www.rcabc.org  l  19 FEATURE from the outside everything that is inside the envelope. Choosing the right materials, and installing them correctly and efficiently, lies at the heart of an air-tight, thermally- efficient building envelope, regardless of which Code we discuss. In a building enve- lope, five key elements – what building envelope experts commonly refer to as “control layers” – work together to sepa- rate the interior environment of a building (conditioned space) from the outside: a.  Water-shedding surface (typical of wall cladding, stucco or steep roof surfaces) b.  Water-resistive or waterproofing layer (for example, the membrane on a low-sloped roof) c.  Thermal control layer d.  Air control layer e.  Vapour control layer Some building components may serve more than one function. For example, a window will function as an air barrier, a vapour control layer, a water-resistive barrier and a thermal control layer. How well it serves any one of these purposes is a function of its design, construction and installation. Likewise, a roof membrane in a Protected Membrane Roof Assembly keeps water out but also regulates the migration of both air and vapour between the interior and exterior environments of a building. Again, function is a matter of material choice and installation. Obviously, supplying and properly installing the water-shedding and water- proofing layers represents the core of what roofing contractors do. People hire roofers to keep their buildings dry, and roofers are specialists in this line of work. Still, there The Step Code is transforming the work of roofing from what it was to what it is already becoming – a specialist trade in the construction of the building envelope. Nearly gone are the days when a roof was just a roof... It`s who we are, it`s what we do Low Slope Roof Systems • Metal Roof Systems • Wall Systems Shingle Roof Systems Phone: 250.336.8088 Toll Free: 1.888.318.8642 www.nelsonroofing.com contact@nelsonroofing.com Comox Valley, Campbell River, Powell River, Lower Mainland Pride, Quality, Innovation, Performance & Safety ENVIROSPEC INCORPORATED Visit our website at www.EnvirospecInc.com or contact us at Phone (905) 271-3441 Fax (905) 271-7552 The PAVE-EL® Pedestal System: • Transforms flat roofs into attractive, maintenance-free, landscaped paver stone terraces. • Elevates paver stones for perfect drainage. • Levels paver stones and ensures their uniform spacing for an ideal roof terrace surface. Turn roof tops into useable, attractive roof decks Designed & Manufactured in Canada