Modular building design

New timber towers in Trondheim illustrate the growing international demand for modular building design and construction.

Population shifts to city living mean housing demand in urban areas is greater than ever and, with limited availability and a consequent rise in the cost of land to build on, the only way is up when it comes to the creation of new residential accommodation. National and local building codes

apply different height restrictions, particularly to timber-based buildings, but tall timber residential projects of between 6-10 storeys are now increasingly common in many countries. Building higher brings its own complications however: for example, restricted access to sites for deliveries of construction materials, the need to reduce construction noise in densely occupied locations, the desire for fast erection whilst maintaining the high-quality standards (especially of good airtightness and thermal efficiency) now required by regulations and market demand.

These, together with public and political awareness of the urgent to meet zero carbon emission targets has required considerable rethinking of the ways in which we build and, in this context, offsite manufacture (OSM) and modern methods of construction (MMC), once seen as desirable approaches, are now recognised as essential, with ever-increasing emphasis on modular design and construction. Being able to precisely manufacture complete sections of buildings in safe and healthy working environments before transporting fully finished modules to site where they can be assembled at speed all makes for fast, accurate, efficient and cost-effective construction – all points that contribute to greater de-risking of projects for property developers and financiers.

Described like this, modular design and construction may sound deceptively simple, but ensuring everything fits together successfully on site requires specialist design and manufacturing experience coupled with considerable pre-planning by all involved. A good example of this is emerging in a project currently under construction at Trondheim in Norway and on which Ergodomus has worked closely with Unihouse SA, the highly experienced Polish manufacturer of modular units. For the Norwegian developer, HeimdalsPorten, the cluster of four apartment blocks are the tallest buildings it has commissioned to date. The project will be constructed in two phases (two seven-storey towers and two eight-storey towers), the modules for the first of which have just been assembled on site.

The story of this project gives some idea of the complex multi-national logistics that can be involved in modern modular building design and construction. In this case, the entire module manufacturing process is carried out in Unihouse’s production hall from where the completed 4.2m-wide units for the first tower were transported by road to the port of Danzig. Once there, the units (which are designed to stack in three levels under roof cover with a further level of units positioned above the roof) were craned onto a special ship – not a container vessel – to enable unloading of the 110-120 modules in the correct order for subsequent assembly on site. Once fully laden, the ship sailed to Trondheim where the modules were lifted off. Normally they would then be transported direct to site but – due to the Covid-19 crisis – they needed to be stored in the port for several days. The final stage of the journey had to take place during night-time hours as vehicles carrying this width of unit are not permitted to travel during the day in Norway.

The reinforced concrete platform and central vertical core of the first seven-storey tower had already been prepared so, once the modules were finally delivered, assembly progressed rapidly. Each of the modules is connected to the vertical core using a special steel connection developed by Ergodomus with Unihouse, with each connection designed to account of the progressively heavy downward load. This first tower was scheduled to take 2-3 weeks to construct, but the precision manufacture of the modules and the effectiveness of Ergodomus’ design of the special connections has resulted in a total assembly time of only 10 days: remarkable speed to create an entire seven-storey building!

Work to construct the second tower begins this month, with towers three and four due for erection in late Autumn 2020. In our next newsletter we’ll be explaining more about Ergodomus’ commitment to Design for Manufacture and Assembly (DfMA) and our approach to the product design, costing and manufacture of timber engineering components such as the special connection designed for this project in Trondheim.

In collaboration with Unihouse