20 l ROOFINGBC l WINTER 2018 TECHNICAL UPDATE www.precisionmetals.ca Call Us, for your Custom Metal Needs. 8081, 132nd St. Surrey B.C. 604.594.6001 Filling needs and producing premier quality products for the construction industry since 1975. • Manufacture to Your Specifications • Will Work with You and Your Customer to Find Solutions 8081, 132nd St. Surrey B.C. Filling needs and producing premier quality products for the construction industry since 1975. Filling needs and producing premier quality products for the construction industry since 1975. 1)  Specifying the actual roof assembly and listing the component mate- rials (what we’ll call the prescriptive approach). 2)  Specifying the type of assembly but leaving the selection of a Tested Assembly or even an assembly with Proven Past Performance to the contractor (the descriptive approach). Prescriptive Pathway The prescriptive approach is some- what like the traditional method of specification writing. In simplified terms, traditional specifications identified the various standards roof construction must comply with, and then listed the materials to be used, perhaps together with approved alternates (commonly done). Since there were no specific securement requirements in the Building Code, specifications invoked an entire array of industry, underwriting and testing standards to make sure all the bases were covered. Inevitably, a certain amount of discretion was left to the contractor who put it all together. That has all changed now. Because the roof must be built to resist specific, calculated negative wind loads, the Design Authority must be more careful in how the specifications are written. Listing materials is fine (and we know that some designers have their favourite or trusted materials), but the Design Authority must be sure there is an acceptable and available roof system that incorporates those materials. If there isn’t, the project could be delayed as contractors try to find assemblies with alternate materials that will satisfy the designer’s wishes. The simplest prescriptive approach, then, is one that lists the specified wind loads and simultaneously specifies the roof assembly that will satisfy the Part 4 requirements. When paired with clear material requirements, this approach ensures bids for the specification section on waterproofed roofs will be comparable (“apples to apples”), and it minimizes the need for clarifications or alternate material and system proposals. To summarize, the key components of a prescriptive specification include: 1.  The specified wind loads for the roof and clear directives concerning roof zone requirements • Roofing • Roofing Systems • Structural Steel • Process Piping • Sheet Metal & HVAC • Cladding • Fabrication • Machining & Millwrighting • Plumbing • Gas Fitting 245 Third St, Kitimat, BC V8C 2N8 4419 Legion Ave, Terrace, BC V8G 1N7 www.101industries.com Phone: 1-877-632-6859 Email: 101first@101industries.com The simplest prescriptive approach, then, is one that lists the Specified Wind Loads and simultaneously specifies the roof assembly that will satisfy the Part 4 requirements.