April 1, 2012
By Bob Marshall, P. Eng., BDS, LEED AP
When it comes to engineering its buildings, Canada has made great strides in durability and energy efficiency requirements with respect to codes and programs such as Leadership in Energy and Environmental Design (LEED). Unfortunately, despite these green leaps, it seems the basic lessons learned over the past decade or so still have not been applied to most building envelopes. In other words, we have structures designed to have service lives of 50 to 100 years, with enclosures only equipped to last for 10 to 15 years.
Even though ‘at-minimum’ laws are in place to provide resistance to deterioration, there are still significant costly premature failures. In British Columbia, less than 50 per cent of the leaky condominiums, part of a $1.5-billion class action, have been repaired. Now, failures reported in the media are suggesting some Ontario condominiums have inefficient glass walls and poorly designed building envelopes susceptible to premature problems. The legal fallout could well exceed its West Coast counterpart. What are the basic strategies for achieving envelope durability and energy efficiency, preventing ‘disposable’ or ‘throwaway’ buildings?
Last October, a Greenbuild session in Toronto on commissioning clearly showed the majority of participants believed in the importance of this quality verification process. Since January 2007, Part 5 of the Ontario Building Code (OBC) has mandated envelope assemblies be in accordance with good practice such as Canadian Standards Association (CSA) S478, Guideline on Durability in Buildings. Further, as of January 2012, there are higher energy efficiency requirements in the code. Nevertheless, energy-inefficient, predominately glass towers continue to be built. To prevent durability failures and energy waste, it is essential to apply five basic lessons learned from the advanced state of green building to all buildings.
1. Smart financial strategy
To achieve a sensible financial strategy, building owners can look at previous failure trends to prevent major payouts. From 1984 to 1994, Tarion Warranty Corporation—which issues warranties on Ontario’s residential construction—had about $23 million in high-rise claims. (Additional costs paid by builders and owners would be significantly higher.)
This author chaired a steering committee that focused on identifying solutions to the key causes of high-rise building failures based on 1991 research of 52 buildings. Most of the claims were related to moisture problems with the envelope rather than structural concerns. The main causes were missing and bad details, along with inadequate inspections. Tarion’s High-rise Residential Construction Guide was co-published in 1995 with the Ontario Ministry of Municipal Affairs and Housing (MAH), and is referenced in the appendix of OBC and the National Building Code of Canada (NBC) to help prevent claims.
In 2001, the Canada Mortgage and Housing Corporation (CMHC) undertook a research study to gain a better understanding of key failure areas that resulted in financial insolvency and to identify risk management measures to provide for healthier buildings and reduce premature problems. (Visit www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/01-140-E.htm). This author looked at the failure trends for this study and compared them to the results of the aforementioned 1991 study. Significantly, about 78 per cent of deficiencies were (still) with walls and wall building envelope components, including windows and doors. To protect the financial health of high-rise condominiums, it was recommended property managers know which areas are potentially problematic; this way, they can ensure performance audits are conducted in the first, second, and seventh years. Identifying performance issues before warranty coverage expires reduces replacement costs and avoids the expense of special assessments.
What is the state of building failures in 2012? Anecdotally, according to Tarion, some building envelope problems continue, but it does not seem to be systemic. However, many of the façades on today’s structures are predicted to have a 10- to 15-year service life, which is significantly less than the structure. Durability of the envelope is important—after all, one can change a mechanical component or a countertop relatively easily, but re-skinning an entire building could cost millions per floor or hundreds of thousands per condo unit.
Notwithstanding the financial benefits of investing a little more into the building cost for durability or envelope commissioning to prevent premature failures and expensive rehabilitation, most owners and financial institutions do not specify these requirements. As a result, two-year-old buildings are being re-skinned and envelopes less than 15 years old are being rehabilitated.
Durability strategies, as required by OBC and envelope
commissioning processes, must be implemented to prevent premature failures and financial distress. Poorly designed and inefficient building envelopes will be significantly expensive to rehabilitate and the cumulative costs could reach billions of dollars. Rather than wait for special assessments or major capital cost expenditures, it makes sense to require them before construction commences.
Infrastructure Ontario (IO) requires LEED’s Regional Priority (RP) Credit 1, Durable Building, and building commissioning (including the envelope) on all public-private partnership (P3) projects where operators are typically responsible for a 30-year operating period. It is smart from a sustainability perspective to select 30-year roofs and exterior walls for durability, along with daylighting, which has a direct positive impact on productivity. (For a discussion on durability and LEED, see the September 2010 issue of Construction Canada for this author’s article, “Five New Ways to Think Green with Concrete.” Visit www.constructioncanada.net and select “Archives.”) ‘Sexier’ components, like premium finishes, can always be added later.
2. Envelope rating for durability and energy use targets
It makes sense to specify durability categories based on the design service life for the building type. The OBC-referenced CSA S478 specifies residential and office buildings as examples of the ‘long-life’ category, requiring a design service life of 50 to 99 years. While this is great for the structure, an appropriate durability target should also be specified for the envelope. It is not smart to design a 15-year building envelope for something expected to last 60 years, especially for the owners who will have to make costly repeated rehabilitation/replacements four times.
Although building envelopes can be complicated, design professionals can find strength in lessons learned based on experience with LEED’s RP Credit 1.
This author has developed a complimentary Building Envelope Rating (BER) spreadsheet tool, based on more than 50 LEED projects. (For more information on BER, contact firstname.lastname@example.org). Using various building envelope targets compatible with the CSA standard categories, the tool targets these levels:
For example, the Platinum (top-performance) target is to last more than a century, while the Throwaway target is 11 to 24 years—ideally limited to buildings that are only going to be rented for short periods.
Gold (i.e. 50 to 99 years) should be the target for residential, commercial, office, and institutional LEED buildings. It should also be the goal for high-rises requiring extensive use of scaffolding and the potential for costly repairs.
For the roof portion of the envelope, a Silver BER target of 30 years is achievable; some industry suppliers can back up the roofs with warranty protection lasting this long. The wall part of the building envelope should be at least equal to the roof. Therefore, a Silver BER target should be specified, using pre-painted metal wall assemblies, as an example. Better yet, one could consider specifying a Gold BER target of 50 years by, for instance, using natural stone and curtain wall in a rainscreen configuration.
It is important to know, however, that RP Credit 1 allows building envelopes to have only 50 per cent of design service life for two CSA categories:
Energy use intensity (EUI) targets can also be important to specify at the concept stage, as utility costs cannot be reduced unless the building’s consumption is measured and managed. To establish an appropriate EUI, one can specify a target consistent with good industry practice in terms of the standard measurement in kWh/m²/year. In Ontario, at minimum, a target should be derived from the three options in OBC effective (or, for other jurisdictions, the prevailing code):
Improved energy-efficient building envelope (e.g. quick-installed insulated metal panels [IMPs]), lighting, and HVAC systems are recommended and a higher-performance EUI target should be considered. For offices, rather than target an average EUI of 170 kWh/m²/year, a target EUI for a 50 per cent reduction to 85 kWh/m²/year or more is possible. Significant improvements in the building envelope at the time of construction or system replacement are possible. For example, vacuum insulated panels (VIPs), with an insulation value of more than R-60 per inch (RSI 10.56 per inch) are available and are being studied at the National Research Council’s Institute for Research in Construction (NRC-IRC’s) Ottawa campus as part of a roof replacement.
Applications of VIPs that are thinner and provide superior condensation and mould resistance, along with higher-performance exterior walls, are being researched. Implementing the lessons learned with these types of innovative technologies can significantly lower the building’s EUI, resulting in higher energy cost savings and resale values.
3. Better building detailing
Improved building envelope detailing is mandatory for achieving better durability and energy efficiency. CSA S478 quality assurance (QA) activities include review of details for the envelope, HVAC, and other systems. For the building envelope, it is extremely important wall/roof interfaces and penetrations (e.g. windows and doors) be detailed to prevent premature deterioration and interior damage due to air and water leakage. There are examples available from CMHC and the aforementioned High-rise Condominium Construction Guide.
Additionally, architects, building science professional engineers, and major system suppliers can develop specialized details that work to achieve material compatibility between critical components in building envelopes. This will help achieve BER Platinum, Gold, and Silver targets.
It is also important to review details with the subcontractors at a preconstruction meeting to determine sequencing and tweak the details with the trades to improve constructability and reduce the need for rework.
4. Field review
Periodic third-party quality field reviews and audits of building envelope construction are good ways to ensure construction conforms to the details. Air barriers, insulation levels, and vapour retarder installation can be checked. Inspections by system suppliers (usually at no additional cost) will provide checklists. These help guide subcontractors to make any necessary repairs so good installations and full warranty coverage are provided.
Focused testing of critical components such as windows and doors for air/water penetration before completing construction is essential for the predicted service life to match the design service life. This author has worked on several landmark buildings where third-party field reviews and commissioning tests meant corrective actions were completed before leaks (and health-related damages) occurred. By completing these major corrective actions before turnover, there was no repair cost to the owners and bigger, future problems were prevented.
5. Documentation by professionals
It is important to know many municipalities do not mandate Letters of Compliance for Part 5, as this is not an OBC requirement. Additionally, for Part 12 (“Energy Efficiency”), documentation of OBC compliance is not usually required. Partially as a result of the B.C. leaky condominium crisis, Letters of Compliance are required in the British Columbia Building Code (BCBC) and in Vancouver from professional engineers and/or architects to show the plans and supporting documents (including details and specifications) substantially comply with the code.
While many municipalities do not require these documents, it is still critical to have third-party professional Letters of Commitment for design/field review and code compliance provided. This helps reduce one’s risks before the money is turned over.
Following these five simple suggestions can help ensure building owners achieve the durability and energy efficiency they expect of their facilities. By specifying an appropriate building envelope rating and energy use intensity target, along with having documentation by professionals, a project team can have peace of mind, prevent throwaway construction, and protect its collective chequebook.
Bob Marshall, P. Eng., BDS, LEED AP, has been appointed to the National Research Council’s (NRC’s) Task Group on Energy Targets. He is Canada’s appointed expert on the International Organization for Standardization (ISO)/TC 163-TC 205 WG4, and a voting member for TC 163/SC 2 on calculation methods. Marshall chaired the U.S. Green Building Council’s (USGBC’s) Greenbuild 2011 ‘Best of Canada’ stream of educational seminars and is a member of the council’s education committees. He is a senior consultant at Yolles, A CH2M HILL Company in Toronto. Marshall can be contacted via e-mail at email@example.com.
Source URL: https://www.constructioncanada.net/an-end-to-throwaway-building-envelopes/
Copyright ©2020 Construction Canada unless otherwise noted.