Energy-efficient renovation: doing the whole house in the right order

The usual advice is to reduce heat loss before replacing the heating. Loft, wall and floor insulation, draught-proofing and better glazing lower the heat a house needs on a cold day. The heating system can then be sized for the house as it will be, not as it was. This matters most for heat pumps, which work best at low flow temperatures and cost more when oversized.

That does not mean everything must happen at once. A written plan that sets out the order, even over several years, prevents work being undone: fitting external wall insulation after new windows, for example, may mean the window reveals have to be reworked. If scaffolding is going up anyway for a roof, it is worth asking what else could be done from it.

Every draught you seal was also carrying some moisture out. After a retrofit, cooking, showers, drying washing and breathing still produce water vapour, and it has to leave the house somewhere. Without enough ventilation, condensation and mould appear, usually in the coldest corners.

Options range from reliable extractor fans in kitchens and bathrooms and trickle vents in windows, through continuous extract systems, to whole-house mechanical ventilation with heat recovery (MVHR), which supplies fresh air and recovers heat from the outgoing air. MVHR only works well in a fairly airtight house and needs space for ducts and regular filter changes. The ventilation strategy should be decided in the plan, not as an afterthought.

When you renovate a quarter or more of an external wall, roof or floor in England, the Building Regulations normally require that element to be insulated to the current standard, where that is technically, functionally and economically feasible. Replacing windows, a new boiler, new electrical circuits and cavity wall insulation are all notifiable work, usually self-certified by installers registered with competent person schemes. Keep every certificate; a buyer's solicitor will want them.

External wall insulation and new cladding need planning permission in conservation areas, national parks, Areas of Outstanding Natural Beauty and the Broads, and listed buildings need listed building consent for significant work. Old solid-walled buildings built with lime mortar and breathable finishes need materials that let moisture escape, and the wrong product can do more harm than good.

Scotland has its own building standards and building warrants, and Wales and Northern Ireland have their own versions of the regulations, so a contractor working there should apply the local rules.

Not every retrofit needs a new heating system straight away. Balancing radiators, fitting thermostatic radiator valves, adding a room thermostat or weather compensation, cleaning a sludged system and lowering the boiler's flow temperature can all improve comfort and efficiency. A condensing gas boiler only condenses, and so reaches its rated efficiency, when the water coming back to it is cool enough.

If you do plan to replace fossil fuel heating, the heat pump grant under the Boiler Upgrade Scheme needs an MCS-certified installer; the insulation work beforehand makes the heat pump smaller and the radiator changes fewer.

• a survey of the building's condition, damp, ventilation and how you use the house
• the measures in order, with the reasons for that order
• the effect of each measure on heat demand and the heating size needed afterwards
• how ventilation will be provided once the house is tighter
• which works need Building Regulations approval, planning permission or listed building consent
• who is responsible for each trade, and who coordinates them
• which grants may apply and what they require

Grants depend on where you live and your income. In England, the Warm Homes: Local Grant funds insulation, heat pumps, smart controls and solar panels for low-income households in privately owned homes rated D to G, usually with a household income of £36,000 a year or less. ECO4, funded by energy suppliers, helps low-income, fuel-poor and vulnerable households across Great Britain until 31 December 2026, with TrustMark overseeing standards.

In Scotland, the Home Energy Scotland Grant and Loan combines grants with interest-free loans for insulation and heat pumps. In Wales, the Nest scheme provides free advice and, for eligible households, free improvements. Installing insulation, heating controls, heat pumps, solar panels and batteries in a home is zero-rated for VAT until 31 March 2027, after which 5% applies; windows and glazing are standard-rated.

Source: gov.uk · gov.uk · ofgem.gov.uk

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