CIBSE TM59 Assessment of overheating risk in homes

CIBSE TM59

Assessment of overheating risk in homes

CIBSE TM59 Assessment of overheating risk in homes

Homes that overheat pose a significant risk to the health and well-being of residents. A trend of higher average outdoor temperatures, coupled with features of modern housing design (such as large areas of south facing windows, high levels of insulation, low air permeability rates and low thermal mass) can result in excessively high internal temperatures during summer months. Situations where this risk is unacceptably high need to be identified as early as possible to allow appropriate changes to be incorporated into the design.

In response to the increasing risk of overheating in dwellings, CIBSE have developed a bespoke methodology to assess the predicted level of thermal comfort within a home: CIBSE TM59. This assessment should be carried out at the detailed design stage by way of Dynamic Simulation Model. For naturally ventilated homes CIBSE TM59 sets two criteria for compliance. A dwelling that fails either of the criteria is deemed to be at unacceptable risk of overheating:

  1. Criterion A: Hours of Exceedance (living rooms, kitchens and bedrooms)

  2. Criterion B: Night hours above 26 °C (bedrooms only)

For homes that are predominantly mechanically ventilated the CIBSE fixed temperature test must be followed.

Our experienced consultants can guide you smoothly through compliance, from concept to completion. In addition to producing a detailed analysis of your project against the CIBSE TM59 thermal comfort metric, our service includes all the support and advice required to ensure every dwelling achieves a pass.

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How Energytest can help

Fast and accurate CIBSE TM59 overheating risk analysis at a competitive price.

Comprehensive advice and support to ensure you arrive at the most economic and feasible solution to achieve compliance.

CIBSE TM59 reports can be used to aid building design, support Planning applications, and satisfy industry requirements.

For projects within the greater London area, an assessment of the risk of overheating must now be included within all Energy Statements to satisfy the requirements of the London Plan.

For Building Regulations compliance we can provide:

Criterion A: Hours of Exceedance

For living rooms, kitchens and bedrooms: sets a limit of 3% on the number of occupied hours that the operative temperature can exceed the threshold comfort temperature, Tmax, by 1K or more during a typical non-heating season – 1 May to 30 September. Tmax is a function of the outdoor running-mean temperature.

Criterion B: Night hours exceeding 26 °C

For bedrooms only: to guarantee comfort during the sleeping hours the operative temperature in the bedroom from 10 pm to 7 am shall not exceed 26 °C for more than 1% of annual hours.

Mechanically ventilated homes: CIBSE fixed temperature test

CIBSE fixed temperature test – all occupied rooms should not exceed an operative temperature of 26˚C for more than 3% of the annual occupied annual hours

Community heating: communal corridors

For buildings with community heating the risk of overheating within communal corridors should be assessed. The overheating test for corridors is based on the number of annual hours for which an operative temperature of 28°C is exceeded. Whilst there is no mandatory target, if an operative temperature of 28°C is exceeded for more than 3% of total annual hours, this should be flagged as a significant risk.

Factors that affect overheating risk

  • The geometry of the building.

  • The fabric of the building, including levels of insulation and thermal mass.

  • External and internal shading, such as overhangs, louvres and blinds.

  • The size and orientation of windows, and presence of solar control glazing.

  • Internal heat gains arising from occupants, lighting and equipment.

  • The level of natural or mechanical ventilation provided.

London Plan

To meet new London Plan requirements, an assessment of the risk of overheating should now be included in all Energy Statements submitted as part of the planning application process. For dwellings, applicants should complete Section 1 of the Domestic Overheating Checklist at the pre-planning stage. At Stage 1 applicants should then:

  • Complete Section 2 of the Domestic Overheating Checklist and include the full checklist in the energy assessment; and

  • Undertake dynamic overheating modelling in line with the guidance and data sets in CIBSE TM59 and TM49 respectively.

What our clients say:

“We have used Energytest to produce all of our SAPs and SBEMs for the last 5 to 6 years. After working with other energy consultants we stuck with Energytest for a number of reasons.  They are very quick to respond with quotes and queries and there is always someone on the other end of the phone. Even if the assessor who produced your calculations isn’t available everyone at Energytest is more than happy to look over the calculations and has the knowledge to answer your query.

They provide more than just a calculation service, they are also problem solvers finding the thermal solutions to make sure our designs pass. I have recently been very impressed with the service we received on a large commercial project. On the calculations for this particular project they produced an additional report alongside the SBEMs detailing how and where we could reduce the specification to significantly save on the build costs whilst meeting the requirements of Part L.”

L Gittens – bi Design Architecture

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