Glossary
Loft insulation glossary
The scheme names, acronyms and loft vocabulary you will meet when applying for free loft insulation or getting quotes, in plain English. Each term links to the page that explains it in full.
The three terms that matter most: ECO4 (the supplier scheme, until 31 December 2026), LA Flex (the council route, income under £31,000) and EPC band (D to G for owners). Get those three straight and most offers make sense.
- Affordable Warmth Scheme
- Northern Ireland Housing Executive scheme for owner-occupiers and private renters with gross household income under £23,000; grants up to £7,500, with loft insulation installed or topped up to 300mm. Read more
- BASRiS
- A medical certificate for people with a terminal illness in Scotland; holding one is a route into Warmer Homes Scotland. Read more
- Cold roof
- A roof where the insulation sits on the loft floor, between and over the joists, so the roof space stays cold. The standard loft insulation job. Read more
- Competent Person Scheme (CPS)
- A government-authorised scheme whose members can self-certify that certain building work meets building regulations. GOV.UK lists the current schemes. Read more
- Condensation
- Water forming when warm, moist air meets a cold surface. A well-insulated loft is colder, so ventilation matters. Read more
- DS1500
- A medical form for people nearing the end of life; a route into Warmer Homes Scotland alongside BASRiS.
- Eaves
- The low edges of a pitched roof, where air usually enters the roof space. Insulation should stop short of them. Read more
- ECO4
- The fourth and final phase of the Energy Company Obligation: a legal duty on medium and large energy suppliers to fund energy-saving measures in lower-income and vulnerable homes in Great Britain. Runs until 31 December 2026. Read more
- EPC (Energy Performance Certificate)
- A rating of a home's energy efficiency from A (best) to G, with a score. Schemes use the band to decide eligibility; look yours up on GOV.UK. Read more
- Fabric first
- The principle of insulating the building (roof, walls, floors) before upgrading the heating. ECO4 applies it through insulation preconditions. Read more
- Great British Insulation Scheme (GBIS)
- A supplier scheme that ran from 25 July 2023 and ended on 31 March 2026. Its non-means-tested council tax band route no longer exists. Read more
- Help to Heat group
- The ECO term for households receiving a qualifying benefit, the standard ECO4 route.
- HES Grant and Loan
- Home Energy Scotland's grant and interest-free loan scheme for homeowners; a loft insulation grant of up to £1,500, no benefit test. Read more
- Joists
- The horizontal timbers forming the loft floor and the ceiling below. The first layer of insulation goes between them, the second across them. Read more
- LA Flex (flexible eligibility)
- The ECO4 route that lets councils refer households not on a qualifying benefit, for example with combined gross income under £31,000. Read more
- LSOA
- Lower Layer Super Output Area: a small statistical area. Living in a deprived LSOA is one of the LA Flex proxies. Read more
- Mineral wool
- Glass or rock fibre insulation, usually sold in rolls; the standard loft material. The EST recommends 270mm. Read more
- Nest
- The Welsh Government scheme providing free home energy improvements, including insulation, to eligible owners and private tenants. Read more
- NISEP
- The Northern Ireland Sustainable Energy Programme, funded by electricity customers through a public service obligation, which can fund loft insulation. Read more
- Obligated supplier
- An energy supplier large enough to have an ECO4 obligation. Ofgem says you can contact any of them, even if they are not your supplier. Read more
- PAS 2035
- The retrofit standard covering assessment, design and installation of energy-saving measures, used for ECO4 and Warm Homes: Local Grant work.
- Pre-existing loft declaration
- A form signed by the installer and the occupier or landlord before ECO4 loft work, recording the insulation already there. A copy stays in the loft. Read more
- Rafters
- The sloping timbers that form the roof. Insulating between and over them creates a warm roof. Read more
- RdSAP / SAP
- The government methods used to calculate a home's energy rating. ECO4 requires an assessment before measures are installed.
- Room-in-roof
- A loft used as a room, with sloping ceilings. Insulating it is specialist work and a separate scheme measure. Read more
- Spray foam
- Polyurethane foam sprayed onto the underside of a roof. The EST calls foam under an old, poorly maintained roof one of the highest-risk options. Read more
- Top-up
- Adding insulation to a loft that already has some. From 120mm to 270mm it saves the EST's £13 to £35 a year. Read more
- TrustMark
- A government-endorsed quality scheme for home improvements; funded retrofit work is registered through it. Read more
- Warm Homes: Local Grant
- England's council-delivered, government-funded scheme for lower-income households in homes rated EPC D to G, running to 31 March 2028. Read more
- Warm Homes Plan
- The government's plan, updated 18 March 2026, committing £15 billion to upgrade up to 5 million homes by 2030. Read more
- Warm roof
- A roof insulated at the rafters, so the roof space stays warmer. More expensive and less efficient than a cold roof. Read more
- Warmer Homes Scotland
- The Scottish Government programme offering support worth £10,000 or more to eligible households; in most cases fully funded. Read more
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