UK INSULATION PLANNING GUIDE · 2026

Keep the heat.
Manage the moisture.

Fabric-first does not mean “insulate everything blindly”. The right measure depends on construction, exposure, ventilation and existing damp. Hearthline helps sequence the questions before the work.

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Loft insulation: often the simplest start

Where the loft is accessible and dry, topping up insulation can be relatively low-disruption. Eaves ventilation, water tanks, pipework, electrical cables and safe storage platforms all need attention. More material is not automatically better if airflow is blocked.

Common planning depth≈ 270mm
DisruptionUsually low
SequenceEarly phase

Cavity walls: survey the exposure

Wall age is only a clue. A competent survey should establish whether a cavity exists, whether it is clear and whether the building’s exposure, defects and moisture condition make the proposed system suitable.

Solid walls: treat the building as a system

Internal and external wall insulation change temperature and moisture behaviour. Junctions, floors, roofs, windows, rain exposure and ventilation need a coherent design. This is not a sensible place to rely on a quick sales survey.

Older homes need a moisture strategy

If the property is historic, listed, solid-wall or already affected by damp, seek independent building-physics or conservation advice before selecting a system.

What an insulation quote should show

  • Existing construction, defect and moisture findings.
  • The exact insulation system, thickness and target performance.
  • How ventilation, eaves, cavities and thermal bridges are handled.
  • Preparation, making good and protection of services.
  • Certification, guarantees and the route if performance is poor.
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