Drain (DWV) Piping For Commercial Buildings

Designers, contractors and building owners face a myriad of factors in selecting the appropriate drain, waste and vent piping for new construction or retrofits. Issues such as flow capacity, longevity, joint tightness, certifications, corrosion resistance, capital cost, installation cost, environmental effects, noise generation and thermal effects all warrant investigation.

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The three main products used today in Canada for commercial construction are cast iron (CI), copper and Polyvinyl Chloride (PVC). This paper briefly addresses how each pipe rates in terms of the key design factors.

Flow Capacity – PVC and copper would each qualify to use a Mannings ‘N’ flow factor of.009 for gravity flow while cast iron would typically require N=.013 to represent its rough interior. Net result means up to 33% more carrying capacity for PVC and copper versus CI when one considers actual inside diameters pipes for smoking.

Longevity – CI is susceptible to many forms of corrosion including galvanic, electrolytic, acidic, moisture induced, road salt attack and stray current effects. Copper has better resistance but is still vulnerable to shortened life due to acidic attacks from aggressive pipeline contents. PVC is virtually immune to all forms of corrosion and thus will outlast the other two, with copper rating second best.

Joint Tightness – CI is joined with rubber lined, metal reinforced mechanical couplings which will adequately meet industry standards and can be easily re-tightened if required during a leaking field pressure test or while in operation. Both copper and PVC are more permanently joined through the soldering process for copper and solvent welding for PVC. Both of these joints could qualify as pressure-rated joints and helps installers by permitting commission-testing of multiple floors at once in buildings.

Certifications – All products must be third-party certified to CSA or ASTM standards. CI must be certified to CSA B70, copper to ASTM B306 and PVC to CSA B181.2. Both cast iron and copper are permitted in all types of buildings while PVC must use a compound (proprietary mixture of resin plus additives) listed by ULC S102.2 to exhibit a Flame Spread Rating of not greater than 25 for all non-combustible construction. In addition, PVC must be listed to also exhibit a Smoke Developed Classification of not greater than 50 for High-Rise Construction or Plenum installations. PVC is not permitted in vertical shafts in most provinces. Products are presently commercially available in the Canadian marketplace to meet these Flame and Smoke requirements.

Capital Costs – Both CI and PVC score well here with stable competitive product pricing while copper tends to be the most expensive and subjected to the high volatility of global copper index pricing.

Installation Costs – CI is heavy to transport and handle on the job but has a relatively simple assembly method when ready to install. Copper is lighter weight and easy to cut but time consuming for soldered joints, especially for smaller lines where many fittings are required. PVC is both light weight to transport and handle and quick and easy for joining due to the straight forward solvent welding process. In sizes 8 inch and larger, users should receive some basic training to assist in properly solvent welding pipe in these sizes.

Environmental Effects – To get a true grasp of this issue, one should insist upon a Life Cycle Analysis on each piping material to capture all aspects of the pipe material’s life from raw materials, to production processes, energy consumption, transport issues, manufacturing locale, ease of recycling, waste product generated and longevity. All three products have some drawbacks, specifically high energy costs for CI production and transport, very long distances of transport and a joining system involving open flames for copper, and a difficulty in using large amounts of recycled material in finished PVC DWV pipe due to strict compound and high performance requirements of local building codes. PVC scores well for local manufacturing, in-house recycling of scrap PVC, low energy consumption in production and transport, and longevity.

Noise Generation – Both CI and PVC have superior sound deadening of drain flow than copper mostly due to thicker pipe walls. PVC offers much better sound attenuation than the common ABS drain pipe used in most single family homes. CI benefits from its rough interior to slow down flow velocities and its rubber couplings act as flexible shock absorbers. Designers agree that if noise suppression is an important concern in building design, it is best addressed by specifying external pipe insulation to the DWV system regardless of material.

Thermal Effects – For storm drains inside buildings, the high rate of thermal conductivity for both CI and copper will warrant external insulation on the pipe to prevent condensation from occurring. PVC has a very low rate of thermal conductivity and as a result is many times used without insulation. It is common however to be conservative and use insulation for the first several feet of the upper horizontal run of rain water leaders from roof drains.

In conclusion, each of these materials CI, copper and PVC offer some advantages and drawbacks towards their use in commercial construction in Canada. Designers, contractors and building owners are encouraged to consider all factors to ensure that well-informed decisions are made.

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