Impact sound insulation of cross-laminated timber/massive wood floor constructions: Collection of laboratory measurements and result evaluation

Abstract

Wooden building systems, including cross-laminated timber elements, are becoming more common. The last few years have seen new developments and documentation of innovative types of cross-laminated timber floor assemblies. Regarding impact sound associated to walking persons, running or jumping children, such floor assemblies can be regarded as a weak part. So far, there are no reliable standardized calculation models available, for prediction of impact sound in the entire frequency range. Therefore the design is always based upon previous experiences and available measurements. This article presents the results of a number of well controlled sound insulation measurements of cross-laminated timber/massive wood floor constructions conducted in laboratories. The collection of data and results analysis highlight some basic phenomena. For instance, how structural differences related to the grouping of the constructions change the frequency distribution of the impact sound level and the single number quantities. Another significant result is the influence of the dynamic stiffness of the resilient interlayer of floating floor systems and the mass per unit area of the floors. Based on this analysis, the aim is to identify similarities and carry out simplifications. The data will be further processed and used in the development of prediction models and optimization process of cross-laminated timber floor assemblies.

Keywords

Lightweight massive wood impact sound insulation building acoustics floor

Introduction

Cross-laminated timber/massive wood building technique

During the last few years, there has been an increasing interest of cross-laminated timber (CLT) constructions among project owners, architects and producers. A more extensive use of wood in buildings is also of strategic interest in the wood industry. Design solutions to fulfil sound insulation requirements between apartments have been an issue for years; see for instance Homb and Austnes¹ and Homb and Brevik.² Recently, we recognize an increased interest on CLT solutions used in other building categories, for instance, student apartments, schools and office buildings. Development and verification of floor constructions are important for all those applications. In today’s solutions, the sound insulation properties of CLT floors are undermined due to flanking transmission of the supporting walls, for instance, shown in Homb.³ Research has been conducted at SINTEF Byggforsk with respect to both vibration properties and sound insulation properties to develop knowledge and support node solutions, see Homb⁴ and Homb and Hveem.⁵

However, the sound insulation properties of the CLT floor itself are limited due to low mass and relatively low stiffness. To fulfil some level of sound insulation requirements, it is therefore necessary to complement the floor with an additional construction above the CLT element, an additional ceiling or both measures. In these studies on vibration properties and sound insulation properties, the focus has mainly been on additional lightweight materials and solutions. German-speaking countries have developed hybrid CLT floors. Such solutions are also highly interesting for different kinds of building categories due to increased mass and stiffness contribution.

When considering research and studies from some years ago and from different countries, a number of laboratory measurement results are actually available. It includes some studies performed on specific CLT/massive wood constructions; see for instance, Acoubois,⁶ Holtz et al.⁷ and Rabold,⁸ beside measurements from unpublished projects.

Objective

This article presents results from numerous well controlled sound insulation measurements performed in laboratories. As the impact sound insulation tends to be the most significant problem for the wooden floor construction building technique, this type of measurements is focused upon here. The main objective is to highlight some specific phenomena, in order to see in what way structural differences related to the grouping of the constructions affect the sound insulation properties. An objective is also to deliver well controlled and systematically performed experimental results that can verify solutions and give input for better prediction tools for CLT/massive wood floor constructions. To this end, results included in this article are first presented by country since floor construction is generally specific to each country: typical construction will depend on regulation requirements and local expertise. However, it will be seen that floor configuration grouping is possible across the European countries considered.

Floor assemblies

Introduction

In the following section, typical CLT/massive wood floor constructions will be presented. The information will be given for each contributing country in alphabetic order. The data collection presented in this article concentrates mainly on typical national solutions but divided into different types depending on structural differences. The grouping of constructions has been based on work in the Silent Timber Build project, see Homb.⁹ Floor assemblies, presented in this article, are the following main types:

I: Single CLT/massive wood floor element;

II: Additional lightweight elements above/below CLT/massive floor constructions;

III: Hybrid CLT/massive wood constructions with floating floor screed and gravel or concrete on the element.

Among the European countries investigated, quite different solutions are found. However, in some cases, solutions correspond to identical or very similar constructions, especially when considering the basic solutions given by the grouping of floor construction. It is not surprising that lightweight floor constructions have been a common tradition in the Nordic countries. The use of hybrid solutions using gravel or concrete is more traditional in the German-speaking countries. Therefore, such solutions dominate the findings when we collect laboratory measurement data from these countries.

France

In France, CLT floor constructions have not been that common so far, but the interest of wooden building technique is increasing. A number of laboratory measurements have been carried out to prepare the construction sector with new possibilities. So far, the interest is mainly with additional lightweight constructions, either above the CLT element, below the CLT element or a combination. A basic drawing of a floor construction with a suspended ceiling is presented in Figure 1(a). Common for these solutions is a ceiling solution based on steel suspension products, often non-spring types but also resilient systems. The ceiling commonly incorporates a layer of mineral wool. A basic drawing of a floor construction with a resilient top floor solution and a suspended ceiling is presented in Figure 1(b). For the floor, a floating system on mineral wool products with a certain limit of dynamic stiffness has been found the most common. The first mentioned solution is in the following coded as FS-CS solutions (corresponding to Floor Stiff – Ceiling Stiff, meaning stiff floor and stiff suspended ceiling), and the second one FR-CS (Floor Resilient – Ceiling Stiff, meaning resilient top floor and stiff suspended ceiling).

Figure 1.

Suggested types of French floor constructions using CLT elements. (a)Type II, FS-CS. (b) Type II, FR-CS.

Austria, Germany and Switzerland

In Austria, Germany and Switzerland very similar floor assemblies of CLT elements are used. For economic reasons, a floating floor screed (cement screed on impact insulation boards) is often used as resilient top floor solution. Due to the required level, it is usually implemented in combination with additional grit or gravel on the floor. Alternatively, composite floors with static connections between a concrete layer and the element are used. Basic drawings of these floor assemblies are presented in Figure 2(a) and (b), respectively, with and without a layer of gravel. Also, solutions within type II, with a resilient lightweight top floor, have been used. See drawings presented in Figure 3.

Figure 2.

Common types of Austrian/German/Swiss CLT/massive wood floor constructions. (a) Type III, FR-CS with gravel or as composite floor. (b) Type III, FR-CS without gravel.

Figure 3.

Common types of Norwegian CLT wood floor constructions. (a) Type II, FR-CS with continuously elastic interlayer. (b) Type II, FR-CS with line elastic support.

Norway

In Norway, the preferable solutions have been based on an additional lightweight structure, typically directly on the CLT floor element. It means type II floor assemblies with different kinds of resilient solutions above the CLT element. The solutions vary between continuously elastic layer (the dynamic stiffness varies), line elastic or point elastic support between the CLT element and the top floor. Similar to some French solution, these are encoded as FR-CS solutions (resilient floor on the wooden element). A basic drawing of this construction type using a continuously elastic layer is presented in Figure 3(a). Figure 3(b) shows a common solution based on line elastic support.

Sweden

The most common floor construction in Sweden based on CLT elements has been developed by Martinsons of which a lot of in-situ measurement results exist as well as some laboratory measurements. For more information and details, see Homb et al.¹⁰ and Simmons et al.¹¹ In fact, the complete floor assembly solution implemented in residential buildings is based on the use of a set of separate independent beams for the ceiling. In the following, this floor assembly is coded as a FS-CN solution (no coupling between CLT element and ceiling construction) within type II. A basic drawing of this construction type is presented in Figure 4.

Figure 4.

Suggested type of Swedish CLT wood floor constructions. Type II, FS-CN.

Impact sound insulation properties

Measurement method and data

The impact sound insulation measurements were carried out according to ISO 140-6 standard, versions valid at the time of measurements. The laboratories in which these measurements were carried out were accredited laboratories following the ISO 140-1 standard. Nowadays, the ISO 10140 standard series apply to such laboratories and acoustic measurements.

Uncertainties for sound insulation have been investigated leading to the publication of ISO 12999-1 standard in 2014. Unfortunately, as indicated in ISO 12999-1 standard, there are no results available of frequency dependent uncertainties for impact sound insulation measurements in laboratories conditions. Inter-laboratory measurements (round-robin tests) for impact sound insulation are not very common and especially not sufficient in numbers to evaluate laboratory measurement uncertainty. Standard uncertainties for single number values of laboratory measurement are however given in ISO 12999-1 standard and estimated to be about 1.5 dB. Furthermore, it should be noted that results presented in Rabold⁸ compare confidence interval according to the old ISO 140-2 standard and laboratory measurement results for wood based floors. The comparison is really good and therefore it is expected that confidence interval are close to those presented in ISO 140-2.

All measurement results presented in this article have been carried out in the frequency range from 50 Hz. The measured normalized impact sound pressure levels in the frequency range 50–5000 Hz are presented as graphs in the following sections. From the test result, different single number quantities for rating the impact sound insulation were calculated, that is, L_n,w, the spectrum adaptation term, C_I,50–2500 and the sum of these, L_n,w + C_I,50–2500, see EN-ISO 717-2:1996.¹²

In the following sections, measurement results compiling comparable laboratory measurement data from the different countries considered are presented. Totally, approximately 60 laboratory measurement data have been collected and evaluated. However, for each construction group, a limited number of records will be reported. The idea has been to extract results only from the most comparable and typical solutions. In section ‘Basic floor constructions’, impact sound insulation data from solutions type I, measured in Austria, Norway and Sweden are presented. In section ‘Floor constructions with resilient top floor’, impact sound insulation results from solutions type II, measured in France, Germany, Norway and Sweden are presented. In section ‘Floor constructions with suspended or independent ceiling’, impact sound insulation results from hybrid solutions type III, measured in Austria and Germany are presented. For all presented data, the total mass per unit area in kg/m² (denoted mpua) of the floor construction is given. In the figures, the total height, h (mm) of the floor structure is also included.

By the analysis of a compilation of measurements, it is expected to observe and deduce what effect has the most influence on the floor’s performance in terms of impact noise. Indeed, it could be expected that mass per unit area, ceiling mounting type and floor covering system (dynamic stiffness of resilient layer for floating system) are of importance.

Basic floor constructions

Laboratory measurement results of single CLT/massive wood floor element are presented in Figure 5, that is, type I according to section ‘Floor assemblies’. Even if the assemblies vary between CLT, gluelam and stacked beams, the similarities in the frequency domain is conspicuous between approximately 100 and 2500 Hz. With respect to the impact sound pressure level, the measurement results seem to vary between different objects and not directly with respect to mpua. In the high frequency range, the impact sound pressure level depends to a high degree on the softness at the contact area between the impact hammer and the material. Further evaluation of the results is given in section ‘Result evaluation’.

Figure 5.

Measurement results of single CLT/massive wood floor elements. NO NBI project report O 8788,¹³ SINTEF project report O 20723,¹⁴ AU Ferk,¹⁵ SE Ljunggren,¹⁶ DE Holtz.⁷

Laboratory measurement results of a basic CLT floor with an additional layer of concrete are presented in Figure 6 together with one gluelam type of element from Figure 5. In this case, the concrete have been poured directly (glued) on the CLT element. Similar to standard concrete floors, the impact sound pressure level increase towards higher frequencies, typically according to basic equations in EN 12354-2:2000.¹⁷ Regarding the two objects with a concrete layer, the shape in the frequency domain correlates well, but the deviation with respect to the impact sound pressure level at medium and high frequencies is rather high. The reason for this is not investigated. Deviation from a typical curve in the high frequency range is not important because it depends very much on the softness of some floor covering normally applied on the top floor surface. All results presented in Figures 5 and 6 are floor assemblies without a floor covering.

Figure 6.

Measurement results of a CLT element with a concrete layer on top. NO NBI project report O 8788,¹³ SINTEF project report,¹⁸ DE Holtz et al.⁷

Floor constructions with resilient top floor

Laboratory measurement results of CLT/massive wood floor element with resilient top floor solutions are presented in Figures 7 –10. Figure 7 focuses on type II solutions with some kind of lightweight top floor assemblies, that is, point elastic, line elastic or continuously elastic interlayer. See Figure 3(a) and (b) regarding typical solutions. The DE floor assembly correspond to measurement without a finish floor covering (plastic floor covering or parquet for instance).

Figure 7.

Measurement results from constructions with resilient top floor, type II. NO NBI project report O 8788,¹³ NBI project report O 8788,¹⁹ SINTEF project report O 20723,¹⁴ DE Rabold,⁸ FR Acoubois.⁶

Figure 8.

Measurement results from constructions with lightweight resilient floor on gravel type III. NO SINTEF project report O 20723,¹⁴ DE Rabold.⁸

Figure 9.

Measurement results from construction type III, FR-CS. NO SINTEF project report,¹⁸ CH Lignum,²⁰ DE Rabold.⁸

Figure 10.

Measurement results from construction type III, FR-CS. CH Lignum,²⁰ DE Rabold.⁸

The results show huge differences between the different solutions. But when looking into properties and principles of the assemblies, the results seem logical from an acoustical point of view. In the DE and FR case, the mpua (respectively, 78 and 84 kg/m²) is rather low and the dynamic stiffness of the continuously elastic interlayer rather high. The measurement object from NO (mpua = 130 kg/m²) is based on a point elastic top floor (also called technical subfloor), product name ‘Granab’. This kind of product has been developed for installing on a basic floor of concrete. The solution does not give the same improvement when installed on a lightweight and softer element of CLT. Measurement cases NO (mpua = 119 and 136 kg/m²) are based on an optimization of line elastic support with a resilient layer of stone wool. The correlation between these two independent experiments is rather high.

Figure 8 shows results from hybrid solutions with gravel below (i.e. directly on the CLT element) and lightweight materials above a continuously elastic interlayer (schematic description similar to Figure 2(a)). The results show a total difference of 7 dB with respect to the L_n,w + C_I,50–2500 values and apparently high correlation between DE (mpua = 282 kg/m²) and NO (mpua = 245 kg/m²) case. But the dynamic stiffness of the elastic interlayer is low in the NO (mpua = 245 kg/m²) case and rather high in the DE case. The rather high dynamic stiffness of the NO (mpua = 235 kg/m²) and DE case is about the same level, see also Table 2. It means that the impact sound insulation properties seem to depend very much on the gravel composition or density in combination with the softness or resilience of the continuously elastic interlayer.

Figure 9 shows also results from a hybrid solution, type III with concrete layer either below or above a resilient layer (see Figure 2(b) regarding the latter type of solution). When the concrete layer is below the resilient layer, it is then directly poured on the CLT element; on top of this concrete/CLT combination a floating system (including a resilient layer) is then installed (the schematic description is then similar to Figure 2(a) when the layer of gravel is replaced by a layer of concrete).

In the CH²⁰ and DE⁸ case with concrete above the resilient layer, the objects have been measured without a top floor covering, that is, the tapping machine positioned directly on the concrete surface. For practical purposes with a top floor covering installed, levels in the high frequency range will be of minor importance. The huge differences between these two results relate probably to the different dynamic stiffness of the continuously elastic interlayer. In the two NO¹⁸ cases, the 60-mm-thick concrete layer has been poured directly on the CLT element, and then a floating system (including a resilient layer) has been applied on top. The results reveal typical impact sound insulation differences between continuously elastic interlayer with relatively low dynamic stiffness (mpua = 241 kg/m²) and a line elastic interlayer (mpua = 265 kg/m²). Similar to other results, a relatively thin continuously elastic interlayer provides limited improvement compared to an optimization of line elastic interlayer.

Figure 10 shows results from a hybrid solution, type III with heavy materials both below (i.e. directly on the CLT element) and above a continuously elastic interlayer (see Figure 2(a) regarding the typical solution). All these floor assemblies have been measured without a floor surface covering.

The results show a total difference of 5 dB with respect to the L_n,w + C_I,50–2500 values. In major parts of the frequency domain, results from CH²⁰ and DE⁸ cases with concrete below the resilient layer correlate relatively well. Higher mpua from the CH²⁰ case seems to compensate for a higher dynamic stiffness of the resilient interlayer compared to the DE⁸ case with concrete also below the elastic interlayer. Solution from DE⁸ with gravel below a soft elastic interlayer is preferable in the medium frequency range, but not necessarily in the low frequency range.

Floor constructions with suspended or independent ceiling

Laboratory measurement results of CLT floor elements with a resilient suspended ceiling or independent ceiling are presented in Figure 11. The suspended ceiling system (FR objects) is a solution based on non-spring steel suspension products, respectively, with (red curve) and without (blue curve) a soft floor covering (of PVC type) on top of the CLT element. Laboratory measurement result of a floor constructions with fully independent ceiling uncoupled from the load-bearing CLT element is also presented in Figure 11, in this case without a floor surface covering on the CLT element.

Figure 11.

Measurement results from construction type II, respectively, FS-CS and FS-CN. FR Acoubois,⁶ SE Ljunggren.¹⁶

Results presented in Figure 11 illustrate the challenge to achieve low impact sound pressure levels in the low frequency range with lightweight constructions. Even when the ceiling is mechanically independent, the limitation in the low frequency range due to low mass is clearly seen from the measurement curve. The figure also shows limitations due to stiff suspension of the ceiling system and the huge effect of the soft floor covering at middle and high frequencies.

Floor constructions with resilient floor and resilient suspended ceiling

Laboratory measurement results of floor constructions with resilient floor and resilient suspended ceiling are presented in Figure 12. The AU measurement object is a hybrid solution, type III with a layer of gravel below a continuously elastic layer (i.e. gravel directly on the CLT element) and a lightweight top floor solution without a floor surface covering (schematic description similar to Figure 2(a)). The other two measurement objects presented in Figure 12 are of type II with a lightweight floor solution. The construction of the ceiling also varies, in the AU case with a resilient fixing of the plasterboard. In the FR cases, the suspended ceiling system is based on non-spring steel suspension products.

Figure 12.

Measurement results from FR-CR constructions, type II and III. AU Ferk,¹⁵ FR Acoubois.⁶

Results presented in Figure 12 illustrate that increased mass not necessarily improves the impact sound properties in the low frequency range, that is, L_n,w + C_I,50–2500 values. Resonance frequencies due to elastic interlayer and small cavities prevent this. But in the high frequency range, the AU case with gravel is certainly preferable especially when a floor surface covering (such as plastic floor covering) will be included. Such solutions will therefore achieve high performance with respect to L_n,w− values.

Result evaluation

Main results

In the following, the main results from previous sections are given. Table 1 shows single number values and corresponding mass per unit area (mpua) of lightweight floor assemblies. The dynamic stiffness is given for objects with continuously elastic floor interlayer. Figure 13 shows L_n,w + C_I,50–2500 – values as a function of the mpua for all objects of type II.

Table 1.

Main results, impact sound insulation from lightweight floor assemblies.

Type I and II	L_n,w (dB)	C_I,50–2500 (dB)	SUM^a (dB)	Mass per unit area (kg/m²)	Dynamic stiffness (MN/m³)	Source
Single	86	−5	86	51	–	AU
Single	86	−5	86	58	–	SE
Single	85	−4	85	68	–	DE
Single	83	−7	83	80	–	NO
Single	87	−5	87	85	–	NO
Single	85	−5	85	89	–	SE
FR	65	0	65	78	50	DE
FR	68^c	0	68	84	50	FR
FR	47^c	8	55	119	Line elastic	NO
FR	57^c	2	59	130	Point elastic	NO
FR	49^c	3	52	136	Line elastic	NO
FS-CS^b	68	−3	68	74	–	FR
FS-CS^b	58^c	5	63	77	–	FR
FS-CN	49	4	53	75	–	SE
FR-CS^b	51	4	55	107	40	FR
FR-CS^b	50^c	6	56	110	40	FR

Negative values of C_I,50–2500 neglected in the sum according to NS 8175.²¹

Some elastic effect of the suspension system.

Measurement object with some type of floor covering.

Figure 13.

Single number values as a function of mass per unit area of type II, lightweight floor assemblies.

Table 2 shows single number values and corresponding mass per unit area of hybrid floor assemblies. The dynamic stiffness is given for objects with continuously elastic floor interlayer. Figure 14 shows L_n,w + C_I,50–2500 – values as a function of the mass per unit area (mpua) for solutions with resilient top floor, that is, type III assemblies.

Table 2.

Main results, impact sound insulation from hybrid floor assemblies.

Type I and III	L_n,w (dB)	C_I,50–2500 (dB)	SUM^a (dB)	Mass per unit area (kg/m²)	Dynamic stiffness (MN/m³)	Source
Single	84	−12	84	204	–	DE
Single	90	−13	90	223	–	NO
FR	55	3	58	179	6	DE
FR	66	−3	66	193	20	CH
FR	56^b	1	57	235	>20	NO
FR	55^b	3	58	241	<10	NO
FR	44^b	6	50	245	<10	NO
FR	47^b	1	48	265	Line elastic	NO
FR	40	7	47	269	6	DE
FR	47	3	50	282	40	DE
FR	47	1	48	298	6	DE
FR	46	6	52	345	20	CH
FR-CR	46	10	56	182	<15	AU

Negative values of C_I,50–2500 neglected in the sum according to NS 8175:2012.²¹

Measurement object with some type of floor covering.

Figure 14.

Single number values as a function of mass per unit area of type III, hybrid floor assemblies.

Result evaluations

Comparing laboratory measurements for similar floor assemblies, sometimes the frequency domain results coincide rather well and sometimes they coincide rather poorly. Table 3 shows an overview of similarities in the frequency domain when influences of the mass per unit area, the dynamic stiffness of the floor interlayer and the floor covering are taken into account.

Table 3.

Similarities in the frequency domain between different measurement objects.

Frequency domain similarities	Type II	Type III
High or medium	Basic, Figure 5 FR-CS, Figure 7	FR-CS, Figure 8 FR-CS, Figure 10
Low		FR-CS, Figure 9 FR-CR, Figure 12

The overview presented in Table 3 shows that all constructions of type II present high or medium similarities in the frequency domain when the mentioned parameters are taken into account. It also means that the results are more or less independent of other details and laboratory conditions. The comparison of constructions of type III shows a spreading regarding the frequency domain results, from high or medium similarities in Figures 8 and 10 to low similarities in Figures 9 and 12. The dynamic stiffness of the floor interlayer, floor covering and the dynamic properties of the resilient ceiling suspension seem to be the main reasons for this spreading. Also the sound radiation from the ceiling may be an important reason due to low frequency modal behaviour depending on suspension types and mounting density as well as stiffness and density of sheet layers.

Looking into single number quantities, results given in Figure 13 shows an overall correlation between the L_n,w + C_I,50–2500 value and the mass per unit area. But there are exceptions, for instance the FS-CN solution and the point elastic top floor FR-solution deviate from the main tendency. But the number of objects is rather limited, so it is necessary to pay attention on how to use these results. The spreading of the single number quantities shows that a number of parameters and components are involved. The spreading also demonstrates that an optimization is possible with respect to, for instance, mpua or floor assembly thickness. Results presented in Table 1 and Figure 13 demonstrate that it is realistic to achieve L_n,w + C_I,50–2500 values in the range 52–56 dB for type II objects.

The compilation of constructions presented in Figure 14 also shows an overall correlation between the L_n,w + C_I,50–2500 value and the mass per unit area. The lack of a floor covering limits some of the objects, see Table 2. It appears from Table 2 that large mpua and low dynamic stiffness of the floor interlayer is preferable for impact sound performance. Similar to type II results, there are of course exceptions from a general tendency due to different ‘element’ combinations and specific properties of products involved, so it is necessary to be precautious when using these results. The spreading of the single number quantities shows also that a number of parameters and components are involved, and therefore an optimization of the floor construction is possible. Results presented in Table 2 and Figure 14 demonstrate that it is realistic to achieve L_n,w + C_I,50–2500 values in the range below 50 dB for type III objects. Comparing results from type II and type III, it is not obvious to choose hybrid floor solutions when the objective is L_n,w + C_I,50–2500 results above 52 dB.

Conclusion

This article presents the results of a number of well controlled sound insulation measurements of CLT/massive wood floor constructions conducted in laboratories. Comparison of results with different solutions, different product and from different laboratories is of course challenging. But the grouping of constructions has been a very helpful tool to compare and analyse the results.

Considering the total collection of massive wood floor construction data of type II (i.e. additional lightweight element), L_n,w + C_I,50–2500 results from 68 to 52 dB from objects with mass per unit area (mpua) from approximately 75 to 140 kg/m² are found. Similarly, the total collection of data from hybrid CLT floor constructions with gravel or concrete (i.e. type III), shows L_n,w + C_I,50–2500 results from 66 to 47 dB from objects with mpua from approximately 180 to 350 kg/m². It means that it is possible to choose solutions within a wide range of impact sound insulation properties and weight of the floor construction.

In the frequency domain, results regarding construction type II, show high or medium similarities when taking the dynamic stiffness of the floor interlayer, mpua and the floor covering into account. The comparison of constructions of type III shows a spreading regarding the frequency domain results, from high to low similarities depending on the properties of chosen products, especially the dynamic stiffness of the floating floor resilient interlayer and properties of the resilient ceiling suspension.

With respect to single number quantities, the picture is a bit different. Regarding both construction type II and type III, results show an overall correlation between the L_n,w + C_I,50–2500 value and the mass per unit area. Within the same range of mpua, individual spreading between different objects may be large. It seems therefore not possible to establish a reliable correlation between the L_n,w + C_I,50–2500 value and the mpua from the collected data. The comparison shows that all types of connections between the massive wood element and floor or ceiling components have an important influence of the impact sound insulation properties. When evaluating measurement results or developing new solutions, a focus should be set on the stiffness properties of all products and elements involved.

The collection of data and result analysis highlight some basic phenomena. For instance, how structural differences related to the grouping of the constructions change the frequency distribution of the impact sound level and the single number quantities. Another significant result is the influence of the dynamic stiffness of the resilient interlayer and the mass per unit area of the floors. When mounted, a ceiling also plays an important role in the floor performance. Within the STB project work, these data and results will give us the possibility to optimize existing solutions or develop new floor construction with respect to the impact sound insulation properties itself, geometrical or mass per unit load limitations and other physical issues. Results from this work will also be used for verification of the ongoing research on prediction tools. When planning complete constructions in real structures, the flanking transmission needs also to be taken into account because supporting walls and other load-bearing elements often limit the sound insulation properties achieved from laboratory measurements.

Footnotes

Acknowledgements

Authors would like to acknowledge all R&D partners of Silent Timber Build project representing the following countries: Sweden, France, Germany, Austria, Norway and Switzerland. We would also like to thank Wood Wisdom Net for recommending financing of this project and, additionally, the financing organizations in each of the involved countries.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

References

Homb

Austnes

JA.

Experiences with sound insulation for cross-laminated timber floors. In: Proceedings of Baltic Nordic acoustical meeting (BNAM 2010), Bergen, 10–12 May 2010.

Homb

Brevik

BG.

Etasjeskillere i massivtre (Cross-laminated timber floors). Building Detail Sheet no. 522.891, SINTEF Building and Infrastructure, Oslo, November 2009, http://www.sintefbok.no/ (in Norwegian).

Homb

Flanking transmission measurements in a cross-laminated timber element building. In: Proceedings of 9th European conference on noise control: Euronoise, Prague, 10–13 June 2012.

Homb

Vibrasjonsegenskaper til dekker av massivtre (Vibration properties of cross-laminated timber floors). Project report SINTEF Building and Infrastructure, no. 24. Oslo, 2008, http://www.sintefbok.no/ (in Norwegian).

Homb

Hveem

Lydoverføring i byggesystemer med massivtreelementer (Sound transmission in CLT element constructions). Project report SINTEF Building and Infrastructure, no. 80, Oslo, 2011, http://www.sintefbok.no/ (in Norwegian)

Acoubois Etapes 2 & 3. Rapport V2.0, Mesures Acoustiques en laboratoire. Qualitel, FCBA & CSTB, June 2014, http://www.codifab.fr/sites/default/files/acoubois_mesures_laboratoire.pdf (in French).

Holtz

Rabold

Hessinger

. Schalltechnische Kennwerte von Massivholzbauteilen, Bestandsaufnahme und Analyse (Acoustic parameters of solid wood elements, data collection and analysis). Labor für Schall- und Wärmemesstechnik, research report 2001.

Rabold

Anwendung der finite element Methode auf die Trittschallberechnung. Doctor Ingenieur Dissertation at Technischen Universität München, Fakultät für Bauingenieur- und Vermessungswesen, 27 May 2010. München, https://mediatum.ub.tum.de/doc/965934/965934.pdf

Homb

Grouping of wood constructions. Silent Timber Build document, April 2015.

10.

Homb

Guigou-Carter

Hagberg

. Impact sound insulation of wooden joist constructions: collection of laboratory measurements and trend analysis. Build Acoust 2016; 23(2): 73–91.

11.

Simmons

Hagberg

Backman

Acoustical performance of apartment buildings – resident’s survey and field measurements. AkuLite, Report 2, SP report 2011:58. Sweden, September 2011, http://www.simmons.se/Filer/PDF-filer/SP%20Rapport%202011–58%20Acoustical%20performance%20of%20apartment%20buildings%20-%20residents%20survey%20and%20field%20measurements.pdf

12.

EN-ISO 717:1996. Part 2. Acoustics – rating of sound insulation in buildings and of building elements – part 2: impact sound insulation.

13.

NBI project report O 8788. Mockup-measurements at Norwegian Building Research Institute, NBI. Commissioned by TEFT/Stjern, Trondheim, 2002.

14.

SINTEF project report O 20723. Laboratory measurements of CLT floor constructions. Commissioned by NTI, Oslo, 2007.

15.

Ferk

Sound insulation in lightweight constructions – Austrian experiences with solid wood panel buildings. In: Proceeding of InterNoise 2006, 3–6 December 2006, Honolulu, HI.

16.

Ljunggren

Ljudisolering i trähus – en handbok för konstruktörer. AkuLite report 1, SP report 2011:10.

17.

EN 12354:2000. Part 2. Building acoustics – estimation of acoustic performance of buildings from the performance of elements – part 2: impact sound insulation between rooms.

18.

SINTEF project report. Laboratoriemåling av lydisolasjon for 140 mm massivtredekker med 60 mm påstøp (Laboratory measurement of 140 mm CLT floor with 60 mm concrete). Project report O 21362, Norwegian Building Research Institute for ‘SundMo AS’ (not published), Oslo, 5 December 2006 (in Norwegian).

19.

NBI project report O 8788. Mockup-measurements at Norwegian Building Research Institute, NBI. Commissioned by Treteknisk institutt, NTI, Trondheim, 2003.

20.

Lignum. Switzerland 2015, www.lignumdata.ch

21.

NS 8175:2012. Acoustical conditions in buildings. Sound classification of various types of buildings.