December 11, 2015 Jenna Maw LineBox Studio Inc. 126 York Street, Suite 502 Ottawa, Ontario K1N 5T2 Dear Ms. Maw: Re: Qualitative Pedestrian Level Wind Assessment St-Charles Market, 135 Barrette Street, Ottawa GWE File No.: 15-120-DTPLW 1. INTRODUCTION Gradient Wind Engineering Inc. (GWE) was retained by LineBox Studio Inc. to undertake a qualitative pedestrian level wind assessment for St-Charles Market, a proposed mixed-use redevelopment project located at 135 Barrette Street in Ottawa, Ontario. This report provides a qualitative assessment of pedestrian level wind comfort for the noted site based on architectural drawings provided by LineBox Studio Inc. in November 2015, consideration of existing and approved future surrounding buildings and statistical knowledge of the Ottawa wind climate, as well as experience with similar projects in Ottawa. In the early stages of design development, a qualitative pedestrian wind assessment is useful to identify any significant massing features or design elements which may adversely impact pedestrian activities within the study area, and to provide initial recommendations for mitigation strategies as may be required. 127 Walgreen Road, Ottawa, Ontario K0A 1L0 T (613) 836-0934 www.gradientwind.com
2. TERMS OF REFERENCE The focus of this qualitative wind assessment is St-Charles Market, a proposed mixed-use redevelopment located approximately two kilometres northeast of the Ottawa downtown core. The study site is bordered to the southwest by St. Charles Street, to the northwest by Beechwood Avenue, to the northeast by a lowrise building and parking lot, and to the southeast by Barrette Street. Upon completion, the proposed development will comprise an eight-storey plus mechanical penthouse building rising to a total height of approximately 22.5 metres above local grade. Above a two level underground parking garage, the ground floor will contain a restaurant unit at the southwest corner of the building with access from St. Charles Street. Near the centre of the site, the southwest portion of the existing church will contain the St-Charles Market. Along the southeast side of the building, there will be residential units and access to the residential lobby from Barrette Street. The west side of the site will contain a patio for the St-Charles Market and a City of Ottawa park, while an outdoor market and patio will be located at the southwest side of the site. An additional patio will be located between the existing church structure and the new building. The study building consists of the existing church and a new L-shaped addition along the southeast side of the development site. At the northwest corner of the building, an outdoor pathway is located between the residential units and the St-Charles church. From the third to seventh levels, the new building rises with a uniform floor plate. At the eighth level, the floor plate reduces at the southwest corner, providing a residential amenity terrace. Above the eighth level, the building contains a mechanical penthouse. Regarding wind exposures, the near-field surroundings of the development (defined as an area falling within a 200 metre radius from the subject site) are characterized by a medium-density concentration of existing low- and medium-rise residential buildings in all directions. Regarding the far-field surroundings (defined as the area beyond the near field and within a two kilometre radius), the region from west clockwise to east comprises a low density concentration of primarily low- and medium-rise developments, while the remaining compass directions comprise a medium-density concentration of primarily low- and medium-rise developments with a few isolated high-rise developments. The ground floor and seventh level terrace plans, including letter tags identifying wind sensitive pedestrian locations considered in this assessment, are illustrated in Figure 1. Qualitative Pedestrian Level Wind Assessment 2
3. METHODOLOGY The main aspects of a qualitative pedestrian level wind assessment include: (i) consideration of the statistical properties of the local wind climate; (ii) knowledge of wind flow behaviour in typical urban, suburban, and open environments; and (iii) an understanding of how common wind conditions relate to typical pedestrian activity types. 3.1. Ottawa Wind Climate The statistical model of the Ottawa wind climate, which indicates the directional character of local winds on a seasonal basis, is illustrated on the following page. The plots illustrate seasonal distribution of measured wind speeds and directions in metres per second. Probabilities of occurrence of different wind speeds are represented as stacked polar bars in sixteen azimuth divisions. The radial direction represents the percentage of time for various wind speed ranges per wind direction during a 40-year measurement period. The preferred wind speeds and directions can be identified by the longer length of the bars. For Ottawa, the most common winds concerning pedestrian comfort occur for west and east quadrants; and the most common wind speeds are below 10 metres per second. However, it is noted that the most prominent wind direction for higher wind speeds originates from the west quadrant. The directional preference and relative magnitude of wind speed changes somewhat from season to season, with the summer months displaying the calmest winds relative to the remaining seasonal periods. Qualitative Pedestrian Level Wind Assessment 3
SEASONAL DISTRIBUTION OF WINDS FOR VARIOUS PROBABILITIES OTTAWA MACDONALD-CARTIER INTERNATIONAL AIRPORT, OTTAWA, ONTARIO Notes: 1. Radial distances indicate percentage of time of wind events. 2. Wind speeds represent mean hourly wind speeds measured at 10 metres above the ground. 3.2. Massing vs. Climate Geometric Effects Qualitative Pedestrian Level Wind Assessment 4
The physical features of a development site that are most influential to the local wind conditions include the massing and relative spacing of surrounding buildings, the geometry and orientation of the study building, and the alignment of the study building with respect to statistically prominent wind directions. Wind flow characteristics which combine to determine how conditions will develop include phenomena known as downwash, channelling coupled with acceleration, and shielding, as illustrated in the image below. Downwash 1 relates to the effect of winds against a tall building, whereby much of the impinging flow on the windward side of the building, nominally below two-thirds of the total height, is directed to lower levels. Taller buildings with smooth façades and no podiums produce the strongest downwash effects at grade, while the presence of protruding balconies and a tower setback from the podium edge mitigates downwash effects at the ground level. Channelling 2 refers to acceleration of wind through gaps between buildings, while acceleration of wind 3 occurs around building corners. Shielding 4 relates to calm zones on the leeward side of buildings, protected from prevailing winds. 2 4 1 3 3 3.3. Pedestrian Wind Comfort Guidelines Qualitative Pedestrian Level Wind Assessment 5
The pedestrian wind comfort guidelines used by GWE, which correspond to industry-accepted standards, are based on the correlation between a variety of pedestrian activity types and acceptable wind speed ranges for those activities. More specifically: Wind conditions are considered to be comfortable for sitting when gust wind speeds less than or equal to 14 kilometers per hour occur at least 80% of the time. The corresponding equivalent mean wind speed is approximately 10 km/h; Wind conditions are considered to be comfortable for standing when gust wind speeds less than or equal to 20 kilometers per hour occur at least 80% of the time. The corresponding equivalent mean wind speed is approximately 14 km/h; Wind conditions are considered to be comfortable for strolling when gust wind speeds less than or equal to 25 kilometers per hour occur at least 80% of the time. The corresponding equivalent mean wind speed is approximately 17 km/h; and Wind conditions are considered to be comfortable for walking when gust wind speeds less than or equal to 30 kilometers per hour occur at least 80% of the time. The corresponding equivalent mean wind speed is approximately 20 km/h. Gust speeds are used in the guidelines because people tend to be more sensitive to wind gusts than to steady winds for lower wind speed ranges. The guidelines are applied to the intended use of an outdoor area. For example, an entrance to a building not served by a vestibule or revolving door should be suitable for standing, but need not be suitable for sitting, while a public sidewalk need only be suitable for walking in most circumstances. 4. ANTICIPATED PEDESTRIAN COMFORT Based on consideration of the proposed development at 135 Barrette Street, surrounding building massing, and the relationship to the local wind climate, the following statements summarize our opinion of how these influences will affect pedestrian comfort at key areas. Sidewalk and Bus Shelter along Beechwood Avenue (Tags A & B): Wind conditions on the sidewalk (Tag A) and bus shelter (Tag B) along Beechwood Avenue are not expected to be influenced by the future building at the southeast side of the site. As such, wind comfort along the sidewalk and at the bus shelter are expected to be suitable for strolling, or better, throughout the year. The noted conditions are considered acceptable for the intended uses of the space. Qualitative Pedestrian Level Wind Assessment 6
Sidewalk and Building Entrances along St. Charles Street (Tags C & D): The sidewalk along the southwest side of the study site (Tag C) will be protected from grade-level winds by the surrounding building massing. Overall, wind conditions along the sidewalk are expected to be suitable for sitting during the summer months, and for standing throughout the rest of the year. The building entrances on the southwest side of the building (Tag D) will experience similar and somewhat calmer conditions than the adjacent sidewalk due to the added protection provided by the building façade. Conditions at the building entrances are expected to be suitable for sitting during the spring, summer, and autumn months, and standing during the winter, which is acceptable. Sidewalk, Building Entrance, and Loading Area along Barrette Street (Tags E & F): The sidewalk along Barrette Street (Tag E) will be protected from direct oncoming westerly and easterly winds by the surrounding building massing. Accordingly, wind conditions are likely to be suitable for standing, or better, during the spring, summer, and autumn months, and for walking during the winter. The building entrance and parking garage entrance, as well as the loading area along the southeast side of the building (Tag F), will experience similar and somewhat calmer conditions than the adjacent sidewalk due to the added protection provided by the building façade. Wind conditions at these locations are expected to be suitable for standing, or better, throughout the year. Pathway and Building Entrances at Centre of Study Site (Tag G): The pathway and building entrances between the existing church structure and the proposed building addition (Tag G) is well-protected by the surrounding building massing. As such, wind conditions are expected to be suitable for sitting throughout the year. City of Ottawa Park and St-Charles Market Patio (Tags H & I): The wind conditions within the City of Ottawa Park and parkette (Tag H) and the St-Charles Market patio (Tag I) along the northwest side of the site are expected to be somewhat calmer than the conditions along the Beechwood Avenue sidewalk, since it will be set back from the roadway corridor. As such, wind conditions within the park are expected to be comfortable for sitting during the summer months, and for standing during the remaining seasons, which is acceptable. Outdoor Patios (Tags J, & K): The outdoor market and patio, as well as the entrance to the indoor market at the southwest side of the existing church structure (Tag J), will be well-protected from oncoming winds by the surrounding building massing. Overall, wind conditions over the patio and at the entrance to the Qualitative Pedestrian Level Wind Assessment 7
indoor market are expected to be suitable for sitting during the typical use period, defined as the late spring through the early autumn, and suitable for standing the remainder of the year. The restaurant patio between the existing church structure and the proposed addition (Tag K) will be wellsheltered, and as such, conditions are expected to be suitable for sitting throughout the year. Level 7 Terrace (Tag L): The amenity terrace at the west side of the seventh level is sheltered from easterly winds by the study building. In order to minimize the influence of westerly winds over the terrace space, it is recommended that a solid vertical wind screen measuring at least 1.6 metres above the walking surface be installed along the full perimeter of the terrace. Provided that the aforementioned wind screen is included in the terrace design, wind conditions on the terrace are expected to be calm and suitable for sitting or more sedentary activities during the typical use period. Existing vs. Future Wind Conditions: The introduction of the proposed development at 135 Barrette Street is not expected to significantly influence pedestrian wind comfort over neighbouring areas at grade. In particular, although modest changes to wind speeds may occur beyond the study site upon introduction of the proposed development, nearby building entrances, sidewalks, and other pedestrian areas will continue to experience wind conditions similar to those that presently exist without the proposed building in place. Within the context of typical weather patterns, excluding anomalous local storm events, such as thunderstorms, tornadoes and downbursts, no dangerous or consistently strong wind conditions are expected anywhere over the subject site on an annual basis. During such events, wind conditions are influenced by specific local meteorological conditions and building geometries that cannot be predicted through a qualitative analysis. Qualitative Pedestrian Level Wind Assessment 8
5. SUMMARY AND RECOMMENDATIONS Based on a qualitative analysis of architectural drawings, surrounding building massing, and the Ottawa wind climate, the following general statements summarize our prediction of future wind conditions for the proposed development at 135 Barrette Street in Ottawa, Ontario. 1. Wind comfort at all grade-level pedestrian-sensitive locations across study site is expected to be suitable for the anticipated uses without mitigation. These areas include nearby sidewalks, pathways, building access points, patio spaces, and the City of Ottawa park. 2. A perimeter wind screen measuring 1.6 metres tall is recommended for the seventh level amenity terrace to mitigate westerly winds, and allow for conditions appropriate for sitting during the warmer months. 3. The presence of the proposed development may result in moderate increases or decreases to local wind speeds over grade-level areas, as compared to existing conditions. However, despite potential changes, the current uses and comfort levels of the majority of pedestrian areas, including nearby building entrances and sidewalks, will not be significantly affected. The foregoing analysis and statements are based on knowledge and experience of wind flow patterns for the study site and in similar settings. As such, this assessment is intended to ensure adequate pedestrian safety relating to wind, and to provide general guidance relating to pedestrian comfort over the full study site. Qualitative Pedestrian Level Wind Assessment 9
This concludes our qualitative assessment of pedestrian wind comfort. Please advise the undersigned of any questions or comments. Sincerely, Gradient Wind Engineering Inc. Steven Hall, M.A.Sc., EIT Microclimate Specialist Vincent Ferraro, M.Eng., P.Eng. Principal Andrew Sliasas, M.A.Sc. Project Manager GWE15-120-DTPLW Qualitative Pedestrian Level Wind Assessment 10