Laboratory Data Examining Impact and Airborne Sound Attenuation in Cross- Laminated Timber Panel Construction - Part 2 Matthew GOLDEN 1 ; Wilson BYRICK 2 1,2 Pliteq Inc., Canada ABSTRACT At INTER-NOISE 15, Pliteq presented part one of our investigation into the laboratory acoustical performance of cross-laminated timbers (CLT). In that study, we tested combinations of a resiliently floating wood raft on the CLT, various floor finishes and a resilient ceiling suspended from the CLT. For this study, we used the same 175mm thick CLT as the main structure of our assemblies and conducted several more tests (STC-ASTM E9 and IIC ASTM-E492). We tested assemblies with wood and tile floor finishes, resiliently supported normal weight and gypsum concrete, different types of resilient underlayments and a resilient ceiling with a lower profile than what was tested previously. As a result of the test program, we have created an informal CLT design guide to achieve IBC section 17 code compliant CLT assemblies. Keywords: Impact, Transmission, CLT I-INCE Classification of Subjects Number(s): 51.3, 51.5 1. INTRODUCTION Cross laminated timber panels (CLT) are a relatively new method of constructing multi-family structures in North America. The panels are composed of numerous layers of wood, each perpendicular to the adjacent layers. Wood is a renewable resource and producing the components of CLT panels consumes roughly half of the energy of concrete. Tall wood buildings have been constructed all over the world. A fourteen-story building in Norway, a ten-story in Australia and an eight-story CLT apartment building in the UK are among the successful projects. A six-story wood building plus mezzanine and penthouse was recently completed in British Columbia, Canada, becoming the tallest wood building in North America. (1,2,3) While CLT has proven successful in other parts of the world, it has not yet been widely adopted in North America. In an effort to better understand how CLT floor ceiling structures perform in impact and airborne sound attenuation testing, we have conducted numerous testing regimes using various single component additive methods. A 175mm thick floor assembly constructed in the laboratory has been the subject of numerous tests, STC (4) and IIC (5), with different floor toppings and with various ceiling assemblies. All tests were performed at Intertek/ATI in York, PA. In early 15, plywood was installed over resilient underlayment of various thicknesses and this data was presented at InterNoise 15.(6) The transmission loss (TL) and normalized impact sound pressure level (NISPL) data was collected with various loading of the floating plywood subfloor. Data is also presented here using a concrete topping. A resiliently mounted ceiling with insulation was tested for InterNoise 15, but this paper provides data on a lower profile resiliently mounted ceiling. The effect of varying the cavity depth from 1 mm to 65 mm can be observed. As a result of these test regimes we hope to aid in the design of International Building Code section 17 code compliant CLT assemblies. 2. Assemblies Tested Several different kinds of assemblies were tested to meet various needs. Designers have requested CLT assemblies that have certain floor finishes, including polished concrete, LVT, wood and tile. They have also requested assemblies that leave the ceiling exposed or are covered with drywall. The following assemblies were selected to meet these design requirements while attempting to meet IBC code requirements. The CLT used was a 5 layer CLT that was 175 mm (6.9 in) thick. It has a surface density of 89.5 kg/m 2 (18.3 lbs/ft 2 ). 1 mgolden@pliteq.com 2 wbyrick@pliteq.com 3782
2.1 Previously Reported Assemblies At INTER-NOISE 15 seven different CLT floor/ceiling assemblies were presented. Several of the assemblies used a wood raft made from two layers of 16mm (5/8 ) Advantech Wood Subfloor. Several other used a resilient ceiling as shown in Table 1. Table 1 - GenieClip LB Resilient Ceiling GenieClip LB [Airspace ~ 1mm (6 )] R13 Fiberglass 38mm (1-½ ) Cold Rolled Channel 16 mm (5/8 ) Drywall Furring Channel 16mm (5/8 ) Type X Gypsum Board The previously reported assemblies are shown in Table 2. Further in the paper, several of these assemblies will be compared to new assemblies. Table 2 - CLT Floor/Ceiling Assemblies Previously Reported Test Report # Above CLT Below CLT STC IIC e5958.1 - - 39 25 e5958.3 e5958.4 e5958.5 e5958.6 e5958.7 e5958.8 Wood Raft GenieMat FF Wood Raft GenieMat FF25 Wood Raft GenieMat FF25 - Vinyl Plank GenieMat RST Vinyl Plank - 45 42-48 44 GenieClip LB Resilient Ceiling 61 55 GenieClip LB Resilient Ceiling 58 45 GenieClip LB Resilient Ceiling 58 58 GenieClip LB Resilient Ceiling 57 54 2.2 New Tested Assemblies This paper presents thirteen additional CLT floor/ceiling assemblies. Three of these assemblies use a GenieClip RST resilient ceiling, Table 3. A summary of these assemblies is shown in Table 4. Table 3 - GenieClip RST Resilient Ceiling GenieClip RST [Airspace ~ 38mm (1.5 )] R8 Fiberglass 16 mm (5/8 ) Drywall Furring Channel 16mm (5/8 ) Type X Gypsum Board 3783
Table 4 - CLT Floor/Ceiling Assemblies with GenieClip RST Isolated Ceilings Test Report # Above CLT Below CLT STC IIC F2761.7 175 mm CLT GenieClip RST Resilient Ceiling 53 45 F2761.8 ½ Engineered Wood GenieMat RST2 GenieClip RST Resilient Ceiling 54 F2761.9 12 x12 porcelain tile GenieMat RST12 GenieClip RST Resilient Ceiling 55 51 Five of the newly reported floor/ceiling assemblies used a mm (4 ) precast concrete slab on top of the CLT as shown in Table 5. Table 5 - CLT Floor/Ceiling Assemblies with mm (4 ) precast concrete slab Test Report # Above CLT Below CLT STC IIC F5.7 mm (4 ) Concrete GenieMat FF6 F5.8 mm (4 ) Concrete F5.9 ½ Engineered Wood GenieMat RST2 mm (4 ) Concrete F5. mm (4 ) Concrete GenieMat FF F5.11 ½ Engineered Wood GenieMat RST2 mm (4 ) Concrete GenieMat FF - 55 45-57 - 56 55-59 54-58 59 Finally, the last five of the newly reported floor/ceiling assemblies a mm (2 ) poured in place gypsum concrete slab on top of the CLT as shown in Table 6. Final reports are not yet. Table 6 - CLT Floor/Ceiling Assemblies with mm (2 ) Gypsum Concrete Test Report # Above CLT Below CLT STC IIC Draft Draft Draft Draft Draft mm (2 ) gypsum concrete ½ Engineered Wood GenieMat RST2 mm (2 ) gypsum concrete LVT GenieMat RST2 mm (2 ) gypsum concrete mm (2 ) gypsum concrete ½ Engineered Wood GenieMat RST2 mm (2 ) gypsum concrete - 52 44-53 49-53 51 Pliteq GenieClip RST 6 52 Pliteq GenieClip RST 59 53 3784
3. RESULTS AND DISCUSSION With all of the assemblies tested above several interesting comparisons can be made. 3.1 Isolated Ceiling with Reduced Air Space Two different floor finishes were tested on top of the CLT with a GenieClip RST ceiling below, shown in Figure 1. The first assembly, Test Report F2761.8, had a 12.5mm (.5 inch) engineered wood floor on top of GenieMat RST2. The second, Test Report F2761.9, had a ceramic tile on GenieMat RST12. There are only minor differences in TL due to adding either floor finish. Both floor finishes increase the TL below 2 Hz and above Hz compared to the CLT without any finished flooring, Test Report F2761.7. These small differences increase the STC 2 to 3 points from the assembly with no floor finish. Both floor finishes significantly help the NISPL and the IIC. There is more improvement in NISPL at higher rather than lower frequencies but still some improvement at low frequencies with both floor finishes. Figure 1 - TL and NISPL of Different Floor Finishes on a CLT with a GenieClip RST Isolated Ceiling 3.2 Compare Isolated Ceiling Two different isolated ceilings were tested shown in Table 1 and Table 3. One using a GenieClip LB isolated ceiling, Test Report e5958.8, and the other using a GenieClip RST isolated ceiling, Test Report F2761.7. The first isolated ceiling had a 1mm (6 inch) cavity that was filled with R13 fiberglass insulation. The second isolated ceiling had a 37 mm (1.5 inch) cavity that was filled with compressed R8 fiberglass insulation When comparing the two isolated ceilings, there were two trends in the data that were noticed, shown in 3785
Figure 2. First, the difference in the transmission loss between the two isolated ceilings is reduced as the frequency increases above Hz. From experience with many other tests at Intertek/ATI, the authors know that these transmission loss values are at or approaching the flanking limit of the lab. If the lab had a higher flanking limit it would be expected that the difference in TL between the two ceilings would remain more or less constant as the frequency increased above Hz. The second feature was the dip in the transmission loss curve and the associated peak in the normalized impact sound pressure level curve. These dips and peaks were thought to be due to a resonance. Unger and Ver have previously published derivations of air stiffness. (7,8) With a few further substitutions the natural frequency due to air stiffness may be recast in a form more useful for this application, Equation 1. f " = 1 2π gp ) γ dw - (1) Where: g = acceleration due to gravity ρ = density of air γ = ratio of specific heats d = air gap = unit area mass of partition w f With the reported mass values for each assembly and published values for air, the air stiffness resonance for the assembly with the GenieClip LB is 37.2 Hz while the assembly with the GenieClip RST is 74.3 Hz. Since these resonance frequencies are much higher than the known elements of the GenieClip LB or GenieClip RST, the resonance does not change much when the isolator stiffness is added to the air stiffness. For the assembly with the GenieClip RST, the dip in TL and the spike in NISPL occur in the 8Hz one-third octave band. This band ranges from 7.2 Hz to 88.4 Hz which spans the resonance frequency calculated above. For the assembly with the GenieClip LB, the dip in TL and the spike in NISPL occur at or below the Hz one-third octave band. The resonance of 37.2 Hz, calculated above, occurs in the the Hz one-third octave band. This band ranges from 35.1 Hz to 44.2 Hz. 3786
Figure 2 - TL and NISPL of Isolated Ceilings Suspended from a CLT verse the Bare CLT 3.3 Isolated Concrete on CLT Three thicknesses of GenieMat FF were used to isolate a mm (4 inch) concrete slab from the CLT below, GenieMat FF6,, and GenieMat FF, Test Reports F5.7, F5.8, and F5. respectively. The performance of all three assemblies compared to a bare CLT are shown in Figure 3. The addition of a resiliently supported concrete slab had a very significant increase in TL compared to the bare CLT, Test Report e5958.1. There was also a marked improvement in TL as the thickness of the GenieMat FF was increased. A similar change was measured in NISPL with the addition of a resiliently supported concrete. The increase in thickness of the GenieMat FF had a much larger impact in NISPL than in TL. Both the TL and NISPL maintained roughly the same shape across all tested assemblies in this group. 3787
Figure 3 - TL and NISPL of a Concrete Slab Isolated from a CLT verse the Bare CLT 3.4 Isolated Concrete on CLT with Floor Finish The addition of a 25mm (1/2 inch) engineered wood floor on GenieMat RST2 on an isolated concrete slab with, Test Report F5.9, and GenieMat FF, Test Report F5.11, changed the TL slightly for both when comparted to the assemblies without the finish floor, Test Report F5.8 and F5. respectively, as shown in Error! Reference source not found.. This small change added up to a 1 STC point improvement for both assemblies tested. Much larger difference in the NISPL were measured. The addtion of the floor finish on both assemblies had a much larger improvement in the NISPL above 8 Hz than below. These changes improved the IIC of both assemblies by 5 points 3.5 Comparison of Isolated Masses on CLT Three different masses were isolated from CLT with. These were a wood raft, Test Report e5958.4, a mm (4 ) concrete slab, Test Report F5.8, and mm (2 ) pour of gypsum concrete. As shown in Figure 5, The assembly with mm (4 ) concrete slab outperformed the other two assemblies in both TL and NISPL. However, at frequencies above 2Hz the assembly with the wood raft performed best. This could be due to the impact surface or the natural damping of wood compared to concrete. It should be noted that none of these assemblies had floor covering. As shown in this paper, a resilient floor covering covering can significantly improve high frequency NISPL. 3788
Figure 4 - The Change in TL and NISPL of a Resiliently Supported Concrete Slab on CLT with the Addition of a Floor Covering 8 8 7 7 Transmission Loss (db re micropa ) 6 Normalized Impact Sound Pressure Level (db re micropa ) 6 4" Concrete, GenieMat FF25, CLT - STC 57 2x Advantech, GenieMat FF25, 175mm CLT - IIC 45 2" LevelRock, GenieMat FF25, 175mm CLT - STC 52 2" LevelRock, GenieMat FF25, 175mm CLT - IIC 44 2x Advantech, GenieMat FF25, 175mm CLT - STC 48 4" Concrete, GenieMat FF25, CLT - IIC 63 125 2 63 125 2 Figure 5 - TL and NISPL of Three Different Isolated Masses on on a CLT 3789
3.6 Floor Finish on Isolated Gypsum Concrete on CLT As with the other floor covering on other assemblies the addition of floor coverings on the assembly with gypsum concrete on, had very little impact on the TL as shown in Figure 6. Only minor changes occurred above Hz. These changes only increased the STC by 1 point. However, the addition of the floor covering did significantly affect the NISPL. Depending on the floor finish, the NISPL decreased by over db at some frequencies and the IIC increased 5 to 7 points. A key result is the assembly with the LVT. This assembly has a finished floor, exposed ceiling, does not use a cementitious topping and meets the IBC code minimum requirements for STC and IIC. 8 8 7 7 Transmission Loss (db re micropa ) 6 Normalized Impact Sound Pressure Level (db re micropa ) 6 LVT, GenieMat RST5, 2" LevelRock, GenieMat FF25, 175mm CLT - STC 53 2" LevelRock, GenieMat FF25, 175mm CLT - IIC 44 Engineered Wood, GenieMat RST2, 2" LevelRock, GenieMat FF25, 175mm CLT - STC 53 Engineered Wood, GenieMat RST2, 2" LevelRock, GenieMat FF25, 175mm CLT - IIC 49 2" LevelRock, GenieMat FF25, 175mm CLT - STC 52 LVT, GenieMat RST5, 2" LevelRock, GenieMat FF25, 175mm CLT - IIC 51 63 125 2 63 125 2 Figure 6 - TL and NISPL of Different Floor Finishes on a CLT gypsum concrete and 3.7 Isolated Ceilings on CLT with Gypsum Concrete Earlier it was shown that an isolated ceiling can significantly improve a bare CLT, Section 3.2. Figure 7 shows that even with an isolated gypsum concrete pour on a CLT, an isolated ceiling can still significantly improve the TL and NISPL, at most frequencies. The TL and NISPL had a dip and peak, respectively, around the frequency associated with the air stiffness resonance calculated earlier. 4. CONCLUSIONS While CLTs are a new and exciting innovation in the construction world, care must be taken to insure that IBC code compliant assemblies are designed. None of the assemblies tested that did not use an isolated ceiling or cementitious toppings meet code. Assemblies that use isolated ceilings or a mm (4 ) concrete slab can meet or far exceed code. Code minimum assemblies using a shallow resiliently isolated ceiling and an mm (2 ) gypsum concrete pour can also be achieved. Finally, to increase performance of the isolated ceiling, the air space must be increased. This decreases the resonance due to air stiffness. 379
8 8 7 7 Transmission Loss (db re micropa ) 6 Normalized Impact Sound Pressure Level (db re micropa ) 6 Engineered Wood, GenieMat RST2, 2" LevelRock, GenieMat FF25, 175mm CLT, GenieClip RST, R8, 5/8" Type C - STC 59 Engineered Wood, GenieMat RST2, 2" LevelRock, GenieMat FF25, 175mm CLT, GenieClip RST, R8, 5/8" Type C - IIC 53 Engineered Wood, GenieMat RST2, 2" LevelRock, GenieMat FF25, 175mm CLT - STC 53 63 125 2 Engineered Wood, GenieMat RST2, 2" LevelRock, GenieMat FF25, 175mm CLT - IIC 49 63 125 2 Figure 7 - TL and NISPL of Floor Finishes on a CLT with an Isolated Gypsum Concrete and Ceiling ACKNOWLEDGEMENTS Thank you to Nortic Structures for the CLT and Huber engineered wood for the Advantech wood raft used in this research. We would personally like to thank Will Bonnycastle and the rest of the Pliteq engineering team. REFERENCES 1. Cross-Laminated Timber: Introduction for Specifiers, [TRADA Wood Information Sheet, WIS 2/3-61], (TRADA Technology, 11) 2. Robert Hairstans, Off-site and Modern Methods of Timber Construction: a Sustainable Approach, (TRADA Technology, UK, ) 3. Worked Example - 12-storey Building of Cross-laminated Timber (Eurocode 5), (TRADA Technology, 9) 4. ASTM E9-9, Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements, ASTM International, West Conshohocken, PA, 9, www.astm.org 5. ASTM E492-9(16)e1, Standard Test Method for Laboratory Measurement of Impact Sound Transmission Through Floor-Ceiling Assemblies Using the Tapping Machine, ASTM International, West Conshohocken, PA, 16, www.astm.org 6. Byrick, W, Laboratory data examining impact and airborne sound attenuation in cross-laminated timber panel construction. Proc INTER-NOISE 15; 9-12 August 15; San Francisco, CA, USA 15. p. -28(9) 7. Ver, I L, Acoustical and Vibration Performance of Floating Floors. Bolt, Beranek and Newman, BBN Project 1352, Report No. 18, 29 July 2969 8. Ungar, E. Design of Floated Floors to Avoid Stiffness Effects of Entrapped Air. Noise Control Engineering, July-August 1975, Vol 5. No 1, pp12-16 3791