18 l ROOFINGBC l FALL 2018 FEATURE is closed so that the entire structure can be pressured up, usually to a steady state of 50 pa. Any leakage can then be measured, even felt; and a smoke test will tell a great deal, pinpointing membrane fish-mouths or other discontinuities where interior air passes through the control layer. One step at a time (or not) Since its inception in 2017, the Step Code has been offered to designers and builders for voluntary compliance. Some munic- ipalities have already implemented the Step Code as policy, a program or part of a building bylaw, and organizations like BC Housing have embraced the principles of the Step Code, utilizing Passive House concepts in a number of projects across B.C. The lower steps are “relatively straight- forward” (www.energystepcode.ca). Step 1, in fact, simply means satisfying the current BC Building Code. But the Upper Steps (3, 4 and 5, depending on building clas- sification and type) will be more stringent and demand a higher level of expertise and methodology, especially for installers. The City of Vancouver is exempt from the Step Code because they have their own plan with stringent requirements. The Zero Emissions Building Plan (ZEBP), a program similar in intent to the Step Code, focuses on reducing GHG emissions to zero by 2030, for all newly constructed build- ings3 . This new set of standards is driven, in part, by the fact that building inefficien- cies currently account for more than 50 per cent of GHG emissions generated by buildings in the City of Vancouver4 . Four strategies are listed in the ZEBP document, all aimed at improving the building enve- lope and ventilation systems, and at imple- menting what they call “neighbourhood energy systems” – shared sources of heating and cooling. Of course, the common link between the ZEBP and the Step Code is the building envelope. Several requirements of the ZEBP are already in force. The Step Code sets out incremental effi- cienciesforPart9buildingsthataredifferent from those for Part 3 structures. There are also regional differences. For example, Part 9 requirements will be implemented across the province, but for now, Part 3 buildings only in Climate Zone 4 will be required to comply (generally speaking, the south coast of B.C., and southern Vancouver Island). Furthermore, while Step 5 (the equivalent to Passive House) applies to all Part 9 resi- dential construction, Part 3 buildings are measured differently. For example, Step 3 will be a requirement only for commercial buildings, and for some concrete residential structures, while other concrete structures and wood-framed multi-residential build- ings will eventually be built to the standards for Step 4. The City of Vancouver has a different set of building classifications than those used by the Step Code – for example, detached housing and low-rise MURB (Multi-Unit Residential Building) – but the point is that change is coming in Vancouver much sooner, and at a greater speed, than anywhere else in British Columbia. And the emphasis, just as it is with the Step Code, will be on the integrity of the building envelope. The envelope, please What is the building envelope? It is, of course, the box – the container of every- thing inside that separates the build- ing’s conditioned space from the outside environment. The envelope, then, is the building’s foundation, bottom slab, walls and roof. And like a paper letter envelope (remember those?), it has to be continu- ously sealed all the way around to separate 3  Three targets are published in the ZEBP document – using only renewable energy by 2050, which is dependent on the other two targets: zero emissions from most new buildings by 2025, and zero emissions from all new buildings by 2030. 4  Zero Emissions Building Plan, 2016 – City of Vancouver