New Belgian requirements for dwellings

Transcription

1 New Belgian requirements for dwellings B. Ingelaere, G. Vermeir, M. Van Damme Belgian Building Research Institute, Lozenberg, 7, B-1932 Sint-Stevens-Woluwe, Belgium, A new Belgian standard, to be published in 2006, imposes new acoustical requirements for dwellings. The criteria concern the airborne and impact sound insulation between dwellings, the façade sound insulation, the limitation of equipment noise and an imposed minimum absorption in entry halls and common spaces of multifamily housing. The requirements are given in a Belgian standard but act as the rules of good craftsmanship and function as such as real obligations for the building industry, similar to laws. The requirements have two quality levels related to cost and acoustic comfort. The so-called normal acoustic comfort level is a compromise between economic building cost and acoustic comfort. In this category, the acoustic requirement level doesn t increase the building cost and is such that at least 70% of the inhabitants are satisfied with the sound insulation. The improved acoustic comfort class allows for more than 90% of the inhabitants being satisfied with the sound insulation but means in general a significant building cost increase. With a rather important increase of 4 to 6 db in requirement levels compared to the old standard of 1977, the new standard is generating a new dynamic in the building industry with new innovative products and systems. The requirements for terraced housing are particularly severe, imposing as such a specific kind of construction. The new standard is in its final draft and will probably be active by the end of Introduction 1.1 Requirements in standards are enforceable Although there are rather severe acoustical environmental legislations in the different Regions of the Belgian federal state, there are up to now no direct laws with requirements about the sound insulation in buildings. But there is a standard with recommendations for the sound insulation between rooms, the façade sound insulation and the impact sound insulation in a large scope of types of buildings (from dwellings, offices to schools and hospitals ). This standard NBN S dates back to 1977 and contains not only recommendations but also a specific Belgian single value rating system (the categories ) derived out of the imposed measurement of the normalized level difference D n. All recommendations in the standard are being expressed in these categories. The term recommendations as well as the fact that they are only given in a standard is misleading: they are real requirements! There is a Belgian law that stipulates that good craftsmanship should always be applied. And the rules for good craftsmanship are given by the standards. So when they are not met, a juridical condemnation will follow So standards with recommendations imply real obligations for the building industry with very similar consequences as would be the case with laws. This is the case for the old and the future standard. The advantage of the system is that standards can be more easily adapted than laws which of course involve politics Another advantage is that the same requirements will apply to the 3 different Regions of the country, simplifying matters for the building industry. In 1987, the NBN S requirements were completed with the publishing of the NBN S with mainly requirements about technical equipment noise and recommendations about the maximum sound level in different types of rooms. 1.2 The necessity of replacing the old standards The publication of the standards EN ISO and 2 in December 1996, made it necessary to at least adapt the standard NBN S01-400:1977. The specifically Belgian categories became obsolete and an obstacle in the European free market of goods and services. It would have been possible to translate the requirements in EN ISO and 2 single values, but a more thorough change in the recommendations and the whole Belgian acoustical building standardisation became necessary. The recommendations in the old standard were based upon research dating back from the sixties and the early seventies. The main purpose of the old recommendations was to guarantee the maintenance of a certain sound insulation quality as was known before

2 the energy crisis of 1973 and not to adapt to new noise sources inside and outside buildings. Indeed, this energy crisis focussed all technical innovation in the building industry on the thermal insulation problem, introducing lighter elements (bricks became light highspeed building bricks, concrete became cellular concrete, etc. ) and other new building methods that were not always so positive for the sound insulation quality. To maintain the same sound insulation levels in the new standard is not possible: since the seventies, the noise sources inside and outside buildings have dramatically changed and increased and the old recommendations in the NBN S01-400:1977 are no longer up to the consumer expectations any more. The old standard contained both requirements for the building elements that would be used in a project and requirements to the finished building. Both requirements were expressed by the Belgian single rating system of the category. The standard suggested that in order to obtain a certain insulation category e.g. II a in situ (rating obtained out of normalized level difference D n measurements in situ), this was possible by careful construction and the use of building elements that had the same category II a (rating obtained out of sound reduction index measurements made in an acoustic laboratory). In order to be able to obtain this relation, the criteria to obtain the same category in situ were adjusted making some rough approximations of the complex relations between both parameters D n,w and R w (e.g. the flanking transmission, the volume/separating surface ratio, ). Of course, for low requirements, this system worked more or less (though numerous problems were encountered especially when reception rooms were much more voluminous than 31 m³). But the same system cannot be withheld in the future standard: having more severe requirements, the influence of the flanking transmission becomes ever more important. So a completely new standard was to be created and that involves answering many questions and taking up positions. 2 The new NBN S Points of departure for the new standard First of all, the commission wanted to comply completely with the units and measurement methods in the European standards EN ISO 140-series, to the single ratings of the EN ISO 717-series and to the EN series that allow estimating the acoustical performance of buildings from the performances of its composing building elements. It was decided that the requirements should concern the finished building only, but that the project should choose building elements and techniques to obey these requirements, eventually using calculation models as can be found in the EN series of standards or by using specific building prescriptions that, with a high degree of certainty, allow for these performances in the future building. The project should not take in account the measurement tolerances indicated in the standard. Indeed, to take in account uncertainties in the prediction models and limitations in precision of the measurement techniques, a tolerance is included in the standard: measurement results up to 2dB lower than the requirement (3 db for façade sound insulation) are still said to comply with the standard. Creating a new standard involves also limitations. A first major limitation is that the new standard will only be applicable to dwellings and not to offices, hospitals, hotels etc. as was the case in the old standard. They will eventually be treated by other standards. Secondly the level of requirements had to take in account economic building costs and acoustic aspects. The commission judged that the new standard should indicate what nowadays could be considered as a rather good sound insulation that can be achieved with reasonable technical means. The requirements that should guarantee this quality, accepting an increase in building costs define the improved acoustic comfort class. This class only applies when the client is expressly formulating wishes in this sense or if the promoter of the building makes publicity about a good sound insulation. But for a large group in society, having an own house or apartment is apparently more important than being perfectly acoustically comfortable. Taking this into account, the commission decided to create an economic class of acoustic sound insulation: the so-called normal acoustic comfort class. For this sound insulation class, the requirement should be as severe as possible without increasing the global building cost compared to the cost of constructions under the present-day old acoustical standard. The standard had to contain all acoustic aspects related to dwellings. That meant that also the aspects of technical installation noise and maximum reverberation times in entrance halls and corridors, now part of another standard, should be included in the same standard.

3 Last but not least, it was the wish of the commission to limit the standard in size and complexity. D nt,w -parameter [1]. This resulted in the final selection of this parameter D nt,w for the new standard. 2.2 Choice of the evaluating parameters For the airborne sound insulation, the possible options in EN ISO are the apparent sound reduction index R w or the corrected difference levels D n,w and D nt,w, all eventually corrected with the spectrum correction terms C or C tr. In the old standard, the normalized level difference D n,w was used. But correcting the level difference to what would occur if the reception room would have an equivalent absorption surface of 10 m², results in many discussions when the reception room is voluminous. Then the correction to absorption leads to a sometimes artificially dramatic decrease of the sound insulation which is not in accordance to the level difference experienced by the inhabitants. Using the apparent sound reduction index R w or the volume/plan independent D nt,w (D nt,w corrected by 10lg(V/3S) is in fact R w ) is an interesting possibility because of the elimination of the effect (being a ratio of powers) of the reverberation time of the reception room. As such, the desired maximum independence of the requirements from the geometric conditions would be optimized: so it is a good way to judge the construction. But it is not based on the sound level differences experienced by the inhabitants, i.e. the real estimation of the comfort sensation of the inhabitant. Moreover it has the inconvenience of the necessity to determine the separating surface S, not always so evident in complicated plans of eventually shifted volumes. The parameter D nt,w is based upon a level difference but has the inconvenience that it is also very dependent on the volume of the reception room and as such of the direction of the measurement. But the correction to the reverberation time of 0.5 s is much more interesting because this corresponds well to the average reverberation time of rooms in dwellings in most European dwellings. In bigger volumes, more furniture will be present and the reverberation time will remain around 0.5 s. The parameter is close to the real level difference experienced by the inhabitants of furnished dwellings. Some research about the relation between the sound insulation expressed by the different parameters and the experienced comfort by the inhabitants showed a very good correlation with the To take into account the volume dependency, the standard prescribes the measurement to be from the larger to the smaller room. If the requirement is then met, it will certainly be the case in the opposite direction. It has been decided not to use the spectrum correction terms yet in this new standard but to wait for a next revision of the standard. The reasons for this are multiple, e.g. such as the not so evident choice for the C-correction term. Nowadays, we can see a rapid evolution of new low frequency sources inside dwellings such as music with dominant low frequency beats, the introduction of home cinema systems etc But then using the typical traffic correction term C tr, as happened in Great Britain, was considered to be a step too far for the building industry to cope with yet. The new requirements as such are more than a challenge for the industry; the use of the correction terms is for a future revision. For the same reasons L nt,w was selected for the requirements concerning the impact sound insulation. Only for the façade sound insulation, the traffic spectrum corrected rating D 2m,nT,w +C tr was selected, being closest to the experienced comfort of the inhabitant and yet already familiar for the building industry because of the old French requirements (R route ) that was often used in Belgium as well in technical documentation and as a requirement in several projects. 2.3 Criteria for the airborne sound insulation Noise levels of maximum 80 db(a) at the neighbours are still considered to be normal. The criteria for the airborne sound insulation take these levels in account. Above these noise levels, the nuisance generated by the noise becomes subjected to the laws of abnormal neighbouring behaviour. Two levels of acoustical comfort, corresponding with different requirements, can be found in the standard: the normal acoustic comfort class and the improved acoustic comfort class. The normal acoustic comfort class is a compromise between the desire not to increase building costs and the wish for an as good as possible sound insulation.

4 For multi-storey dwellings, this requirement between dwellings or between dwellings and common circulation spaces within the building seems to be D nt,w 54 db. Research [2] shows that this leads to an estimated 70 % of inhabitants that are satisfied with this sound insulation. As an exception to the rule of not increasing building costs, the requirement is increased with 4 db up to 58 db when a living space (living room, kitchen, ) is next to a bedroom of another apartment in order to maintain 70% satisfied inhabitants. It is clear that an architect should avoid this kind of situation. For terrace houses when both adjacent houses are constructed at the same time, thanks to the system of special uncoupled cavity walls, the requirement can be up to D nt,w 58 db without increasing the building costs. The building industry is yet familiar with this type of construction. If the neighbouring house was constructed before the publication of the standard, due to complications with laws about common walls between terrace houses, the requirement remains D nt,w 54 db. To avoid substandard construction practices inside houses (even in alone standing houses), a minimum D nt,w of 35 db is required between two rooms of which at least one has a function that is sensitive to noise from the other room. The improved acoustic comfort class wants to offer real acoustic comfort so that more than 90 % of the inhabitants are satisfied with the sound insulation. In multi-storey dwellings, the requirement to obtain this is D nt,w 58 db between dwellings. The same requirement applies to the sound insulation between a dwelling and a common circulation room. Again this requirement is increased with 4 db up to 62 db when a living room is adjacent to a bedroom of another dwelling. So architects have all the reasons not to do so! In terrace houses, the criterion for improved acoustic comfort is 62 db if both adjacent houses are built after the publication date of the standard, if not, the requirement decreases to 58 db. Inside the same dwelling, the requirement is D nt,w 43 db between rooms if they can be disturbed by noise coming from one or both rooms. Special requirements apply to the situation where the neighbouring room is not a dwelling. The following rule applies both for normal and higher acoustic insulation: If the neighbouring room is not a dwelling (e.g. office, shop, restaurant, pub, ) then the required sound insulation is increased with L Aeq,T 80 db(a) if this last value is positive. For impulsive or short timed intense noise levels, the required sound insulation should be increased with L A5,T -80 db(a) if this last value is positive. Both L Aeq,T and L A5,T have to be measured during the time in which the noise levels can be expected to be most disturbing for the dwelling. 2.4 Criteria for the impact sound insulation The requirements for the impact sound insulation L nt,w are the maximum values that cannot be trespassed neither for the screed floor nor for all the possible floor finishing such as carpets, laminate floors or stone tiles that the supporting floor can carry. The two comfort classes apply here also. For the normal acoustic comfort class the requirement is L nt,w 58 db from any other space outside the room to a day room (= living room, kitchen) inside the dwelling and L nt,w 54 db from any non-night room outside to a night room (= bedroom, study room) inside the dwelling. For the improved acoustic comfort class the requirements become in both cases L nt,w 50 db. 2.5 Criteria for the façade sound insulation There are separate requirements for environments in which railway and/or air traffic noise is the dominant noise source and other requirements for the more general environmental noise. For the general case in which railway and/or air traffic noise is not dominant, there are different requirements for day rooms (living room, kitchen) and night rooms (bedroom, study). No differentiation is made for the comfort classes. The required façade sound insulation depends on the sound level L 1,2m measured 2m in front of the façade of the constructed room for the period 07h-23h and for the period 23h-07h. That means that already in the project phase, the estimation, measurement or calculation of this value has to be made and indicated in the project files that are submitted to the authorities. An informative annex to the standard helps the architects/engineers of the project to determine correctly this value. There is no verification by the authorities at that phase of the project of the correctness of the estimated, measured or calculated value. The values L 1,2m,07h-23h and L 1,2m,23h-07h represent an L Aeq,T of the outside noise during a continuous

5 measurement period of 30 during the time that the noise charge is the most important in the time interval of 7h till 23h and similarly in the time interval between 23h and 7h. The required façade sound insulation is expressed by D 2m,nT,w +C tr and should preferably be measured with the outside noise as sound source. Only when this is impossible, the loudspeaker method can be used. The measurements have to be executed with all the ventilation devices functioning so as to comply with the ventilation requirements. The façade sound insulation should always at least be superior to 30 db. For both day and night rooms, the supplementary requirement is D 2m,nT,w +C tr L 1,2m,07h-23h -35 db. Night rooms get one more requirement: D 2m,nT,w +C tr L 1,2m,23h-07h -30 db. The standard has an informative annex helping architects to determine the necessary façade sound insulation for smaller projects in function of the type of environment. The tables used there lead to a rather safe and thus in general over dimensioned façade sound insulation but allows cutting down on measurement expenses. For the normative annex concerning the façade insulations in environments dominated by air traffic and/or railway traffic, we refer to the presentation held in Inter.Noise Prague [3]. 2.6 Criteria for installation noise This part of the standard is still under a lot of discussion as well for the aspects of the measurement method as for the level of the requirements and is probably due to quite a lot of change in the months before the congress takes place. These criteria concern both the limitation of the noise in dwellings due to technical equipments inside the considered room and the limitation of the noise transmitted from technical installations outside the considered room. For the noise of equipments installed in the same room, the requirements are based upon a measurement method that with a high probability will not be the EN ISO 16032, deviating in this way from the points of departure for establishing this new standard. The motivation lies in the building industry being familiar with the old standard that uses a simpler, although less precise method. The industry wishes to maintain this simple system of evaluation even if it is less precise. The method is based upon the measurement of an L Aeq,T during a period T that is representative (to be motivated in the test report) for the working regime of the equipment. For noise measurements of equipment inside the same room, the measurement point should be taken at a height of 1.5 m above the floor level, if possible in a central area outside the direct field of the equipment. The measurement point has to be indicated on the test report. The requirements in the standard apply to the noise levels in the room with its interior furnishings as foreseen in the project. If measurements are made without the intended interior furnishings, an adaptation taking in account the different reverberation time has to be made and the calculation has to be précised in the test report. The measurement method has the advantage to be simple in furnished rooms but is less precise than the measurement method in EN ISO 16032: e.g. the A-weighting underestimates the low frequency noise in technical rooms with somewhat higher noise levels nor doesn t it take in account the modal behaviour in the room and the higher noise levels in corners and near walls The noise levels expressed by this L Aeq,T should be inferior to maximum levels indicated in the standard. For technical rooms (rooms for heating equipment, pumps, ventilation, air conditioning equipment and lifts), there is no distinction between the normal and improved acoustic comfort. The mentioned maximum levels must allow architects to determine the necessary sound insulation so that the acoustic comfort in day and night rooms is guaranteed for both normal and improved acoustic comfort. For the equipment in the day and night rooms themselves, maximum noise levels are imposed depending of the intended acoustical comfort class. Requirements are made to the noise levels due to toilets, mechanical ventilation and air extraction, refrigerators, dish washers, kitchen hoods, The exact level of the requirements is still under discussion. The noise due to technical installations outside the considered room and the noise due to water supplies and drainages eventually inside the room is also limited. For this, the concept excess noise is defined as the difference L Aeq,1s,max L A95,T. Measurements have to be done with the intended interior furnishings present. L Aeq,1s,max represents the maximum value measured while the noise source is functioning (during a complete working regime). It has to be determined by continuously measuring the L Aeq -value with integration times of 1 s. The L A95,T -value represents the background noise, i.e. a measurement while the equipment that is to be evaluated is not functioning. The excess noise has to be limited to 6 db(a) in day rooms and to 3 db(a) in night rooms except if the global level inside the rooms remains below 30 db(a) in day rooms and 26 db(a) in night rooms. For the moment no distinction is made between the

6 requirements for normal and improved acoustic comfort. 2.7 Criteria for common corridors, entrances and staircases To limit noise due to excessive reverberation in common circulation spaces in multi-family dwellings, a minimal total weighted equivalent absorption surface A w is imposed. A w should be superior to 0.3 times the horizontally projected accessible surface S H of corridors, stairs and landings. In the case of an atrium as an access space, the nominal reverberation time should be lower than the longest of both values: 1.5 s and lg (V/50) s. 3 CONCLUSION In order to comply with the European standards and customer expectations, a new standard with more strict requirements became a necessity. The requirements for normal acoustic comfort, a comfort level that is a compromise between acoustic comfort and economic considerations, are quite accessible for the building industry and should certainly not be considered as revolutionary. It becomes a lot tougher to obey the requirements for the improved acoustic comfort. The new standard, even in its draft, is already stimulating industry to abandon old habits and products and to introduce new building materials, procedures and innovative systems. The BBRI and the K.U.Leuven have several research projects trying to establish new building guidelines and helping building industry to create new products and building systems, taking in account the new requirements. We refer to another paper presented during Forum Acusticum [7],[8]. For the moment, there is still some discussion about the installation noise part in the standard. The standard will probably know its final draft around September This final draft will become the standard 1 year after the publication of the final draft. So the new standard is to be expected in the end of REFERENCES [1] Vermeir G., Mees P. Geluidisolatievoorschriften in de woningbouw. Rapport betreffende de onderzoeksopdracht vanwege het Ministerie van de Vlaamse Gemeenschap Afdeling Algemeen Milieu en Natuurbeleid. (KULeuven, 1999). [2] Rindel, J.H., Acoustic quality and sound insulation between dwellings. (Conference in Building Acoustic Acoustic Performance of Medium-Rise Timber Buildings, Dublin, 1998). [3] Ingelaere B., Vermeir G., Blasco M. Crispin C., Developing a new façade sound insulation requirement for dwellings: building solutions and their cost. (Inter.noise Prague 2004, 2004) [4] Ingelaere B., Mees P., Vermeir G., Eindverslag Berekening en kostenraming van geluidisolatie in de nieuw- en vernieuwbouw ten opzichte van buitenlawaai veroorzaakt door weg-, vlieg- en spoorverkeer. (KUleuven, 2003) [5] NBN S01-400:1977 Criteria van de akoestische isolatie Critères de l isolation acoustique (NBN, Brussel, 1977) [6] NBN S01-401:1987 Akoestiek Grenswaarden voor de geluidniveaus om het gebrek aan comfort in gebouwen te vermijden / Acoustique Valeurs limites des niveaux de bruit en vue d éviter l inconfort dans les bâtiments (NBN, Brussel, 1987) [7] C. Crispin, C. Mertens, M. Blasco, B. Ingelaere, M. Van Damme, D. Wuyts, The vibration reduction index Kij: laboratory measurements versus predictions EN (2000), (Proceedings of INTERNOISE 2004, Prague, Czech Republic.) [8] C. Crispin, M. Blasco, B. Ingelaere, M. Van Damme, D. Wuyts, The vibration transmission loss at junctions including a column, (Proceedings of FORUM ACUSTICUM 2005, Budapest) 4 Acknowledgements The authors wish to acknowledge the financial assistance of the Belgian Ministry of Economic Affairs.