Published 14 April 2026 · Sash Window Draught Proofing
The regulatory landscape for London's period properties shifted significantly on 24 March 2026, when the Ministry of Housing, Communities and Local Government published the updated Part L regulations. For homeowners of Victorian and Georgian terraces in areas like Chelsea, Kensington, and Westminster, these changes represent both a challenge and an opportunity to enhance the thermal efficiency of their properties.
Understanding the Part L 2026 Update
The primary objective of the Part L 2026 update is to accelerate the UK's transition toward net-zero housing by tightening thermal compliance across all residential dwellings. For standard modern homes, the new U-value target for replacement windows is now approximately 1.4 W/m²K. Heritage assets — listed buildings, Conservation Area properties and buildings of local historic interest — are covered by a "reasonable practicability" clause.
Heritage Exemptions
Standard double glazing is almost never approved by conservation officers for Grade II listed sash windows. Under Part L 2026 the focus shifts to high-performance, reversible upgrades: high-quality draught elimination, professional sash window refurbishment, and internal secondary glazing.
The Compliance Hierarchy
For most London period homes we recommend starting with conservation-grade draught proofing (£150–£300 per window, ~30% heat-loss reduction, ~2 year ROI) and layering internal secondary glazing where higher thermal or acoustic performance is required (£400–£800 per window, up to 70% heat-loss reduction, up to 50dB noise reduction). See our detailed Victorian sash window guide and secondary glazing vs draught proofing comparison.
Why Professional Restoration is Non-Negotiable
The 2026 regulations place a higher burden of proof on homeowners. Our window restoration and heritage window restoration services cover sash cord replacement, hardware refurbishment, timber stabilization and precision balancing — all backed by a 10-year workmanship guarantee.
Homeowners in Chelsea, Kensington and Westminster should audit their windows now. Our emergency services are available during peak winter months. Call 0207 060 1573 for a free survey.