For this edition of The Expert Insight Series, we engaged with an MEP Technical Lead of a well known Main Contractor. In which we discuss the evolution of Part L, who is responsible for compliance and the level of expectations put to the MEP Designers and Contractors.
The UK’s Building Regulations, particularly Part L, have long dictated the path towards energy efficiency in buildings. From its initial introduction to today’s increasingly stringent updates, compliance with Part L has continually reshaped the role of the MEP (Mechanical, Electrical, and Public Health) engineer. With each revision, the expectations placed on MEP professionals grow, often creating challenges that seem insurmountable within the commercial and residential construction landscape.
For MEP engineers, the demands of Part L go far beyond theoretical compliance. In practice, they must navigate the intricate balance of efficiency, cost, and design practicality, often under immense pressure from developers, contractors, and regulatory bodies. But has Part L evolved to support genuine sustainability, or has it become an ever-expanding burden on MEP engineers? Let’s take a deep dive into the reality of compliance from the perspective of those at the heart of the process.
The Evolution of Part L: From Simplicity to Complexity
The journey of Part L began with a straightforward goal—reduce energy waste in buildings. The early versions of the regulations primarily addressed basic insulation and boiler efficiencies, but over time, they have evolved into a complex web of requirements covering airtightness, system efficiencies, metering, and renewable technologies.
“Part L used to be a relatively simple exercise in achieving better insulation and ensuring some level of system efficiency. Now, it’s a completely different beast. Every aspect of building services must be modelled, calculated, and justified to demonstrate compliance.” The amount of work involved often goes unnoticed and now forms part of ‘normal expectations’ and is regarded as ‘simply part of the design process’.
With the introduction of SAP (Standard Assessment Procedure) for residential buildings and SBEM (Simplified Building Energy Model) for non-residential buildings (sometimes both), compliance moved beyond prescriptive measures to detailed performance-based assessments. As energy targets became tighter, the focus shifted from simple fabric improvements to demanding system-wide efficiencies.
“The reality is that the MEP team often carries the heaviest burden of making a project Part L-compliant because improving the building fabric isn’t always an option developers want (or are able) to take. Instead of significantly enhancing insulation or upgrading glazing, we’re expected to push system efficiencies to near-impossible levels.”
This isn’t always the case, especially with the Pasivhaus strategies being adopted more frequently. This being said, there is always an element of MEP system enhancements, I doubt we’ll escape this.
The Core Challenges of Part L for MEP Engineers
As Part L evolved, so too did the responsibilities of MEP engineers. Today, compliance is no longer just about designing efficient systems—it’s about proving and verifying them throughout a building’s lifecycle. Here are some of the biggest challenges we face:
1. Super-Efficient Plant and Systems
Many developers prioritise cost savings over fabric performance upgrades, meaning MEP teams must specify high-performance heating, cooling, and ventilation systems to compensate for somewhat less efficient building envelopes.
“Clients often assume that as long as we put in a high-efficiency boiler or heat pump, we’re good to go. But that’s not how it works. Every component—pumps, fans, ducts, controls—must be optimised, and that takes an enormous amount of coordination.”
In addition, the increased use of air source heat pumps (ASHPs), low-temperature heating, and mechanical ventilation with heat recovery (MVHR) has introduced new challenges. These systems must not only perform efficiently on paper but also be installed and commissioned correctly to achieve their intended savings. Not to mention space is already at a premium on these developments, now it’s on Architects and MEP engineers to try and fit all this kit inside our buildings… not an easy task!
2. Stricter Air Tightness and Thermal Bridging Requirements
While improving the fabric of a building is often the best way to enhance energy performance, many developers resist investing in higher-specification insulation or better glazing. Instead, MEP teams are expected to mitigate energy losses through advanced system designs and airtightness strategies.
“The pressure to compensate for poor fabric performance can be relentless. It’s one thing to design a system that meets Part L on paper, but ensuring it actually performs in the real world—when you have ductwork running through uninsulated ceiling voids—is another challenge entirely.”
The Ongoing Shift: Part L 2021 and the Future
The most recent update to Part L in 2021 introduced even stricter energy efficiency requirements, setting the stage for the Future Homes and Buildings Standard in 2025. These changes aim to reduce carbon emissions by 30% for new homes and 27% for new non-domestic buildings compared to previous standards.
To meet these ambitious targets, MEP engineers are increasingly expected to incorporate:
- Low-carbon heating solutions (heat pumps replacing traditional gas boilers)
- Demand-controlled ventilation systems to reduce unnecessary energy use
- More advanced metering and monitoring to track energy consumption in real-time
- Renewable energy integration such as photovoltaic (PV) panels, which introduce further design complexities
While these measures align with broader sustainability goals, they also come with practical and financial challenges. Developers often push back against higher capital costs, leaving MEP engineers in a difficult position—designing to meet regulations while still working within tight budgets.
“We often see MEP contractors willing to absorb significant risk with Part L compliance, with many unknown elements about the specified plant suitability just to try to secure a project. It’s no secret how competitive MEP can be, and many contractors feel that if they don’t take the risk, someone else will. Not a place any of us want to be”
An Endless Expectation? The Future of MEP Compliance
Looking ahead, it is clear that Part L will continue to evolve, likely imposing even stricter energy performance standards in pursuit of the UK’s net-zero carbon targets.
So, what does this mean for MEP engineers?
- Increased Responsibility: With net-zero ambitions on the horizon, MEP engineers will face even greater pressure to design and coordinate ultra-efficient systems that integrate seamlessly with renewable energy.
- Greater Collaboration: Achieving compliance will require closer cooperation between architects, structural engineers, and developers to ensure that energy efficiency is approached holistically rather than leaving it solely to the MEP team. Early engagement is a must!
- More Advanced Digital Tools: The industry is already seeing a push towards digital twins, dynamic simulation models, and AI-driven building management systems, all of which will play a critical role in ensuring real-world performance aligns with Part L requirements. The software platforms aren’t cheap, capital costs and licencing costs aren’t always an affordable option for numerous contractors and deisgners.
Despite these trends, many MEP professionals feel that the industry does not fully appreciate the extent of their contributions.
“Everyone expects us to solve energy efficiency problems without really acknowledging the constraints we work under. We’re fighting against budgets, space limitations, and sometimes unrealistic performance expectations, yet when a building doesn’t meet its energy targets, it’s the MEP engineer that ends up with the issue”.
Conclusion: A Growing Burden or a Necessary Challenge?
For this article, The MEP Source wanted to explore an overlooked symptom of Part L compliance; the endless expectation of the MEP engineer. Part L has undeniably driven improvements in energy efficiency, but the increasing complexity of compliance often places an unfair burden on MEP engineers. While technological advancements and regulatory tightening are essential in the pursuit of sustainability, a more balanced approach is needed—one that considers the practical limitations of real-world construction.
For MEP engineers, the challenge is not just meeting regulations, but ensuring that their expertise is recognised and valued within the wider industry. As the expectations continue to grow, so too must the industry’s understanding of the pivotal role they play in shaping a sustainable built environment.
“The bottom line is this, Part L is here to stay, and it will only get stricter. But if the industry doesn’t start sharing the responsibility for compliance, we’ll be stuck in a cycle where MEP engineers are constantly expected to perform miracles.”
The future of Part L compliance may be demanding, but one thing is certain—without the expertise, resilience, and innovation of MEP engineers, the UK’s journey to net zero would be impossible.
