Getting building energy performance right is essential for net zero – part II

This is the second post in my series on the energy performance of buildings. The first looked at the Government’s primary building energy target, measured by the flawed Energy Performance Certificate. This post will look at the wider issues around the factors driving the energy performance of buildings and how they should be measured in order to ensure that through each step in the building development process, optimal decisions are made.

The design process for new buildings in the UK has is described by the Royal Institute of British Architects (“RIBA”) as having seven stages as set out in the RIBA Plan of Work shown below.

Clearly, building designers can have a great deal of influence on the environmental impact of their designs, by re-using existing buildings, selecting low-impact materials, and optimising building operations, but in order for sustainable designs to deliver on their objectives a number of things must happen:

• the right design elements must be selected, which deliver the intended benefits;
• they must be correctly installed during the construction phase;
  
• users must (where relevant) be familiar with their correct use; and
  
• there must be proper follow-up to ensure that problems are identified and corrected and that poorly performing elements are replaced in future projects.

The performance gap and poor modelling contribute to the problem

Typically in the design stage, models are used to compare design options and check compliance with standards or regulations. This is not the same as trying to predict the energy performance of the proposed building, although it is often mistakenly used as such. There is extensive evidence that buildings have much higher energy in use than was modelled in the design phase, a phenomenon known as the “performance gap”.

This is not only because compliance modelling is incorrectly used to predict performance, but also because of a range of factors including issues arising in the design phase, poor communication between key stakeholders, deviations from the initial design during construction due to wrong or missing construction details, lack of design simplicity or buildability, poor construction sequencing or the inclusion of inefficient or oversized systems.

Imam et al identified energy efficiency modelling as a key issue, particularly the lack of rigour in incorporating realised performance into the modelling process. The study involved interviews with 108 building modelling professionals about 21 common energy-related design aspects of a building. Data were gathered from a real building for which detailed energy, occupancy and temperature data had been recorded, compared with the answers of those surveyed.

There was poor agreement among the professionals on which factors were important and which were not, with the level of qualification or experience of the individuals having no bearing on the accuracy of their responses. There was also a poor correlation between the views of the professionals and the control data.

“Using a three-part definition of literacy, it is concluded that this sample of modellers, and by implication the population of building modellers, cannot be considered modelling literate. This indicates a new cause of the performance gap,”
– Imam et al

Another problem is that building models are very building specific, aiming to represent the characteristics of that building, which is all very well for one-off projects, but less useful for schemes such as housing developments where many similar units are built on different sites around the country, and as a result they are less suited to addressing questions around the fundamental assumptions upon which initial designs are founded.

Importance of post-construction testing

The Imam study identified a school in Plymouth which was rebuilt, and found that the energy bills for a month in the new, supposedly energy efficient building were the same as for an entire year in the 1950s building it replaced. Unfortunately there is no systematic requirement to test the actual energy performance of buildings – as noted in my previous post, the EPC process is a cost measure based on perfect building condition – so there are few opportunities for building designers and modellers to learn what works and what doesn’t.

Domestic appliances, another key factor in household energy consumption, are required to undergo laboratory testing to confirm their energy performance ratings. While these tests can have limitations they do at least provide some basis for manufacturers to feed performance testing back into the product design process as well as allowing for comparisons across brands.

No such testing is required for buildings, so nothing is learned about which efficiency measures actually work in practice. In the Imam study, the U-value of walls was found to have the greatest impact on gas consumption in the test building, yet the modellers ranked it third behind the glazing ratio (12^th in the test data) and the installed window U-value (7^th in the test data).

As a consequence, homeowners could be persuaded to change the number and distribution of windows in their property (no more than 25% of south-facing walls should be glazed in the UK, and as little as possible of north-facing walls), when improving wall insulation would give better energy consumption results.

In practice, changing the number and location of windows would be a major undertaking, requiring planning approvals, so anyone who went to this trouble only to find that it had a 0.91% impact on energy consumption compared with improving the wall insulation which had a 17.22% impact would likely feel cheated.

Poor installation creates further problems and undermines confidence in new heating approaches

Linked to the performance gap is a functionality gap which is emerging as new types of heating systems are poorly installed by an insufficiently trained workforce, meaning consumers struggle to achieve their desired comfort levels. Similar problems have also arisen around the district heating schemes which are mandatory in some new developments, where costs are significantly higher than expected and consumers have suffered major outages including during the winter.

The Green Homes Grant which is designed to help homeowners fund the de-carbonisation of homes has been fraught with problems primarily around the tight application deadline, scheme complexity and a lack of available approved installers.

Problems relate to both poor choice of projects and poor installation, and apply to both new build and retrofit schemes. Google “problems with new homes” and a slew of reports and articles appears indicating high levels of customer dis-satisfaction with the build quality of new homes, and very long snagging lists. These are exacerbated when complex new heating systems are specified. Bespoke metering arrangements on some low carbon heating schemes can lock consumers in to high tariffs and inhibit switching.

These issues also affect the retrofitting of existing homes, where even the existing wiring in homes can present challenges when replacing carbon intensive heating with electric boilers. But many of the biggest issues with retrofitting relate to the creation of new problems, in particular excess moisture, poor ventilation and excess heat.

Often home improvement schemes involve cavity wall insulation, but previous government schemes such as ECO and Warmfront showed that in many homes, rather than reducing building energy consumption, the process locked dampness and humidity into the structures. This is because cavities filled with air are good at preventing internal walls from becoming wet even if the outside wall is in poor condition. But once those cavities are filled with insulation, even if the product is of high quality and installed correctly, they can become wet and allow moisture transfer. Increased issues with water ingress to retrofitted buildings can be seen in all forms of retrofit.

“Quite simply, cavity walls exist for good reason and that is to provide a barrier against rainwater penetration. The problem is that a great many of these cavity voids are either simply unsuitable for cavity wall insulation, or unqualified specialists have overpacked the cavity with insulation, resulting in rainwater travelling through the insulation and reaching the internal wall. Thus, creating problems with penetrating damp, mould, condensation and rot,”
– James Berry, Technical Manager, Property Care Association

This matters because excessive humidity provides the ideal conditions for condensation and the growth of mould. Fresh air in buildings is needed, not only for controlling moisture, but also to supply air for breathing and for fuel-burning appliances, enable the dilution and removal of pollutants, and for temperature control.

As well as creating issues with moisture, inappropriate or poorly installed insulation can create other problems, including excess heat, something which has been described as a potential “public health disaster”. The focus on maintaining warmth in winter can make homes too warm in summer, which can be dangerous to the health of vulnerable people…during the 2003 heatwave, there were some 70,000 excess summer deaths in Europe.

Post occupancy evaluations should be mandatory to root out systemic problems

A key part of the process described in the RIBA Plan of Work gets too little attention in practice: “Verify project outcomes including sustainability outcomes”. This verification is not mandatory – RIBA requires all architects to promote post occupancy evaluation (“POE”) to clients as a core service, but there is no obligation for the client to accept this service. Categorising the POE as an optional client benefit ignores the need for the building design and construction industries to gather data that will support the improvements to their processes needed if the Perfomance Gap is to be closed. There is also no requirement as to the form of POE undertaken.

In 2019, RIBA issued guidance on sustainable outcomes in construction, which is an important step in the right direction, but it is only guidance to RIBA members, produced in the absence of industry-wide standards or regulation. 

“The performance gap in operational energy is now well recognised. For example, predicted energy from SBEM Part L2 and in UK EPC ratings bears very little relation to actual energy use: it covers only “regulated” energy use, and uses standard operational assumptions that seldom match real-life situations. This gap is inherent in Part L, making it solely a compliance tool,”
– RIBA Sustainable Outcomes Guide

(The SBEM (or Simplified Building Energy Model) is the non-domestic equivalent of the Standard Assessment Procedure which is the basis of the EPC for domestic buildings, and is used in Part L of the Building Regulations.)

Despite half a century or more of discussion in the construction industry about the need for POEs, even architects that accept the benefits of POE tend to only carry it out on a project-by-project basis rather than as a routine part of all work undertaken. It is clear that the internal drivers within the construction industry for improvement in energy performance or otherwise, are not strong enough to incentivise these behaviours, whether due to short-termism, the strength of demand for more buildings rather than better buildings, or other factors.

There are also concerns around liability and reputation should negative outcomes be identified, making some architects reluctant to promote POEs with their clients, and also how the process should be funded.

The Government should act to regulate the POE process, possibly as a condition of the Building Control Certificate – the certification process could be split into two with initial certification that the building work has been done in accordance with Building Regulations and a second part after one-two years’ of use where tests are carried out to ensure the building energy performance is in line with design expectations (with suitable adjustments for the consumption choices made by the occupants for example excluding any high energy use equipment or devices the consumer may have installed subsequently).

The increasing importance of embodied emissions

The current Government focus is on reducing operational energy, but the embodied emissions should also be considered ie the emissions required in the construction and ongoing maintenance of the building, which is impacted by the materials used, and how far those materials need to travel in order to reach the construction site, and also the end-of life emissions – the way in which the building is de-commissioned, demolished and what happens to the materials thereafter (such as whether any materials re-cycled).

Studies (cited here) have shown that life-cycle analysis of new projects is rarely done, due to its cost, and where it is done, it tends to be after the deign is finalised. In other words, life-cycle analysis of a building’s emissions rarely if ever forms part of the design process.

It has also been found that low-energy buildings that have installed photovoltaics, high-performance insulation and other means of reducing operational energy consumption tend to have higher embodied emissions. In some cases, the carbon payback period for these energy-reduction technologies exceeds the service life of the technology itself resulting in an overall increase to the whole-life environmental impact of the building. This is something that should not be ignored when planning for a net-zero carbon economy.

As policy drivers to reduce operational emissions take effect, the proportion of a building’s total emissions made of up embodied emissions increases – several recent reports suggest that the embodied impacts of new buildings will exceed 60% of their whole-life impacts. For most buildings, the initial embodied impacts, ie those from the building materials and construction process, exceed the cumulative operational impacts for approximately the first 20 years of operation. This means that the initial embodied impacts of new buildings will be of key importance in the period to 2050.

Carrying out life-cycle assessments of new buildings is therefore of great importance, but it needs to be done properly, and at the design stage – currently post-completion life-cycle emissions assessment is still the most common practice. Roberts et al showed that life-cycle assessment tools are “hindered by lack of transparency, out-dated background information, and need to be adapted to suit designer requirements”.

A significant change in approach is needed if building emissions are to be meaningfully reduced

If the emissions from buildings are to be reduced in reality rather than just in theory, some serious changes in approach will be needed, and the following issues will need to be addressed:

• There is a Performance Gap between energy use expected in the design phase and that achieved after construction;
• There is no requirement to carry out Post Occupancy Evaluations meaning there is no true understanding of which measures deliver energy reductions in practice, or whether environmental systems have been correctly installed (where consumers may assume they are failing to operate the systems properly rather than there being an installation fault); and
• Life-cycle emissions are often ignored, and some energy reduction technologies have embedded emissions that exceed the lifetime of the technology resulting in an overall increase in the environmental impact of the building.

There are essentially three problems:

Firstly, building energy performance is not measured in practice and the current means of labelling it, the EPC process, measures cost rather than emissions meaning it is linked to the price of input fuels which introduces a significant bias, and is a theoretical value that is not well aligned with actual building energy performance.

Secondly, the absence of measurement means there is no learning across the construction or energy industries about which measures are actually effective in reducing building energy consumption, and by extension, emissions. This is likely to lead to sub-optimal decision-making in the design of new buildings and the retro-fitting of existing buildings.

Finally, the embodied emissions of buildings are currently ignored, yet as the energy delivered to buildings de-carbonises, embodied energy will form an ever larger component of building emissions which needs to be taken into consideration.

Failing to act on these problems will essentially mean that the efforts to de-carbonise the buildings segment will fail, while consumers will waste money on unsuccessful building improvements and bills will rise significantly as the move away from gas is likely to increase the unit costs of heating. And worse still, consumers may find themselves unable to maintain their desired comfort levels.

The Government wants to see the EPC rating for all homes improved, but the system is flawed: electric heating which generates lower emissions than gas heating is heavily penalised while the condition of buildings is assumed to be perfect.

This makes it difficult for consumers to make effective improvements to buildings that both reduce costs and emissions.

Read more…

Consumer decision-making has a major impact on building energy performance. The way we heat our homes, the appliances we use, and the timing of consumption all contribute to the energy use of buildings. Some of this is discretionary, but even climate-conscious consumers often fail to make sustainable choices, since they find it hard to accurately visualise the energy each activity requires.

Read more…