Integral features are a fixed statutory list of building systems: electrical and lighting systems, cold water systems, heating, powered ventilation, air cooling and air purification, lifts and escalators, and external solar shading. Spending on them, together with long life assets, thermal insulation, solar panels and higher emission cars, goes into the special rate pool, which attracts writing down allowances of 6% a year, although the annual investment allowance and, for companies, the 50% first year allowance can give faster relief.

What exactly is an integral feature?

Section 33A(5) of the Capital Allowances Act 2001 (CAA 2001) lists five integral features of a building or structure:

  • an electrical system, including a lighting system;
  • a cold water system;
  • a space or water heating system, a powered system of ventilation, air cooling or air purification, and any floor or ceiling comprised in such a system;
  • a lift, an escalator or a moving walkway; and
  • external solar shading.

Only items on the list are integral features (CA22320). Expenditure on them is treated as plant regardless of whether it would pass the case law tests explained in what counts as plant and machinery. That was the point of the 2008 reform: before then, ordinary electrical and cold water systems were usually part of the building and attracted nothing (CA22320).

Section 33A(6) excludes any asset whose principal purpose is to insulate or enclose the interior of a building or to provide a permanent interior wall, floor or ceiling. A permanent false ceiling installed to hide new wiring therefore gets nothing, while a plenum ceiling that forms part of the air conditioning ductwork can qualify (CA22320).

Where are the boundaries between integral features and main pool items?

An electrical system takes its ordinary meaning: the system taking power from the point of entry or generation and distributing it through the building (CA22330). It does not include other systems that happen to use wiring. HMRC lists communication, telecommunication and surveillance systems, fire alarms and burglar alarms as separate List C items, so they can go in the main pool. Ducting follows the system it serves, and ducting shared by two systems is apportioned on a fair and reasonable basis.

Gov.uk guidance describes the water element as hot and cold water systems but not toilet and kitchen facilities, so sanitary ware and fitted kitchens remain main pool plant. In a typical office fit out, therefore:

Item Pool if writing down allowances are claimed
Power and lighting circuits, light fittings Special rate
Heating, air conditioning, ventilation Special rate
Cold water pipework and tanks Special rate
Data cabling and CCTV Main
Fire and intruder alarms Main
Kitchen units, sinks, toilets and basins Main
Lift Special rate

When is spending on an existing integral feature a replacement rather than a repair?

Under section 33B, spending is treated as replacing the integral feature, and so as capital, if it is more than 50% of the cost of replacing the whole feature at the time. If the first tranche is 50% or less but further spending within 12 months takes the total over 50%, all of it is treated as replacement. Section 33A(3) then prevents the same cost being deducted as a repair.

HMRC’s examples at CA22340 show how this works. A factory owner who pays 40% of a new electrical system in one period and the remaining 60% six months later is caught. A shop owner who rewires one floor for £48,000 against a quote of £100,000 for the whole system stays below the 50% line, so the work is not a replacement under these rules, and HMRC does not expect several quotes to be obtained. Spending below the threshold is then judged under the ordinary capital versus revenue principles.

What goes into the special rate pool?

Section 104A defines special rate expenditure as:

  • thermal insulation and integral features, from 1 April 2008 for companies and 6 April 2008 for income tax;
  • long life asset expenditure;
  • cars that are not main rate cars, from 1 April or 6 April 2009;
  • cushion gas, from 1 April 2010; and
  • solar panels, from 1 April 2012 for companies and 6 April 2012 for income tax. HMRC explains that solar panels were generally already special rate as integral features or long life assets, and the change made this explicit (CA22335).

Section 104D sets the writing down allowance at 6% of the pool balance. The main pool rate is 14% from 1 April 2026 for corporation tax and 6 April 2026 for income tax, having been 18% before, according to gov.uk. The special rate did not change in 2026, so no hybrid rate is needed for the special rate pool, although one is needed for a main pool where the period straddles the change (CA23222).

What is a long life asset?

Under section 91, a long life asset is plant or machinery which, when new, could reasonably be expected to have a useful economic life of at least 25 years. The useful economic life runs until it is no longer likely to be used by anyone as a fixed asset of a business, which can be longer than the depreciation life in the accounts (CA23720). The test applies to the asset as a whole, not its components.

Two important carve outs apply:

  • Section 93 excludes fixtures in, or plant provided for use in, buildings used wholly or mainly as a dwelling house, hotel, office, retail shop or showroom. HMRC accepts wholly or mainly where at least 75% of the building is so used (CA23730). Cars are also excluded.
  • Section 99 sets a monetary limit of £100,000 a year. If total long life expenditure in the period is no more than the limit, the long life rules do not apply. The limit is reduced proportionately for a short period and shared between associated companies. Gov.uk notes that in a partnership with a company member, all long life costs go to the special rate pool.

The long life rules are most relevant to manufacturers, utilities and similar businesses buying heavy equipment, such as large presses, turbines or ships.

How can special rate expenditure get faster relief?

Annual investment allowance

The annual investment allowance of £1 million can be claimed on integral features (CA22320). Where total spending exceeds the allowance, allocating it to special rate items first gives the most benefit, because main pool items get a faster rate on the balance.

The 50% first year allowance

Companies within the charge to corporation tax can claim a 50% first year allowance on new and unused special rate plant and machinery bought from 1 April 2023, other than cars, alongside full expensing for main rate assets. The remaining 50% joins the special rate pool in the following period (CA23174AB). On a later disposal, half of the disposal value is taxed immediately as a balancing charge where the 50% allowance was claimed on the full cost (CA23174AE). The 40% first year allowance available from 1 January 2026 is for main rate assets only.

Small pools

If the special rate pool balance is £1,000 or less, the whole amount can be claimed as a small pools allowance (CA23225).

What does this look like in practice?

Illustration only. A company with a 31 March year end spends £1,400,000 on a new factory fit out: £600,000 on electrical, heating and ventilation systems and £800,000 on new production machinery.

Allocation Amount Relief in year
AIA against integral features £600,000 £600,000
AIA against machinery £400,000 £400,000
Full expensing on remaining new machinery £400,000 £400,000
Total £1,400,000 £1,400,000

Had the AIA been used on the machinery alone, £400,000 of integral features would have had only the 50% first year allowance, with the rest relieved at 6% a year.

What mistakes come up most often?

  • Putting lighting or heating in the main pool because the business regards it as equipment.
  • Putting fire alarms, data cabling or sanitary ware in the special rate pool when they are main pool items.
  • Deducting a major rewire or boiler replacement as a repair when section 33B treats it as capital.
  • Forgetting that a buyer of a building can generally only claim for integral features the seller claimed for, and must agree a fixtures value with the seller; see capital allowances explained.
  • Overlooking the long life rules for heavy equipment once spending exceeds £100,000.

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Sources

Reviewed by Christine Anderson, Broker, Solar Protect. Last reviewed 8 October 2026. Part of Accountapedia, the Solar Protect guide to UK tax and accounting. This page is general information, not personalised advice.