Start With a Plan, Not a Purchase

The temptation with retrofit is to buy something. A new boiler, a shiny smart thermostat, an air source heat pump you spotted on offer. But the homeowners who get the warmest house for their money almost always started with a plan instead. Before you spend a penny, work out what your house actually needs and in what order.

A useful starting point is your EPC, but treat it as a rough compass rather than a gospel. It will flag the obvious gaps — uninsulated lofts, single glazing, an old boiler — but it will not tell you where your house leaks air or where the cold bridges are. If your budget stretches to it, a retrofit assessment or a thermal imaging survey will show you the real weak spots. Many local authorities and community energy groups offer low-cost or free assessments.

Once you have that picture, write a phased plan covering the next five to ten years. Fabric first, heating second, renewables last. Every stage should make the next one cheaper or more effective. That single principle will save you more than any bargain you find online.

Airtightness and Draughts: The Cheapest Wins

Draughts are the most cost-effective thing you can tackle, and the most overlooked. A house that changes its air five times an hour is paying to heat the street. Sealing obvious gaps can knock hundreds of pounds off annual bills before you touch insulation.

• Fill gaps around window and door frames, skirting boards, and where pipes and cables pass through walls and ceilings.
• Fit draught excluders to letterboxes, keyholes, loft hatches and open chimneys (a chimney balloon is a tenner and unobtrusive).
• Check suspended timber floors — gaps between boards in older homes can be significant, and sealing from below with a breathable membrane works well.
• Do not seal kitchen or bathroom extract fans, and make sure any open-flued appliance still has its required ventilation.

Here is the caution: sealing a house without controlled ventilation can trap moisture and cause condensation and mould. If you are going hard on airtightness, budget for trickle vents, humidity-sensing extract fans, or mechanical ventilation with heat recovery further down the line. Aim for a house that is airtight and properly ventilated, not one wrapped in plastic.

Insulation in the Right Order

Insulate in the order that gives the best return for the least disruption. Loft insulation is almost always first: top up to at least 270mm and make sure you do not block the eaves ventilation. If you have cavity walls, cavity wall insulation is next, assuming your walls are suitable — some exposed or coastal properties are not.

Then look at floors and solid walls. Solid wall insulation is expensive and disruptive, so it needs careful thought. External wall insulation keeps your floor area and avoids cold bridging, but it changes the look of the house and may need planning permission in conservation areas. Internal wall insulation is cheaper but loses you a little space and demands meticulous detailing to avoid interstitial condensation. Get this wrong and you create damp problems that cost more to fix than the insulation saved.

Windows and doors come later than most people expect. If your double glazing is sound, sealing it is often better value than replacing it. Secondary glazing on heritage windows can perform surprisingly well.

Heating and Hot Water

Only after you have reduced demand should you size a new heating system. A well-insulated, draught-free house needs a much smaller heat source, and that changes the economics entirely. Radiators sized for a leaky house at 80°C flow temperature are oversized for a retrofit house running at 45°C — which is exactly what a heat pump wants.

• If your boiler is on its last legs and you cannot afford a heat pump yet, a modern condensing boiler sized correctly is a reasonable interim step.
• When you do move to a heat pump, plan for larger radiators or underfloor heating in the rooms you use most.
• Insulate your hot water cylinder and pipework — a poorly lagged cylinder loses heat all year round.
• Set your heating schedule around occupancy rather than leaving it on constant, and lower the flow temperature if your system allows it.

Funding, Trades and Sequencing

There is help available, and it changes often, so check current government and local authority schemes before you assume you are on your own. Grants have historically favoured insulation and low-carbon heating, and some are means-tested. Your local authority may also run area-based schemes where a whole street gets work done more cheaply.

On trades: ask for a retrofit coordinator or an experienced installer who understands whole-house performance, not just their own trade. A cavity wall installer who does not think about ventilation, or a heat pump installer who ignores radiator sizing, will cost you later. Get three quotes, ask for references from similar properties, and be suspicious of anyone who promises dramatic savings without surveying first.

Keeping the Plan on Track

Retrofit is a marathon with a finishing line. Keep a simple file of what you have done, when, and to what standard, plus any warranties. It helps when you sell, and it stops you paying twice for the same survey.

Review your plan each year. Energy prices move, technology improves, and your circumstances change. What matters is that each step leaves the house warmer, drier and cheaper to run than the last — and that you never spend money on heating a house that is still leaking heat through its walls and floors.