AI-generated retrofit concept. Suitable measures depend on a property assessment. This is not a photograph of a completed Marwells project.
A home can look freshly decorated and still feel cold, difficult to heat or uncomfortable in summer. Retrofit looks at how an existing property performs and how carefully chosen improvements can make it work better for the people who live there. The best starting question is therefore: what needs to improve in this particular home, and how will we know the work has achieved it?
What retrofit means and why it matters
Home retrofit can include insulation, ventilation, heating upgrades and technologies that generate or store electricity. The aim may be to reduce energy use and carbon emissions, improve comfort, or address shortcomings in the indoor environment. Because changing one part of a building affects others, Energy Saving Trust recommends considering the whole home, even when the work happens in stages. [1]
A planned approach matters because building work creates opportunities that may be difficult to repeat. If you are already renewing finishes or opening up rooms, ask whether suitable energy improvements should be designed into the same project. Conversely, a working system need not be replaced simply to make a specification look more ambitious. Decisions should follow the property's condition, your budget and the outcome you actually want.
Start with a survey and a clear brief
For traditional buildings, Historic England emphasises construction, condition, significance, use and exposure when planning improvements. Repair and maintenance are part of energy performance: unresolved water ingress should not simply be covered by a new finish. Its guidance also explains why a rigid interpretation of 'fabric first' may be inappropriate for some historic properties. [2]
Bring a short record of the home's problems to the initial meeting. Which rooms feel cold? When does condensation appear? Are there leaks, difficult controls or a room that overheats? Include your EPC, available drawings and previous work records. These observations help the team decide what to investigate; they are not a diagnosis by themselves.
Ask for uncertainties to be written down. An inspection may show that further checks are needed before a wall, roof or floor upgrade can be specified. Agree who will investigate, what permission is needed and how the findings could change the price. A useful brief makes room for these questions rather than treating every assumption as a confirmed fact.
Understand the options and the checks behind them
The following table is a conversation guide, not a ready-made specification. Several options may belong in one project, while others may be unsuitable or unnecessary. Request a reasoned comparison that explains what you gain, what changes elsewhere and what you will need to maintain.
- Roof, wall or floor upgrades: Reduce unwanted heat loss through the building fabric. [1] Questions for the design team: Is the existing construction suitable, and how will edges and junctions be resolved?
- Heating and controls: Match heat delivery to the home and make operation easier. [6, 7] Questions for the design team: What assessment supports the system size, emitter choices and control strategy?
- Ventilation improvements: Provide planned air movement as the home changes. [5] Questions for the design team: Where does replacement air enter, how does it reach extract points, and how will performance be checked?
- Glazing and shading: Coordinate daylight, winter comfort and summer conditions. [3] Questions for the design team: What are the effects of orientation, shading and the amount of glass?
- Solar or other suitable technologies: Support an agreed energy strategy. [1] Questions for the design team: Does the proposal fit the roof, services, usage pattern and future maintenance plan?
The broad options follow established retrofit guidance; their suitability needs individual assessment. RICS also highlights measures such as appropriate glazing, solar shading, heating controls and attention to air leakage, alongside the need to consider moisture when improving airtightness. [3]
Insulation moisture and ventilation belong in one design
Insulation work is more than choosing a board thickness. PAS 2035 draws attention to interfaces: corners, junctions and edges, together with the relationship between the fabric, services and occupants. It also links ventilation provision to the building's air permeability. These connections are central to making a package of measures work as intended. [4]
Improving airtightness reduces uncontrolled draughts, but a home still needs controlled ventilation. Cooking, bathing and everyday occupation produce moisture, while indoor pollutants also need consideration. Replacing leaky components without reviewing ventilation can leave a property under-ventilated. The answer is a designed strategy suited to the altered home, followed by appropriate installation and commissioning. [5]
For an illustrative refurbishment, ask the team to mark the intended insulation and ventilation routes on the same set of drawings. Who resolves the junction behind the new kitchen? Who checks a duct before a ceiling is closed? Who confirms that a late product substitution still fits the design? These are useful coordination questions because they put responsibility against details that a homeowner may never see again.
Plan the heating system around the improved home
A heat pump should be considered as a designed system with emitters, controls and, where needed, hot-water storage. An air-to-water heat pump transfers heat from outdoor air to the water serving radiators or underfloor heating. Installation requirements and running costs vary with the property, the system being replaced, the electricity tariff and operation. Some projects need radiator changes; this should be assessed rather than assumed for every room. [6]
Room-by-room heat-loss calculations help a heating designer select equipment and emitters for the intended indoor conditions. Existing homes need suitable survey information; uncertainty about construction and airtightness affects the result. If fabric improvements are planned, tell the heating designer so the calculation represents the intended home rather than an obsolete starting condition. [7]
Ask how the transition will work if the heating needs replacing before the full refurbishment. Can the chosen approach support later work? What space and access should be reserved? Request the assumptions behind the recommendation and an explanation of how controls will be demonstrated at handover. A phased plan should remain useful when real life forces a change in sequence.
Think about summer comfort as well as winter bills
A retrofit brief should include the rooms that become uncomfortable in hot weather. RICS identifies solar shading as one way to help limit summer overheating. Ask the designer to consider the actual orientation and use of the rooms alongside glazing and ventilation choices. [3]
For example, a home office occupied throughout the afternoon deserves a different discussion from a room used occasionally. Explain when you need quiet, whether windows can safely remain open and how the room will be furnished. These everyday details help the team evaluate whether the proposed arrangement will suit your life after the builders have left.
Can retrofit be completed in stages
Yes. A whole-home plan can set a destination without requiring everything to be installed at once. Energy Saving Trust highlights the opportunity to coordinate energy upgrades with other renovation, for example when roof access is available or floors and internal finishes are already being renewed. Combining work can reduce repeated disruption, provided it supports an overall plan. [8]
Consider this illustrative sequence for an older terrace. First, the owner commissions investigation and deals with identified defects. Next, the team agrees a complete improvement strategy and carries out the measures suited to the first refurbishment phase. Preparation for later work is recorded. Before a subsequent heating phase, the designer reviews what has actually been built and updates the assumptions. This is an example of planning logic, not a prescribed order for every terrace.
What PAS 2035 means for a homeowner
PAS 2035 provides a framework for domestic retrofit covering assessment, coordination, design, installation, testing, handover and evaluation. It distinguishes the roles involved and addresses the interaction between measures. Ask whether your funding scheme or contract requires a particular standard, who is responsible for each role and what evidence will demonstrate compliance. A claim of following a process should be supported by the appropriate appointments and records. [4]
Do not assume every construction business holds every specialist retrofit qualification. Establish the services included in the appointment and the specialists needed for your project. The useful outcome is a clear chain of responsibility from the initial assessment through to the completed work.
Budget for the whole job and check support early
Compare quotations against the same scope. Include investigation, design, repair, access, ventilation, service changes, making good and commissioning where relevant. Ask for allowances and exclusions to be explained. If one proposal omits work another includes, its lower total may not describe the same project.
Eligible households in England may receive support through the Warm Homes: Local Grant, subject to the property's characteristics, household circumstances and available local funding. The council arranges the survey and agreed works under that scheme. Check eligibility and the required process before making commitments; do not assume an independently ordered project will be reimbursed. [9]
Check the result and understand your home
Agree the handover information before construction begins: final specifications, relevant installation and commissioning records, maintenance instructions and explanations of the controls. Building performance evaluation can also consider measured conditions, energy use and occupants' experience, rather than relying only on design predictions. For older buildings, Historic England describes evaluation as a way to understand both technical performance and use. [10]
Keep a simple list of any issues after occupation and raise them through the agreed project process. A system you cannot operate confidently needs a clearer demonstration; a recurring problem needs investigation. Practical feedback helps distinguish a setting that needs adjustment from a defect requiring corrective work.
Discuss your retrofit with Marwells
Marwells provides an engineering-led approach to retrofit, refurbishment and residential construction in London and surrounding areas. We can discuss how your improvement priorities fit the building work and identify the specialist input needed. Share your drawings, EPC and goals with info@marwells.co.uk, or call 07340 094028 for a free quote discussion.
Related: Retrofit and refurbishment · Construction consultancy and project management · Get a quote
Sources and further reading
- Energy Saving Trust: Retrofit explained
- Historic England: Improving energy efficiency through mitigation
- RICS: Retrofitting and improving the energy efficiency of your home
- BSI: PAS 2035:2023
- Energy Saving Trust: Ventilation
- Energy Saving Trust: Air source heat pumps
- Energy Saving Trust: Heat-loss calculations: detailed guidance
- Energy Saving Trust: Energy saving upgrades for home renovation
- GOV.UK: Apply for the Warm Homes: Local Grant
- Historic England: Building performance evaluation for energy efficiency
