ground floor and 2nd floor noise transmission study ... · design guidelines for a new glazing...

Suite 500 416 977-5335

144 Front Street West Fax 416 977-1427

Toronto, ON M5J 2L7 www.rjc.ca

Canada

GROUND FLOOR AND 2ND FLOOR

NOISE TRANSMISSION STUDY

FINDINGS AND RECOMMENDATIONS

TORONTO CITY HALL

100 QUEEN STREET WEST, TORONTO, ON

December 17, 2013

Prepared for:

City of Toronto, DCAP

2nd Floor, Metro Hall

55 John Street

Toronto, Ontario M5V 3C6

Attention: Mr. Chris Sheldon

Prepared by:

Read Jones Christoffersen Ltd.

Suite 500, 144 Front Street West

Toronto, ON M5J 2L7

RJC # TOR.100775.0004

Toronto City Hall, 100 Queen Street West

Ground Floor and 2nd Floor – Noise Transmission Study

Findings and Recommendations

Dceember 17, 2013 Page i

RJC No.: TOR100775.0004


Table of Contents

Page

1.0 Introduction 1

2.0 Background 2

2.1 Building Description 2

2.2 Drawing and Document Review 2

2.3 Interview with Building Operations and Maintenance Staff 3

3.0 Observations 4

3.1 Exterior Observations 4

3.2 Interior Observations 4

4.0 Discussions and Conclusions 5

5.0 Closing Remarks 7

Appendix ‘A’ – Photographs

Appendix ‘B’ – Acoustic Sub-Consultant Report

Appendix ‘C’ - Figures




Dceember 17, 2013 Page 1

RJC No.: TOR100775.0004


1.0 Introduction

Read Jones Christoffersen Ltd. (RJC) performed a noise study investigation at the above noted

areas of Toronto City Hall to understand the current performance of the system and recommend

design guidelines for a new glazing system to reduce future noise transmission from exterior

events.

As part of this review, the following work briefly described below was undertaken:

.1 Review of available drawings and documents describing the architectural system and

glazing shop drawings.

2. A visual walk-through examination of the areas to determine the as-built construction.

No test openings were created.

3. Sound data collection was conducted over a two-week period as well as during a live

music even in Nathan Philips Square. Data collected was analyzed to determine the

current performance level of the glazing/wall system.

This report is exclusively for the use and benefit of the City of Toronto and is not for the use or

benefit of, nor may it be relied upon by any other person or entity. The contents of this report

may not be quoted in whole or in part or distributed to any person or entity other than the client.





RJC No.: TOR100775.0004


2.0 Background

2.1 Building Description

The Toronto City Hall building located on the west side of Bay Street between Queen Street West

and Hagerman Street in Toronto, is an irregularly shaped multi-story, multi-tower complex

constructed between the years of 1961 and completed in 1965 for government purposes. While

the building's base is rectangular, its two towers are curved in cross-section and rise to differing

heights. The east tower is 27 storeys tall and the west tower is 20 storeys. Between the towers is

a low rise domed council chamber (rotunda). The building is of traditional cast in place normally

reinforced construction.

The rotunda wall system appears to be aluminum framed curtain wall with both vision and

spandrel areas. The ground floor wall system appears to be a single glazed curtain wall set in a

non-thermally broken aluminum frame with stainless steel snap caps. The ground floor wall

system appears to be un-drained and is reported to date from the original construction (Refer to

Photos 1 to 2 in Appendix ‘B’)

The second story glazing consists of insulating glass units dating from 1998 and the system is

reported to have been repaired in the late 1990’s. The second floor slab edge is covered by a

prefinished metal spandrel section.

2.2 Drawing and Document Review

.1 A previous sound study was provided by City of Toronto staff and was undertaken by City

Staff from August 14 to 29, 2013. We understand from the study that:

.1 The exterior City Event space is to have a maximum 75 dB.

.2 The measured levels inside the offices ranged from 47 to 53 dB over 6 separate

events on different days.

.3 Councillor Kelly’s office appeared to have the highest measurement of 53 dB on

5 of the 6 measurement times with the sixth measurement not taken due to a

meeting.





RJC No.: TOR100775.0004


2.3 Interview with Building Operations and Maintenance Staff

We had discussions with Jim McGuffin, the building Maintenance Lead, and he advised the

following:

.1 The curtain walls were last repaired in the early 2000’s.

.2 Recently repairs in the soffit area have been conducted due to animals previously

entering into the office areas via the un-sealed soffit space. The repairs consisted of

adding drywall and metal liners to the interior side of the soffit to seal off the space.

They are reported to be functioning well.

.3 Insulating glass is replaced on an as-needed basis if it fails.

.4 The age of the single glazed units at grade is unknown.

.5 Councillors report different levels of noise transmission depending on the different

exterior events; however, the problems are reported to have become worse since the new

exterior stage was constructed.

.6 The ground floor has less noise complaints than the second floor offices. This may be

due to the ground floor being more an open plan office with multiple discussions being

held and the second floor generally consisting of private offices.





RJC No.: TOR100775.0004


3.0 Observations

3.1 Exterior Observations

The general construction of the cladding is described in Section 2.1. The ground and second floor

areas of complaint face south, towards Queen Street. Southwest of the main entrance a new

stage has been constructed as part of the Nathan Phillips Square revitalization. There are

anecdotal reports that the level of noise increased following the use of the new stage for outdoor

performances.

The arrangement of the building’s south elevation creates a large overhang/soffit directly outside

the areas with noise transmission issues. The large overhang is supported by cast-in-place

reinforced concrete columns. The soffit is un-insulated and finished with prefinished metal slats.

The construction of the soffit allows air and noise to pass through and will allow increased sound

transmission due to the construction.

Field measurements indicate that the typical ambient sound environment in the square typically

ranges from 65 to 70 dBA and increases to 85-90 dBA during a live event at Nathan Philips

Square.

Specific noise study observations and analysis are outlined in Appendix B.

3.2 Interior Observations

The interior of the ground floor curtain wall was generally consistent and as noted to have a

radiant heater located at the floor and a metal slat ceiling similar to the exterior soffit

construction. The back of the metal spandrel panel, the opaque panel between the vision glass at

the ground floor and 2nd floor, was not visible as plywood has been added to the interior of the

assumed back-pan (Refer to Photos 4 and 5 in Appendix A).

The interior of the second floor varies more than the first as it is comprised of private city

councillor offices. The councillor’s office typically faces the south elevation with a radiant heater

noted at the floor and a drop acoustical tile ceiling. The space above the acoustical tile was

reported to be a mechanical plenum space with the backside of the plenum sealed with plywood

and gypsum board to separate the interior and exterior (Refer to Photos 6 and 7 in Appendix A).





RJC No.: TOR100775.0004


4.0 Discussions and Conclusions

Based on our visual observations, interviews and noise study data the sound transmission

performance of the current wall system can be improved to reduce the amount of noise

transmission experienced from outdoor events.

In general the wall systems are performing at or slightly below industry guidelines with respect to

acoustical performance. It is likely that the original curtain wall system may not have been

designed for high acoustical resistance; which is typical for the majority of curtain walls.

The large soffit can lead to micro-concentrations of sound transmission, in particular if there are

areas of the wall above the curtain wall, within the soffit space, that has discontinuities within the

air barrier that will also allow sound transmission. These discontinuities should be addressed

during any large scale rehabilitation as part of the continuity of the curtain wall system.

Based on the observations the current curtain wall appears to be performing as expected with

much of the sound intrusion blocked with the majority of sound intrusion measured was in the

low frequency range. To realize an improvement over the existing system an increase to the

following Sound Transmission Classification (STC) ratings will be required:

Building Area Lower Level STC Upper Level STC

Ground Floor 40-41 35-36

2nd Floor- Councillor Offices 45-46 40-41

A 5 dB improvement over the existing appears to be sufficient for the ground floor as it is open

and has less noise complaints. The second floor appears to require an improvement of 10 dB in

acoustical performance to be noticeable to the occupants.

For design purposes the glazing is typically modified to improve the acoustical performance. The

following possible curtain wall constructions are feasible to achieve the above noted STC ratings:

Building Area Lower STC Glass

Make-up

Upper STC Glass

Make-up

Ground Floor 9L or 6L-6-3 16L or 6L-13-6L or 9L-13-6

2nd Floor- Councillor Offices 9L-13-6 6L-25-6L or 13L-50-9 or 6L-

25-6L-13-6L

*Note: L denotes a laminated glass lite and the glass make-up numbers are arranged “glass

thickness-air space-glass thickness” for double glazed and “Glass thickness-airspace-glass

thickness – air space – Glass thickness” for triple glazed.





RJC No.: TOR100775.0004


To achieve the higher STC ratings a split frame curtain wall assembly is required, which is difficult

to construct in curtain walls and is not widely used in exterior applications. These acoustic frames

are typically used in interior applications. This means that the outer and inner portion of the

frame is broken up by thermal break, typical in windows but not curtain walls. Split frames are

not traditionally used in curtain walls due to the significant reduction in structural performance.

Further, the insulating glass unit air spaces larger than 16 mm will likely carry a reduced warranty

from sealed glass unit manufacturers and very few manufacturers are able to create the larger

air space within the glass unit, which will result in a cost premium as well. The relative opinion of

probable cost differences between the various recommended options are provided in the table

below:

Glass Make-up Relative Cost Per Sq. Ft.

($/SF)

Ground Floor - 6L-6-3 126

Ground Floor - 6L-13-6L 132

2nd Floor- Councillor Offices - 9L-13-6 132

Optional: VIG 160

The opinion of probable costs above relate to the demolition, supply and installation of a new

curtain wall and do not include costs that would be typically carried by a general contractor such

as bonding, mobilization, demobilization, etc. The opinion of probable cost above should be used

for comparative purposes and may not reflect the final costs for a curtain wall replacement

project which is dependent on a multitude of factors beyond the scope of this study.

A newer technology that could also be used in traditional curtain wall framing is vacuum

insulated glass units (VIG). VIGs have a very high thermal performance, an order of magnitude

greater than typical high-performance insulating glass units, and also very high acoustical

resistance. However, VIGs do not have a proven history of durability with the longest in-service

installation being about six (6) years. The cost for these units is roughly an additional $25/sf,

however this cost increase may be slightly offset by the smaller aluminum framing required,

reduced heating and cooling costs and ability to use a standard curtain wall frame.

Based on the above we recommend the City consider utilizing thermally broken traditional

curtain wall framing (a sample diagram is provided as Figure 1 in Appendix C) with a 6L-13-6L glass

unit for the ground floor and 9L-13-6 glass unit for the second floor. These insulating glass

assemblies set in thermally broken curtain wall framing are expected to have an improvement of

more than 5 dB but less than 10dB. This improvement does not account of likely repairs to the

soffit and other acoustic flanking locations which may improve the dB reduction towards the

desired 10 dB threshold.





RJC No.: TOR100775.0004


While a true “acoustical frame” and/or larger air space units would provide additional acoustical

performance we are of the opinion that the benefits do not adequately compensate for the

disadvantages (i.e. the increased costs, reduction in structural performance, and likely lack of

warranty on the units).

5.0 Closing Remarks

In closing, Read Jones Christoffersen Ltd. would like to thank you for selecting us for this noise

assessment. RJC would be pleased to assist you with the implementation of the

recommendations. Please do not hesitate to contact our office.

Yours truly,


Reviewed by:

Duncan Rowe, M.Eng., P.Eng., LEED AP BD+C W. (Bill) Gladu, P.Eng., MBA, LEED AP

Project Engineer Principal

Building Science and Restoration Building Science and Restoration





RJC No.: TOR100775.0004


Appendix ‘A’

Photographs





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Photo # 1: Overview of ground and second floor curtain wall with metal soffit above

Photo # 2: Overview of curtain wall showing ground floor, spandrel and second floor





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Photo # 3: Overview of ground floor from interior

Photo # 4: Close view of base of curtain wall at ground floor indicating radiant heater and single

glazed light





RJC No.: TOR100775.0004


Photo # 5: view of ceiling space above ground floor metal slat sealing indicating plywood and other

material applied to the backside of the spandrel

Photo # 6: General view of second floor councillor office indicating curtain wall position, acoustical

drop ceiling, and concrete column





RJC No.: TOR100775.0004


Photo # 7: View of plenum space above second floor offices with plywood noted above curtain wall as

part of a past repair to separate the interior plenum from exterior vented soffit





RJC No.: TOR100775.0004


Appendix ‘B’

Acoustic Sub-Consultant Report

project number: 13280

Toronto City Hall - Ground Floor and Second Floor

Curtain Wall Window Glazing Noise Intrusion Study

Prepared for:

Read Jones Christofferson Limited

Prepared by:

Aercoustics Engineering Limited 50 Ronson Drive, Suite 165 Toronto ON M9W 1B3

6 December 2013

aercoustics.com

Toronto City Hall - Ground Floor and Second Floor Curtain Wall Window Glazing Page 2 of 14 Noise Intrusion Study 6 December 2013

1 Introduction

Aercoustics Engineering Ltd. (AEL) has been retained by Read Jones Christofferson to provide acoustic expertise in regards to assessing the current performance of window glazing sound isolation at the south side of the Toronto City Hall Ground Floor (Staff) and Second Storey (Councillor Offices). A study area site plan is given in Figure 1.

Figure 1: Study Area Site Plan

In addition, it is also proposed to establish Acoustic Design Guidelines for cost effective replacement of the window glazing system. As part of this work, long term sound level monitoring was conducted in order to gather and capture the sound level variation in the site specific ambient environment outdoors and indoors; and this would include the sound levels attributable to a high level live event that was held on September 26/2013 at the stage at Nathan Phillips Square.

Therefore the purpose of this report is to provide the design guidelines as well as recommendations for the upgraded window design for Toronto City Hall.

aercoustics.com


2 Acoustic Design Guidelines for

Background Sound Level and Required Sound Isolation

The sound level standard used in this study is the NC (noise criterion) descriptor, which is an industry standard for defining sound level environments in interior spaces. Typically, the accepted standard for open office areas such as the Ground Floor areas of City Hall is in the range of NC40. The sound level standard for private offices such as the Councillor offices would typically be in the range of NC35. Any Boardrooms with video-conferencing capability should be required to meet a standard of NC 25 to NC 30. These acoustic performance parameters are further substantiated by the recommended background noise criterion for different rooms as defined by ASHRAE (American Society of Heating, Refrigeration and Air Conditioning Engineers).

It should be stated at the outset that the objective in this project is to achieve a noticeable degree of improvement, as per defined acoustical guidelines defined above. This improvement will be observed in the subject offices and will be noticeable in the form of improved sound isolation from outdoor sound sources. Existing flanking paths such as the window frame, soffit to ceiling space and other structural constraints will limit the degree of acoustic performance that is achievable. It is therefore noteworthy that although outdoor sound levels will be attenuated, noise from live events and other spurious outdoor sounds will on occasion still be audible.

Background sound levels are described by a series of target sound spectra curves, i.e. NC (Noise Criterion). The background sound level criteria sets the maximum allowable levels in a space due to the building systems (mechanical, electrical, etc.), as well as noise from the exterior environment such as road traffic, industry, and other steady state outdoor events or activities.

Sound isolation between spaces, as provided by building systems such as walls, windows, roofs and floor assemblies is described by the Sound Transmission Class (STC) of the subject component.

A site visit was conducted to review the site specifics and to position four long term sound monitors that were installed as identified in Figure 2 and as follows:

1. Indoors, ground floor - open office, near window. The window was evaluated and determined to be nominal 6mm thick monolithic glass (6.6mm actually measured)., thus corresponding to an acoustic performance of STC 30/31

2. Indoors, second floor – in the Councillor’s office, near window. The window was evaluated determined to be nominal 6mm double glazing with a 17mm air space, thus corresponding to an acoustic performance of STC 35/36.

3. Outdoors, at 2nd floor level, just outside window of the Councillor’s office.

4. Outdoors, at 2nd floor level, at edge of soffit located between the offices and the live stage.

aercoustics.com


Figure 2: Monitoring Locations (September 24 to October 3, 2013)

The existing constraints that will limit the performance of the window glazing include the curtain wall (i.e. window frame and wall assembly) as well as the soffit system which is part of the sound transmission path that `short circuits’ the window system. The façade design or window glazing system will require a balance between the wall frame and glazing, such that neither are a significant limiting factor to the net acoustic performance.

Similarly, the floor and ceiling construction as well as the room finishes in the office areas exist and play a role in the net acoustic effect; and they are therefore not part of this acoustic review. Therefore this report does not examine the reverberant or other acoustic attributes of the space(s) in question.

The sound data acquired from the long term monitors from September 24–October 3, 2013 is summarized in Figures 3ab and 4ab respectively for indoor (Locations 1 and 2) and outdoor (Locations 3 and 4)measurements with raw data included in Appendix A. The ambient sound environment outdoors is typically in the 65 to 70 dBA range and increases to a range of 85-90 dBA during a live event at Nathan Phillips Square. The spot check sound data was acquired during the live event that occurred on September 26, 2013 at Nathan Phillips Square.

aercoustics.com


Figure 3a: Long Term Monitoring at Location 1 (September 24 to October 3, 2013)

Figure 3b: Long Term Monitoring at Location 2 (September 24 to October 3, 2013)

aercoustics.com


Figure 4a: Long Term Monitoring at Location 3 (September 24 to October 3, 2013)

Figure 4b: Long Term Monitoring at Location 4 (September 24 to October 3, 2013)

Live Event Sept 26, 2013

Live Event Sept 26, 2013

aercoustics.com


Similarly, the sound level environment indoors is typically in the range of NC-40 to 45 for the Ground Floor and NC35 to 40 in the Councillors’ offices.

In both cases, an approximate 10-12 dB(A) intrusion was observed, which is actually less intrusion than was expected and thus indicating that the current window system is performing to expectation. The majority of the intrusion was in the low frequency range below about 250 Hz, with some speech frequency range intrusion also evident.

It is this acoustic energy that eventually dictates the acoustic requirements for the window upgrade. Octave band sound levels from the live event (both indoors and outdoors) along with existing background sound levels at both the City Hall Ground Floor and 2nd Floor offices and the target NC-30 to NC-40 spectra levels are shown in Table 1 and 2 respectively.

aercoustics.com


2.1 Noise Levels and Design Goals Table 1: Reference Noise Levels (all in dB) for Ground Floor from Live Event:

OBCF (Hz) 63 125 250 500 1kHz 2kHz 4kHz 8kHz

Event LEQ @1m – Grd. Glass/out*

82‐87 85‐90 80‐85 78‐84 73‐78 71‐76 68‐72 60‐67

Event SPL @1m ‐Grd. Glass/in*

63 63 55 51 46 45 39 35

Ground Fl. Background

61 58 54 47 43 42 41 38

NC‐25 54 44 37 31 27 24 22 21

NC‐30 57 48 41 35 31 29 28 27

NC‐35 60 52 45 40 36 34 33 32

NC‐40 64 56 50 45 41 39 38 37

NC‐45 67 60 54 49 46 44 43 42

In‐Out (dB) 21‐26 27‐32 26‐31 31‐37 30‐35 29‐34 27‐31 22‐29

Table 2: Reference Noise Levels (all in dB) for 2nd Floor from Live Event:

OBCF (Hz) 63 125 250 500 1kHz 2kHz 4kHz 8kHz

Event LEQ‐L05 @1m – 2nd. Glass/out*

81‐86 83‐89 79‐83 79‐84 77‐82 77‐82 69‐72 60‐65

Event SPL @1m ‐2nd Glass/in*

65‐69 61‐64 56‐59 48‐51 41‐43 43‐45 38‐39 34‐35

2nd Fl. Background

57 53 51 42 38 39 38 34

NC‐25 54 44 37 31 27 24 22 21

NC‐30 57 48 41 35 31 29 28 27

NC‐35 60 52 45 40 36 34 33 32

NC‐40 64 56 50 45 41 39 38 37

In‐Out (dB)+ 24‐29 30‐36 28‐32 37‐42 39‐44 38‐43 31‐34 26‐31

Notes:

*Levels measured at 1m from window in/out during the live event have been used to determine the intrusion spectra. +In-Out denotes the approximate transmission loss, TL, required in dB for the window upgrade.

aercoustics.com


The level of upgrade for the 2nd Floor will require a high performance window design that will entails a split independent frame, along with laminated glass construction for the thicker pane section or equivalent.

The following STC performances are therefore recommended. It should be noted that the measured in situ or field STC performance may be >5 dB lower than published lab data.

Room Required STC (within 5 db target spectra)

Modest Upgrade in STC (~10 dB intrusion)

2nd Fl.- Councillor Office 45/46 40/41 Ground Floor 40/41 35/36

The subject Ground Floor and Second Floor should therefore respectively have minimum STC-35 and STC-40 ratings in order to achieve a noticeable degree of change in reducing the intrusion noise from the live events at Nathan Phillips Square. To achieve these STC ratings within a reasonable size of window frame size, the design will entail laminated glass. The higher relative STC performance is attributable to the damping that arises from the glass and laminating layers. The glazing construction shown in Figure 5 is required to achieve a 10 dB improvement and thus meet the intent of the design standards defined by ASHRAE; and to limit the noise intrusion to about 5 dB in each octave band. It should be noted that the two glass panes should be in independent frames as detailed in Figure 5.

Figure 5: Double Pane Glazing – Conceptual Illustration with Independent Frame

aercoustics.com


3 Recommended Window Glazing Design Guidelines. Window design guideline considerations to consider include the following:

1. In order for the window upgrade to result in a noticeably significant improvement, a 10 dB jump in acoustic performance would normally be recommended, even though noise from live events will still be audible (i.e. octave band intrusions of about 5 dB). A 5 dB upgrade at the 2nd Floor would be a noticeable improvement (i.e. octave band improvements of about 10 dB) yet may not be sufficient to adequately buffer the noise complaints for the worst case live events.

2. A 5 dB improvement is considered to be both a noticeable and practical improvement for the

ground floor based on our understanding of the noise complaints.

3. This would mean that the ground floor glazing if upgraded, should meet at least STC 35 and this could be accomplished with 9mm laminated solid glass or a double pane with 6mm laminated glass, 3mm insulating glass and a 6mm air space.

4. Meeting STC 40/41 for the ground floor (i.e. a 10 dB improvement) would entail upgrading to

a laminated single pane of 16mm or a double laminated double pane (6L-13-6L)mm or a laminated-insulating combination of (9L-13-6)mm. The double glazed system provides higher acoustic performance in the speech range frequency range than the single pane.

5. The current upgrades for the 2nd floor offices that are being evaluated range from a 5 dB

improvement to STC 40/41 or a 10 dB improvement to STC 45/46. In each case, low frequency, LF, performance of the glass assembly is being treated as a priority given equivalent STC ratings.

6. STC 40/41 can be met with a laminated insulating double glazed combination of (9L-13-6)

mm. As noted, the double glazed system provides higher acoustic performance in the speech range frequency range than a single pane.

7. STC 45/46 can be met with the following double glazed construction (and isolated frames for

each glazing assembly) as follows, where L-denotes laminated glass for the given glass pane layer:

o 6L-25-6L mm o 6L-50-4.5 mm

These two glazing systems result in only a modest LF improvement over the existing 2nd Floor glass, despite the significantly higher STC 46 for both designs

o 13L-50-9 mm

This system provides the best LF performance improvement realized at a rating of STC 46.

8. Alternatively, an improvement over the existing assembly can also be realized with triple

glazing using laminated glass; for instance, 6L-25-6L-13-6L mm (STC 49); but the laminated-insulating double glazed, 13L-50-9mm, at STC 46 is better in the LF range.

aercoustics.com


9. The use of laminated glass along with a split frame in the assembly would be a further design

guideline recommendation for a double glazed section requiring STC 39 or greater performance.

10. Having dissimilar glass pane thicknesses will generally result in fewer deficiencies in the

transmission loss characteristics across the audible frequency range.

11. Consideration should also be given to improving other façade components in order to limit flanking and maximize the performance of the upgraded glazing and thus optimizing the overall assembly.

aercoustics.com


Appendix A

Summary of Long Term Unattended Sound Data

AEL 10/13

aercoustics.com






RJC No.: TOR100775.0004


Appendix ‘C’

Diagrams





RJC No.: TOR100775.0004


Figure 1: Typical Plan view of thermally broken curtain wall showing both vision and back pan

conditions.

ground floor and 2nd floor noise transmission study ... · design guidelines for a new glazing...

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