When a contractor quotes a single price to build an extension that happens to include insulation, HMRC generally treats the whole supply as a single standard-rated construction service at 20%. The insulation does not attract the 0% energy saving materials rate because it is incidental to the principal supply of building an extension. HMRC Notice 708/6 uses exactly this example. The 0% ESM rate is available when insulation installation is the principal supply — for example, a contractor engaged specifically to insulate walls, lofts, or floors with no broader construction works.
HMRC's single-supply rule means the VAT treatment of the dominant element of a contract applies to the whole contract. An extension builder who also fits cavity wall insulation is primarily supplying construction — the insulation is incidental. A specialist insulation installer who does nothing else is primarily supplying insulation (ESM). Getting this distinction wrong means either paying 20% when 0% was available, or incorrectly applying 0% and risking an HMRC correction.
A building contractor who quotes to build an extension — foundations, structure, roof, fit-out — is making a single supply of construction services. Insulation fitted as part of that contract takes the 20% rate of the principal supply.
A contractor engaged solely or principally to install qualifying insulation (cavity wall, loft, floor, solid wall) is making a qualifying ESM supply under Notice 708/6. The 0% rate applies to the whole of that supply until 31 March 2027.
If you engage a separate specialist to install insulation as a standalone contract (not bundled with the extension), that contract may qualify for the 0% ESM rate, separate from the 20% extension contract.
If your extension includes significant insulation works, consider whether splitting the contracts (one for construction, one for insulation) changes the VAT treatment and creates a legitimate 0% supply.
VATBuild is not affiliated with HMRC. References to HMRC publications are for informational purposes. Always consult a qualified tax adviser before making decisions about VAT on your project.
VATBuild checks each invoice and line item against the principal-supply test and HMRC's published ESM rules. It identifies whether an insulation line on an extension invoice is part of a single construction supply (20%) or a qualifying standalone ESM supply (0%), and flags any apparent misapplication of the 0% rate.