Cavity Wall & Loft Insulation
Loft, cavity wall and floor insulation costs, savings and suitability for UK homes - then get introduced to one vetted local installer based on your home’s real EPC data.
Check My PropertyLoft and cavity wall insulation are usually the quickest, most cost-effective ways to make a home more energy efficient, because they cut the heat that escapes rather than just generating more heat to compensate. In a typical uninsulated UK home, the Energy Saving Trust estimates that around 26% of heat is lost through the roof and around a third through the walls - which is why these are often the first measures recommended for a standard cavity-wall home built after the 1920s.
Loft insulation is laid between and over the ceiling joists in the roof space. Cavity wall insulation is injected into the gap between the two layers of a modern external wall through small drilled holes. Floor insulation, fitted between or under a suspended timber floor or as boards under a solid floor, is the third measure in this group. Each is relatively affordable, but each also depends on your home’s construction and condition, and on ventilation being kept clear to avoid damp.
Eco Renovate does not install insulation. We use your home’s real government EPC data to identify which improvements are likely to be relevant to your property, then introduce you to one vetted, qualified local installer who can survey your home and confirm what is actually suitable and what it will cost.
Key benefits
Loft and roof insulation
Usually the cheapest and quickest measure to install. Energy Saving Trust figures put the cost at roughly £900 to insulate an empty loft up to the recommended 270mm depth (Great Britain average), or around £750 to top up existing 120mm insulation to 270mm. Suitable for almost any loft with a standard trussed or joisted roof; ventilation at the eaves must be kept clear to prevent condensation forming in the roof space.
Cavity wall insulation
Small holes are drilled into the external wall and insulation is injected into the cavity, then the holes are sealed. The Energy Saving Trust puts the average Great Britain cost at around £2,700, with estimated annual savings ranging from about £110 (flat) to £410 (detached house) and a typical payback of around five years. Best suited to homes built after the 1920s with an unfilled cavity of at least 50mm in good structural condition.
Floor insulation
For suspended timber floors, insulation is fitted between or under the joists; solid concrete floors need rigid insulation boards, usually laid when a floor is being replaced. The Energy Saving Trust estimates £1,400 to £2,500 for a typical suspended floor, with annual savings of around £70 for a semi-detached house rising to about £120 for a detached house. Underfloor airbricks must be kept clear to maintain sub-floor ventilation.
The quickest wins in a retrofit
Compared with solid-wall insulation or a heat pump, loft and cavity insulation are low-cost, low-disruption measures that can often be completed in a day or two. That combination of modest cost and meaningful bill savings is why they are usually the first step for a home that has an unfilled cavity or an under-insulated loft.
Ventilation done right
The most common problem after insulating is trapped moisture, caused by blocked ventilation or the wrong measure for the property. A qualified installer keeps eaves and underfloor airbricks clear and confirms your cavity is suitable before filling it - which is exactly why a proper survey matters more than the insulation material itself.
What it typically costs
Roughly £750-£900 for loft insulation, around £2,700 on average for cavity wall insulation, and £1,400-£2,500+ for floor insulation. These are approximate national averages from the Energy Saving Trust; your installer’s quote after a site survey is the figure to rely on.
- Which measure your property needs - loft, cavity or floor (loft is typically the cheapest)
- Property size, the wall area to be filled, and the floor area to be insulated
- How much insulation is already in place (topping up an existing loft costs less than starting from empty)
- Access and existing condition, e.g. loft clutter, floor type, or walls needing repair before filling
- Whether your cavity is confirmed suitable and in good condition on survey
- Your region - Energy Saving Trust’s Northern Ireland estimates differ from Great Britain averages for the same measure
From EPC check to finished work
Free EPC-based check
You give us your address and we pull your home’s real government EPC data - no guesswork or generic assumptions about your property.
Introduced to one vetted local installer
Based on what your EPC shows, you’re introduced to a single qualified, vetted installer operating in your area - not a list of leads sold to multiple companies.
Site assessment and quote
Your local installer visits (or surveys remotely where appropriate) to confirm which measure suits your property, check the cavity, loft or floor and existing ventilation, and provide a firm quote.
Installation
The installer carries out the agreed work, including any necessary ventilation measures, to relevant industry standards - often within a day or two for loft or cavity work.
Updated EPC rating
Once complete, an updated EPC assessment can reflect the improvement, which may move your property into a better EPC band depending on your home’s starting point.
Frequently asked questions
Is my home suitable for cavity wall insulation?
Most homes built after the 1920s have a cavity that can be filled, provided it is at least around 50mm wide, unfilled, and in good structural condition. It is not usually recommended for walls exposed to severe driving rain or in poor repair, and homes built before the 1920s often have solid walls with no cavity at all. A qualified installer confirms suitability on survey before any work goes ahead.
Is it worth topping up my existing loft insulation?
Often yes. The recommended depth is around 270mm, and many older homes have less than that. Topping up from an existing 120mm to 270mm costs less than starting from an empty loft, and it is one of the simplest measures to install. Whether it moves your EPC band depends on your starting point - your installer can give a property-specific view.
Will loft or cavity insulation cause damp or condensation?
Not if it is specified and installed correctly, but poor ventilation or the wrong measure for your property type is a recognised cause of damp after insulation work. Eaves and underfloor airbricks need to stay clear, and a cavity should only be filled if it is confirmed suitable. This is exactly why a proper site assessment by a qualified installer matters.
Will insulation move my home up a full EPC band?
It depends on your starting point and which measure is installed. Insulation improvements are among the measures most commonly recommended on EPC certificates, but the size of the change varies by property - a full band jump is not guaranteed from a single measure. Your local installer can give you a property-specific view after a survey.