COMMON ERRORS DURING CONSTRUCTION OF NEW BUILDINGS AND EFFECT OF WORKMANSHIP

Transcription

1 Harmonization of European Sound Insulation Descriptors and Classification Standards Florence, December 14 th 2010 COMMON ERRORS DURING CONSTRUCTION OF NEW BUILDINGS AND EFFECT OF WORKMANSHIP Patrizio Fausti (1), Bart Ingelaere (2), R Sean Smith (3) and Chris Steel (3) 1) Department of Engineering, University of Ferrara, Ferrara, Italy patrizio.fausti@unife.it 2) Department of Acoustics, Energy and Climate, BBRI, Brussels, Belgium bart.ingelaere@bbri.be 3) Institute for Sustainable Construction, Edinburgh Napier University, Edinburgh, UK se.smith@napier.ac.uk, c.steel@napier.ac.uk 1. Introduction Variability of results in acoustic measurements in buildings depends on different factors. Among others (uncertainty of the measurement method, nature of the materials, setting conditions, etc) the effects of bad practice and workmanship may lead to results very different from those expected. This could happen not only because of errors but also because the construction details may not have been clearly defined or could have been misunderstood. Therefore, during the design phase, it is important to define the best technological solutions that will ensure good acoustic design, but it is also important to make it easy to understand the details and the procedures. In addition, a failure to consider the impact of changes to non-acoustic issues can have a significant effect on sound insulation. Another important issue to consider is the difference between the way a partition is built in the laboratory and in the field, which may lead to different results from those expected using the laboratory data in the calculation models. A typical example is the cavity wall with horizontal hollow bricks. Therefore, it is always important to check that the technological solution chosen in the design phase is what will effectively be built. While it is possible that builders will construct in a way that may not reflect the detailed drawings issued to site, it is also true, as said above, that this often occurs because the detailing issued is insufficient or because detailing has not been issued to those working on site. This is most common where alterations occur during the building process or when detailing of services has not been cross-referenced with other detailing issues such as fire regulations and, of course, acoustics. EAA-COST_2010_07

2 One of the aims of COST Action TU0901 [1] is to produce a compendium of good and bad practices and effects of workmanship, and of ways to avoid accidentally reducing sound insulation performance during the new built construction sequence. The collection of typical EU construction designs, practices and workmanship could also help non acousticians (e.g. architectural and structural designers, house builders, contractors, product manufacturers) to avoid mistakes and provide more robust construction designs. In this paper we report some examples of good and bad practices and effects of workmanship, with the help of drawings and photos. Furthermore, a draft list of typical errors has been prepared as a starting point for the collection of information among the members of the COST Action. The idea is to ask members to make comments on typical construction errors related to technical solutions and acoustic requirements, particularly for on-site construction but also for industrialised elements (off-site). 2. Typical examples of good and bad practice Although the sound insulation performance for newly built housing in many countries is now a mandatory requirement, the attention to this aspect during the design phase and during construction is not always adequately taken into consideration. In the next paragraphs some examples of typical good and bad practice are reported, in some cases also with the indication of the possible reduction of performance. 2.1 Example 1 This example is reported not only because it is typical of good and bad practice, but also because the quality of the isometric drawings available [2] make it easy, also for non acousticians, to understand the problem. Figure 1a Bad practice Figure 1b Correct practice The two illustrations show a typical junction between partition and ceiling. In figure 1a there is no barrier to the passage of airborne noise in the hollow flooring blocks. The proposed solution (fig. 1b) shows the insertion of a riddle to interrupt the continuity of the hollow flooring blocks over the separating walls between dwellings. Usually, when the floor slab is built on site it is easy to realise the correct solution. When the floor slab is precast, and the separating walls do not correspond with the structural beam, it is necessary to have a good coordination with the designer and the builder to have all the correct special pieces for the building under construction. EAA-COST_2010_07 pag. 2

3 Obviously, the problem does not exist when the partition wall is positioned in correspondence with a structural beam. The figure 2 below shows, for a similar problem, a comparison between the airborne sound insulation of two partition walls of the same building, identical in terms of type of layers, with similar dimensions, built with the same workmanship. Neither wall had the structural beam on top (the floor slab between the two pairs of rooms was continuous over the partition wall). The only difference was the direction of the hollow flooring clay blocks of the floor slab: parallel and perpendicular to the partition walls. In the second case the poorer result obtained is due to the noise transmission through the holes of the hollow flooring clay blocks, continuous between the two test rooms. The parallel positioning improves results, although a more efficient solution is with the one illustrated in figure 1b. [db] [Hz] Hollow clay blocks parallel to the party wall (R'w=50 db) Hollow clay blocks perpendicular to the party wall (R'w=48 db) Figure 2 Frequency comparison between the two configurations Example 2 In some countries the external wall is not broken at the junction with the separating wall. This continuous inner leaf can reduce performance depending on the type of hollow bricks, the cavity thickness and absorbing material. In the example shown in the figure 3 [2], with horizontal hollow bricks, the performance can be reduced typically by 8 to 10 db with respect to the expected results. EAA-COST_2010_07 pag. 3

4 Figure 3a Bad practice Figure 3b Correct practice 3. Examples of effect of workmanship In the next paragraphs some examples related to the effect of workmanship are reported. 3.1 Example 1 Impact sound insulation One of the most common errors in the floating floor details can be found in the French window doorstep area. The present example shows the influence of this workmanship error on the impact sound insulation performance of a slab. During the first measurement, a high amount of noise coming from the French window area was heard in the receiving room. Thus the first row of ceramic tiles and a little part of the floating mortar near the French window doorstep were removed (figure 4): the main problem of noise transmission was due to the lack of the perimeter resilient band under the French window that caused a rigid contact between the tiles and part of the floating mortar with the marble doorstep of the French window itself. Once the builders solved the problem, placing the perimeter resilient band up to the marble doorstep, a second measurement was carried out, by the same operator, with the same equipment and using the same positions of the impact generator and microphone. The comparison is shown in figure 5. The impact sound insulation index L n,w improved by approximately 10 db (from 70.2 db to 60.6 db). The decimal places for the indexes were used only for comparison. In terms of frequency comparison the main differences were at high frequencies, with improvements of up to 12 db. The floating floor provides good performance only if properly installed; it must be completely discon- EAA-COST_2010_07 pag. 4

5 nected from the perimeter walls, so it is free to vibrate and thus damp the mid-high frequencies. Even a small perimeter section not properly realised (in this example the rigid contact affected a length of 140 cm) could significantly reduce the acoustic performance of the whole floating floor. Figure 4 View of the French window area with the first row of tiles and floating mortar removed (on the left) and after the repair (on the right) [db] [Hz] Config. before repair L'n,w = 70.2 db Config. after repair L'n,w = 60.6 db Figure 5 Frequency comparison between the floating floor before and after the repair(decimal places for the indexes used only for comparison) Example 2 Façade sound insulation The acoustic performance of a façade strongly depends on the type and installation of the windows: this example reports the influence of the window fine setting. The main acoustical defects detected on the window before the correct setting were the presence of chinks between the shutters (figure 6) and the fixed frame and an opening in the central locking mechanism. EAA-COST_2010_07 pag. 5

6 After a careful setting these problems were solved, and the performance of the façade improved of approximately 4 db (D 2m,nT,W from 35.6 db to 39.0 db, figure 7). The greater improvement (up to 12 db) was observed at medium frequencies. The complete study included approximately 20 façades, measured before and after the fine settings obtaining an average difference of approximately 7 db. Figure 6 Details of the main windows defect (left picture) and detail of window fine setting (right picture) [db] Window before fine setting D2m,nT,w = 35 db Window after fine setting D2m,nT,w = 39 db [Hz] Figure 7 Frequency comparison of a façade before and after the window fine setting 4. Draft list of typical errors and next stage of WG3 of the TU0901 In the following tables a list of typical bad practice or workmanship errors, subdivided by acoustic requirements, are reported. These lists are an initial draft that will be used to collect information under the activity of WG3 of COST Action TU0901. Each member will be asked to select or make comments on typical construction errors for a number of technical solutions, changing the description or adding new typical construction errors for their countries and including drawings or photographs. In case of available data, the information related to the possible reduction of the performance could also be included. EAA-COST_2010_07 pag. 6

7 Table 1 Typical examples of construction errors for airborne sound insulation between dwellings Description of the errors Lack of riddle or structural beam on the floor slabs above the separating walls (design error) Inner leaf of the external walls not interrupted in correspondence with the junction with the partition walls (design error) Attic rooms: roof (ventilated or not) not interrupted in correspondence with the junction with the partition walls (design error) Lack of mortar in vertical joints, leaving partially filled joints between blockwork for walls that require mortar also in vertical joints Service zones made symmetrically (not staggered) on both sides of the wall (electrical box, ventilation pipes, etc) Sound absorbing material not continuous in the cavity of cavity walls Tears in the sound absorbing material inside the cavity of cavity walls due to service zones or pipe chases: the subsequent filling with mortar may create a bridge between the two leaves of the cavity wall Pipe chases for building services not properly filled with mortar Lack of the plaster (3 rd plaster) on one side of the cavity in the cavity wall when prescribed in the chosen technical solution Resilient layer, used as isolation mechanisms at wall-floor junctions, under the single heavy walls (risk of crushing of resilient layer)... Ordering in term of typical case Possible reduction of the performance (db) Table 2 Typical examples of construction errors for façade sound insulation Description of the errors Fine setting of doors and windows not made or made incorrectly In case of use of rolling shutter: opening between the rolling shutter and the external wall too wide and/or lack of the brush between the rolling shutter and the external wall In case of use of rolling shutter: rolling shutter box sides too light and/or absence of sound-absorbing material inside the box In case of use of rolling shutter: rolling shutter box incorrectly connected to the wall (presence of gaps between the rolling shutter box and the wall) Lack of sealing in some areas between the frame and the counter-frame, hidden by windows profiles Lack of mortar in some areas between the counter-frame and the walls, hidden by windows profiles Counter-frame empty inside (lack of foam or sound-absorbing material) Contact areas between glass and window shutter not properly sealed... Ordering in term of typical case Possible reduction of the performance (db) EAA-COST_2010_07 pag. 7

8 Table 3 Typical examples of construction errors for impact sound insulation Description of the errors Skirting board in direct contact with ceramic floor Ceramic tiles against the walls Perimeter resilient band not properly adherent to the walls and the consequent presence of mortar between the band and the walls Perimeter resilient band too short or cut before the placing of the ceramic floors Perimeter resilient band not continuous, especially in corners Rigid contact between the ceramic tiles or the floating mortar with the French window marble doorstep Lack of structural separation between the floating mortar in correspondence of the door of the rooms Floor surface below the resilient material not perfectly flat or not properly cleaned (presence of brick or iron pieces) Tears in the resilient material of the floating floor Presence of pipes not fully embedded into the lightened mortar (under the resilient material)... Ordering in term of typical case Possible reduction of the performance (db) Table 4 Typical examples of construction errors for the service equipments Description of the errors Waste water pipes embedded in the mortar: lack of acoustic insulation material around the pipes next to the floor, walls or other pipes Supply pipes without acoustic insulation material (acoustic bridge) Tears of the acoustic insulation material surrounding the pipes, especially in areas of other pipes engagements Connection between waste water pipes and walls made with rigid fixing clamps Waste water pipes curvature areas without acoustic insulation material Lack of sound-absorbing material inside the cavities... Ordering in term of typical case Possible reduction of the performance (db) 5. Acknowledgements The authors wish to acknowledge the support from the COST Action TU0901 WG3 members and member countries involved. 6. References [1] COST Action TU0901. Integrating and harmonization of sound insulation aspects in sustainable urban housing constructions, [2] Isosystem technical specifications, [3] S. Smith, C. Steel, BSV Building Performance 1: Acoustics and Sound Insulation. EAA-COST_2010_07 pag. 8