Decking Installer
Tax & MTD Guide

Decking installation is a tools-and-van trade with a tax twist most office-based freelancers never deal with: the Construction Industry Scheme. You quote a job, lay the joists, screw down the boards, and somewhere in that process a contractor has already taken 20% of your labour before the money reaches your account. That changes the whole shape of your tax year. Instead of saving up to pay HMRC each January, most decking fitters have overpaid through the year and are owed money back.

This guide is built around how installers actually earn and spend: CIS deductions and the refund that usually follows, the van, tools, blades and bought-in materials that make up your costs, the record-keeping that turns a shoebox of receipts into a clean refund claim, and the VAT reverse charge that trips up so many trades. Get the CIS statements and receipts in order and the annual return becomes straightforward.

How Tax Works for a Self-Employed Decking Installer

As a sole trader you pay Income Tax on profit, which is your total income from decking and landscaping work minus your allowable expenses. For 2025/26 the personal allowance covers the first GBP 12,570, then you pay 20% to GBP 50,270, 40% to GBP 125,140 and 45% above, with the personal allowance tapering away between GBP 100,000 and GBP 125,140 to create an effective 60% band. Class 4 National Insurance is 6% on profit between GBP 12,570 and GBP 50,270 and 2% above, while Class 2 NIC is settled through Self Assessment.

The key point for a CIS subcontractor is that contractors deduct that 20% from your labour based on turnover, before any personal allowance or expenses are considered. So the tax taken at source is almost always more than you actually owe. Your Self Assessment reconciles the two: you declare your full income, deduct your expenses and allowances, work out the real tax and NIC, then offset the CIS already paid. The result is normally a refund.

Scottish installers pay Scottish Income Tax on profit through six bands (19%, 20%, 21%, 42%, 45% and a 48% top rate) and carry an S-prefixed tax code; Welsh installers have a C-coded code at rates currently matching the rest of the UK. National Insurance stays UK-wide. If a PAYE side job or an old employment is distorting your code, run it through the tax code checker.

CIS: The Part That Defines Your Tax Year

Installing decking, fencing, pergolas, paving and associated groundworks counts as construction operations, so when you work as a subcontractor for a builder, developer or landscaping company, the Construction Industry Scheme applies. They verify you with HMRC and deduct tax from your labour before paying: 20% if you are verified and registered, 30% if you are not. Registering for CIS as a subcontractor and getting verified is the single quickest way to stop losing an extra 10%.

A few important details for decking fitters:

• The deduction is on labour, not materials. If your invoice separates materials from labour, CIS is only taken on the labour element. Always itemise materials separately so the contractor does not deduct 20% from your decking boards, joists and fixings.
• Work direct for homeowners is outside CIS. A private homeowner is not a contractor, so a deck you build directly for a household is paid gross with no deduction. You still declare that income and pay tax on it through Self Assessment.
• Keep every CIS statement. Each contractor must give you a monthly deduction statement showing what they paid and what they took. These are your proof of tax paid; lose them and you cannot reclaim it.

Our full CIS subcontractor tax guide walks through registration, verification and how the deductions flow through to your return.

Why You Usually Get a Refund

Because CIS takes 20% off your labour turnover before any reliefs, the tax deducted ignores your personal allowance and every penny of your expenses. Once you file and apply them, your real liability is almost always lower than what was taken. HMRC refunds the difference.

A simple way to see it: a fitter invoicing GBP 40,000 of labour has roughly GBP 8,000 deducted under CIS through the year. After the GBP 12,570 personal allowance and several thousand pounds of van, tool and material costs, the actual Income Tax and Class 4 NIC due is far less than GBP 8,000, so a refund follows. The CIS tax calculator lets you estimate your own refund from your turnover and deductions before you file.

Allowable Expenses for Decking Installers

An expense is allowable when incurred wholly and exclusively for the business. For an installer the list is dominated by the van, tools and consumables that keep you working.

Van and Mileage: Pick One Method

The van is usually an installer's biggest single cost. You can either claim actual running costs (a fair business proportion of purchase or lease, fuel, insurance, tax, servicing and repairs) or use HMRC's simplified mileage rate of 45p per business mile for the first 10,000 miles and 25p after that. You cannot mix the two for the same vehicle, and once you choose mileage for a van you generally stick with it for that vehicle. For a fitter doing long runs to sites with materials in the back, the actual-cost method often wins; for shorter local jobs, mileage can be simpler and sometimes larger. Work it out both ways once.

What You Cannot Claim

The private share of dual-use costs, your home-to-base commuting, ordinary clothing worn on site, fuel for personal trips, and meals during a normal working day are not allowable. Tools bought before you started trading are pre-trading expenditure, claimed when you begin rather than ignored.

Worked Example: A Decking Installer on GBP 45,000 Turnover

Take a fitter working mainly as a CIS subcontractor for landscaping firms, invoicing GBP 45,000 over the year split between labour and materials.

Turnover: GBP 45,000 (labour GBP 32,000, materials recharged GBP 13,000)

Allowable expenses:

• Materials bought in for jobs: GBP 13,000
• Van running costs and fuel (actual method): GBP 5,200
• Tools, blades, fixings and consumables (incl. AIA): GBP 2,400
• PPE, workwear and insurance: GBP 900
• Skip hire and waste charges: GBP 700
• Phone, home office and accountancy: GBP 800
• Total expenses: GBP 23,000

Taxable profit: GBP 45,000 minus GBP 23,000 = GBP 22,000

Income Tax: GBP 22,000 minus GBP 12,570 = GBP 9,430 at 20% = GBP 1,886

Class 4 NIC: GBP 9,430 at 6% = GBP 566

Total Income Tax and NIC due: GBP 2,452. But CIS already took roughly 20% of the GBP 32,000 labour = GBP 6,400 through the year. Offsetting that against the GBP 2,452 due leaves a refund of around GBP 3,948. Run your own figures through the sole trader tax calculator to sense-check the liability before applying your CIS credit.

Record-Keeping That Protects the Refund

Site work is messy and receipts get destroyed. A few habits make the difference between a clean refund and a guess:

• Photograph every receipt the day you get it. Thermal receipts from merchants fade within months, so capture fuel, materials and consumables straight away.
• File CIS statements as they arrive. One per contractor per month; total them at year end as your tax-paid credit.
• Separate labour and materials on every invoice. This keeps CIS off your materials and makes your turnover figures clean.
• Log mileage or fuel consistently. Decide on actual costs or mileage early and record what that method needs.
• Use a separate business bank account. It makes income and expenses obvious and saves hours at year end.

VAT and the Domestic Reverse Charge

You must register for VAT once taxable turnover exceeds GBP 90,000 in any rolling 12-month period. Because installers invoice materials plus labour, that threshold arrives faster than for labour-only trades, so watch your rolling total.

For construction work, the domestic reverse charge usually applies when you subcontract to another VAT-registered, CIS-registered business. Instead of adding VAT to your invoice, you state that the reverse charge applies and the contractor accounts for the VAT to HMRC. It removes VAT from your cashflow on those jobs but means you no longer hold the VAT you used to. Work direct for private homeowners is normal VATable supply, not reverse charge. The rules are fiddly, so take advice before you register or as you approach the threshold.

MTD for Income Tax: What Changes for Installers

Making Tax Digital for Income Tax Self Assessment replaces the once-a-year return with quarterly digital submissions and a year-end finalisation. The thresholds are based on gross income, not profit, and crucially that is gross turnover before CIS deductions:

• April 2026: Combined gross trading and property income over GBP 50,000
• April 2027: Over GBP 30,000
• April 2028: Over GBP 20,000

A busy decking fitter can clear GBP 50,000 of invoiced work even after 20% CIS is taken, so check your gross turnover, not the net amount that hit your account. Under MTD you record each invoice, material purchase and van cost digitally as it happens and send HMRC a quarterly summary, then finalise the year. For a trade where receipts go missing and CIS statements pile up, capturing everything continuously is a genuine improvement. Our guide to MTD for sole traders walks through the quarterly rhythm.

Common Mistakes Decking Installers Make

Not registering for CIS as a subcontractor. Unverified subcontractors lose 30% instead of 20%, tying up more cash until the refund.

Losing CIS deduction statements. Without them you cannot prove the tax already paid, so you cannot reclaim it.

Letting contractors deduct CIS from materials. Always itemise materials separately so the 20% only hits labour.

Mixing van methods. You cannot claim mileage and actual running costs for the same van; pick one and stick to it.

Forgetting direct-to-homeowner income. A deck built straight for a household has no CIS taken, but it is still taxable and must go on your return.

People also ask

Is decking installation covered by CIS?

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When does Making Tax Digital apply to decking installers?