A bare 5-ply cross-laminated timber floor rates just IIC 25, half the IIC 50 the International Building Code requires between apartments (WoodWorks, Acoustics and Mass Timber 2021). Airborne performance is closer but still short: a 175 mm CLT panel measured STC 41 and STC 42 in two NRC Canada lab tests three years apart (NRC Client Report A1-006070.10, 2015). Meanwhile the building type is spreading quickly, with 2,833 U.S. mass timber projects built or in progress as of June 2026 (WoodWorks Mapping Mass Timber 2026). Most of the acoustic work in these buildings happens at the junctions, where flanking transmission decides whether a good lab assembly becomes a good apartment, a problem shared with the low-frequency structure-borne paths covered in our subwoofer and HVAC noise transmission statistics. We aggregated data from WoodWorks, the National Research Council Canada, SINTEF, Luleå University of Technology, the University of Bologna, Japan’s National Institute for Land and Infrastructure Management, and a dozen more journal and conference sources.
TL;DR
- 2,833 U.S. multifamily, commercial or institutional mass timber projects were built or in progress as of June 2026 (WoodWorks Mapping Mass Timber 2026).
- A bare 5-ply CLT floor rates STC 41 and IIC 25, against code minimums of STC 50 and IIC 50 (WoodWorks, Acoustics and Mass Timber 2021).
- A bare 160 mm CLT slab tested at Ln,w 84 dB, and engineered overstructures cut that by up to 28 dB (Luison et al., Forum Acusticum 2026).
- Asymmetric fixings at CLT junctions can add up to 10 dB of lateral transmission versus theoretical values (Di Bella and Mitrovic, Sustainability 2020).
- Decoupling a CLT floor slab with a resilient interlayer raised the low-frequency vibration reduction index by 11.3 dB (Barbaresi et al., Forum Acusticum 2026).
- Wall-to-wall junction attenuation drops about 1.0 dB per storey at X-junctions and 1.6 dB at T-junctions lower in CLT buildings (Nilsson et al., Buildings 2023).
- Field R’w of double CLT walls landed within -2 to +1 dB of comparable lab results (Homb and Conta, SINTEF, Forum Acusticum 2023).
- The standard impact rating explained only 18% of residents’ footstep annoyance across 23 Swedish buildings, versus 77% when measured from 25 Hz (Ljunggren et al., Applied Acoustics 2017).
- 25.3% of Japanese residents in wooden apartment buildings were very dissatisfied with sound insulation, against 13.0% in reinforced concrete (NILIM Annual Report 2023, MLIT 2018 survey data).
1. The Mass Timber Pipeline: How Many Buildings Need Acoustic Answers
The project count matters for acoustics because almost every multifamily mass timber building needs a tested floor-ceiling and wall detail. WoodWorks counted 2,833 U.S. multifamily, commercial or institutional mass timber projects built or in progress as of June 2026, a figure it updates quarterly on its Mapping Mass Timber page. WoodWorks notes that “details on in-design projects are not publicly available,” so that count leaves out the design pipeline.
Growth is steady rather than explosive. A Mercer Mass Timber analysis reported by IWF Atlanta describes a 20 percent annual growth rate in place since 2015, and the same article cites the 2024 International Mass Timber Report for annual building counts. More buildings means more repeat details, and repeat details are where tested acoustic assemblies pay off.
| Metric | Value | Source |
|---|---|---|
| U.S. mass timber projects built or in progress (June 2026) | 2,833 | WoodWorks Mapping Mass Timber 2026 |
| U.S. mass timber projects built, under construction or in design (2026) | 2,746 | WoodWorks via Woodworking Network, June 24, 2026 |
| U.S. projects built or in progress at end of 2025 | Over 2,500 | Mercer Mass Timber analysis via IWF Atlanta |
| Annual growth rate in project count since 2015 | 20 percent | Mercer Mass Timber analysis via IWF Atlanta |
| Mass timber buildings constructed per year, Canada and U.S. | 151 (2019) to 279 (2023) | 2024 International Mass Timber Report via IWF Atlanta |
| Mass timber production, Canada and U.S. | 158,000 m3 (2019) to 393,000 m3 (2023) | 2024 International Mass Timber Report via IWF Atlanta |
Context note: the 2,746 figure reported by Woodworking Network is described as including design-phase projects, yet it is lower than WoodWorks’ own 2,833 built-or-in-progress count. Neither source explains the gap; see the Data watch note.
2. Bare Panels: What CLT Delivers Before Any Treatment
Bare CLT is heavy for wood but light for a floor slab. WoodWorks compares a roughly 7 inch CLT panel at about 18 psf and STC 41 with a 6 inch concrete slab at about 80 psf and STC 53, which explains the whole acoustic problem in one line: mass drives sound insulation, and the CLT panel carries about 23% of the slab’s weight (18 psf divided by 80 psf). Its Acoustics and Mass Timber solution paper states that bare mass timber panels rarely provide adequate noise control on their own.
Impact noise is the larger gap. A bare 5-ply floor rates IIC 25 and a 7-ply floor IIC 30, while code asks for IIC 50. European lab data shows the same picture in ISO terms: a bare 160 mm CLT slab measured Ln,w 84 dB and Rw 35 dB in a 2026 University of Bologna and Isolgomma campaign (Luison et al., Forum Acusticum 2026).
| Metric | Value | Source |
|---|---|---|
| Bare 5-ply CLT floor, 6.875 in. | STC 41, IIC 25 | WoodWorks, Acoustics and Mass Timber 2021 |
| Bare 7-ply CLT floor | STC 44, IIC 30 | WoodWorks, Acoustics and Mass Timber 2021 |
| Bare 175 mm 5-ply CLT (91 kg/m2), lab tests in 2012 and 2015 | Floor STC 41 and 42, wall STC 39 and 37 | NRC Client Report A1-006070.10, 2015 |
| Bare 131 mm CLT floor | STC 39 | NRC Client Report A1-006070.10, 2015 |
| Bare 160 mm CLT floor (ISO lab) | Ln,w 84 dB, Rw 35 dB | Luison et al., Forum Acusticum 2026 |
| Bare CLT floors, normalized impact level by thickness | Ln,w 81-87 dB | Di Bella and Mitrovic, Sustainability 2020 |
| Bare CLT wall vs standardized lightweight wall of similar mass (about 70 kg/m2) | Rw 37 dB vs 33 dB | Di Bella and Mitrovic, Sustainability 2020 |
Outlier note: a 120 mm CLT wall tested in Taiwan reached Rw 45 and STC 45 without added layers (Lin et al., Materials 2021), well above the Rw 32-33 dB that SINTEF compiled for 78-100 mm single CLT walls tested in Canadian, Austrian and Norwegian labs (Homb and Conta, Forum Acusticum 2023). NRC’s repeat testing also warns of a variation of about plus or minus 2 STC points when bare CLT assemblies are rebuilt. Most recent available data for the NRC series: NRC Canada, 2015.
3. Code Targets and What Occupants Actually Hear
Code minimums describe a legal floor, not comfort. The ICC benchmark for multifamily housing is STC 50 and IIC 50 in the lab, relaxed to 45 for field tests, as summarized in the University of Oregon’s 2019 TallWood acoustic lab testing report on CLT and mass plywood panels. Canada moved further toward field reality in 2015 by letting designers show either ASTC 47 or a lab STC 50, according to a 2024 review of the National Building Code in Construction Canada.
FPInnovations’ perception thresholds explain why consultants push past code. Below a field rating of 45 neighbours are clearly audible, and only above 60 do occupants hear nothing except low-frequency footsteps on lightweight floors. A bare CLT floor at IIC 25 sits 20 points under even the lowest of those bands (45 minus 25), although that compares a lab rating with a field threshold.
| Metric | Value | Source |
|---|---|---|
| IBC requirement, lab (STC and IIC) | 50 | University of Oregon TallWood acoustic report 2019, citing ICC |
| IBC requirement, field tested | 45 | University of Oregon TallWood acoustic report 2019, citing ICC |
| Canada NBC 2015 option for dwelling separations | ASTC 47 or lab STC 50 | Construction Canada, Busch 2024 |
| Canada NBC: year STC 50 between dwellings was adopted | 1990 | Construction Canada, Busch 2024 |
| Field rating below which neighbour sounds are clearly audible | Under 45 | FPInnovations Report E-4874, 2014 |
| Field rating at which sound is heard as muffled | Above 50 | FPInnovations Report E-4874, 2014 |
Context note: Construction Canada reports that the next NBC edition was expected in 2025 with impact insulation (IIC) under consideration, since the 1995 code referenced IIC without requiring design or testing for it. Most recent available data for the FPInnovations thresholds: FPInnovations, 2014.
4. Toppings, Floating Floors and Ceilings: Closing the Gap
Every route to code adds layers, and the numbers show which layers do the work. A hung ceiling combined with a topping took 175 mm CLT floors to STC 62-75 in NRC Canada’s lab, across a test program of 16 floor assemblies on a 175 mm base, 10 on a 131 mm base and 8 walls (NRC Client Report A1-006070.10, 2015). A heavy topping of 100+ kg/m2 on a resilient membrane alone yields at least STC 50.
Impact performance responds most to the floating layer and the ceiling. In the 2026 Bologna campaign, a dry floating screed brought Ln,w down to 46-53 dB, and adding a suspended ceiling pushed it to 36-40 dB. The architectural tension is real: the authors note suspended ceilings are “most of the times not accepted by designers” who want the timber exposed. Testing the full assembly before specifying it is the same discipline described in our anechoic chamber and acoustic testing statistics.
| Metric | Value | Source |
|---|---|---|
| 5-ply CLT floor with topping and acoustic mat, before finish floor | STC 50-59, IIC 35-60 | WoodWorks, Acoustics and Mass Timber 2021 |
| Same assemblies with finish flooring | IIC 60+ | WoodWorks, Acoustics and Mass Timber 2021 |
| 175 mm CLT floors with hung ceiling and topping | STC 62-75 | NRC Client Report A1-006070.10, 2015 |
| CLT walls with gypsum linings | STC 53 or higher (best: STC 71) | NRC Client Report A1-006070.10, 2015 |
| Reduction in Ln,w from engineered overstructures on 160 mm CLT | Up to 28 dB (Rw up to +25 dB) | Luison et al., Forum Acusticum 2026 |
| CLT plus suspended ceiling and floating screed | Ln,w 36-40 dB | Luison et al., Forum Acusticum 2026 |
| Impact improvement of the same floating floor on CLT vs concrete | Delta Lw 31 dB vs 34 dB | Luison et al., Forum Acusticum 2026 |
| CLT walls with single-sided vs double-sided linings | Up to 60 dB vs up to 70 dB | Di Bella and Mitrovic, Sustainability 2020 |
Outlier note: the Bologna team found a timber-batten overstructure with polyester fibre infill at about 16 kg/m2 performed close to sand or cement layers at 90-100 kg/m2, which matters because every kilogram of topping adds structural load to a timber frame. The same paper notes that once low frequencies are counted (LI,50), dry and wet screed systems converge at 54-55 dB. Engineered absorbers inside these assemblies follow the same physics as those in our acoustic metamaterials and soundproofing statistics.
5. Flanking Transmission at Junctions: Where Lab Ratings Leak
Flanking is the reason a good separating floor can still fail in the field. CLT is stiff and radiates efficiently, so vibration crosses junctions and re-radiates from the floor or wall next door. In a 2026 University of Bologna full-scale X-junction mock-up, splitting a continuous 100 mm CLT floor slab and adding a resilient interlayer raised the low-frequency vibration reduction index from 9.6 dB to 20.9 dB, an 11.3 dB gain (Barbaresi et al., Forum Acusticum 2026).
The ISO 12354 calculation in the same paper puts that into apartment terms. Without a false ceiling, decoupling lifted the apparent sound reduction index R’w from 46.5 dB to 49.3 dB; with a ceiling the gain shrank to 0.8 dB because the ceiling already makes the major contribution on the ceiling-to-ceiling path. Building height compounds the problem: across four CLT buildings of 5 to 10 storeys, junctions lower in the building attenuated less (Nilsson et al., Buildings 2023).
| Metric | Value | Source |
|---|---|---|
| Average Kij, continuous vs decoupled CLT floor (200-1250 Hz) | 10.7 dB vs 17.6 dB (+6.9 dB) | Barbaresi et al., Forum Acusticum 2026 |
| R’w gain from floor decoupling, no false ceiling (ISO 12354 calc) | +2.8 dB (46.5 to 49.3 dB) | Barbaresi et al., Forum Acusticum 2026 |
| Ceiling-to-ceiling (Ff) flanking path improvement from interlayer | +5.8 dB | Barbaresi et al., Forum Acusticum 2026 |
| Wall-wall Kij decrease per storey lower in the building | 1.0 dB (X-junctions), 1.6 dB (T-junctions) | Nilsson et al., Buildings 2023 |
| Junctions measured in that field study | 12 junctions, 36 flanking paths, 4 buildings | Nilsson et al., Buildings 2023 |
| Extra lateral transmission from asymmetric fixings | Up to 10 dB vs theoretical values | Di Bella and Mitrovic, Sustainability 2020 |
| Prediction error of a wave-based model for a CLT T-junction with interlayer | Below 10 dB in all 1/3-octave bands | Moons, Reynders and Lanoye, INCE conference proceedings 2024 |
| Extra vibration reduction from a 12 mm elastomer layer inside CLT panels (simulated) | About 40% | Bohman et al., Journal of Building Engineering 2025 |
Context note: the Bologna paper is a preliminary conference document co-authored with a fastener and acoustic-strip manufacturer (Rotho Blaas), and its R’w figures come from a calculation rather than a built apartment. Field evidence points the same way: a 2026 measurement study of three mass timber schools in the Pacific Northwest found flanking “strongly affects” both ASTC and AIIC results (Blount, JASA 2026). On the materials side, swapping spruce laminations for birch or compressed spruce cut simulated vibration response by about 30% and 50% (Bohman et al., 2025).
6. Field vs Lab: How Much Performance Survives Construction
The gap between lab and field is smaller than many designers fear, but only when workmanship cooperates. SINTEF’s comparison of double CLT walls found field R’w deviated from comparable lab results by only -2 to +1 dB (Homb and Conta, Forum Acusticum 2023). The same study shows how easily it goes wrong on site: compressed blown-in cavity insulation cost 9 dB of R’w compared with a soft installation in the same apartment building.
North American guidance builds in the expectation of loss. Canadian code commentary states an ASTC “will always yield a value equal to or lower than the STC” for the same configuration, because the field-type rating adds every flanking path to the direct one. FPInnovations’ field program found bare 175 mm CLT floors struggled to exceed a rating of 50 without a dropped ceiling (FPInnovations Report E-4874).
| Metric | Value | Source |
|---|---|---|
| Field vs lab deviation, double CLT walls (R’w vs Rw) | -2 to +1 dB | Homb and Conta, SINTEF, Forum Acusticum 2023 |
| Field R’w of double CLT walls, three apartment buildings | 50-55 dB | Homb and Conta, SINTEF, Forum Acusticum 2023 |
| Lab Rw of comparable double CLT walls | 47-54 dB | Homb and Conta, SINTEF, Forum Acusticum 2023 |
| R’w penalty from compressed blown-in cavity insulation (field) | 9 dB | Homb and Conta, SINTEF, Forum Acusticum 2023 |
| ASTC compared with STC for the same configuration | Always equal or lower | Construction Canada, Busch 2024 |
| Bare 175 mm CLT floors without a dropped ceiling, field ratings | Struggled to exceed 50 | FPInnovations Report E-4874, 2014 |
| Mass timber schools measured in situ, Pacific Northwest | 3 schools; exposed CLT ceilings can meet a 0.6 s reverberation target if walls are treated (preliminary) | Blount, JASA 2026 |
Context note: the SINTEF authors conclude that, in general, R’w of 55 dB or more is not achievable for these double CLT walls without additional measures, which they describe as the common requirement between apartments. That makes the target a design problem, not just a construction-quality one.
7. Occupant Noise Satisfaction: The Low-Frequency Problem
Residents judge timber buildings by footsteps, and the standard ratings miss most of what they hear. Across 23 Swedish apartment buildings, the conventional impact rating L’nT,w explained only 18% of residents’ footstep annoyance; extending the evaluation down to 25 Hz raised that to 77%, and to 85% after removing one outlier building (Ljunggren, Simmons and Öqvist, Applied Acoustics 2017). Six of those 23 buildings were CLT, and roughly 800 completed questionnaires fed the analysis.
The national picture from Japan is blunter. In the 2018 Comprehensive Survey of Housing and Living, 25.3% of residents in wooden apartment buildings said they were very dissatisfied with sound insulation and 41.5% rated it somewhat unsatisfactory, against 13.0% and 37.1% in reinforced concrete (NILIM Annual Report 2023). Adding the two categories gives 66.8% dissatisfied in wooden buildings (25.3 + 41.5) versus 50.1% in concrete (13.0 + 37.1). Low-frequency annoyance is also a factor in shared workplaces, as our open-plan office distraction statistics show.
| Metric | Value | Source |
|---|---|---|
| Share of footstep annoyance explained by L’nT,w | R2 = 18% | Ljunggren et al., Applied Acoustics 2017 |
| Share explained by L’nT,w + CI,50-2500 | R2 = 49% | Ljunggren et al., Applied Acoustics 2017 |
| Share explained when evaluated from 25 Hz | R2 = 77% (85% excluding one outlier) | Ljunggren et al., Applied Acoustics 2017 |
| Rating increase from L’nT,w,50 to the 20 Hz AkuLite rating, CLT buildings | 6.0 dB on average (lightweight 9.2 dB, concrete 0.6 dB) | Ljunggren et al., Applied Acoustics 2017 |
| Questionnaire reply rate per building | 33-83% (about 800 returned) | Ljunggren et al., Applied Acoustics 2017 |
| Very dissatisfied with sound insulation, wooden apartments (Japan) | 25.3% (n=314) | NILIM Annual Report 2023, MLIT 2018 survey |
| Very dissatisfied, reinforced concrete apartments (Japan) | 13.0% (n=1,125) | NILIM Annual Report 2023, MLIT 2018 survey |
Context note: the Japanese category covers fireproof and non-fireproof wooden construction as a whole, not CLT specifically, so it describes the perception problem that CLT designers inherit rather than CLT performance itself. Most recent available data: Ljunggren et al., 2017, and MLIT survey data from 2018. The Swedish study also found footstep annoyance at least twice as high as annoyance from other impact sources.
Summary: CLT and Mass Timber Acoustics by the Numbers
| Metric | Value | Source |
|---|---|---|
| U.S. mass timber projects built or in progress (June 2026) | 2,833 | WoodWorks Mapping Mass Timber 2026 |
| Annual growth rate in project count | 20 percent | Mercer Mass Timber analysis via IWF Atlanta |
| Mass timber buildings constructed per year, Canada and U.S. | 151 (2019) to 279 (2023) | 2024 International Mass Timber Report via IWF Atlanta |
| Bare 5-ply CLT floor | STC 41, IIC 25 | WoodWorks, Acoustics and Mass Timber 2021 |
| IBC minimum, lab / field | 50 / 45 | University of Oregon TallWood acoustic report 2019 |
| Canada NBC dwelling separation option | ASTC 47 or STC 50 | Construction Canada, Busch 2024 |
| Field rating below which neighbour sounds are clearly audible | Under 45 | FPInnovations Report E-4874, 2014 |
| Hung ceiling plus topping on 175 mm CLT | STC 62-75 | NRC Client Report A1-006070.10, 2015 |
| CLT with suspended ceiling and floating screed | Ln,w 36-40 dB | Luison et al., Forum Acusticum 2026 |
| Low-frequency Kij gain from decoupled floor slab | +11.3 dB | Barbaresi et al., Forum Acusticum 2026 |
| R’w gain from floor decoupling, no false ceiling | +2.8 dB | Barbaresi et al., Forum Acusticum 2026 |
| Wall-wall Kij loss per storey lower in building | 1.0-1.6 dB | Nilsson et al., Buildings 2023 |
| Asymmetric fixings, extra lateral transmission | Up to 10 dB | Di Bella and Mitrovic, Sustainability 2020 |
| Field vs lab deviation, double CLT walls | -2 to +1 dB | Homb and Conta, SINTEF, Forum Acusticum 2023 |
| Extra vibration reduction from a 12 mm elastomer layer in CLT panels (simulated) | About 40% | Bohman et al., Journal of Building Engineering 2025 |
| Footstep annoyance explained, standard vs 25 Hz rating | 18% vs 77% | Ljunggren et al., Applied Acoustics 2017 |
| Very dissatisfied with sound insulation, wooden vs concrete apartments (Japan) | 25.3% vs 13.0% | NILIM Annual Report 2023, MLIT 2018 survey |
Methodology and Sources
- WoodWorks, Mapping Mass Timber (June 2026 count): U.S. built and in-progress project count, updated quarterly.
- WoodWorks, Acoustics and Mass Timber: Room-to-Room Noise Control (2021): bare panel STC/IIC, topping assembly ranges, IBC Section 1206 summary.
- IWF Atlanta, 2025 Was a Pivotal Year for Mass Timber Construction: Mercer Mass Timber analysis and 2024 International Mass Timber Report figures.
- Woodworking Network, Mass Timber Takes Center Stage at IWF (June 24, 2026): WoodWorks total including design-phase projects.
- NRC Canada, Client Report A1-006070.10 for Nordic Engineered Wood (2015), hosted by the Canadian Wood Council: ASTM E90 tests of bare and lined CLT floors and walls.
- University of Oregon, TallWood Design Institute acoustic lab testing of CLT and MPP assemblies (2019): ICC lab and field benchmarks.
- Construction Canada, Decibels and Dwellings: Noise Control Evolution in the NBC (Busch, 2024): NBC acoustic requirement history.
- FPInnovations Report E-4874, Serviceability of next-generation wood buildings: sound insulation (Hu, 2014): field rating perception thresholds.
- Luison et al., Design implications for impact sound insulation in timber floors, Forum Acusticum 2026: ISO 10140 lab tests on a 160 mm CLT slab.
- Barbaresi et al., Flanking sound transmission reduction through a decoupled CLT floor, Forum Acusticum 2026: ISO 10848 Kij measurements and ISO 12354 calculations.
- Nilsson, Ménard, Bard and Hagberg, Effects of Building Height on the Sound Transmission in CLT Buildings, Buildings 2023: field Kij in four CLT buildings.
- Di Bella and Mitrovic, Acoustic Characteristics of Cross-Laminated Timber Systems, Sustainability 2020: review of CLT lab data and junction behaviour.
- Lin, Yang and Tsay, A Study on the Sound Insulation Performance of Cross-laminated Timber, Materials 2021: Taiwanese CLT wall tests.
- Homb and Conta, Sound insulation properties of single and double CLT walls, SINTEF, Forum Acusticum 2023: lab vs field comparison.
- Ljunggren, Simmons and Öqvist, Correlation between sound insulation and occupants’ perception, part II, Applied Acoustics 2017: 23-building Aku20 field and questionnaire study.
- NILIM (Japan), Study on Standard Floor Section Specifications for Wooden Buildings, Annual Report 2023: cross-tabulation of MLIT 2018 Comprehensive Survey of Housing and Living.
- Blount, Field evaluation of acoustic performance in mass timber school buildings, JASA 2026: conference abstract on three Pacific Northwest schools.
- Bohman et al., Vibration reduction in CLT panels using various lamination materials and integrated elastomer layers, Journal of Building Engineering 2025: finite element study, abstract figures.
- Moons, Reynders and Lanoye, Prediction and validation of flanking sound transmission in CLT junctions with resilient interlayers, INCE conference proceedings 2024 (DOI 10.3397/in_2024_3493, abstract read via the OpenAlex index): abstract figure only.
- Data watch: the U.S. project counts conflict. WoodWorks’ own page reports 2,833 built or in progress (June 2026), while Woodworking Network quotes WoodWorks at 2,746 including design-phase projects, and the Mercer analysis says over 2,500 at end-2025; neither intermediary explains the gap, so we treat the WoodWorks page as authoritative. The two Forum Acusticum 2026 papers are preliminary documents not reviewed by the conference board, and both have industry co-authors. The Barbaresi R’w values are ISO 12354 calculations, not field measurements. Several core datasets are older than three years (NRC 2015, FPInnovations 2014, Ljunggren 2017, MLIT 2018 survey, WoodWorks 2021 paper). The WoodWorks Inventory of Acoustically Tested Mass Timber Assemblies is gated behind a form and was not used. NRC Research Report RR-335 (Apparent Sound Insulation in CLT Buildings) is the standard North American ASTC prediction reference, but we could not retrieve its full text, so no figures from it are cited. Construction Canada expected the next National Building Code edition in 2025 with impact insulation (IIC) under consideration; whether a mandatory impact requirement was adopted should be checked at the next refresh.
Last updated: October 18, 2026. We update this roundup quarterly, and the next refresh is expected when WoodWorks publishes its next quarterly Mapping Mass Timber project count.