---
title: "CIBSE TM13 explained: minimising the risk of Legionnaires' disease in buildings"
source_url: https://legionella.io/articles/cibse-tm13-explained-minimising-the-risk-of-legionnaires-disease-in-buildings/
canonical_url: https://legionella.io/articles/cibse-tm13-explained-minimising-the-risk-of-legionnaires-disease-in-buildings/
pillar: "UK Legionella Law & Compliance"
summary: "CIBSE TM13 is the engineer's companion to L8 and HSG274. See what it adds, where the three documents overlap, and how to use it without duplicating effort."
primary_keyword: "CIBSE TM13"
date_published: 2026-03-20
date_reviewed: 2026-06-26
author: "Legionella.io editorial team (REMOTE TECH LTD)"
reviewed_against: "HSE L8 and HSG274 guidance"
region: "United Kingdom"
license: "(c) REMOTE TECH LTD. Quote freely with attribution and a link to source_url."
---

# CIBSE TM13 explained: minimising the risk of Legionnaires' disease in buildings

CIBSE TM13 is the building services engineer's companion to the Health and Safety Executive's material on Legionella. Where L8 sets the legal duty and HSG274 sets the technical method of control, TM13 speaks to the people who design, install and commission the pipework, calorifiers and plant in the first place. It is referenced constantly in specifications. It is read far less often.

If you manage an existing building, the practical value of TM13 is that it describes what a well-built water system should have looked like at handover. That gives you a yardstick for the system you actually inherited.

This is not a 101 on how Legionella grows. It assumes you already know that, and focuses on where TM13 fits, what it adds beyond the HSE documents, and how to use it without doing the same work three times.

## What TM13 actually covers

The three documents people lump together do different jobs. L8 is the Approved Code of Practice — it has special legal standing, so a court can treat a departure from it as evidence of a breach unless you achieved compliance another way [1]. HSG274 is the HSE's technical guidance on operating and monitoring systems day to day, published across hot and cold water, evaporative cooling and other risk systems [2].

TM13 sits slightly to one side of both. Its centre of gravity is the engineering: how a system should be designed and specified so that control is achievable later, and what the building services team should hand over so the duty holder can run it. Think material selection, pipe routing that avoids stagnation, sizing of storage, the layout of flow and return on hot water, and the commissioning evidence that proves the installed system behaves the way the drawings claimed.

That emphasis is why TM13 complements rather than repeats the HSE guidance. HSG274 tells you to keep dead legs out of your system; the design-stage thinking in TM13 is where you stop one being built in the first place [4]. The two meet at handover, and the [explainer on HSG274](https://legionella.io/articles/hsg274-guidance-explained-practical-legionella-control/) covers the operational half in detail.

## Why the design stage decides your operational fate

Most of the Legionella risk you spend years managing was set before anyone moved in. An oversized cold water tank that turns over slowly, a hot water loop that does not reach the furthest tap, a capped spur left from a value-engineered sink — these are design and installation decisions, and no amount of diligent monthly monitoring undoes them.

This is the honest case for caring about an engineer's document even when you only operate the building. The features HSE names as the usual sources of risk — calorifiers and water heaters, long runs and dead legs, anything that stores or stagnates water in the growth range — are largely baked in during construction [4]. TM13's contribution is to push the thinking upstream, so the system is controllable by design rather than rescued by procedure.

The temperatures the design works to are the familiar ones: hot water stored hot, commonly around 60°C and still hot at the tap, with cold water held below roughly 20°C [3]. The difference at design stage is that you size plant and route pipe so those figures are achievable at the worst-served outlet, not just at the calorifier. A loop that hits 60°C at the plant room and 48°C at the end bedroom passed nobody's real test.

For new build and refurbishment, this overlaps with statutory design duties; the [piece on Legionella and building regulations](https://legionella.io/articles/legionella-and-building-regulations-design-stage-considerations/) covers that angle.

## The handover evidence checklist

Here is where TM13 earns its place for an FM. When you take over a building — at practical completion, or when you inherit a contract — the design and commissioning information is the only proof you have that the system started life controllable. Walk this list before you accept it.

- **As-installed schematic.** Confirm the drawing matches the building, not the tender design. Value engineering changes pipework; the schematic must show what was actually installed.
- **Commissioning temperature records.** Look for evidence that hot water reached temperature at the sentinel (nearest and furthest) outlets, and that cold ran cold, before occupation — not just at the plant.
- **Calorifier and water heater data.** Capacity, stored temperature, and any stratification or drain-down arrangement. Note what feeds it and how it recovers.
- **Flow and return verification.** Proof the return loop circulates and balances, so hot water stays hot to the far end rather than cooling in a long dead run.
- **Dead leg register.** Any blind ends, capped spurs or future connections, with their length. These are the stagnation points you will be flushing for the building's life.
- **TMV schedule.** Every thermostatic mixing valve located and listed. Blended water downstream of a TMV sits in the growth range, so each one is a maintenance commitment you are now signing up to.
- **Materials and components list.** So you can check nothing wetted is a known nutrient source or out of specification.
- **Cleanliness and disinfection certificate.** Evidence the system was cleaned and disinfected before being put into use.

Record where each item lives and which are missing. A gap here is not paperwork pedantry — it is a part of the system you cannot yet prove was ever right.

## Trade-offs and where TM13 stops

TM13 is guidance for competent people, not a substitute for competence. It will not tell you that your specific building is safe, and reading it does not make a non-engineer able to sign off a design. The pragmatic call is to treat it as the engineer's reference for getting the asset right, and L8 and HSG274 as the operator's reference for keeping it right — and to make sure someone competent owns the join between them.

The other limit worth naming: a well-designed system still fails if it is run badly. Commissioning records prove a good start, not a good year. Monitoring frequency, remedial action and review all follow your risk assessment and the system's real behaviour, not a fixed calendar inherited from a handover file [5]. In my view the most common mistake is assuming a strong design buys a quiet operational life. It buys a fair chance; the rest is operation.

## A note on applying this

This is general orientation, not advice on your building or its design. TM13, L8 and HSG274 are written to be applied through a competent, site-specific risk assessment, and the temperatures, intervals and remedial actions that suit your plant depend on what is installed and who uses it. Where design or commissioning falls outside your competence, bring in a building services engineer rather than interpreting the document yourself. Nothing here is legal or engineering advice for your premises.

## FAQ

### Is CIBSE TM13 a legal requirement?
No. The legal duty comes from health and safety law and the L8 Approved Code of Practice, with HSG274 as the HSE's technical guidance [1][2]. TM13 is industry guidance from CIBSE aimed at building services engineers. It is widely cited in specifications and is a recognised reference for good design practice, but compliance is demonstrated against the HSE documents.

### Does TM13 duplicate HSG274?
There is overlap, because both address the same systems, but the emphasis differs. HSG274 is weighted towards operating and monitoring a system in service. TM13 is weighted towards designing, specifying and commissioning it so control is achievable. Use TM13 when shaping or assessing the asset, and HSG274 when running it.

### Who actually needs to use TM13?
Primarily building services designers, specifiers, installers and commissioning engineers, plus anyone assessing whether an existing system was built to be controllable. As an FM or duty holder you do not need to apply it line by line, but knowing what it expects at handover lets you challenge the design and commissioning evidence you are given.

## Your next move

Pull the handover file for one building and run the checklist above against it. The first missing item — a commissioning temperature you cannot find, a TMV that is not on any schedule — is the gap to close, because it marks a part of the system whose history you cannot yet prove. If that evidence lives in folders nobody opens, that is the moment a digital logbook earns its keep: design records, asset register and ongoing monitoring held together where the next person can actually find them.

## Related reading

- [HSG274 guidance explained: practical Legionella control](https://legionella.io/articles/hsg274-guidance-explained-practical-legionella-control/)
- [ACoP L8: understanding the UK Legionella Code of Practice](https://legionella.io/articles/acop-l8-understanding-the-uk-legionella-code-of-practice/)
- [Legionella and building regulations: design-stage considerations](https://legionella.io/articles/legionella-and-building-regulations-design-stage-considerations/)

## Sources

[1] HSE, "Legionnaires' disease. The control of legionella bacteria in water systems - ACoP and guidance (L8)". https://www.hse.gov.uk/pubns/books/l8.htm
[2] HSE, "Legionnaires' disease: Technical guidance (HSG274)". https://www.hse.gov.uk/pubns/books/hsg274.htm
[3] HSE, "Hot and cold water systems". https://www.hse.gov.uk/legionnaires/hot-and-cold.htm
[4] HSE, "Systems most likely to create legionella risk". https://www.hse.gov.uk/legionnaires/risk-systems.htm
[5] HSE, "Testing and monitoring your water system for legionella". https://www.hse.gov.uk/legionnaires/testing-monitoring-water-system.htm