At a glance
Short answer
Where homes lose heat cannot be judged from one national average; use the figures below as context and rely on a property survey, an itemised quotation and the rules that apply where you live.
How the system connects
The basic energy path
- 1Heated rooms
- 2Roof and walls
- 3Windows and gaps
- 4Outside air
What this guide covers
This page brings together where homes lose heat, preparing you to compare written proposals without treating general guidance as a site-specific design.
Identify the construction, existing defects and moisture risks before choosing a measure; Insulation must work with ventilation, rain protection and the way the building manages water vapour.
Current reference figures
- 33%: Energy Saving Trust says walls account for around 33% of heat loss in an uninsulated home. Official context (accessed 27 September 2026).
- 270 mm: Its loft guidance uses 270 mm as the minimum recommendation for new builds. Official context (accessed 27 September 2026).
- £2,200: Its September 2026 typical cavity-wall installation cost is about £2,200. Official context (accessed 27 September 2026).
These numbers are comparison anchors rather than promised costs, savings or performance; confirm the date, eligibility conditions and property assumptions behind every figure in a quotation.
How to compare proposals
Ask the surveyor to show continuity at eaves, floors, openings and junctions; Small untreated gaps can undermine comfort and create cold surfaces even when the main area is insulated.
Record the intended thermal result, ventilation changes, preparation, finishes and making good; Monitor humidity and visible defects after the work instead of judging success from appearance alone.
Worked household example
A three-bedroom semi-detached household in Leeds is comparing proposals, so it records present energy use and asks three suppliers to quote the same scope; one quotation is set aside because access work and commissioning are omitted, a second gives a plausible headline result without its supporting calculation, and the third progresses because its survey, assumptions, exclusions, warranties and responsibilities can be checked line by line.
This example does not identify a universally best product; it demonstrates why comparable evidence should influence the decision before the equipment choice does.
UK rules and responsibilities
Check which planning, network, consumer-protection and funding requirements apply in the relevant UK nation; confirm the council, network operator and scheme administrator before signing, and request written cancellation information for a distance or off-premises contract.
Questions to ask
- What property evidence supports this recommendation?
- Which calculations determine the proposed specification?
- What work and permissions are excluded?
- Which warranties apply, and who handles claims?
- What commissioning evidence will I receive?
- Which current standards govern the work?
Independent sources
- Energy Saving Trust retrofit costs (accessed 27 September 2026).
- Energy Saving Trust loft insulation (accessed 27 September 2026).
Last updated .