in which part of the building is transferred from the site, exposed to all weather, to a controlled factory environment. In this way, a controlled manufacturing line approach can be applied to reduce waste in the component production. In fact, several advantages to offsite systems stem from the factory production process:

Value

• Quality – in the factory there is greater opportunity to implement product quality control.
• Customer satisfaction – higher levels of quality to reduce snagging on site.
• Technical – higher levels of quality assurance require higher levels of tolerance improving technical attributes such as air tightness.

Efficiency

• Time – offsite provides the opportunity to reduce the build programme by completing the offsite manufacturing simultaneously with the groundworks.
• Waste – in the factory environment material flow can be optimized and controlled, and a waste management plan can be implemented.
• Flexibility – standardized components can be assembled in different configurations to provide the client with an efficient yet custom design, this mass-customization principal is borrowed from the automotive industry.

Sustainability

• Social – having a static place of work instead of several building sites reduces travel time for the workers. In the factory, working at heights is eliminated and equipment is used to remove the need for heavy lifting.
• Environment – through waste minimization and opportunities to deliver products with high levels of insulation and high airtightness.
• Economic – in offsite there is potential to improve cash flow through early completion of projects and corresponding early revenue collection.

Advantages and disadvantages:

However, several building systems fall within the timber offsite category, each of which has its own advantages and disadvantages. The offsite building systems are categorised as:

• 2-dimensional timber frame panels – these can be either floor cassettes, wall panels or roof cassettes, typically up to 10 metres in length. 2D Timber frame panels can be either open (only the structural skeleton and sheeting on one side), closed (including insulation and sheeting on both sides) or enhanced (including windows, doors, and services routing guides).
• 2-dimensional solid timber panels – these are engineered timber products such as Glue-Laminated timber (Glulam), Cross-Laminated Timber (CLT), Nail-Laminated timber (Nail-lam) and Dowell-Laminated Timber (Dowel-lam). Also referred to as ‘mass timber systems’, these panels are manufactured with high precision and can have pre-cut openings for windows, doors, and services. If you would like to know more about mass timber construction.
• 3-dimensional pods – in construction projects areas with a high concentration of services are sometimes manufactured offsite as three-dimensional pods. Pods are typically either bathroom or kitchen (or combined) units and are smaller in size than modules.
• 3-dimensional modules – the offsite system with the highest degree of prefabrication, where space (or volume) is completely enclosed, hence also referred to as ‘volumetric’. 3D modules include insulation, MEP services, internal finishes, windows, doors, built-in furniture and lightweight cladding. On-site, the volumetric modules can be stacked and joined to form larger spaces.

This blog post was written by Mila Duncheva and Dr Robert Hairstans, from the Centre of Offsite Construction and Innovation Structures at Edinburgh Napier University.