How do we address the existing stock of high-rise buildings that are no longer efficient of desirable in an increasingly sustainability-minded world?
This article was originally published in Blue 02: Systems and Structure in 2010. You can see the article in its original format, and other articles, online.
Ongoing experiences in the commercial office sector have shown that the traditional 1970s, 1980s and 1990s developer-driven edict of simply seeking to maximise net to gross floor area in the search for the highest yielding property no longer has the same relevance.
Now instead workplace practices – how individual office-workers behave, whether alone, in clusters, as teams, as departments, and how each might engage with the other and with their clients or suppliers – has become profoundly important in planning space. The emergence of terms such as break-out, hub, winter-garden, third space or place pervade and allude to quality not quantity – effectiveness not efficiency. The employee has become more valuable as an asset and their working environment more considered, and with this change has come a wave of buildings that are well-organised spatially. They tend to have adaptable, uninterrupted large floorplates, serviced by side or multiple cores, and are low to medium rise.
In parallel with this evolution of commercial space, an
energy-conscious era is also upon us, with individual buildings planning highly
efficient and adaptable ventilation and lighting systems working in tandem with
passive and active façades and coupled with sophisticated Building Management
Controls. So where does this leave our existing building stock and what might
we do with the huge stock of vertically stacked, small floor-plate high rise
buildings planned around very tightly constrained central cores?
For decades many high-rise towers were erected around the world with little regard for energy consumption. The implementation of passive systems within many of these towers was almost unheard of and at the time of their inception would most likely have been ridiculed. Many towers conceived at this time did not even employ double glazing to their façades, and while electricity was cheap and abundant, there was little or no consideration of carbon emissions, or life-cycle cost. Both were ignored or left unconsidered for the benefit of minimising capital expenditure at the time of construction, to maximise the developer’s immediate profit.
Within developed societies we are now acknowledging that our current building stock is too inefficient to sustain, and yet it is also now too large a problem to ignore.
"80 billion British Thermal Units of energy are embodied in a typical 50,000 square foot commercial building, the equivalent of 640,000 gallons of gasoline.
A commercial building of this size releases about the same amount of carbon into the atmosphere as driving a car 2.8 million miles. Demolishing it creates nearly 4,000 tonnes of waste.
Recent research indicates that even if 40% of these materials are recycled, it takes nearly 65 years for a green, efficient new office building to recover the energy lost in demolishing an existing building."
source: advisory council on historic preservation
The argument for retrofitting over demolition should – and will – prove to be irrefutable and with this the focus will turn rapidly to upgrading old buildings.
Our existing building stock presents us with a multitude of common issues, including high heat gain through poor orientation or inadequate façade systems; difficult and inefficient to regulate locally with ageing mechanical systems which themselves are highly energy consumptive; uninhabitable areas immediately adjacent to the northern and north western elevations due to excessive radiant heat; and seriously constrained vertical connection relying solely upon the central core bank of lifts. Additionally, very tight floor-to-floor heights and constrained vertical risers give limited options for the reticulation of primary building services from the core, and only restricted internal planning options are available due to constant and small core to façade depths.
A result of these issues we are witnessing many buildings, which are evidently suitable for retrofitting, undergoing a re-cladding, often in parallel with mechanical plant replacement or overhaul.
If upgrades to plant and façades are done well then the obvious advantages in not having to demolish a building include the maintaining of embodied energy, the creation of high energy savings at low capital cost, the reduction of carbon output and with it pre-empting the large potential energy cost increases as a result of future emerging carbon taxation.
However, this seems to ignore the other fundamental issues that many central-core high-rise towers have; that they have become unsuitable to many organisations who wish to have inter-departmental links, greater connectedness between departments, greater varied open-planned space, and spaces that are special, and more human.
If owners are spending money sorting out energy consumption, might it not be worth contemplating investing more capital to create additional space with greater flexibility? The argument might be for a new zone rather than just a new skin. As I have been thinking of this while living in the southern hemisphere in Australia, I refer to it as the North Face.
While a new skin or façade system, coupled with an upgrade or replacement of the ventilation or cooling systems, will achieve greater energy efficiency, by simultaneously introducing an interstitial floor zone on the north (sunny) façade of a building then this zone can be designed to rectify issues of light penetration, passive heat and ventilation regulation, services and social inter-connectivity. The opportunity seems to exist to not only improve the energy efficiency of building stock but also to create a more flexible, adaptive and healthier (and therefore more valuable) office space, thus creating a new asset to an old building.
The north face zone might provide an additional five or six metres' depth of space to that frontage, which will give greater flexibility, allowing offices to offer a combination of deep and perimeter space; passively reduce radiant heat into the building; save energy by separating the northern zone from the main building; allow greater control of daylight; offer the promotion of social and inter-departmental connection between floors; promote a healthier workplace environment through the introduction of winter-gardens; promote better ventilation air filtration and subsequent reduction of Sick Building syndrome; create a new zone for services reticulation which is peristitial rather than interstitial; and create greater net to gross efficiencies and more adaptable plates.
The inclusion of this buffer zone offers the introduction of social, winter-garden, meeting and write-up areas, as well as the possible interaction between floors through open or fire compartmented staircases that create both dynamic and efficient working environments.
The second skin on the new external face allows a greater passive buffer zone for seasonal adjustments. Using trickle vents, planting for shade, internal partitions on the old façade line can be closed to insulate or retain heat during periods of excessive cool/hot. Vitiated air may be drawn through a “double-skin façade”. Light shelves and louvres are incorporated to reduce direct or excessive solar gain, whilst reflecting light further into the floorplate.
High rise buildings have been traditionally set back from the street frontage with the incorporation of a podium. This zone which was designed to set buildings away from streets may be partially or wholly sacrificed to allow buildings to have a true second life. It might be that by populating this zone, the street linings themselves become more active and greener.
The dead load of the new structure will most likely need to be taken vertically through the podium base, although floor extensions could also be 'hung' depending on the depth of the north face zone and the strength of the structural frame. Concrete framed buildings, having cured over time, will have substantial additional strength and stiffness, meaning that lateral and vertical loads could be supported without additional strengthening.
Furthermore, construction might well be possible on a floor-by-floor basis, using the existing façade as the construction hoarding barrier and then breaking through for occupation. Thus the phasing allows continuous occupation.
Architecturally, it is clear that every building will have different issues and requirements, and maybe this solution cannot be employed into the historically important one-off, unique or special forms; however, many bland structures may well be substantially improved and humanised by 'adjuncts' that hang from some or all of their floors, adding vibrancy and life to their periphery that is currently absent.