Home Insulation Guide UK: Loft, Cavity, Solid Wall & Floor

Insulation can reduce heat loss and improve comfort, but the right measure depends on construction, condition, moisture and ventilation. Use the comparisons as survey prompts, not promised savings, EPC movement or grant eligibility.

Insulation types to compare in a survey-led order

The numbered order is an editorial way to review common options, not a national cost, savings or payback ranking. Reorder it after the home's construction, condition, access, ventilation and objectives are verified.

1. Loft Insulation

An uninsulated roof can be a material heat-loss path. Check depth, continuity, eaves ventilation, services, roof condition and safe access before deciding whether a top-up is appropriate.

Standards & Recommendations

• Existing evidence: Record material, depth, coverage, compression and gaps
• Ventilation: Keep required eaves and roof airflow clear
• Design: Compare target thermal performance, not depth alone, across materials

Costs & Savings

Historical loft funding (GBIS ended)

Great British Insulation Scheme (GBIS): Previously funded loft insulation for some EPC D–G homes in eligible council tax bands. GBIS ended 31 March 2026(GOV.UK). Do not plan current work as free via GBIS. Check ECO4 or local programmes for any live support.

2. Cavity Wall Insulation

Wall construction is related to age but cannot be confirmed from age alone. A cavity must be surveyed for width, exposure, defects, contamination and existing fill before material is specified.

How to Check if You Have Cavity Walls

• Desktop clues: Brick pattern, wall thickness, age and EPC are prompts—not proof
• Survey evidence: Borescope inspection and records of any existing fill
• Condition: Check driving-rain exposure, pointing, damp and cavity bridges
• Responsibility: Use a competent installer; do not drill or infer construction casually

Installation Process

Professional installers drill small holes in mortar, inject insulating foam or beads, then seal holes. Access, area, material, weather and remedial work determine duration.

Costs & Savings

Cavity wall funding routes

GBIS: Historical only — scheme ended 31 March 2026; not a current free install route.
ECO4: May support some eligible households, but scope and customer contribution require written confirmation. ECO4 ends 31 December 2026 under current policy.

3. Floor Insulation

Floor heat loss varies with construction, perimeter, air leakage and what is beneath it. Two common situations need different approaches:

Suspended Timber Floors

Common in older homes. Insulation boards or mineral wool fitted between floor joists from below (if accessible) or from above (lifting floorboards).

Solid Concrete Floors

Rigid insulation boards laid on top of concrete, then covered with new flooring. This can raise floor level and affect doors, stairs, skirtings and fitted furniture; the design must resolve thresholds and moisture.

Costs & Savings

4. Solid Wall Insulation

Homes built before 1920 or some later non-standard builds have solid walls (single layer, no cavity). These lose more heat than cavity walls and require more expensive insulation.

Internal Solid Wall Insulation (IWI)

Insulation boards (typically 50-100mm) fixed to internal walls, then plastered over.

Pros:

• Can cost less than an external system on some homes—compare complete designed scopes
• No planning permission required (usually)
• No scaffolding needed
• Can be done room-by-room

Cons:

• Reduces room size by ~10cm per wall
• Requires moving radiators, sockets, switches
• Disrupts occupancy (messy, time-consuming)
• May cause condensation issues if poorly installed

External Solid Wall Insulation (EWI)

Insulation boards fixed to external walls, then rendered or clad.

Pros:

• Can create a continuous external layer where junctions are properly designed
• No loss of internal space
• Protects external brickwork
• Improves appearance (can refresh look of property)

Cons:

• Often a major capital project with scaffolding, detailing and enabling work
• May require planning permission (especially conservation areas, listed buildings)
• Changes external appearance significantly
• Risk of moisture issues if poorly designed/installed

Costs & Savings

Grant Funding for Solid Wall Insulation

ECO4: May support solid-wall work for some eligible households. Do not assume full funding, a particular system or suitability until the scheme and design are confirmed.

Insulation funding routes explained

Great British Insulation Scheme (GBIS) — ended

Status (as of 2026-07): GBIS installations ended 31 March 2026. The GOV.UK referral service closed earlier. Treat the bullets below as historical criteria only — not a current application path.

Historical eligibility (for context):

• Property EPC rating D, E, F, or G
• Council Tax band A–D (England) / related rules elsewhere
• Typically loft or cavity measures (not solid wall)

For current support, check ECO4, local authority programmes, or supplier offers — eligibility is not assessed on this page.

ECO4 (Energy Company Obligation)

Eligibility:

• Household member on means-tested benefits (Universal Credit, Pension Credit, etc.)
• Property EPC rating D, E, F, or G
• Low income (income threshold varies)

Coverage: Eligible measures can include insulation and heating work. Funding may be full or partial, and scope is determined through the scheme—not this page.

How to apply: Contact energy suppliers or local authority referral schemes.

Common Insulation Mistakes to Avoid

1. Blocking Loft Ventilation

Mistake: Covering eaves ventilation with insulation.
Risk: Condensation, dampness, roof timber rot.
Solution: Use ventilation spacers at eaves, maintain airflow above insulation.

2. Compressing Insulation

Mistake: Squashing insulation to fit in tight spaces.
Risk: Reduces the designed thermal performance.
Solution: Use correct thickness, never compress mineral wool.

3. External Wall Insulation Moisture Issues

Mistake: Poor installation creates cold bridges or traps moisture.
Risk: Condensation, mold, structural damage.
Solution: Use certified installers, ensure proper vapour barriers and breathable finishes.

4. Cavity Wall Insulation in Exposed Areas

Mistake: Installing cavity insulation in homes exposed to driving rain (coastal, hilltop).
Risk: Water penetration through cavity, damp internal walls.
Solution: Get professional survey, consider partial fill or alternative insulation.

5. Ignoring Thermal Bridging

Mistake: Leaving gaps around windows, pipes, joists.
Risk: Heat loss continues through uninsulated areas.
Solution: Ensure continuous insulation layer, seal all gaps.

Insulation Materials Compared

Lower declared thermal conductivity generally means less material is needed for the same target resistance, but installed performance also depends on thickness, continuity, moisture and workmanship.

Impact on EPC Rating

Insulation can affect EPC ratings, but the result is calculated from the full property model:

• Loft: Impact depends on recorded existing depth, area and continuity
• Cavity wall: Impact depends on construction, area and recognised system evidence
• Solid wall: Impact depends on area, design and how the assessor records the work
• Floor: Impact depends on floor type, area and evidence available to the assessor

Combined loft + cavity wall insulation can move some Band E homes toward Band C, but the result depends on the full EPC assessment and is not compliance certification.

Compare value without inventing a universal ROI

Insulation and Condensation

Important: Improved insulation changes how moisture behaves in your home.

Preventing Condensation Issues

• Improve ventilation: Trickle vents in windows, extractor fans in bathrooms/kitchens
• Design moisture control: Use a construction-specific vapour and ventilation strategy
• Address thermal bridges: Ensure continuous insulation layer
• Consider MVHR: Mechanical ventilation with heat recovery for airtight homes

Maintenance and Lifespan

Do not assume a universal service life. Product, design, exposure, installation, defects, guarantee terms and later building work all affect inspection and maintenance needs.

• Loft insulation: inspect after leaks, access or services work; check compression and ventilation paths
• Cavity wall insulation: retain survey and guarantee evidence; investigate damp or exposure-related symptoms
• Solid wall insulation: follow the specified finish, sealant, fixing and junction inspection schedule
• Floor insulation: retain the design and completion evidence; investigate moisture or ventilation changes

Planning Permission and Building Regulations

Planning Permission

• Loft and cavity measures: often do not need planning permission, but confirm property and area constraints
• Internal insulation: check listed-building, lease, fire and building-control constraints
• External insulation: check appearance, boundaries, listed status, conservation-area and local planning rules

Building Regulations

Insulation work can require Building Control involvement. Confirm who is responsible for notices, design evidence, inspection and completion documents before work starts; do not assume the installer has handled it without receipts.

Next Steps

1. Get your EPC: Check current rating and recommendations
2. Prioritize safely: Start with defects, evidence and lower-risk suitable measures
3. Check live funding: ECO4 or local programmes may help some households; GBIS has ended — do not assume free installs
4. Get multiple quotes: Compare more than one competent installer using the same scope
5. Check warranties: Verify duration, provider, exclusions, transfer and remediation
6. Plan ventilation: Ensure adequate airflow to prevent condensation