Part L’s new Target Emission Rate (TER) represents a 25% improvement over the previous regulations and is in line with achieving Code for Sustainable Homes Level 3. Meanwhile, both Approved Part L and F include a number of detailed major revisions which underpin compliance with stated minimum energy efficiency levels for all ventilation systems. With the launch of Part L’s new Domestic Building Services Compliance Guide ventilation performance levels are highlighted. Here for the first time a specific fan power requirement of less than 0.5 watt/sec is included for intermittent fans used in both refurbishment and new build developments.