Project Type: High-Risk / Whole-House Decarbonisation
Property: Pre-1919 Stone End-of-Terrace
The Objective: Transform a historic, carbon-heavy property into a modern, highly efficient home without compromising its structural health.
The Challenge
The client wanted to completely decarbonise their Victorian-era home and move away from fossil fuels. However, heritage properties are built to be vapour-permeable (breathable). Standard synthetic insulation materials would trap moisture, leading to severe dampness and the rotting of ancient timber joists. Furthermore, the property was highly complex, featuring suspended timber floors and original architectural details that needed preserving.
Our PAS 2035 Approach
This was a rigorous Path C project. Our team utilised advanced hygrothermal modelling—calculating exactly how moisture and heat move through this specific type of stone—to specify safe materials. We engineered a phased “deep retrofit” that respected the building’s historic physics while pushing its energy efficiency to the absolute maximum safe limit.
Measures Implemented
Breathable Internal Wall Insulation (IWI): To preserve the stone exterior, we insulated the inside using natural, vapour-permeable wood-fibre boards finished with lime plaster. This keeps the walls warm while allowing moisture to escape naturally.
Suspended Floor Insulation: We carefully lifted the original floorboards to install breathable insulation nets between the joists, eliminating the severe draughts coming from the sub-floor void without trapping ground moisture.
Low-Carbon Heating Transition: With the fabric now highly efficient and heat loss minimised, we replaced the old boiler with an optimally sized Air Source Heat Pump (ASHP), paired with new low-temperature radiators.
Renewable Energy Integration: We installed a 4kW Solar PV array on the rear roof elevation to heavily offset the new electrical demand of the heat pump.
The Results
EPC Jump: Rating improved from a G (15) to a highly efficient B (86).
The Impact: Taking a 19th-century solid stone property to an EPC B is an exceptional achievement in retrofit engineering. We successfully took a cold, damp building and turned it into a flagship of modern efficiency. The home is now decoupled from fossil fuels, features a perfectly balanced indoor climate, and preserves all its historic charm and structural integrity for the next century.
