English (Canada)
čeština (Česká republika)
magyar (Magyarország)
Deutsch (Deutschland)
eesti (Eesti)
español (España)
português (Portugal)
English
suomi (Suomi)
français (France)
italiano (Italia)
Nederlands (Nederland)
norsk, bokmål (Norge)
polski (Polska)
svenska (Sverige)
Türkçe (Türkiye)
Written by Hitesh Pattni (North) and Neil Kirwan (South) - Specification Managers in SFS Group Fastening Technology Ltd.
Contents:
The term 'performance gap' is most commonly used in association with energy efficiency and thermal performance, but performance gaps can exist in any area of building design and operation. A performance gap occurs when design intent is not realised in the finished building, leading to worse-than-expected performance or operating costs.
There are many and various reasons why performance gaps occur, across design, specification and construction. It can be said that performance issues and most common causes are likely to occur for the following reasons;
Arguably, the avoidance of performance gaps on construction projects is low on the list of priorities, especially when specifications are challenged during the later RIBA Plan of Work stages.
Achieving the right balance of performance and capital expenditure is one thing, but increasingly the question must be asked whether the planet can afford buildings that repeatedly fall short of what is promised.
For a performance gap to be identified, there has to be some measurement of how a building behaves in use.
The measured performance can then be compared to what was predicted in design stage calculations and specifications, to establish whether a gap exists and what the extent of it is. In-use monitoring, or post-occupancy evaluation (POE), is not commonplace in UK construction. There is no regulatory requirement for it, so it only tends to happen when a study is specially commissioned, or when a client is particularly committed to understanding how their building works.
However, some elements of performance are easier to measure than others.
From an energy efficiency perspective, the operational performance of a building can be established by gathering data using sensors to measure actual thermal transmittance (U-values), carrying our air pressure tests to establish airtightness, and monitoring energy consumption. When studies are undertaken to measure the actual energy performance of buildings, it's not uncommon to see figures quoting the actual heat loss and/or energy consumption as anything from three times, to ten times greater than was predicated.
This can be determined because there is a clear benchmark in terms of the as-designed prediction, and a measured outcome due to the monitoring.
How, though, can you measure whether there is a performance gap in the fire safety of a building?
There is no measurement or monitoring of the building fabric that can highlight whether something will fail in the event of a fire. The only time that a performance gap becomes clear is when it is too late to do anything about it.
Updates to national building regulations occur frequently, and recent changes have made some effort to begin addressing performance gaps.
There is a wealth of guidance available on meeting regulations, as well as voluntary standards, but as-built performance does not feature as much as it could.
Time and financial pressures on most projects mean on-site monitoring and inspection can almost never provide the quality assurance necessary to translate 'as designed' into 'as built'. There is a wealth of guidance available on meeting national building regulations, and yet as-built performance does not feature.
Where performance can be calculated (as in the case of energy efficiency), the data entered into the calculation assumes perfect installation of products and the correct commissioning of services, delivering their optimum performance.
The introduction of Part L 2021 in June 2022 sought to begin addressing this by requiring photographic evidence.
The Approved Documents now include a list of typical details that should be recorded during construction, including for air tightness work and building services installation. The pictures, taken "at appropriate construction stages" prior to the closing up of work, should be made available to the energy assessor and the Building Control Body.
In some ways, this approach mimics the approach of the voluntary Passivhaus standard. Quality control is an essential aspect of Passivhaus, requiring attention to detail to exceed the minimum standards mandated by national building regulations.
A significant difference remains, however: on Passivhaus projects, better thermal performance and air tightness, and a higher standard of record-keeping during the build, is typically backed up by specialist training for both designers and contractors.
Additional training is not a feature of the updated Part L. It remains to be seen, therefore, whether the requirement for photographic evidence alone will encourage designers and contractors to update their practices to achieve better collaboration and reduce performance gaps in energy efficiency.
If a building does not deliver its expected energy efficiency, its energy consumption, energy costs and carbon emissions will be higher than predicted.
Building occupants are more likely to experience discomfort and there may be potential long-term health implications from that. Alternatively, a building might not deliver expected levels of fire safety. Should a fire break out, there could be extensive damage to the building's structure and its contents or, worse, injury to occupants or loss of life.
It's easy to go through each area of building performance and identify the potential consequences if a performance gap is present in each one. But such approach perhaps misses the point. There's a much simpler way to look at the problem of performance gaps in complex building envelope specifications. Clients are not getting what they asked for, and the construction industry is not delivering what it should.
The first paper in this series identified several qualities of a robust specification. One was that it "meets the clients needs", but performance gaps instantly show those needs aren't being met. If there is a gap in performance then today's performance criteria are not being met, and the building is not fit for the future (two other qualities). And if the client isn't getting what they paid for, then the specifications is not delivering value - which was the final quality.
There are few industries in which that would be acceptable. And yet clients rarely - if ever - have any comeback regarding performance gaps that occur in their buildings. And that is assuming they even know about any such gaps.
Getting clients engaged is key for specifiers to know what goals they should be trying to achieve wither their designers and specifications, and for holding the wider construction industry to account more often.
The next whitepaper in this series looks at how clients can be engaged to help close performance gaps.
Just as no individual specifier can be an expert in all areas of the building envelope so one document cannot cover all areas of building envelope specification in the necessary level of detail.
This paper is one of a series exploring different areas of the building envelope specification, and looking at the performance criteria that must come together in order to meet the client's needs.
Ultimately, we went to show why and how prioritising early engagement on construction projects can lead to better building envelope specifications. Specifications that are robust, and which are the best for the individual project.
It's no exaggeration that specifiers face a more complex and evolving landscape than ever before. Throughout these documents, we'll show why the benefits of early specification, based on technical expertise provided by external parties, can far outweigh any potential drawbacks.
This defines the gap between current performance and desired or designed performance of a measurable element of a building.
What is the impact of performance gap?
A performance deficiency will generally cause an increase in operational costs or a negative experience for the building users. At the extremes it can cause a failure of a component or system of the building, impacting its operational use.
What causes performance gaps?
There are many reasons that cause a gap, typically this would be down to products fitted that do not match the original design, poor quality or workmanship.
Robust Building Envelope Specifications
Paper 2: The problem of performance gaps
Contents:
- Why do performance gaps occur?
- Measuring performance gaps
- The role of regulations in performance gaps
- Performance gaps and robust specifications
- SFS robust specification series
- About SFS construction UK
Why do performance gaps occur?
There are many and various reasons why performance gaps occur, across design, specification and construction. It can be said that performance issues and most common causes are likely to occur for the following reasons;
- Quality control issues on site.
- Regulatory requirements around as-built performance are not strong enough.
- Little or no monitoring takes place once buildings are in use.
Arguably, the avoidance of performance gaps on construction projects is low on the list of priorities, especially when specifications are challenged during the later RIBA Plan of Work stages.
Achieving the right balance of performance and capital expenditure is one thing, but increasingly the question must be asked whether the planet can afford buildings that repeatedly fall short of what is promised.
Measuring performance gaps
The measured performance can then be compared to what was predicted in design stage calculations and specifications, to establish whether a gap exists and what the extent of it is. In-use monitoring, or post-occupancy evaluation (POE), is not commonplace in UK construction. There is no regulatory requirement for it, so it only tends to happen when a study is specially commissioned, or when a client is particularly committed to understanding how their building works.
However, some elements of performance are easier to measure than others.
From an energy efficiency perspective, the operational performance of a building can be established by gathering data using sensors to measure actual thermal transmittance (U-values), carrying our air pressure tests to establish airtightness, and monitoring energy consumption. When studies are undertaken to measure the actual energy performance of buildings, it's not uncommon to see figures quoting the actual heat loss and/or energy consumption as anything from three times, to ten times greater than was predicated.
This can be determined because there is a clear benchmark in terms of the as-designed prediction, and a measured outcome due to the monitoring.
How, though, can you measure whether there is a performance gap in the fire safety of a building?
There is no measurement or monitoring of the building fabric that can highlight whether something will fail in the event of a fire. The only time that a performance gap becomes clear is when it is too late to do anything about it.
The role of regulations in performance gaps
There is a wealth of guidance available on meeting regulations, as well as voluntary standards, but as-built performance does not feature as much as it could.
Time and financial pressures on most projects mean on-site monitoring and inspection can almost never provide the quality assurance necessary to translate 'as designed' into 'as built'. There is a wealth of guidance available on meeting national building regulations, and yet as-built performance does not feature.
Address performance gaps
The introduction of Part L 2021 in June 2022 sought to begin addressing this by requiring photographic evidence.
The Approved Documents now include a list of typical details that should be recorded during construction, including for air tightness work and building services installation. The pictures, taken "at appropriate construction stages" prior to the closing up of work, should be made available to the energy assessor and the Building Control Body.
In some ways, this approach mimics the approach of the voluntary Passivhaus standard. Quality control is an essential aspect of Passivhaus, requiring attention to detail to exceed the minimum standards mandated by national building regulations.
A significant difference remains, however: on Passivhaus projects, better thermal performance and air tightness, and a higher standard of record-keeping during the build, is typically backed up by specialist training for both designers and contractors.
Additional training is not a feature of the updated Part L. It remains to be seen, therefore, whether the requirement for photographic evidence alone will encourage designers and contractors to update their practices to achieve better collaboration and reduce performance gaps in energy efficiency.
Performance gaps and robust specifications
Building occupants are more likely to experience discomfort and there may be potential long-term health implications from that. Alternatively, a building might not deliver expected levels of fire safety. Should a fire break out, there could be extensive damage to the building's structure and its contents or, worse, injury to occupants or loss of life.
It's easy to go through each area of building performance and identify the potential consequences if a performance gap is present in each one. But such approach perhaps misses the point. There's a much simpler way to look at the problem of performance gaps in complex building envelope specifications. Clients are not getting what they asked for, and the construction industry is not delivering what it should.
The first paper in this series identified several qualities of a robust specification. One was that it "meets the clients needs", but performance gaps instantly show those needs aren't being met. If there is a gap in performance then today's performance criteria are not being met, and the building is not fit for the future (two other qualities). And if the client isn't getting what they paid for, then the specifications is not delivering value - which was the final quality.
There are few industries in which that would be acceptable. And yet clients rarely - if ever - have any comeback regarding performance gaps that occur in their buildings. And that is assuming they even know about any such gaps.
Getting clients engaged is key for specifiers to know what goals they should be trying to achieve wither their designers and specifications, and for holding the wider construction industry to account more often.
The next whitepaper in this series looks at how clients can be engaged to help close performance gaps.
SFS Robust Specification Series
Just as no individual specifier can be an expert in all areas of the building envelope so one document cannot cover all areas of building envelope specification in the necessary level of detail.
This paper is one of a series exploring different areas of the building envelope specification, and looking at the performance criteria that must come together in order to meet the client's needs.
- Defining robust specification
- The problem of performance gaps
- Getting clients active and engaged
- Early engagement: how do we get more of it?
- Thermal performance and sustainability
- Fire safety
- Corrosion, warranties and supply chain challenges.
Ultimately, we went to show why and how prioritising early engagement on construction projects can lead to better building envelope specifications. Specifications that are robust, and which are the best for the individual project.
It's no exaggeration that specifiers face a more complex and evolving landscape than ever before. Throughout these documents, we'll show why the benefits of early specification, based on technical expertise provided by external parties, can far outweigh any potential drawbacks.
FAQs
What do you mean by performance gap?This defines the gap between current performance and desired or designed performance of a measurable element of a building.
What is the impact of performance gap?
A performance deficiency will generally cause an increase in operational costs or a negative experience for the building users. At the extremes it can cause a failure of a component or system of the building, impacting its operational use.
What causes performance gaps?
There are many reasons that cause a gap, typically this would be down to products fitted that do not match the original design, poor quality or workmanship.
