Public health
Public health engineering
Hot and cold water services, above and below ground drainage, gas and rainwater design to CIBSE Guide G and the relevant water byelaws.
- Discipline
- Public health
- Typical timescale
- Stage 2 concept in 1 to 2 weeks; Stage 4 technical design typically 4 to 8 weeks
WHAT IT IS
Public health engineering covers the water into a building and everything that leaves it: hot and cold water services, sanitary provision, above ground drainage, below ground drainage, rainwater and attenuation, and gas services.
It is the discipline most often treated as an afterthought and the one with the most direct consequences when it is — a legionella risk from a poorly designed hot water system, a drainage layout that cannot achieve fall, or an attenuation requirement discovered after the levels are fixed.
At SDE the public health services are delivered by the mechanical team and listed alongside the rest of the mechanical design — domestic water services, drainage and gas each have their own page. This page covers the discipline itself: the compliance regimes those three sit inside, and the decisions that have to be made before any of them can be sized.
WHEN YOU NEED IT
From Stage 2, alongside the mechanical and electrical design. Below ground drainage and attenuation in particular need to be resolved while site levels are still adjustable, because a drainage run that cannot achieve gravity fall becomes a pumped solution with a maintenance liability attached.
OUR PROCESS
Cold water demand calculated by loading units, storage sized against the demand profile and the risk of stagnation, and hot water generation selected against the same. Pipe sizing calculated rather than defaulted.
Above ground drainage designed to BS EN 12056 with stack sizing and ventilation checked. Below ground drainage designed to gradient and to the receiving authority's requirements, with attenuation sized where the discharge rate is limited.
Legionella risk is designed out at the layout stage — dead legs, oversized storage and long branch runs are cheaper to remove on a drawing than to manage for the life of the building.
DELIVERABLES
What you receive
- Cold water demand and storage calculations
- Hot water generation sizing
- Pipe sizing calculations
- Above ground drainage design and stack sizing
- Below ground drainage layouts and levels
- Rainwater and attenuation calculations
- Gas service design and pipe sizing
- Legionella risk considerations recorded at design stage
STANDARDS
Standards applied
The editions in force at the time of design. Where a standard is amended mid-project we confirm which edition the appointment is based on.
- CIBSE Guide GPublic Health and Plumbing EngineeringCIBSE
- BS EN 806Specifications for installations inside buildings conveying water for human consumptionBSI
- BS 8558:2015Guide to the design, installation, testing and maintenance of services supplying water for domestic useBSI
- BS EN 12056Gravity drainage systems inside buildingsBSI
- BS EN 752Drain and sewer systems outside buildingsBSI
- HSG274 Part 2Legionnaires disease — the control of legionella bacteria in hot and cold water systemsHSE
- ACOP L8Legionnaires disease — the control of legionella bacteria in water systemsHSE
- Water Supply (Water Fittings) Regulations 1999England and Waleslegislation.gov.uk
- The Water Supply (Water Fittings) (Scotland) Byelaws 2014Scotland — made by Scottish Ministers, enforced by Scottish Waterlegislation.gov.uk
- Approved Document HDrainage and waste disposal (England)GOV.UK
QUESTIONS
Common questions
What is public health engineering in construction?
Public health engineering is the design of a building’s water and drainage systems: hot and cold water services, sanitary provision, above and below ground drainage, rainwater and attenuation, and gas services. It is one of the three core MEP disciplines alongside mechanical and electrical.
How is cold water demand calculated for a building?
Demand is calculated using the loading unit method set out in BS 8558 and CIBSE Guide G, where each appliance is assigned loading units and the total is converted to a simultaneous flow rate. Storage is then sized against the demand profile and against the need to avoid stagnation.
When does surface water attenuation need to be designed?
Whenever the receiving sewer or watercourse limits the permitted discharge rate, which is now common on most developments. It needs to be resolved at concept stage because attenuation storage takes up space and depth, and retrofitting it after site levels are fixed is disruptive.