Smart Controls and PAS2035: What the Standard Requires

Smart controls are increasingly integral to retrofit projects, but PAS2035 sets specific requirements that retrofit coordinators must understand and implement. This guide explains what the standard demands and how to ensure compliance.

Why Smart Controls Matter in PAS2035

PAS2035:2019 recognises that insulation and fabric improvements alone cannot achieve optimal energy performance. Smart controls—including thermostats, heating controls, and building management systems—play a critical role in:

• Optimising energy consumption post-retrofit
• Preventing performance gaps between design and operational outcomes
• Supporting long-term building performance monitoring
• Meeting Building Regulations Part L requirements

The standard explicitly links control systems to the retrofit's overall success, making them non-negotiable elements rather than optional add-ons.

Core PAS2035 Requirements for Controls

1. Heating Controls and Thermostatic Radiator Valves (TRVs)

PAS2035 requires that:

• All radiators (except those in rooms with programmable room thermostats) must have TRVs fitted
• Boiler interlock must be installed where a heating system is replaced or upgraded
• Controls must allow users to set and maintain temperature at desired levels
• Systems must prevent overheating in well-insulated buildings where fabric improvements have been made

2. Thermostats and Temperature Control

The standard specifies that retrofit projects must install:

• Programmable or smart room thermostats capable of at least two daily scheduling periods
• Manual temperature adjustment capabilities with clear user interfaces
• Thermostats positioned appropriately to avoid false readings from drafts, direct sunlight, or heat sources

Where properties have undergone significant fabric improvements, consider whether existing thermostat settings remain appropriate—upgraded insulation means buildings retain heat longer, potentially causing overheating if controls aren't recalibrated.

3. System Integration and Commissioning

PAS2035 demands that controls are:

• Properly commissioned and tested before handover
• Integrated with the heating system to function as a unified whole
• Documented in the building's operation and maintenance manual
• Set to default positions that optimise energy performance

Smart Controls Beyond Minimum Standards

Whilst PAS2035 sets baseline requirements, many retrofit projects benefit from enhanced smart controls:

Weather Compensation Systems

These automatically adjust heating output based on external temperature, improving efficiency in insulated buildings where fabric performance is optimised. They're particularly valuable post-retrofit when buildings hold heat longer.

Building Management Systems (BMS)

For multi-unit properties or larger retrofits, a BMS allows:

• Remote monitoring and adjustment of heating schedules
• Real-time energy consumption data
• Early fault detection and performance anomalies
• Coordination across multiple heating zones

Demand-Controlled Ventilation

Where mechanical ventilation with heat recovery (MVHR) systems are installed, PAS2035 considers smart controls that vary ventilation based on occupancy and air quality beneficial for preventing unnecessary heat loss.

Common Compliance Issues

Underspecification of Controls

Many retrofit projects fail to adequately specify controls at the outset. Ensure controls are detailed in:

• Energy performance calculations
• Design specifications
• Installation contracts
• Handover documentation

Poor Commissioning Practice

Controls must be commissioned by competent persons with documented evidence. Common shortfalls include:

• Failure to test heating system response to control inputs
• Inadequate user training on new systems
• Missing or incomplete commissioning certificates

User Guidance Gaps

PAS2035 emphasises that occupants must understand how to use controls effectively. Retrofit coordinators should ensure:

• Clear, jargon-free operating instructions are provided
• User manuals explain both basic and advanced functions
• Training is offered for complex systems (BMS, MVHR controls)

Monitoring and Ongoing Performance

PAS2035 recognises that controls contribute significantly to closing the performance gap—the difference between predicted and actual energy consumption. Post-retrofit:

• Monitor energy consumption data where smart meters or BMS systems provide it
• Compare actual performance against design predictions
• Adjust control settings if initial performance data reveals discrepancies
• Document any adjustments made during the defects liability period

Integration with Building Regulations

Building Regulations Part L now requires smart controls as standard. PAS2035 compliance typically exceeds minimum Building Regulations requirements, providing a clear pathway to regulatory approval. Ensure retrofit designs:

• Meet both PAS2035 and Part L standards simultaneously
• Document how controls contribute to demonstrating compliance
• Include control specifications in Building Control submissions

Key Takeaways

Smart controls are not peripheral to PAS2035—they're central to retrofit success. Retrofit coordinators must ensure controls are:

• Properly specified from project outset
• Installed by competent persons
• Fully commissioned with documented evidence
• Understood and usable by building occupants
• Monitored post-retrofit to verify performance

When approached systematically, smart controls transform retrofits from fabric-only improvements into integrated, performance-optimised building upgrades that genuinely deliver the energy savings PAS2035 projects.