Insulation installers working on new-build sites or retrofit schemes typically work under CIS because they are subcontractors to a main contractor. ECO4 and other government-backed retrofit programmes route work through approved main contractors, meaning self-employed installers receive CIS-deducted payments whether or not they realise it. The materials content of insulation work (rigid board, mineral wool, spray foam, membranes) is significant and should be excluded from the deduction base on every job.
Government-backed retrofit programmes (ECO4, SHDF, LAD) deliver work through approved main contractors. Self-employed installers engaged by those contractors are CIS subcontractors, even if the ultimate client is a housing association or local authority. Many installers are unaware of this and either miss the refund or suffer the higher 30% unregistered rate because they never registered for CIS.
Insulation materials (rigid board, mineral wool, spray foam, breather membranes, vapour barriers) represent a large proportion of a typical insulation invoice. CIS deductions apply to the labour element only. If your main contractor is applying the 20% rate to the full invoice value rather than the labour split, you are overpaying on every job. We review your deduction slips and identify the gap.
Working in loft spaces, on external walls and in roof voids requires specialist PPE (dust masks rated for mineral fibre, disposable overalls, eye protection) and sometimes hired access equipment. These costs are allowable. Scaffolding hire charged through to the main contractor should also be excluded from the deduction base where it is separately identified on your invoice.
Retrofit programme volumes can push a sole-trader installer above the gross payment status threshold (£30,000 net CIS turnover per year) relatively quickly. A limited company structure allows real-time reclaim of CIS deductions via the Employer Payment Summary rather than waiting for the annual Self Assessment return. We model both structures for your income level.
We review every deduction statement, verify the labour and materials split, identify any overpayment where the deduction base included materials, and submit your Self Assessment return. Most insulation installers receive their refund within 8 to 12 weeks of a correctly filed return.
If you are not yet registered for CIS, we register you immediately (cutting your rate from 30% to 20%). Once your net CIS turnover exceeds £30,000, we manage the GPS application so that main contractors pay you in full with no deduction at all.
Annual Self Assessment, income and expense records, and Making Tax Digital quarterly updates if your gross income exceeds the applicable threshold. From April 2026 the MTD threshold is £50,000 gross (not net after deductions).
“I had been on ECO4 jobs for two years and had no idea CIS applied. Once we got registered and the materials were split out properly, the refund covered two full years of overpayment.”
Composite snapshot based on client patterns. Name and figures anonymised. The tax mechanics are real.
Book a free call. We will talk through your CIS position, your deduction history and whether there is anything worth changing. No hard sell, no obligation.
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