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Façade facelifts could save billions

The following article discusses some of the important elements involved in “overcladding” retrofits of older multi-unit residential buildings that were constructed in an era when energy costs were not a prime consideration. It is estimated that if all of these building in Ontario were retrofitted by 2030 we would save close to $60 Billion in energy costs. This research into residential retrofits offers valuable tools for commercial,
industrial and municipal energy professionals considering similar projects.

The GTA has an enormous stock of multi-unit residential buildings (MURBs) and although these buildings are showing their age they are considered an extremely valuable resource. 


October 26, 2009
By Brian Burton

These buildings were constructed in an era when energy efficiency was not a priority consideration, thus the thermal performance of these buildings is poor. Structurally, they are in reasonably good shape, however some exposed structural components such as balcony slabs and projecting shear walls require attention. The solid exterior masonry walls of these structures offer an excellent substrate for the support of “overcladding” systems and can cut the total energy requirements of the buildings by one half.

How the GTA came to possess such a tremendous stock of these buildings is an interesting and unique story. For example, the city of Chicago has almost a half million more residents and yet it has only half the number of residential high-rises. (The Tower Renewal Guideline document provides an excellent overview of the background and history in this regard. For more details visit:  http://www.daniels.utoronto.ca/trg.)

It should also be considered that these buildings represent what amounts to a tremendous “storehouse of energy” in themselves. The structural elements, if properly protected by replaceable facades, could quite easily remain usable for hundreds of years. 

Another fact regarding energy consumption that is often overlooked is the fact that these buildings are often in clusters, meaning that a tremendous amount of energy is saved because residents are close to stores, public transit, recreational facilities and other amenities.

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On the other side of the energy coin is the consideration of the amount of energy that would be required to demolish and dispose of them. I spoke to several experts on this topic and there was general agreement that we don’t really have much of a choice, we have to maintain these buildings as best we can. 

This type of housing is also common in European cities. Several of these cities have already successfully retrofitted apartment blocks, demonstrating the feasibility of the concept.

Overcladding strategies
Overcladding offers a relatively simple solution to the problem of keeping rainwater out of buildings, and there are several variations of this concept.

Basic overcladding involves the installation of an air barrier and insulation protected by an exterior cladding applied to opaque wall elements (excluding balconies) and includes a replacement of the windows in the building.

Comprehensive overcladding involves the same approach as the basic methodology, however the cladding is installed over the entire opaque wall area and over open balconies and also includes a window replacement.

Integrated overcladding is somewhat more complex in that it involves installation of a secondary framing system that enables updating of building services and is more like a double façade that allows for natural ventilation and sound control. The ventilated cavity uses the pressure effects of the wind to dissipate the energy of driven rainwater and includes drainage paths that direct the water away from the cavity.

The success of any of these approaches requires a detailed knowledge of the physical principles and materials involved. This knowledge must also be incorporated into the design details. And if the experts are correct, no single approach or system can address all structures. As a result, each structure requires a comprehensive assessment to determine which approach best suits its needs.

Benefits
Overcladding technology is almost certainly an “exportable” technology. It will also lead to a tremendous amount of job creation opportunities and significant overall economic stimulus in the multi-residential and commercial sectors particularly. Additional advantages include:

•    Compared to demolishing buildings and reconstruction, overcladding is almost certainly more financially and ecologically responsible.
•    Improves thermal performance and air tightness and enables transfer of the dew point outside the structural wall element.
•    Optimises the use of thermal mass.
•    Overcladding contributes to improved sound insulation.
•    Quality control is improved as the insulation coverage is visible.
•    Can be installed with minimal impact on occupancy.
•    Increases the life expectancy of the building.
•    Limits disruption to the façade of the building and does not reduce the size of the rooms.
•    Improves appearance of structure, lowers maintenance costs and allows upgrading of building services.
•    Improves air quality and, when controlled ventilation is supplied, overcladding helps eliminate internal problems such as dampness, condensation and mould growth.

And last but not least overcladding retrofits eventually pay for themselves.

Limitations
•    Overcladding systems may not be as durable as solid construction and as a result in damage can lead to dampness and weathering problems.
•    Overcladding process can take a considerable length of time to complete, requires state–of–the art scaffolding systems and may be quite noisy. These factors may annoy tenants however there are strategies to address these issues.
•    Detailing is critical and requires knowledgeable design and care during installation.
•    The installation of overcladding systems is premature where an existing substrate is structurally unsound or where repairs have not been completed.
•    Overcladding systems are not generally suitable for historic buildings.

Challenges
According to Architect Ivan Saleff, the current condition of multi-residential buildings ranges everywhere from reasonably good to urgently in need of attention and must be established by an initial conditional assessment to determine feasibility strategies and associated costs.

Saleff, who is given credit for getting the ball rolling several years ago when he offered a research-based elective course on the subject at the University of Toronto, also adds that “When we examine the numerous high-rises in Toronto we also encounter almost every construction material and system employed over the past 40 years — not to mention balconies, ledges, canopies, parapets, disconnect enclosures, roofing components and a whole host of building appendages.”

Overcladding designs will need to consider a comprehensive list of performance criteria, of which many may be unknown quantities at the present time, such as connection details, fasteners, thermal & moisture movement, loads on the system, maintenance and serviceability. The key performance issues in broad terms are safety, occupant comfort, stability, structural performance, acoustics, energy efficiency, control strategies, air quality/ventilation, daylighting, maintenance/cleaning and cost.

The designs will also need to consider acoustics, air permeability, cavity ventilation, water penetration resistance, condensation, fire performance, electrical continuity and the potential for corrosion.

On a broader scale the building site itself will have to be part of the consideration along with water management as well as building permits, quality control and an incredible amount of logistics.  Another key factor, as one might expect, is the need for financial incentives and addressing issues related to the building permit process, building code and by-law requirements.
 
Brian Burton is Business Development Manager for CAN-BEST (Canadian Building Envelope Science and Technology) and writes a column for Glass Canada entitled Fenestration Forum. He can be reached at brian@can-best.com