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Question: 07-01 Code Section: 7 Date: OBC 2006 Reference:,, (1)

Question: An addition to an existing house to provide additional family members. Additional fixtures to be added to the existing total of at least 15 fixtures due to additional bathroom, laundry etc. states that no water system shall have a capacity that is less than the peak demand flow. It appears that the existing water service pipe is ¾” then is reduced to ½”. What authority do we have to increase the piping size to ¾” to allow for peak demand if, at the end of the day, ½” will not provide for peak demand (the definition of peak demand would appear to be somewhat vague even though it appears to be easy enough to define). P.S.I. and gpm’s would fall into the equation but this is also variable depending on other factores (eg. Main line pressure and volume).

It appears the plumber probably priced for only ½” to get the job. Now the owner wants more than he paid for. A knowledgeable plumber would have least indicated that ¾” mains for hot and cold would be required and possibly 1” but not necessarily so. On jobs that require engineers, they have access to tables and calculations to size piping but this would not be the case for residential single family uses. What suggestions might the OPIA have and how would it be enforced in referring to any standard or table that is not in the code. A simple conversation with the plumber might work in some cases but if push comes to shove, I don’t believe we can enforce this.

Interpretation: The members of the Code Technical Committee consisting of qualified Plumbers, Inspectors and Pipe Trades Professors would use “Good Engineering Practice” to ensure adequate water pressure throughout any building that they were responsible for. We recognize the difficulty in testing to enforce adequate flow pressure and now the addition of sentence (3) to of the new code removes the requirement of "peak demand flow" conformance in column 3 of Table "Minimum Flow Pressure (1), kPa (gauge)" for single dwelling units. Under renovations, by enforcing “ (1) Where an existing building system is materially altered or repaired, the performance level of the building after the material alteration or repair shall be at least equal to the performance level of the building prior to the material alteration or repair”, it may be difficult to prove.

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