SBEM, the official Part L software, was meant to make it easy to calculate the energy efficiency of any building, even ones like this. In fact, it struggles with anything more complicated than this. So what are the alternatives?

Since Part L came into action in April specifiers have had just one wish – to find some software that would help them design buildings that comply with the new regulations. Unfortunately, their general feeling is that the government’s Simplified Building Energy Model (SBEM) has been disappointing. Neville Rye, a director of engineering consultant WSP Buildings, thinks that SBEM, which was created to demonstrate compliance in buildings other than dwellings, is useful only for very simple and conventional building design. He says: “The problem with SBEM is that it is not very flexible and the input geometry can only be used for the most simple building forms.”

Stuart Barlow, technical manager at Reid Architecture, identifies two of the main problems of SBEM as the long time spent inputing data and its lack of visual information. He says: “SBEM only produces cold figures. It takes longer than it should and we are never sure what the relationship between the elements in the building should be because it doesn’t generate visuals.”

Even more crucial to compliance with Part L is the inability of SBEM to take into account factors such as heating, ventilation and cooling and transfer them onto a visualisation of the building. If specifiers wish to produce more sophisticated data they have to turn to computer modelling using thermal simulation software.

The alternatives

Luckily, there are alternatives available. Software compliance tools from providers such as IES and Environmental Design Solution (EDSL) have been accredited by the government. These thermal modelling software systems assess compliance by estimating the carbon emissions for different elements of the building separately and then combining them to get the final result. They use information that SBEM could provide, but in a more sophisticated visual form – for example a screen showing a visualisation of the building containing calculations about the building services. They also allow elements such as airflow, ventilation shading from adjacent buildings to be considered. IES and EDSL have even developed simpler versions of their software for architects who might not be building-services savvy. The question is whether they succeed where SBEM apparently has failed.

WSP Buildings adopted IES because it required software to check compliance with not only Part L but other aspects of the design process such as ventilation, which is covered by Part F, and solar control. All this can be simulated using IES’ VE Compliance software, says Rye. He adds that technologies like ground heating, cooling and bio fuels can be evaluated more accurately using thermal simulation software than through SBEM.

Meanwhile HLM Architects is using EDSL’s Tas software – “a slightly favourable option,” says director David Cafferty, “because it provides a greater degree of flexibility in the evaluation process”. Tas thermally simulates buildings, so specifiers can compare heating and cooling strategies, facade design for equipment sizing and energy demands.

Reid’s Barlow says software tools calculating the thermal performance of the building enable architects to do the job without involving M&E people. Reid has swapped SBEM for IES’ software because it gives “a more comprehensive study of the building and more accurate results”. One key thing for Barlow is that IES allows the user to export CAD drawings and create models.

Software tools calculating the thermal performance of a building enable architects to do the job without involving M&E

Stuart Barlow, technical manager at Reid Architecture


However Darryl Nash, technical adviser at architect Scott Brownrigg, warns that even the more sophisticated software tools have limitations. He says: “The degree of building services knowledge required to operate [the tools] can be a huge problem for the architect. As a CAD modelling tool, it’s quite simple, but the challenge is to get sufficient knowledge to operate the software and understand its results.”

The introduction of Part L and relevant compliance tools has changed the way specifiers work together within the design team. HLM’s Cafferty says a more fully collaborative process is necessary from the early stages of the project. He says: “The new Part L makes it necessary to continuously determine how design decisions will influence the performance of a building. This requires input from both the architect and the building services engineer.

However, only architects can keep an overview of how a design progresses.”

Nash, who has tested a series of compliance tools for Scott Brownrigg, says the most recent developments target architects. Manufacturers like Corus, Kingspan, and Knauf now have services to assist specifiers.

Barlow says Reid Architecture has been looking at Southfacing Services’ Carbon Checker software, which claims to supersede SBEM because it allows the entry of the geometrical representation of a building. He says that the practice might use this or a similar product with IES software.

There is still some ground to cover to offer specifiers what they really want. Nash would like to see an “M&E wizard”. But for now the specifiers’ task of complying with Part L remains something of a dark art.