good housing-prevailing wind exposure

WHAT is prevailing wind exposure?

How do we know when to expect the prevailing wind? The Earth is being divided into Northern hemisphere (China, Russia, Europe, etc.) and Southern hemisphere (Australia, New Zealand) with Equatorial countries in between. Both Northern and Southern hemisphere experience distinctive 4 seasons while Singapore being located at the equator experience tropical climate which is either sunny or rainy day with constant changes of cloud coverage. When the Northern hemisphere going through Winter (China usually around December), the Southern hemisphere will go through Summer (Australia around the same time) and vice versa.  

When the Northern hemisphere experience Winter, the air pressure is higher and it will move towards Southern hemisphere where the air pressure is lower (Australia is entering Summer and hot air rises) and vice versa. Being located along the equator, Singapore will experience this major air movement which is what we refer to as prevailing wind.  ​

During the Northeast Monsoon Season, the prevailing wind is from North/ Northeast while during the Southwest monsoon season, the wind is mainly from South/ South to Southwest. In between monsoon season, there will be wind movement from other directions like Northwest or Southwest but less frequent.

WHY is it important to understand prevailing wind pattern?

We enjoy breezy days, but it may bring along pollutants if the source of pollution is along the prevailing wind path. Let us explore the pull and push factors of having prevailing wind, so homeowners will better understand how to balance the pro and cons when choosing a residential unit.

​
Pull factor

Prevailing wind as the main source of passive ventilation. Wouldn’t it be nice if every time you open your windows or standing at the balcony, a stream of gushing wind flows through and cool down your unit? Best of all, it’s free! The challenge would be to know how to benefit from the prevailing wind by knowing where and when does the prevailing wind happen. Singapore receives mostly South Eastern wind, therefore the next question would be how to make sure that the surrounding environment (i.e. building, future development, etc.) won’t block this prevailing wind potential.
 
Promote indoor air exchange. Designing a unit which allows cross ventilation is a tough act as designers need to balance privacy needs vs allocating more openings (i.e. windows) for cross ventilation. Current housing unit generally separate public area (Living and Dining room) from private area (Bedrooms) and a common corridor connecting these two areas. The corridor in between the rooms at the front and bath at back will reduce air movement potential. To promote cross ventilation, all doors (Main door, bedroom, kitchen door) and windows should be left open. This ideal situation may not happen most of the time, thus there’s a high concentration of stagnant air within the interior spaces. This stagnant air consists of particles as well as microbes which may cause sickness. If a unit is facing a prevailing wind path, once the doors and windows are open, air exchange will happen at a quicker pace compare to a unit not facing the prevailing wind path as it will need to be induced by air pressure differences between outdoor and indoor spaces.  

"… Your (hausanalyst) attention to detail which you helped me understand the various concept of wind direction, sun analysis and unit facing is indeed a league of its own. I am extremely pleased with the quality of customer service you provided to me. …" May 2016

(Mr.Yong engaged us after purchasing the unit at Brownstone EC, Canberra)

" I have moved into my unit (translated). Your (hausanalyst) sun analysis super accurate. The shadow casting on balcony and all is exactly. Wind analysis also quite accurate (translated)" Jan 2019

(We re-engaged Mr. Yong to checked on his completed unit after moving in)

Mr. Yong | design engineer, Oil and Gas | The Brownstone EC, 2016

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Push factor

Assist in the surrounding pollutant movement. As described earlier on, should there be a construction activity going on just across your unit and prevailing wind happens to move along the same direction towards your unit, then you will be experiencing massive dust pollution. If you think of the pollutants as a gas, then maybe the most recent (July 2019) pollution at Pasir Gudang in Johore Bahru will give you a better idea of what to expect. The challenge will be to know in advance what sort of surrounding your future home will be surrounded by before you decide. We will discuss on this in the later part of this article.   
 
Assist in rain water splashing issue.   
Gushing wind with heavy rainfall always translates to water leakage through the window or sliding door edges if the design is not water tight or it’s not being done properly. This situation was recorded in the Internationally acclaim residential project, Waterway Terraces 1 at Punggol back in the year 2015. The reply from the developer is as follow (as published by straits times dated 2015 July 16):

… "Preliminary checks indicate that because of the intense rainfall and direction of the wind, rainwater had accumulated at the balcony area and, in some cases, had also seeped into the living rooms or bedrooms connected to the balcony….
 
Based on the location of the affected units as well as the direction of wind during that exact period, we deduced that the shape of the building could also play a part in inducing excessive wind flow, which accelerate the water seepage issue apart from than the size of the balcony as well as poor workmanship and construction detailing. 
 
This is just one of the instances that facing a prevailing direction may bring about negative impact unless there’s an in-depth understanding of the development (i.e. layout, design, details, etc). 

​HOW to make the right decision to benefit from prevailing wind potential

Basic understanding of where and when the prevailing wind happens. As described earlier, if we know that China is entering winter, then we should expect wind from North East to happen as air movement flow from Northern part of Earth towards Southern part of Earth. To maximize the prevailing wind intake, the wall with the most opening (i.e. windows) should be perpendicular to the prevailing wind direction.
 
Understand the location of the project as well as the surrounding present and future situation. (i.e. building heights, plot ratio, building shapes, distance between buildings, etc.).
 
We know that the city core (in the city state like Singapore) tends to have taller buildings while city fridge with lower building heights. Singapore skyline is mainly guided by the URA masterplan which will be reviewed every 5 years to plan for future 10 to 15 years land use. A neighbourhood with mostly taller building will create wind tunnel effect whereby wind being channeled between the gap of 2 neighbouring buildings and thus increase the wind speed after it moved through the building’s gap. This wind load (from wind tunnel effect) may not be what you as a residential occupant will enjoy due to its higher intensity. Note: A high-rise building being defined by SCDF as any building taller than 24m (8 storeys of a typical HDB).

So, how do you know if you will get a tall building next to your chosen development? As explained earlier, Singapore land use is guided by URA Masterplan (latest review in 2019). The masterplan will reflect the intended land use in the near future with plot ratio, which determine how much floor area can be developed within the particular land. On top of this, height control will be imposed on certain area due to flight zone restriction, etc. A high plot ratio usually can be traced to mature area due to higher land cost and readily availability of amenities. While a layman or even industry expert may guess the future surrounding development based on given plot ratio, only a trained professional will make the closest assumption of what the future layout will be in terms of building block placement, density, etc. Knowing the future surrounding development will give you the edge over others who don’t.

Back in 2015, the international acclaimed public housing, Waterway Terraces I made headlines for the wrong reason when mini flash flood hits a number of units. While the report pointed to intense wind with heavy rainfall as well as leaky balcony as the main culprits, we noticed that the incident only happens in a selected area of the development (A spokesman said: "Most of these units face an open field, making them more prone to impact by heavy downpours."). At this particular facing, the shape of the building is an inward form of a partial hexagon, almost similar to an armchair shape. Theoretically, when wind moves diagonally towards this surface, the intensity will increase similar to tunnel effect as wind being ‘directed’ to a single point of the surface. 

At hausanalyst, we deduce the prevailing wind movement based on multiple factors with some mentioned above and most, specific to each site and development. While we can’t deduce the exact wind speed or wind direction during a specific time, you can be sure that the major air movement won’t change unless the world gone through a massive weather pattern change when suddenly the Northern and Southern hemisphere not having 4 seasons anymore! In micro settings like immediate neighbourhood surrounding, things are clearer with existing conditions like surrounding building height, usage, shape, building block placement, etc.  

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