1 The Evolution of Multi-storey Timber Construction

Indoor Air Quality – The Influence of Timber Construction

Maren Kohaus, Holger König

A 5.1 Wood interiors, kindergarten, Bludenz (AT) 2013, Bernardo Bader, Monika Heiss – Farbe & Design A 5.2 Recommended TVOC levels and resulting recommendation for action A 5.3 Thermal effusivity coefficients of select building materials A 5.4 Classification of chemical compounds by boiling point

A 5.1

Wood has been in use as a construction material for human dwellings for centuries. Contemporary building continues to use wood and wood-based materials in a wide range of ways – as a construction material, for flooring, wall and ceiling cladding and for fittings and furnishings. The material is highly valued now as ever for its natural character and authenticity. Wood surfaces in particular, due to the specific character, colour, grain, texture and structure of the material, are generally regarded as appealing to the senses, as Maximilian Moser’s study “Interaktion Mensch und Holz” confirms [1]. Characteristics of wood specific to the material and related to building physics, such as low thermal conductivity (Å-value = 0.11– 0.17 W/mK) and low thermal effusivity coefficient or b-value (Fig. A 5.3) mean that wood surfaces are perceived as warm. Untreated wood surfaces also support the control of indoor climates, because wood enables the ab sorption of indoor air moisture and its timedelayed release. The scent of wood, which is made up of emissions of volatile substances, has a pleasantly calming effect on some people. A 2003 study by the Joanneum Research Forschungsgesellschaft on the potential effects of stone pine wood in the immediate environment on people’s circulation and sleep found that it improved their performance and general well-being [2]. Maximilian Moser’s 2007 study “Schule ohne Stress” (School without Stress) analysed the effect of solid wood fittings and furnishing in classrooms. The study states that the calming effect of wood, estimated by measuring the students’ heart rates and vagal tone, might yield positive health effects [3]. The 2017 metastudy HOMERA presents an analysis of 44 research projects regarding the interrelation between emissions and wood and /or engineered wood on the one hand and indoor air quality on the other, as well as the possible effects on humans. Analyses of current testing and measuring methods that serve as basis for legal boundary values show how complex this topic is and also indicate the need for further research projects in order to synthesise results [4]. Until further findings become available, discussions on the extent to which emissions from wood and wood-based materials in contemporary timber buildings can be regarded as either harmful to health or as inherent to wood and, therefore, natural, harmless or even promoting health, are ongoing. To offer clients, users and planners a degree of security and bring clarity to the discussion, relevant aspects will be examined in detail below.

A Healthy Indoor Climate

Regardless of construction type, a building must provide an indoor climate that users perceive as pleasant and must accommodate the activities it was planned for. Comfort criteria (as specified in DIN EN 15 251) offer guidance on the factors that need to be taken into account: • protection from weather-related low /high temperatures and moisture /dampness • protection from high levels of use-related moisture, resulting condensation and mould risk • protection from interior and exterior noise exposure • optimum lighting and adequate daylight intake, as well as protection from excessive sunlight (heat /overheating risk) • sufficient ventilation for the particular use and resulting reduction of CO2 levels in the air • protection from ionising (e.g. radon) and non-ionising radiation (e.g. electric smog) • poor indoor air quality due to building materials, equipment and devices

Adequate air exchange provided by manual or mechanical ventilation ensures that emissions produced by building products, electronic devices and by occupants are removed. However, the use of toxin-free building materials wherever possible is advised.

Emissions in Indoor Air

Materials used in building interiors can impact indoor air by discharging particles in the form of particulate matter and fibre or by emitting gases. User behaviour and indoor climate conditions (indoor humidity, temperature, etc.), as well as the situation and integration of construction materials into building components and their contribution to diffusion processes are relevant for levels of indoor air pollutants [5]. When discussing emissions in indoor air and wood-based materials, two terms are highly relevant: VOCs (volatile organic compounds) and formaldehyde.

VOCs

In both construction practice and the ana lysis of interiors, VOC gases are classified according to their boiling point (Fig. A 5.4): • VVOC: very volatile organic compounds • VOC: volatile organic compounds • SVOC: semi-volatile organic compounds

During construction, many different VOCs are temporarily discharged into indoor air. These higher-than-usual concentrations can usually be greatly reduced by heavy ventilation during and after work. VOCs are considered a single group of substances, albeit a very diverse one. They can be harmless, become a nuisance due to their smell or even be harmful to health. The most familiar VOCs are alkane /alkene, aromatic compounds, terpenes, halogenated hydrocarbons, esters, aldehydes and ketones. Wood exudes small amounts of terpenes and aldehydes that are perceived as typical wood scent. They are termed nVOC (natural Volatile Organic Compounds) due to their origin in natural raw materials. The toxicity of different types of VOCs varies significantly. Carcinogenic benzene is a particularly harmful indoor air pollutant, while numerous VOCs, such as terpene originating in natural oils, natural colours or natural wood resin are considered com- paratively harmless. In high concentrations (e.g. perceivable smell of turpentine oil), they may impair people’s well-being and be allergenic, but are not harmful to health in the concentrations usually present in timber buildings.

VOC emissions from building products

There are no Europe-wide statutory limits or prohibitions imposed on VOC emissions from building products. Since 2004 the AgBB evaluation scheme of the DIBt approval process, introduced by the Committee for Health-related Evaluation of Building Products (Ausschuss zur gesundheitlichen Bewertung von Bauprodukten), has served as the basis for the healthrelated evaluation of building product emissions. Updated in 2018 and adopted by the Model Administrative Provisions – Technical Building Rules (Musterverwaltungsvorschrift Technische Baubestimmungen, MVV TB) in 2019, it sets maximum emission values for building products and determines exclusion criteria according to which building products are not permitted for use. However, emissions tests of individual products should not serve to conclude what the expected indoor air concentration might be [6]. This is due to the fact that it is dependent on the influence of other factors. These factors include e.g. the situa-

Material Thermal effusivity coefficient

b value [KJ/Km2√s] insulation (mineral fibre) 0.06 cork 0.10 wood 0.4 ... 0.5 human skin 1.0 ...1.3 glass 1.3 ...1.5 water 1.6

concrete 1.8 ... 2.2 steel 14

copper 36 Materials with high thermal effusivity coefficients such as metals are perceived as cold when their temperature is lower than that of human skin. In contrast, materials with low thermal effusivity coefficients such as wood or insulation are perceived as warmer at the same temperature.

A 5.3 Recommended TVOC levels (indoor air) Hygiene assessment and recommendations for action

Level 1: TVOC< 0.3 mg/m3 (< 300 μg/m3) • hygienically acceptable as long as levels for individual substances are not exceeded • “target level” (= hygienic prevention range; recommended)

Level 2: TVOC> 0.3 mg/m3 (> 300 μg/m3 and and < 1.0 mg/m3 < 1,000 μg/m3) • hygienically acceptable as long as levels for individual substances are not exceeded • increased ventilation necessary

Level 3: TVOC> 1.0 mg/m3 (> 1,000 μg/m3 and and < 3.0 mg/m3 < 3,000 μg/m3) • hygienically questionable, occupation only for limited time periods • health impact of substances exceeding recommended levels must be tested; individual toxicological evaluation recommended

Level 4: TVOC> 3.0 mg/m3 (> 3,000 μg/m3 and and < 10.0 mg/m3 < 10,000 μg/m3) • hygienically unsound, occupation only for limited time periods • individual toxicological evaluation recommended

Level 5: TVOC> 10 mg/m3 (> 10,000 μg/m3 and and < 25.0 mg/m3 < 25,000 μg/m3)

• hygienically unacceptable, occupation to be avoided • individual toxicological evaluation recommended A TVOC concentration of more than 3,000 μg/m3 is regarded as hygienically unsound. BNB/DGNB certification only to be issued if TVOC levels are in the range of 300 μg/m3 (non-defined measurements) to 500 μg/m3 (defined measurements).

A 5.2

Abbreviation Name Boiling point [°C] Examples

VVOC very volatile organic compounds 0 to 50 (-100) formaldehyde, acetone, acetaldehyde VOC volatile organic compounds 50 (-100) to 240 (-260) many solvents, such as styrene and xylene SVOC semi volatile organic compounds 240 (-260) to 380 (-400) plasticisers, biocides, flame retardants, PCBs POM particulate organic matter > 380 PAH in bituminous building materials

MVOC microbial volatile organic compounds (produced by mould and bacteria)

within VOC range wide range of different substances and substance classes A gas /substance with a high boiling point is less volatile and is discharged into the surrounding atmosphere at slower rates. A gas /substance with a low boiling point is highly volatile and is therefore discharged at faster rates. Values analogous to WHO classification.

Part B Structural Systems

1 Structures and Structural Systems 42 From Linear to Planar Member 43 Combining Construction Elements 45 Combining Materials 45 Structural Engineering in Timber Construction 48 Timber Construction in Comparison 49 Conclusion 54

2 Construction Components and Elements 56 Dowel Laminated Timber Walls 57 Frame Wall Construction 58 Cross-laminated Timber Walls 60 Laminated Veneer Lumber Walls 61 Beams 62 Dowel Laminated Timber Ceilings 63 Beam Ceilings 64 Box Ceilings 66 Cross-laminated Timber Ceilings 68 Laminated Veneer Lumber Ceilings 69 Timber-Concrete Composite Ceilings 70 A Comparison of Timber Construction Elements 72

IPE 270 Beech laminated veneer lumber

Beech glued laminated timber Spruce laminated veneer lumber

Spruce glued laminated timber

h = 270 mm w = 135 mm m = 36.1 kg/m h = 270 mm w = 160 mm m = 29.4 kg/m h = 440 mm w = 160 mm m = 48.8 kg/m h = 360 mm w = 160 mm m = 29.4 kg/m h = 460 mm w = 160 mm m = 31.3 kg/m

Assumptions: Steel S 235: m = 1.00 fy/x = 235 N/mm2 Beech and spruce laminated veneer lumber: use class 1 k mod = 0.9 m = 1.20 (EN 1995-1-1) Beech and spruce glued laminated timber: use class 1 k mod = 0.9 m = 1.25 (EN 1995-1-1)

B 1.19

fer vertical loads, new dimensions in timber construction become possible. Additional processing (hardwood-based glued laminated timber or laminated veneer lumber) can contribute to further advancements (Fig. B 1.19). For this purpose, it is also necessary to develop corresponding highperformance connections. The increasing availability of hardwood leads to new opportunities in the production of beams predominantly subject to bending forces. The elasticity modulus of such flexural construction components – and, as a result, their rigidity – does not increase to the same extent as their strength. Beech laminated veneer lumber has assumed an important role as an economically feas ible construction material for trusses, which are predominantly subject to normal forces. The connection and fastening technology facility in Waldenburg is an impressive example, featuring trusses made of beech laminated veneer lumber as primary and secondary beams spanning 18.30 m to 42 m (Fig. B 1.21). Compared to steel or reinforced concrete, this permitted the creation of a structure of significantly lower weight and resulted in lower expenditure for required foundation work and assembly of the large-size beams. Fire protection requirements were also realised at substantially lower costs. The nodes between members comprise butt joints and carpentry-style woodworking joints that make use of the high lateral stress resistance and shear strength of the material. Employed comprehensively for entire structures, beech laminated veneer lumber often also finds use when specific beams or columns of a load-bearing structure are supposed to bear stronger loads without having to deviate from the dimensions of the other members of the structure. Beech laminated veneer lumber is also an interesting option for multi-storey timber frame construction if columns and beams are required to bear heavy point loads (Fig. B 1.20). The expectancy is that further timber construction materials made of hardwood or hybrid construction materials comprising softwood and hardwood will become marketable in the future. This includes, for instance, wood-reinforced timber consisting of softwood and hardwood veneer [7], hardwood cross-laminated timber or hybrid hardwood and softwood cross-laminated timber [8].

Conclusion

Timber construction has undergone an astounding evolution in the last decades, accessing more and more fields of application. Building with wood has become a high-quality alternative to conventional construction methods. The combination of different timber construction types, yet also combinations of materials, by including other construction materials such as concrete or steel, allows for precise and custom solutions for very different building-related tasks. Timber buildings are becoming increasingly competitive in the context of everyday activities. Prefabrication as a specific construction process is also receiving increased appreciation. It impacts topics relevant to the future of building, such as the improvement of construction quality and speed or opportunities of digitalised and automated production processes. In addition, timber construction and its unique advantages in ecological terms offers answers to urgent societal challenges, such as energy and resource efficiency, suitability for purposes of a circular economy or climate neutrality. When architectural design and structural engineering take into account the specific characteristics of timber as a construction material while making use of hybrid construction types as required, there are hardly any limits to building with wood.

Notes:

[1] Deplazes, Andrea: Holz indifferent, synthetisch. In:

DETAIL 1/2000, p. 23 [2] CEN / TS 19 103 Design of Timber Structures –

Structural design of timber-concrete composite structures – Common rules and rules for buildings www.bgu.tum.de [3] Basic rules of stiffening: at least one ceiling plane is connected to three wall planes with their axes not intersecting in one point, or four wall planes with their axes intersecting in at least two points. [4] Horizontal slabs or horizontal or vertical plates are planar elements that can bear out-of-plane loads or in-plane loads; combined loading often occurs in wall, ceiling and roof elements [5] Newcombe, M.; Pampanin, S.; Buchanan, A. H.:

Governing criteria for the lateral force design of posttensioned timber buildings. WCTE 2012 Proceedings, Final Papers, Auckland 2012, p. 148ff. [6] Wanninger, Flavio; Franghi, Andrea: Experimental and analytical analysis of a post-tensioned timber frame under horizontal loads. Engineering Structures,

Vol. 113, Kidlington 2016, p. 16 – 25 [7] Lechner, Markus; Winter, Stefan: Hybride Holzbauteile aus Laubholz-Furnieren und Brettschichtholz aus Nadelholz – Holzbewehrtes Holz. Research project Technical University of Munich. Bundesinstitut für Bau-, Stadt- und Raumforschung (BBSR),

Bonn, Research initiative “Zukunft Bau”; SWD10.08.18.7-18.21. Termin ation date 06/2021 [8] Kaufmann, Hermann et al.: Research project. Development of a material and energy-efficient timber construction system with hard- and softwood (LaNaSYS).

Fachagentur Nachwachsende Rohstoffe (FNR),

Gülzow. Termination date 06/2023. www.ar.tum.de and www.bgu.tum.de

B 1.19 Comparison of different glued laminated timber and laminated veneer lumber (beech and spruce) column cross sections with a steel IPE 270 Å-beam B 1.20 Nine-storey administration building, Risch- Rotkreuz (CH) 2018, Burkard Meyer Architekten a, b timber-concrete composite beam ceiling with beech laminated veneer lumber primary frame construction (columns /downstand beams) c The facade visually displays the frame construction and the rhythm of structural members. B 1.21 Connection and fastening technology production hall, Waldenburg (DE) 2020, Hermann Kaufmann + Partner a primary truss girder, supported by column, high-performance beech laminated veneer lumber woodworking joint b secondary truss girder, supported by a primary beam, woodworking joint c production hall with a roof structure comprised of primary and secondary beech laminated veneer lumber truss girders

b