Slim floor coverings for refurbishment of old buildings. L. Weber, A. Fügmann Fraunhofer Institute for Building Physics (IBP), Stuttgart

Transcription

1 Page 1 of 8 Abridged Version of Research Report B-BA 3/28 Slim floor coverings for refurbishment of old buildings L. Weber, A. Fügmann Fraunhofer Institute for Building Physics (IBP), Stuttgart This research report was financed by the Bundesamt für Bauwesen und Raumordnung (BBR, Federal Office for Building and Regional Planning) (reference number Z / II ). The author is responsible for the contents of this report. 1 Objective of the research project Refurbishment measures of floors in old buildings are aimed at maintaining the existing room height and at avoiding disadvantages, e.g. cost-intensive reworking of door openings resulting from lifting the ground level. Thus, slim floor coverings i.e. dry screeds made of wood-based materials and gypsum fiber boards with reduced height are increasingly applied. The insulation layer of this kind of constructions is frequently only a few millimetres thick. The widely used systems of floating laminate or parquet floors are based on similar conditions. There is little information on the acoustic properties of these slim floor coverings so far, although they are increasingly applied in construction due to their advantages, as e.g. fast installation and low costs. This fact, however, results in the reduction of planning reliability and in an increase of the risk of deficiencies in sound insulation. Therefore, the research project was aimed at developing secured fundamentals for building acoustic planning and design by measuring and investigating the acoustic properties of slim floor coverings. This comprises constructional influences such as mass and stiffness of the floor panels as well as the influence of structural boundary conditions. Moreover, guidance on design and construction for practical use as well as measures to optimize impact sound insulation were developed. 2 Accomplishment of the research project Since the existing computational tools did not allow sufficiently precise statements, the necessary investigations were performed by experiments according to the following procedure: Extension of the linear reduction of impact sound L lin according to DIN EN ISO to the frequency range from 5 to 1 Hz to develop a practice-oriented single number value for the reduction of footfall noise. Construction of a lifting device for the investigated floor coverings. The device is used for the rapid and simple replacement of the insulation layer to allow a great number of measurements within the framework of the research project. Systematic series of measurements on slim floor coverings of different construction on a timber and on a solid floor. All measurements were carried out under defined conditions in building acoustic test facilities. The measurements were aimed at identifying the relations between the technical and acoustic properties of the floor coverings. Analysis and description of acoustic relations, development of a guidance for the practical use of slim floor coverings in massive and lightweight construction.

2 Page 2 of 8 Development of measures and proposals to optimize the reduction of impact sound of slim floor coverings. The investigations included dry screeds with reduced thickness of the insulation layer as well as floating parquet and laminate floors. 3 Fundamentals 3.1 Construction of slim floor coverings Slim floor coverings comprise two fundamentally different types of construction: dry screeds with reduced thickness of the insulation layer and floating parquet or laminate floors. Fig. 1 shows the two constructions in a schematic diagram: dry screed 4) 3) 2) floating laminate floor 5) 1) 1) base floor 2) insulation layer 3) floor panel (e. g. gypsum fibre boards) 4) floor covering (e. g. carpeting) 5) laminate or parquet flooring Fig. 1 Construction of dry screeds and floating laminate floors (schematic, not to scale). In case of dry screeds a stiff floor panel is installed above the insulation layer usually consisting of large-area single elements which are connected rigidly at the joints. The materials used are besides wood-based boards (OSB boards or chipboards) mainly gypsum fibre boards. The floor panel is usually not used as a floor surface to walk on but serves as a bearing surface for the real floor covering made of e.g. carpets, plastic coverings or tiles. To guarantee the required stiffness the floor panel must at least have a thickness of approx. 2 mm resulting in a minimum height of approx. 3 mm for the total construction in connection with the floor covering and the insulation layer, even if thin insulation boards are used. In contrast to dry screeds floating parquet and laminate floors are ready to directly walk on making any additional floor covering unnecessary. The thickness of the floor elements is only approx. 7 to 1 mm. Since the elements are frequently not glued at the joints but only stuck together (the so-called "click connection"), a considerably lower stiffness of the floor panel occurs in comparison to dry screeds. Moreover, parquet and laminate are not used as large-area boards but as panels resulting in a much higher number of joints. Due to the small height of construction parquet and laminate are frequently used as an alternative to carpeting.

3 Page 3 of Testing Measurements were performed according to DIN EN ISO 14-8 and -11 [1, 2] in a building acoustic test facility for floors. Excitation of the floor to be analyzed was achieved by a standard tapping machine, and the resulting sound level was measured in the room beneath the floor. In order to characterize the acoustic effect of floor coverings, the reduction of impact sound was determined from the measured sound levels with and without covering L n and L n, L L n L. (1) n The weighted reduction of impact sound according to DIN EN ISO [3] serves as single number value for the measured data determined as third octave spectrum, designated in dependence of the type of base floor either as L w (for solid floors) or as L t,1,w (for wooden joist floors). Since the weighted reduction of impact sound describes the sound insulation related to the excitation of the floor by a human walker in an only insufficient way, the linear reduction of impact sound L lin according to DIN EN ISO is used in addition as practice-oriented single number value for the reduction of footfall noise. In this report it is designated as L lin,5-25 comprising also the frequency range from 5 to 1 Hz for the correct simulation of human hearing perception [4, 5]. The designation for the wooden joist floor is accordingly L lin,t,1,5-25. Since the acoustic effect of floor coverings depends on the construction of the base floor to a large degree, measurements were performed on a solid floor as well as on a wooden joist floor. The floor constructions were as follows: Solid floor: 14 mm massive reinforced concrete, mass per unit area m'' = 32 kg/m 2, weighted normalized impact sound level L n,w = 77.8 db, Wooden joist floor: reference floor type 1 according to DIN EN ISO 14-11, d = 24 mm, m'' = 3 kg/m 2, L n,w = 68.6 db (construction see Fig. 2). 1 chipboards, d = 22 mm 2 wooden joists, w x h = 12 mm x 18 mm, centre distance 625 mm 3 mineral wool, d = 1 mm, flow resistivity per unit length r = 5 kpas/m 2 4 battens, w x h = 48 mm x 24 mm, centre distance 625 mm 5 gypsum boards, d = 12,5 mm Fig. 2 Construction of the wooden base floor used for the experimental investigations (reference floor type 1 according to DIN EN ISO 14-11).

4 Page 4 of 8 4 Test results Reduction Trittschallminderung of impact sound L level [db] L [db] L [db] Solid floor 12 db/oct Wooden joist Frequenz floor [Hz] Frequency Frequenz [Hz] elast. plasticized EPS, d EPS, = 2,2 d mm = 2,2 mm elast. plasticized EPS, d EPS, = 5 mm d = 5 mm PE-Schaum, foam, d = d 3 = mm 3 mm Kork, cork, d = 2 mm Wellpappe, corrugated d cardboard, = 2,5 mm d = 2,5 mm Kautschuk, rubber, d = d 2 = mm 2 mm Kautschuk, rubber, d = d 3 = mm 3 mm ohne without Dämmung insulation Mineralwolle, mineral wool, d d = = 122 mm Fig. 3 Reduction of impact sound level by a dry screed consisting of OSB boards (d = 22 mm, m'' = 13.5 kg/m 2 ) in conjunction with various slim insulation layers (d = 2-5 mm, s' = 1-19 MN/m 3 ). For comparison a conventional impact sound insulation board made of rock wool (isover Akustic EP 3, d = 12 mm, s' < 4 MN/m 3 ) was also included in the investigations. The measurements took place on a solid floor (above) and a wooden joist floor (below). The appropriate single number values are given in Tab. 1. Insulation layer Single number value for impact sound insulation [db] Solid floor Wooden joist floor L w L lin,5-25 L t,1,w L lin,t,1,5-25 slim layers No mm rock wool without insulation Tab. 1 Single number quantities for the measuring results in Fig. 3. Since the results for the slim insulation layers hardly differ from each other, only the mean value plus / minus standard deviation is mentioned for these samples.

5 Page 5 of 8 Reduction Trittschallminderung of impact sound L level [db] L [db] OSB-Platten boards (L w = 14,6 db) Laminat laminate floor (L w = 19,4 db) cork, d = 2, mm Solid floor Frequency Frequenz [Hz] Fig. 4 Reduction of impact sound level by a dry screed made of OSB boards (d = 22 mm, m'' = 13.5 kg/m 2 ) and a floating laminate floor (d = 7. mm, m'' = 5.8 kg/m 2 ) in conjunction with the same insulation layer (cork, d = 2. mm). The measurements were performed on a solid floor. Results for further insulation layers are given in Tab. 2. L w (laminate) - L w (OSB boards) Insulation layer [db] plasticized EPS, d = 2.2 mm 6.4 plasticized EPS, d = 5 mm 6. PE foam, d = 3 mm 5.8 cork, d = 2 mm 4.8 corrugated cardboard, d = 2.5 mm 3.4 rubber, d = 2 mm 6.6 rubber, d = 3 mm 6.2 mean value 5.6 Tab. 2 Difference between the weighted reduction of impact sound level by a dry screed made of OSB boards and a floating laminate floor in conjunction with various insulation layers. All measurements were performed on a solid floor. The technical specifications for the two floors coverings are given in Fig. 4.

6 Page 6 of 8 Verschlechteruntion [db] Deteriora- [db] Solid floor Frequency Frequenz [Hz] a) b) Verschlechteruntion [db] Deteriora Schraube, screw, loose lose (L n,w =, db) 4 Schrauben, screws, loose lose(l n,w =,1 db) 8 Schrauben, screws, loose lose(l n,w =,1 db) 8 Schrauben, screws, firm fest (L n,w =,5 db) Wooden joist floor Frequency Frequenz [Hz] a) screw loosely turned in b) screw firmly tightened 1 Schraube, screw, loose lose (L n,w =,1 db) 4 Schrauben, screws, loose lose(l n,w =,2 db) 8 Schrauben, screws, loose lose(l n,w =,4 db) 8 Schrauben, screws, firm fest (L n,w = 1,1 db) Fig. 5 Deterioration of the impact sound insulation of a dry screed (22 mm OSB boards on 3 mm PE foam) by structure-borne sound bridges. The measurements were carried out on a solid floor (above) and a wooden joist floor (below). To create the structure-borne sound bridges the floor panel of the dry screed was punctually connected to the base floor by means of screws. The investigations showed numerous new findings on the acoustic behaviour of slim floor coverings. The most important results are: Compared to a conventional floating screed the acoustic effect of slim floor coverings is clearly lower. Whereas mineral screeds allow a weighted reduction of impact sound of almost 4 db under optimal conditions on solid floors, the maximum value for slim floor coverings is only slightly higher than 2 db. As is also the case with other constructions, the reduction of impact sound of slim floor coverings is considerably lower for wooden joist floors than for solid floors. The difference depends on the kind of covering to a large degree. The difference is approx. 8 to 1 db for dry screeds, i.e. coverings with a thick stiff floor panel. In contrast, the difference for laminate or parquet is frequently higher than 15 db. Manufacturer information on weighted reduction of impact sound of thin insulation layers (L w 2 db) are generally correct or on the safe side. It must be taken into consideration, however, that the information is related to laminate floors which are installed on a solid base floor for sound insulation testing according to the valid building acoustic standards. This construction is very rare in practice, since compliance with minimum requirements by law for impact sound reduction cannot be guaranteed in most cases. If slim floor coverings

7 Page 7 of 8 are installed on floating screeds in mineral construction, as is usual in massive buildings, they are almost without any effect with regard to impact sound reduction. As can be seen in Fig. 3 and Tab. 1 the acoustic differences between commercial impact sound insulation layers with a thickness from approx. 2 to 5 mm are very small. It is surprising that the impact sound insulation will hardly change, even if the insulation layer is completely removed and the screed is directly installed on the base floor. The effect can probably be attributed to the contact stiffness at the surface between screed and base floor and will disappear, if the screed is rigidly connected to the base floor by glueing. The reduction of impact sound of slim floor coverings is independent on the insulation layer used at a large extent, but the type of floor panel is of remarkable importance with regard to acoustics. It is decisive whether the covering is installed on a solid floor or on a wooden joist floor. Thin flexible coverings (laminate or parquet) are more advantageous on solid floors in comparison to thick stiff floor panels (e.g. OSB boards or chipboards) and achieve average values for the weighted reduction of impact which are approx. 3 % higher (see Fig. 4 and Tab. 2). As concerns wooden joist floors the result is vice versa. The influence of structure-borne sound bridges, local and static loads as well as floor unevenness is almost negligible as concerns slim floor coverings (see Fig. 5). This is a further significant difference in comparison to conventional screeds which are extremely sensitive against structure-borne sound bridges. Slim floor coverings mainly develop their acoustic effect at high frequencies. Their efficacy, however, is only small in the range of low frequencies which is significant for protection against impact sound. Therefore, the weighted reduction of impact sound according to DIN EN ISO is generally no adequate criterion for sound protection in practice. It suggests improvement which is not achieved in real life (excitation of the floor by human walkers). If the linear reduction of impact sound L lin,5-25 is taken as a practice-oriented single-number value for the reduction of footfall noise, the improvement is approx. 7 % lower compared to the weighted reduction of impact sound. This applies for solid floors as well as for wooden joist floors. As concerns customary parquet and laminate the panels are mostly connected by the socalled click system. If the panels are glued instead, a slight deterioration of the impact sound reduction will occur which is, however, very low (approx. 1 db) so that it can be actually neglected. The acoustic properties of slim floor coverings are considerably improved by the installation of carpeting. The weighted reduction of impact sound increases by approx. 6 to 7 db, thus clearly exceeding the values which could be achieved by means of the floor covering or the carpeting alone. This applies for solid as well as wooden joist floors and probably also for other flexible floor coverings (made of plastics, felt, cork, etc.), but this is not yet investigated. Although measures to improve the acoustic properties of slim floor coverings are considerably limited due to their low height, various possibilities were developed to optimize impact sound reduction. Examples are dot- or line-shaped elastic support as well as the application of bitumen layers for damping of structure-borne. However, most measures are still at laboratory stage and need adjustment and optimization before being practically applied. For research and development it is reasonable to perform exploratory acoustic measurements on constructions with scaled-down dimensions, i.e. pieces of screed in this case. Investigations show that the reduction of the screed area has a relatively low influence on the measurement result for slim floor coverings. If the area of the covering is reduced from approx. 18 m 2 (total floor) to.23 m 2 (surface area of the standard tapping machine), the weighted reduction of the impact sound is changed by only 2 to 3 db.

8 Page 8 of 8 The application of the modified tapping machine according to DIN EN ISO 14-11, Annex C for impact sound excitation of slim floor coverings causes significant problems. Before the modified tapping machine can be used as reliable measuring system further research and development is required. 5 Summary The potential for acoustic improvement of slim floor coverings as simple and cost-efficient constructions can be considered to be significant at medium and high frequencies. The efficacy, however, is very small at low frequencies, i.e. in the frequency range decisive for protection against impact noise. Thus, the weighted reduction of impact sound clearly falls short of conventional systems, e.g. mineral screeds and dry screeds of customary height. On the other hand the installation of slim floor coverings is very simple and fast, and structural deficiencies, as e.g. floor unevenness or structure-borne sound bridges hardly affect the acoustic behaviour. Within the framework of the research project the acoustic properties and characteristics of slim floor coverings could be clarified to a great extent by extensive measurements. Numerous new findings were achieved, and the influence of relevant construction parameters and type of building (solid or timber construction) on the resulting impact sound insulation was determined in particular. The investigated constructions were selected with regard to their practical importance so that the measurement results are representative in spite of the great variety of slim floor coverings. Although some questions remain unanswered concerning detailed acoustic mechanisms of interaction, the research results now offer sufficient and reliable information on practical dimensioning of slim floor coverings as well as on building acoustic design. 6 References [1] DIN EN ISO 14-8: Akustik - Messung der Schalldämmung in Gebäuden und von Bauteilen - Teil 8: Messung der Trittschallminderung durch eine Deckenauflage auf einer massiven Bezugsdecke in Prüfständen (1998). [2] DIN EN ISO 14-11: Akustik - Messung der Schalldämmung in Gebäuden und von Bauteilen - Teil 11: Messung der Trittschallminderung durch Deckenauflagen auf leichten Bezugsdecken in Prüfständen (25). [3] DIN EN ISO 717-2: Akustik - Bewertung der Schalldämmung in Gebäuden und von Bauteilen - Teil 2: Trittschalldämmung (26). [4] Jeon, Y.; Jeong, J. H.: Objective and Subjective Evaluation of Floor Impact Noise. Journal of Temporal Design in Architecture and Environment 2, S (22). [5] Kühn, B.; Blickle, R.: Trittschalldämmung und Gehgeräusche-Immissionen von Geschossdecken aus Holz. wksb, H. 52, S (24).