Frequently Asked Questions

Question	Answer
1. What exactly is a sanitary articulation plan?	It is an engineering drawing set that shows how below-slab sanitary drains will be “articulated” with flexible couplings or swing joints so they can move with reactive soils without cracking. Articulation is needed because underground pipework is subject to soil swelling-shrinkage cycles; without movement joints the pipe stresses can lead to leaks and footing damage. -
2. Why must the plan be certified by an RPEQ engineer?	Professional engineering services in (or for) Queensland must be carried out or directly supervised by a Registered Professional Engineer of Queensland under the Professional Engineers Act 2002. Certifiers therefore insist on a Form 15 design certificate from an RPEQ for sanitary articulation plans. Department of Housing and Public Works
3. When is a sanitary articulation plan legally required?	Schedule 6 of the Plumbing & Drainage Regulation 2019 makes a plan mandatory whenever: 1) sanitary drainage is part of the proposed work and 2) the soil classification report shows Class H, E or P (highly reactive or problem site). A copy of the soil report and the articulation plan must accompany every Form 1 permit application. Department of Housing and Public Works
4. Who is allowed to prepare the articulation design?	The Regulation permits three categories: (a) an RPEQ with relevant competency, (b) a QBCC-licensed hydraulic services designer, or (c) a QBCC plumbing/drainage licensee preparing work they will personally install. Only an RPEQ, however, can issue the Form 15 certificate that is recognised statewide. Department of Housing and Public Works
5. What information must the plan show?	At minimum it must detail how the sanitary drain passes through or under the slab edge beam, indicate all expansion couplings (location, type and spacing), show invert levels, ORG location, pipe grades and the connection point to sewer. Department of Housing and Public Works
6. Are there any situations where council may waive the requirement?	Yes. Local government can accept a permit application without a site-classification report or articulation plan when the drainage is beyond the building perimeter, the building is raised on poles, or there is no ground-floor slab. Some councils will also accept an RPEQ statement that soil movement risk is negligible. Department of Housing and Public Works
7. Which soil classes do not need articulation plans?	Class A, S and M sites (≤ 40 mm characteristic surface movement) are exempt unless a council imposes specific conditions. Department of Housing and Public Works
8. How does STA Consulting’s “Safety Zone” method reduce costs?	Their engineering review showed the high-risk “internal perimeter zone” could be narrowed from 2.0 m to 1.2 m on Class H sites and from 3.0 m to 2.0 m on Class E sites. Fewer joints are needed, saving materials and labour while retaining compliance. STA Consulting Engineers
9. What is the difference between generic detailing and a site-specific design?	Generic detailing gives plumbers broad rules and often leads to (a) under-articulation—insufficient joints outside the safe zone—or (b) over-articulation—unnecessary joints that inflate costs. A site-specific RPEQ design calculates the safe zone and joint layout precisely for each house footprint, avoiding both pitfalls and transferring liability to the engineer. STA Consulting Engineers
10. What documents should accompany my Form 1 plumbing permit application?	1. Form 1 application; 2. Site-classification report (AS 2870); 3. RPEQ Form 15 covering the sanitary articulation plan; 4. The drawings themselves. Supplying all four items prevents time-consuming RFIs from certifiers. (Derived from Schedule 6 workflow.) Department of Housing and Public Works
11. How does articulation protect building foundations?	Broken drains leak wastewater into reactive clays around footings, accelerating soil expansion and footing heave. Installing flexible joints at calculated positions keeps pipes intact, preventing moisture ingress and the secondary structural damage frequently reported in subsidence claims. Department of Housing and Public Works
12. What commercial advantages do RPEQ-certified plans offer builders?	• Faster council sign-off thanks to complete Form 15 documentation • Fewer call-backs and insurance claims • Optimised joint count lowers plumbing cost • Clear coordination with slab/piers minimises site clashes • Transfer of design risk to a PI-insured engineer—an easy marketing differentiator. STA Consulting EngineersSTA Consulting Engineers