TM52/59 Reports: How do they Impact on Planning?

As homes become more energy efficient, they run into a different problem – overheating. TM52 and TM59 reports provide an accurate assessment of what risks you might face.

Overheating is a growing problem for homes in the UK and it’s one which can render homes uninhabitable during summer heat waves. They can make life miserable for occupants and, in some cases, they can lead to serious health problems. Indeed, according to a recent study from the university of Loughborough it can be linked to premature mortality. This is, then, something which has to be taken seriously which is where TM52 and TM59 reports come in.

In part, the problem of overheating is down to ongoing attempts by the Government to ratchet up the requirements for the reduction in CO2 emissions from buildings. Designers are focusing on energy efficiency. This means more insulation which is great during the winter – it reduces the need for central heating which keeps energy bills down and helps the Government towards its overall goal of reducing carbon emissions. The problems come when we move into summer.

TM52/59 Reports: How do they Impact on Planning?

As homes become more energy efficient, they run into a different problem – overheating. TM52 and TM59 reports provide an accurate assessment of what risks you might face.

Overheating is a growing problem for homes in the UK and it’s one which can render homes uninhabitable during summer heat waves. They can make life miserable for occupants and, in some cases, they can lead to serious health problems. Indeed, according to a recent study from the university of Loughborough it can be linked to premature mortality. This is, then, something which has to be taken seriously which is where TM52 and TM59 reports come in.

In part, the problem of overheating is down to ongoing attempts by the Government to ratchet up the requirements for the reduction in CO2 emissions from buildings. Designers are focusing on energy efficiency. This means more insulation which is great during the winter – it reduces the need for central heating which keeps energy bills down and helps the Government towards its overall goal of reducing carbon emissions. The problems come when we move into summer.

What are they?

As we’ve already covered elsewhere, SAP assessments can already be used to highlight an increased risk of overheating, but these can be relatively inaccurate and builders can find ways to get around them. TM52 AND TM59 reports, on the other hand, are much more accurate.

They were developed by the Chartered Institute of Building Services Engineers (CIBSE) to assess overheating risks. TM52 can be applied to any type of building, while TM59 has recently been added to specifically target overheating in homes.

Why are they needed?

The reports use diametric 3D modelling of buildings, which is a much more analytical and accurate reflection of how a building will behave. Developers may want to have these reports as part of the design package to ensure the building will work well when put into use and will not overheat.

The report will produce a 3D analysis of each room to show where overheating may become an issue. For this, all the details will need to have been inputted correctly. This includes the geometry of the building and details about the heating and ventilation strategy.

A building will be considered to have failed the assessment if it falls down on two or more of the following criteria:

Hours of exceedance: Sets a limit for the number of hours the temperature can exceed the threshold comfort temperature.
Daily weighted exceedance: This looks at the severity of the overheating and is often as serious as the frequency.
Upper temperature limit: If the building exceeds an upper temperature limit, it could fail. These temperature limits will vary for TM52 but for TM59 they are placed at 25°C. These temperatures will lead to serious discomfort, stress and anxiety. At night, when bedroom temperatures exceed 26°C, that can lead to severe discomfort and lack of sleep.

These reports will be commissioned to accompany the application stage. They will go to the planners and, if certain elements of the developments are shown to fail the reports, they can ask for mitigating measures. For example, one of the most common mitigating measures requested will be to require mechanical ventilation to be included in order to reduce external temperatures.

Addressing problems

So, if it does fail, what can be done? In many cases, mechanical ventilation will be the only solution. A building may have already reached a stage where it is difficult to make major changes to its construction. Cooler air will need to be introduced into the environment.

However, if the reports are run at earlier stages of the design, it is possible to design in other measures such as cross-ventilation. Designers will try to design buildings with windows on both sides allowing a flow of air, although this might not always be possible, especially in urban situations where the buildings may be tightly constrained by their environments.

If possible, you might also address orientation. In an ideal world, you should avoid west-facing windows, because these attract low summer sun, which can lead to overheating. If you do have west-facing windows, you may be able to mitigate these problems by looking at the specification of the glass being used. You can adjust this to ensure that external solar gain is reduced by using specific values of glass.

When should it happen?

Of course, this all depends on when the assessment happens. It normally happens at the planning stage. TM52 and TM59 come hand in hand with the planning application. It may be slightly later when the main application has been completed, but generally speaking the maxim with these reports is: the sooner they can happen the better. If you can run them early it is much less likely that you will encounter serious problems.

More often than not, though, these reports are a case of working with what we have. For example, we recently worked on a town centre regeneration project. We modelled the buildings and identified two or three areas where there was a distinct overheating risk in the original designs. From a practical standpoint, these designs were obviously constrained in key areas such as the construction and orientation of the buildings, but there was still much which we could do.

The main discussion centred around the heating and ventilation strategies. We had to ask ourselves if we should adopt a different heating strategy to reduce the potential for overheating. The buildings used a community heating system, which can cause all sorts of problems. Pipework can run through the structure which may result in significant heat loss into the building, risking overheating. We had to ensure that pipes were adequately insulated and kept away from residential units.

The ventilation strategy had to take into account the fact that most apartments would not have any cross-ventilation. The only option, therefore, was to introduce mechanical ventilation to cool things down.

Overheating in homes is a serious issue. The desire to improve energy efficiency is laudable but a knock-on effect has been to turn some new-build homes into greenhouses during the summer months. TM52 and TM59 reports are increasingly vital at an early stage to ensure designers can address problems at an early stage.