What Insulation Does My Home Need? UK Guide (2026)
Insulation is the highest-return energy improvement for most UK homes — it reduces heating costs immediately and often has the shortest payback period of any eco upgrade. The right insulation type depends on when your home was built, its construction type, and what's already in place. This guide walks through each type and helps you identify what applies to your property.
Suitability checklist
Every home with a cold loft should have it: quick to install (2–4 hours), cheap (£300–£700), and often free under ECO4 or GBIS grants. The recommended depth is 270mm of mineral wool. If your loft has less than 100mm, topping up is a priority — it can save £150–£300/year on heating bills.
Homes built roughly between 1920–1980 typically have a cavity wall that can be filled with mineral wool, polyurethane foam or EPS beads (drilled from outside, usually half a day's work). Payback is typically 3–6 years. Often free or subsidised under GBIS for eligible households. Not all cavities are insulate-able — some have been rendered, or have damp issues that need addressing first.
Homes built before roughly 1920 typically have solid walls (no cavity). External wall insulation (EWI) wraps the outside with insulation board and render; internal (IWI) lines the inside, reducing room size slightly. Both are major works costing £8,000–£22,000 but dramatically reduce heat loss. ECO4 can fund this for eligible households.
Suspended timber ground floors (common in Victorian and Edwardian homes) can be insulated from below by filling the void between joists with mineral wool or rigid board. Solid concrete floors can have rigid insulation added on top (requires raising the floor level and possibly moving skirting boards and door frames). Typically costs £800–£2,500.
Converted lofts or rooms with sloping ceilings often have inadequate insulation in the roof slope. Rigid board or spray foam can be added between and below rafters, but access is difficult without redecoration. An installer will survey what's achievable without major disruption.
This checklist is a starting point — an MCS-certified installer survey gives the most accurate picture for your specific property.
How do I know if I have cavity walls?
The easiest way is to check when your property was built — most homes built between 1930 and 1985 in the UK have cavity walls. For older homes (pre-1920), solid walls are most common. Some 1920s–1930s homes have hybrid construction.
You can also check by measuring the depth of an external wall around an open door or window — 260mm or more suggests a cavity. Your home's EPC certificate (if you have one) should note the wall construction. An installer can confirm with a borescope or by drilling a small test hole.
Important: not all cavities are insulate-able. Some have been partially filled, some are too narrow, and some have damp issues. A qualified installer will assess the cavity before recommending treatment.
Available grants for insulation
Two main schemes fund insulation for eligible UK households:
- Great British Insulation Scheme (GBIS): Targets homes in council tax bands A–D with an EPC of D or below. No strict income test. Can fund cavity wall insulation, loft insulation, or solid wall insulation at no or very low cost to the homeowner.
- ECO4: Targets lower-income households on qualifying benefits. Broader scope than GBIS — can fund solid wall insulation, heating upgrades, and a package of measures. Often combined with heat pump or first-time central heating grants.
An MCS-certified installer can assess your eligibility for both schemes before any work begins — there's no obligation and no upfront cost.
What order should I insulate?
- 11. Loft insulation first: Cheapest, fastest payback, least disruptive. If your loft is under 100mm, topping up is the first priority.
- 22. Cavity wall insulation: If you have unfilled cavities, this is the second highest-return measure — usually free or subsidised under GBIS.
- 33. Floor insulation: Particularly important for suspended timber ground floors in older homes — often overlooked but can make a noticeable difference.
- 44. Solid wall insulation: The most expensive measure but the most impactful for pre-1920 solid-walled homes. ECO4 can fund this for eligible households.
Common questions
Can insulation cause damp or condensation problems?
Done correctly by a qualified installer, no. However, poorly installed cavity wall insulation (especially in exposed locations or properties with pre-existing damp issues) can sometimes worsen damp. This is why using an MCS-certified or CIGA-guaranteed installer is important. External wall insulation includes breathable render that manages moisture correctly. An installer survey should identify any pre-existing damp before work begins.
How long does cavity wall insulation last?
Properly installed mineral wool or EPS bead cavity wall insulation lasts the life of the building — it doesn't settle or degrade significantly. Most installations come with a 25-year guarantee (CIGA guarantee for cavity wall, BBA certificate for EPS bead). Polyurethane foam insulation can be problematic and is now rarely used.
Will insulation improve my EPC rating?
Yes, significantly. Loft insulation can improve your EPC by one band (e.g. D to C). Cavity wall insulation often improves by 1–2 bands. Solid wall insulation is the most impactful — external wall insulation can improve EPC by 2–3 bands in some cases. A better EPC rating improves mortgage options and makes the property easier to sell or rent.
Is there a good time of year to have insulation installed?
Loft insulation can be installed any time of year — the loft space itself isn't affected by weather. Cavity wall insulation is also year-round in most conditions, though installers avoid very wet or very windy days for scaffold-free jobs. External wall insulation is best installed in dry weather (spring, summer, early autumn) as it involves external render that needs time to cure.
How much could I save with loft insulation?
A home with no loft insulation currently can save £150–£300/year on heating bills after adding 270mm of mineral wool. If you have less than 100mm currently and top up, savings are £80–£180/year. The Energy Saving Trust publishes model savings by property type and current insulation level — an MCS-certified installer can give you a property-specific estimate.
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