Improving the Energy Performance of an Older Home

The homes that perform least well on energy efficiency are often the ones most worth keeping — older buildings with thick solid walls, original sash windows, and a material character that took generations to acquire. The challenge of improving their thermal performance without compromising what makes them valuable is one of the more interesting design problems in residential architecture, and one we encounter regularly across our Hampshire and London projects.

This guide is for owners of older homes — pre-1919 in particular, where solid wall construction is the norm — who want to understand the options for improving energy performance, what the constraints are in listed and unlisted buildings, and what a sensible approach looks like in practice.

Why older buildings are different

Modern buildings are designed to be airtight and insulated, with vapour barriers and cavity walls that control moisture movement through the fabric. Older buildings work on an entirely different principle: they are designed to breathe. Solid masonry walls, lime mortars and plasters, timber floors, and sash windows all allow moisture to move through the fabric and evaporate, keeping the building dry and its materials in good condition.

The single most common mistake made in retrofitting older homes is applying modern insulation and sealing systems to a building designed to breathe. Introducing a non-breathable layer — cavity wall insulation foam, impermeable render, rigid insulation boards bonded to historic plaster, or polyurethane spray foam in roof voids — traps moisture within the fabric. The result is condensation, salt crystallisation, damp, mould, and in time the decay of timber and finishes. In listed buildings, such works would almost certainly require listed building consent — and carrying them out without it is a criminal offence.

The starting point for any retrofit of an older building is understanding how it currently manages moisture — and ensuring that whatever measures are introduced work with that behaviour rather than against it.

Fabric first

The most effective and least disruptive approach to improving energy performance in any older building is to address the fabric before considering mechanical systems. Reducing the amount of energy a building loses is always more valuable than increasing the efficiency with which it generates heat — and in older buildings, the fabric-first approach avoids the risks associated with introducing powerful heating systems into a building that has not been prepared to receive them.

The fabric measures that deliver the greatest impact in older homes, roughly in order of return on investment, are as follows.

Draughts and air leakage. A disproportionate amount of heat loss in older homes occurs not through walls or windows but through gaps — around sash windows, under floorboards, at skirting boards, through chimneys, and around pipe and cable penetrations. Draught-proofing is cheap, reversible, and highly effective. Sash windows can be fitted with brush seals that dramatically reduce air infiltration without altering their appearance or requiring consent in most cases. Chimneys not in use can be sealed with a removable chimney balloon.

Loft insulation. Where a roof space is accessible and unoccupied, insulating the loft floor with a breathable natural fibre — sheep's wool, wood fibre, or recycled cotton — is straightforward, effective, and reversible. Around 25–30% of heat loss in older homes occurs through the roof. This is one of the highest-return measures available and rarely requires consent.

Floor insulation. Suspended timber floors above unheated voids are a significant source of heat loss. Where original floorboards are in good condition, insulating between the joists from below — or carefully lifting boards to lay insulation from above — is achievable using breathable materials such as wood fibre boards or sheep's wool. Where original flagstone or clay tile floors sit directly on the ground, the situation is more complex, and any insulation strategy must be designed carefully to avoid moisture accumulation beneath the floor.

Internal wall insulation. Solid walls in older buildings lose more heat than modern cavity walls, but insulating them requires care. The only appropriate approach in a traditionally built home is breathable internal wall insulation — wood fibre boards, hemp batts, or insulating lime plaster — applied over the existing wall without sealing the historic fabric behind. These materials allow moisture to move through the assembly and prevent condensation at the interface between old and new. In listed buildings, any works to internal finishes require listed building consent, and the conservation officer will need to be satisfied that the approach does not harm historic plaster, joinery, or other significant fabric. Our guide to working with listed buildings covers the consent process in detail.

Windows. Secondary glazing — a discreet inner frame fitted within the existing window reveal — is the most effective and most widely accepted approach to improving the thermal performance of sash windows in listed and conservation area buildings. Well-designed secondary glazing can achieve double-glazed performance levels while preserving the original window entirely. Replacement windows in listed buildings require consent and are subject to a high evidential bar — the case for removal of original fabric must be compelling. For unlisted homes in conservation areas, the replacement of original timber sash windows with UPVC is refused as a matter of policy across most local authorities.

Heat pumps in older homes

Air source heat pumps are increasingly the default heating choice for rural homes off the gas grid, and for homes where a gas boiler replacement is due. They are highly efficient when conditions are right — but those conditions matter.

Heat pumps operate most effectively at low flow temperatures, typically 35–45°C, which means they work best with underfloor heating or large-format radiators rather than the small, high-temperature radiators that most older homes were designed for. In a home that has not had its fabric improved, a heat pump will run continuously at low efficiency, producing high running costs rather than lower ones.

The practical implication is that a heat pump is best introduced as part of a broader retrofit strategy, after the fabric measures described above have been addressed. A building that has been draught-proofed, has good loft insulation, and has had its floor and wall losses reduced meaningfully will respond well to a heat pump. One that has not may not.

In rural Hampshire, where many of our clients are off the gas grid and operating on oil boilers, the transition to heat pumps is both environmentally and economically rational — oil prices are volatile and the carbon intensity of oil heating is high. The Boiler Upgrade Scheme currently offers a £7,500 grant towards the installation of an air source heat pump, reducing the capital cost meaningfully. The scheme is available for both listed and unlisted properties.

What requires consent

In unlisted homes outside conservation areas, fabric improvement measures rarely require planning consent. In listed buildings, the position is more complex. Any works that affect the character of a listed building require listed building consent — and this includes many retrofit measures: internal wall insulation applied over historic plaster, the lifting of original floors, the replacement of windows, the installation of roof lights to improve natural ventilation, and the introduction of mechanical ventilation systems that require penetrations through historic fabric.

Historic England's guidance on Energy Efficiency and Historic Buildings is the key reference document for retrofit in listed buildings. It sets out a fabric-first approach, emphasises breathability and reversibility, and provides detailed guidance on specific measures. Conservation officers across Hampshire and London use it as their primary reference when assessing retrofit applications.

The important thing to understand is that retrofit and listing are not in conflict. Listed buildings can and should be made more energy-efficient — the question is how, and the answer almost always involves breathable materials, reversible interventions, and a clear understanding of how the building currently manages moisture.

An integrated approach

The projects that achieve the best energy outcomes are those where retrofit is considered as part of a broader design process — not as a separate exercise applied after the fact. When a renovation or extension is already planned, the opportunity exists to address insulation, airtightness, heating, and ventilation in a coordinated way, without the additional disruption of returning to the building later.

We approach energy performance as an integral part of the design of every project, working with structural and building services engineers to develop strategies that are appropriate for the specific building and its planning context. If you are thinking about improving the energy performance of an older home in Hampshire or London, we would be glad to discuss what is possible. Get in touch.