Pre-fabrication has increased its market share over the past ten years, and new products, particularly CLT, have become viable options in the construction of hall-like buildings. Wooden roof elements are also gaining ground, increasingly taking the place of roofs built on site. The original HalliPES 1.0 design guide from 2014 became obsolete due to technical advancements and changes in legislation.

Authors: Henri Salonen, A-Insinöörit Suunnittelu Oy and Sauli Ylinen, Puutuoteteollisuus ry

HalliPES 2.0 is intended to be a how-to manual for all types of buildings where the frame structures are partially or entirely composed of the wooden construction products and elements presented in the guide. Whether a structure is all-wood or a hybrid, the use of wood supports low-carbon goals and other environmental aims and is an incredibly competitive way of constructing buildings with vast open spaces. The new guide provides up to date information, aiming to make it easier for companies to design new wooden halls.

Finnish investors often favour hall-like buildings in their projects. In 2023, developers built 4.4 billion euros worth of new industrial and warehouse buildings alone, while the share of multi-storey buildings was only 3 billion euros. Hall-like buildings include various commercial and office buildings as well as specific public structures, such as sports facilities. The total value of new building construction in 2023 was approximately 16 million euros. The HalliPES design guide has been downloaded thousands of times each year from Puuinfo’s website, so there is clearly a need for an up-to-date version.

While researching the update, we came to realise that its audience needed process and business-oriented information in addition to mere planning guidance. All project stakeholders need improved awareness so that their project can leverage all the benefits of their chosen construction method.

HalliPES 2.0 has three significant updates:

1. Legislation and reference instructions were updated.
2. CLT structures are now included.
3. The most common hybrid structures, such as wooden roof elements on steel or concrete frames, are also included.

Fire safety legislation

HalliPES 2.0 includes the latest updates to fire safety regulations and points out the essential changes concerning glulam frames and hall-like buildings with wooden wall structures.

Unlike for similar steel structures, the fire safety regulations for wooden structures are still under discussion, particularly those for the roof ventilation spaces, the fire compartmentalisation of roof structures based on the location and spread of fires, and the official definitions vs. realities of load-bearing sections. Due to the complexity of the issues involved, interpretations of these regulations can vary by municipality. After careful consideration, the plethora of interpretations was excluded from the HalliPES 2.0 update.

With regards to progressive collapse, the new guide retains the earlier version’s guidelines on accidents in hall buildings with wooden roof elements. With further research and more detailed analysis, wooden roof elements could be leveraged even better than they are today in cases of progressive collapse.

In 2014, the fire safety of buildings was still governed by sections E1 and E2 of the Finnish building regulations. The Ministry of the Environment issued new regulations on January 1, 2018, and some sections on the fire safety of buildings changed further on January 1, 2021.

CLT structures now included in HalliPES 2.0

The design guide now includes structural models for both insulated and non-insulated non-load-bearing CLT walls, as well as joint detailing for CLT wall structures and eaves. CLT joints and connection principles still vary somewhat depending on the CLT supplier, structural designer, and installation method, so it is wise to double check compatibilities carefully before construction.

Hybrid structures included

In this context, “hybrid structures” are defined as buildings with a load-bearing frame that is composed of more than one load-bearing material. A wooden roof element with a steel or concrete beam is a typical example. In hybrid projects, structural engineers typically need to consider the interfaces and connection principles of different product components. For this reason, the updated design principles include typical joint details.

Modern designs often include glulam beams installed atop steel or concrete pillars, but the details for this joint type were excluded from the update as they are already quite well known.

Other changes and updates

Even though the procurement process for prefabricated building components or buildings seldom differs from the construction industry’s other procurement operations, the procurement process for prefabricated wooden elements is now described in paragraph “0 General”. We felt it was important for buyers to understand the specificities of wooden element production to be able to leverage all its benefits.

The simple installation of roof elements in place of on-site construction is an excellent example of the advantages of wooden pre-fabrication, particularly in chilly winter months. The update includes information on the manufacture, storage, and installation of wooden roof elements, and the guidelines and construction principles for roof top ventilation spaces, eaves, and water drainage now reflect current best practices, guidelines, and legislation. The most common building types for wooden roof elements have also been updated for today’s realities, with less common types now moved to section 13, Special situations.

For glulam frames, the recommended dimensions are now more specific, and the guidelines now include the popular two-nave central girder frame type that allows for more space between centre columns. Placing cranes on a glulam frame is still not recommended, even though it is technically possible.

Seldomly used sections of HalliPES 1.0 have been deleted, and the remaining sections have been recombined to improve coherency.

The update was financed by the Ministry of Education and Culture, with A-Insinöörit Suunnittelu Oy serving as the author and Puutuoteteollisuus Oy in charge of project management. The guide is published by Puuinfo Oy. Lapwall Oyj, Crosslam Oy, and Versowood Oy participated in the project’s steering group. The guide is freely available to everyone and will be published on Puuinfo’s website in June 2024.