Costs & Pricing
181 sources in the library on costs & pricing, 40 on this page cited in a published note. Each one says what the document covers and what it is good for. Name a source to see which document it is and where to read it. One at a time. Page 1 of 5.
- very strong RN-3H4H1C cited
Department for Business, Innovation and Skills
The government's construction material price index for all work, Table 1: annual averages rising from 122.0 in 2008 to a provisional 130.3 in 2010.
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Department for Business, Innovation, Science and Trade
The official accredited statistics series on UK building materials, published monthly by DBT and BIST, first collected here on 2 October 2013 and last updated 5 August 2026 with the July 2026 bulletin. Each edition has a commentary plus Excel and ODS data tables. It carries monthly data on material price indices and on bricks and concrete blocks, quarterly data on sand and gravel, slate, concrete roofing tiles, ready-mixed concrete and imports and exports of construction products, and annual cement data. Methodology, a calendar of future publication dates and DBT's statistics error policy are on the same page. This is the source for verifiable claims about material price movement rather than merchant marketing figures.
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Department for Digital, Culture, Media and Sport
The government's statutory criteria for listing. It says nearly all pre-1700 and most 1700 to 1850 buildings with original fabric are of special interest, with more selection after 1850.
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Department for Energy Security and Net Zero
Published 21 January 2026 and last updated 18 March 2026. It commits £15 billion of public investment over this Parliament, 2025/26 to 2029/30, to upgrade up to 5 million homes by 2030, targeting over 450,000 heat pump installations a year by 2030 and solar panels on up to 3 million additional homes. The Boiler Upgrade Scheme gets £2.7 billion to 2030, keeping the £7,500 grant for hydronic heat pumps, adding new £2,500 grants for air-to-air heat pumps and heat batteries used for central heating, and £5,000 for biomass boilers in rural areas. A Warm Homes Fund provides a £5 billion financial transactions facility including £1.7 billion for low and zero-interest consumer loans, rolling out in phases from 2026, and the Warm Homes Social Housing Fund and Local Grant merge into a single low-income scheme from 2027/28. Private rented sector properties must meet EPC Band C across two metrics by October 2030, subject to a £10,000 spending cap, and an EPC C standard is introduced for the social rented sector for the first time. Future Homes Standard regulations were to be laid in Q1 2026.
Cited in Combi vs System vs Regular Boilers.
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Department for Energy Security and Net Zero (GOV.UK)
The current statutory floor on rented-property energy work, and the source of the £3,500 figure that governs landlord retrofit budgets. Since 1 April 2020 a landlord cannot let or continue to let a domestic property with an EPC rating below band E unless a valid exemption is registered. The cost cap is £3,500 including VAT: a landlord who has spent that much without reaching band E can register a high cost exemption. Exemptions and their durations: all relevant improvements made, 5 years; high cost, 5 years; wall insulation where the required measure would damage the property, 5 years; third party consent refused, 5 years, or until the tenancy ends where it was tenant consent that was withheld; property devaluation of 5% or more, 5 years; and recently becoming a landlord, 6 months. Every exemption must be registered on the PRS Exemptions Register before letting. Penalties per property per breach: up to £2,000 for renting out a non-compliant property for less than 3 months, up to £4,000 for 3 months or more, up to £1,000 for false or misleading register information, and up to £2,000 for failing to comply with a compliance notice, capped at £5,000 in total per property.
- very strong RN-VTMJ4Z cited
Department for Energy Security and Net Zero (GOV.UK)
Status page for the Great British Insulation Scheme (formerly ECO+), the obligation on larger energy suppliers to fund single insulation measures. Two facts matter for costing: the scheme runs to 31 March 2026, and the central GOV.UK eligibility checker has closed, so applications now go direct to energy suppliers, some of which are still taking them. The page also states that whether a household pays anything depends on a property assessment rather than a fixed rate, which is why no per-measure figure is published. It points to Ofgem for the detailed general group and low income group criteria (council tax band, EPC band and benefits tests). Cite this for the scheme's existence, closing date and the fact that any customer contribution is assessment-dependent, not for the eligibility bands themselves.
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Department for Energy Security and Net Zero (GOV.UK)
The £150 one-off discount off an electricity bill, relevant to any running-cost or payback calculation on heating and insulation work. The money is never paid to the household: the electricity supplier applies it to the bill, or issues a voucher to a prepayment meter customer. The scheme is currently closed and reopens in October 2026 for winter 2026 to 2027. Eligibility differs by nation, with separate criteria for England and Wales and for Scotland, and the discount is not available in Northern Ireland at all. Most eligible customers receive it automatically. It sits alongside, and does not reduce, Cold Weather Payments or Winter Fuel Payments. Use it as the authority for the discount value and the automatic application mechanism; the nation-specific qualifying criteria are on the linked regional pages rather than here.
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GOV.UK
The England-only successor to the Home Upgrade Grant, delivered by local councils. Eligibility: household income of £36,000 a year or less (with postcode and benefit-based exceptions), privately owned home, EPC rating D to G. Funds wall, loft and underfloor insulation, air source heat pumps, smart controls and solar panels, with the council organising and paying for the work. Explicitly 'only available in England'. Use this whenever a note says HUG closed and a successor is awaited: it is live and taking applications.
Cited in Insulation Grants 2026: ECO4, GBIS & What You Can Get, LPG Conversion Cost: 2026 UK Price Guide.
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GOV.UK
You must own the property, which can be a business premises, second home or rental, and you must be replacing a fossil fuel heating system such as oil, gas, electric or LPG. Properties that have already had government funding for a heat pump or biomass boiler, social housing, and most new builds still under construction are excluded, though a finished new build with a fossil fuel boiler and an owner-built self build can qualify. A biomass boiler additionally requires the property to be off the gas grid, in a rural location as defined in Ofgem guidance, and the boiler to hold an emissions certificate. The installer must commission and install the heat pump within 120 days of applying for the grant or it will not be eligible, and the application is made through an MCS certified installer.
Cited in Air Source Heat Pumps: Cost, Grants & Is It Worth It, Boiler Upgrade Scheme & Heating Grants 2026, Fireplaces & Flues Explained, Ground vs Air Source Heat Pumps and 1 more.
- very strong RN-9EFNVZ cited
GOV.UK
The grant values: £7,500 towards an air source heat pump, £7,500 towards a ground source heat pump including water source heat pumps and those on shared ground loops, and £5,000 towards a biomass boiler. A further £1,500 is available until March 2027 where the property is heated by oil or LPG and has no mains gas connection. Only one grant is available per property. Capacity limits are 45kWth for an individual system, 70kWth for multiple heat pumps and 300kWth for shared ground loops. Hybrid systems pairing a gas boiler with a heat pump are not eligible, and an existing low carbon heating system cannot be replaced under the scheme.
Cited in Air Source Heat Pumps: Cost, Grants & Is It Worth It, Barn & Outbuilding Conversions: Feasibility & Cost, Boiler Problems & Common Faults, Boiler Replacement & Central Heating Costs (UK) and 21 more.
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GOV.UK
Countryside Stewardship capital item FG3. Payment rate £5.66 per metre. Specification: erect wire fencing at least 1.05 m high using a minimum of 4 mild steel or high tensile plain wires, with a mains-operated energiser installed to the manufacturer's recommendations. Wooden straining posts at least 150 mm top diameter by 2.1 m long, intermediates 1.65 m long by 65 mm top diameter, struts 2.1 m by 75 mm; metal straining posts at least 2.4 m and intermediates at least 1.65 m. One of very few official per-metre rates for fencing, useful as a sanity check on market prices in a cost note.
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GOV.UK
The guidance that kills the common claim that second-hand building materials get no VAT treatment of their own. Margin schemes let a business pay VAT at 16.67 per cent, one sixth, on the DIFFERENCE between what it paid for an item and what it sells it for, rather than on the full selling price. Eligible goods are second-hand goods, works of art, antiques and collectors' items. The scheme cannot be used for any item on which the business was itself charged VAT, nor for precious metals, investment gold or precious stones. Building materials are not on the exclusion list, so reclaimed brick, slate, timber and fittings bought in without VAT can legitimately be sold on the margin, and a reclamation yard's quote may be on either basis. Separate schemes exist for second-hand vehicles, houseboats and caravans, horses and ponies, pawnbroking and high volume low value goods (global accounting). Records of the purchase and sale of each item must be kept.
Cited in Reclamation Yards & Salvage: Buying Reclaimed Materials.
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Health and Safety Executive
HSE guidance on silica dust in construction. It says tiles and mortar contain silica and that some of the dust is fine enough to reach deep into the lungs.
Cited in How to Regrout Tiles, How to Repair Damaged Bricks.
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Health and Safety Executive
HSE guidance on safe isolation, which says non-contact devices such as volt sticks should not be used to prove a low-voltage circuit dead.
Cited in How to Wire Ceiling Rose.
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Health and Safety Executive
HSE guidance on construction work near overhead power lines: treating lines as live, consulting the line owner, safe clearances and keeping scaffold poles and plant out of reach.
Cited in Scaffolding Costs Explained.
- very strong RN-2KFK3D cited
Health and Safety Executive
HSE's scaffolding page states that employers and self-employed contractors must assess the risk from work at height and plan the work so it is done safely, providing general access scaffolds wherever practicable. Scaffolding must be designed, erected, altered and dismantled only by competent people under the direction of a competent supervisor, following NASC Safety Guidance SG4 'Preventing falls in scaffolding operations' or equivalent manufacturer guidance for system scaffold. Strength and stability calculations are required unless the scaffold matches a generally recognised standard configuration for which a note of calculations exists, and a competent person must draw up an assembly, use and dismantling plan. Covers guard rails, toe boards, scaffold design, structures needing bespoke design, operative competence and scaffold inspection.
Cited in Repointing Brickwork: Cost & How, Scaffolding Costs Explained.
- very strong RN-TNB7SU cited
Health and Safety Executive
HSE's separation distance table for bulk LPG storage vessels, by capacity, giving one distance that applies equally to buildings, boundary, property line and fixed sources of ignition. Single vessel 0.05-0.25 tonnes (typical water capacity 150-500 litres): 2.5 m without a fire wall, 0.3 m with, 1 m between vessels. Over 0.25 to 1.1 tonnes (over 500 to 2,500 litres): 3 m without, 1.5 m with. Over 1.1 to 4 tonnes (over 2,500 to 9,000 litres): 7.5 m without, 4 m with. Points to LP Gas Association COP 1 part 1 for location and spacing and COP 1 part 4 for buried or mounded vessels. The citable substitute for Liquid Gas UK CoP 1, which is paywalled.
Cited in LPG Conversion Cost: 2026 UK Price Guide.
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Historic England
Historic England's owner guidance on listed buildings: listed building consent is needed for most work that affects a building's special architectural or historic interest, inside or out.
Cited in Cost to Paint a House.
- very strong RN-KBNHMB cited
HM Revenue & Customs
HMRC's main VAT notice for building work, last updated 26 August 2026. Sets out that construction of a new building and work to an existing building is normally standard rated at 20%, with exceptions: 0% for new qualifying dwellings and for housing association conversions of non-residential buildings, and 5% for a 'changed number of dwellings' conversion (section 7) and for renovation or alteration of a dwelling not lived in during the 2 years immediately before work starts (section 8, conditions at 8.1.2 and 8.3). Cites the law: VAT Act 1994 section 30 and Schedule 8 Group 5 for zero rating, section 29A and Schedule 7A Groups 6 and 7 for the reduced rate. Also explains the developer input tax block on goods that are not building materials (VAT (Input Tax) Order 1992 articles 2 and 6) and points self builders to the DIY housebuilders refund scheme.
Cited in Average Loft Conversion Cost: Real 2026 Breakdown by Type, Barn & Outbuilding Conversions: Feasibility & Cost, Bedroom Extension Cost: 2026 UK Price Guide, Bringing an Old Building Price to Today's Money and 18 more.
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HM Revenue & Customs
HMRC guidance published 7 June 2019 and last updated 24 September 2020. The VAT domestic reverse charge must be used for most supplies of building and construction services at the standard and reduced rates where both parties are VAT registered in the UK and the supply is reported within the Construction Industry Scheme. The covered services match the CIS list of construction operations, except supplies of workers by employment businesses, and include constructing, altering, repairing, extending, demolishing or dismantling buildings or structures, works forming part of the land such as walls and roadworks, and installing heating, lighting and air conditioning. Points to CIS 340 for contractors and subcontractors. Explains why a subcontractor's invoice to a main contractor shows no VAT while the homeowner still pays VAT to the main contractor.
- very strong RN-1HRJJ7 cited
HM Revenue & Customs
Section 2.1 sets a zero rate of VAT on the installation of energy-saving materials in residential accommodation from 1 May 2023 to 31 March 2027, after which the rate reverts to the 5% reduced rate; section 2.22 extended it to buildings used solely for relevant charitable purposes from 1 February 2024. Section 2.7 lists the qualifying materials: central heating and hot water controls, draught stripping, insulation to walls, floors, ceilings, roofs, lofts and pipes, solar panels, wind turbines, water turbines, ground source heat pumps, air source heat pumps, micro combined heat and power units and wood-fuelled boilers, with water source heat pumps, batteries for energy storage and smart diverters added on 1 February 2024. Section 2.3 is the critical rule for a renovation note: relief applies to an installation service, or materials supplied and installed together, but materials bought without installation stay standard-rated at 20%.
Cited in Air Source Heat Pumps: Cost, Grants & Is It Worth It, Builders' Merchants: The Complete UK Guide (2026), Builders' Merchants Explained: How They Work & How to Buy, Cost of a New Bathroom (Full Breakdown) and 8 more.
- very strong RN-77JNIW cited
HM Revenue & Customs
HMRC's A to Z of goods and services that are allowable and disallowable in a VAT refund claim under the DIY housebuilders scheme, including building materials, fitted items, appliances and professional fees (disallowed).
Cited in Self-Build & Custom Build Basics.
- very strong RN-FG9RYD cited
HM Revenue & Customs
HMRC's rate table for Landfill Tax, which applies to all waste disposed of by way of landfill at a licensed landfill site on or after 1 October 1996 unless exempt. The tax is charged by weight at two rates, with inert or inactive waste at the lower rate. Standard rate is 130.75 pounds per tonne from 1 April 2026, 126.15 pounds from 1 April 2025 and 103.70 pounds from 1 April 2024; the lower rate is 8.65 pounds per tonne from 1 April 2026, 4.05 pounds from 1 April 2025 and 3.30 pounds from 1 April 2024. This is the single largest fixed input in a skip hire price and explains why mixed skips cost far more than clean inert loads.
Cited in Bringing an Old Building Price to Today's Money, Roof Repair Costs & Common Problems (UK).
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HM Revenue & Customs
The DIY housebuilders' scheme lets someone building a new home, or converting a non-residential building into one, reclaim VAT on building materials. Work completed before 5 December 2023 had to be claimed within 3 months of completion; work completed on or after that date must be claimed within 6 months. Only one claim can be made per person and the HMRC DIY enquiries line is 0300 322 7073.
Cited in Church Conversion Cost: 2026 UK Price Guide, Roofing Merchants & Suppliers Guide, Self-Build & Custom Build Basics, VAT on Home Renovations & the DIY Reclaim Scheme.
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HM Revenue & Customs
HMRC's notice on VAT reliefs for disabled people. Section 6.3 zero-rates providing, extending or adapting a bathroom for a disabled person's condition in their private residence.
Cited in Cost of a New Bathroom (Full Breakdown).
- very strong RN-Q24A2A cited
HM Revenue & Customs
HMRC guidance (published 5 December 2023, updated 6 November 2025) on claiming back VAT on building materials for a self-built new home. Claims must be made no more than 6 months after completion for builds completed on or after 5 December 2023 (3 months for earlier completions). Sets out what a VAT invoice must show, including the customer's name and address on invoices over £250, and gives processing times of 3 weeks for online claims and 6 weeks by post.
Cited in Self-Build & Custom Build Basics, VAT on Home Renovations & the DIY Reclaim Scheme.
- very strong RN-GLZAMU cited
HM Revenue & Customs (GOV.UK)
The SDLT band table for a single residential property: zero up to 125,000 pounds, 2% on the portion from 125,001 to 250,000 pounds, 5% from 250,001 to 925,000 pounds, 10% from 925,001 to 1.5 million pounds and 12% above 1.5 million pounds. A 5% surcharge is usually added on top of these rates if the buyer already owns another residential property. HMRC's worked example gives 4,750 pounds on a 295,000 pound purchase (0 plus 2,500 plus 2,250). New residential leaseholds pay SDLT on the lease premium at these rates, plus 1% on the portion of the net present value of rent above the 125,000 pound threshold; this does not apply to assigned leases. This is the moving cost that has to be set against an extension or loft conversion budget.
Cited in Does a Loft Conversion Add Value? UK Data & ROI, Extension vs Loft Conversion vs Moving House, How to Renovate a House: The Complete UK Guide.
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HM Revenue & Customs (GOV.UK)
Sets the three UK VAT rates: standard 20% on most goods and services, reduced 5% on some goods and services such as children's car seats and home energy, and zero 0% on zero-rated goods such as most food and children's clothes. The standard rate rose to 20% on 4 January 2011 from 17.5%. Some supplies are exempt rather than rated, including postage stamps and financial and property transactions. This is the reference for converting a merchant's ex-VAT trade quote into the figure a homeowner actually pays.
Cited in Aggregate, Sand & Landscaping Suppliers Explained, Average Loft Conversion Cost: Real 2026 Breakdown by Type, Brick Driveway Cost: 2026 UK Price Guide, Builders' Merchants: The Complete UK Guide (2026) and 20 more.
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HM Revenue and Customs
HMRC's 2024 to 2025 employer rates page gives the old secondary threshold of £9,100 a year and the 13.8% employer rate that applied before 6 April 2025.
Cited in What an Hour of Labour Actually Costs.
- very strong RN-9KXRWL cited
HM Revenue and Customs
The section that kills the persistent claim that work to a listed building is VAT free. With effect from 1 October 2012 the zero rate for the first grant of a major interest in a substantially reconstructed protected building was withdrawn in cases where zero rating relied on three-fifths of the work, measured by cost, being approved alterations. The transitional relief that softened the change expired on 30 September 2015, and was only ever available where a relevant consent was applied for or a written contract entered into before 21 March 2012, or where 10 per cent of the substantial reconstruction was complete before that date. Zero rating survives only where the first grant of a major interest relates to a protected building substantially reconstructed from a shell. Defines a major interest as the freehold, in Scotland the absolute interest, or a lease of over 21 years, though not less than 20 years in Scotland. Ordinary alteration work to an occupied listed home is therefore standard rated at 20 per cent.
Cited in Reclamation Yards & Salvage: Buying Reclaimed Materials.
- very strong RN-ZYLCD2 cited
HM Revenue and Customs
The 5 per cent conversion rate and, importantly, what it does not cover. A qualifying conversion into single household dwellings arises where the premises after conversion contain a greater or lower number, but not fewer than one, of single household dwellings, and includes a property never lived in such as an office block or a barn, a bedsit block, non-self-contained living accommodation such as staff rooms above a pub, and a dwelling previously adapted in its entirety to another use such as offices or a dental practice. It expressly does not include the creation of living accommodation that is not a single household dwelling, naming most granny annexes and additional bedrooms at a care home, nor the renovation of living accommodation used for other purposes without adaptation, such as a flat above a shop used for storage, which is directed instead to the section 8 empty homes rate. Paragraph 7.3.1 makes clear that work unrelated to changing the number of dwellings cannot be reduced rated, and works three examples through a block of sixteen flats showing that parts of a building are examined independently. Goods that are not building materials, such as carpets or fitted bedroom furniture, remain standard rated along with their installation.
Cited in Church Conversion Cost: 2026 UK Price Guide, Who Buys the Materials: You or the Builder?.
- very strong RN-FX7S48 cited
HM Revenue and Customs
The section that carries the 5 per cent empty home rate, which most renovation budgets miss. A contractor may charge VAT at 5 per cent instead of 20 per cent on renovating or altering an eligible dwelling that has not been lived in during the 2 years immediately before the work starts. Paragraph 8.3.2 sets out what proves the two years: Electoral Roll and Council Tax records, utilities companies, or an Empty Property Officer at the local authority, and states that a letter from an Empty Property Officer certifying two years empty is sufficient on its own with no other evidence needed. Paragraph 8.3.3 lists occupation that can be ignored: illegal occupation by squatters, occupation by guardians installed to deter squatters and vandals, and non-residential use such as business storage, but expressly not occasional use as a second home, which defeats the relief. Paragraph 8.3.4 allows the reduced rate to continue on all the work even where people move in while the work is carried out, provided the two-year test was met when work started. Goods that are not building materials, such as carpets or fitted bedroom furniture, must still be standard rated including the installation charge.
Cited in Roof Repair Costs & Common Problems (UK), Who Buys the Materials: You or the Builder?.
- very strong RN-26FMBT cited
HM Revenue and Customs
HMRC's internal manual chapter on the approved alteration zero rate, whose very title fixes the date the relief ended: the rules it explains are those prior to 1 October 2012, so a note that still tells readers to claim zero-rated VAT on approved alterations to a listed home is out of date by more than a decade. Manual published 19 March 2016 and updated 4 August 2026. The chapter contents show what the old test required and remains useful for pre-2012 work and for understanding the terms still used: VCONST08100 the basic conditions for zero-rating, VCONST08200 whether the work is to a protected building, VCONST08300 whether the work is an approved alteration, VCONST08350 whether the work is approved, VCONST08450 the distinction between alterations and repair or maintenance, VCONST08550 incidental alterations, VCONST08600 structures in the curtilage of a building, VCONST08700 certificates, VCONST08750 services excluded from zero-rating and VCONST08800 apportionment.
Cited in Reclamation Yards & Salvage: Buying Reclaimed Materials.
- very strong RN-KJH9DW cited
HM Revenue and Customs
GOV.UK lists what CIS deductions are not taken from: VAT, consumable stores, plant hired for the job, manufacturing or prefabricating materials, and materials the subcontractor paid for directly.
Cited in What an Hour of Labour Actually Costs.
- very strong RN-SRHQXS cited
HM Revenue and Customs
GOV.UK's CIS overview says contractors deduct 20% from registered subcontractors and 30% from unregistered ones, and that deductions count as advance payments towards tax and National Insurance.
Cited in What an Hour of Labour Actually Costs.
- very strong RN-GKII48 cited
HM Revenue and Customs (GOV.UK)
The statutory floor under any labour rate quoted for building work in 2026-27. Employer secondary Class 1 National Insurance is charged at 15%, with the secondary threshold at £96 per week, £417 per month or £5,000 per year, and the Employment Allowance at £10,500. National Living Wage for workers aged 21 and over is £12.71 per hour from 1 April 2026. National Minimum Wage: £10.85 per hour for 18 to 20 year olds, £8 per hour for under 18s, £8 per hour for apprentices under 19, and £8 per hour for apprentices aged 19 or over in the first year of their apprenticeship. The tax year rates run 6 April 2026 to 5 April 2027, but the minimum wage rates commence 1 April 2026, a week earlier. These are the figures to build up an honest labour cost from: the gross hourly rate plus 15% employer NI above the £5,000 threshold, before any allowance for holiday pay, pension, tools, travel or overhead.
Cited in What an Hour of Labour Actually Costs.
- very strong RN-5RLFNX cited
HM Revenue and Customs (GOV.UK)
Paragraphs 5.1 to 5.8 of Notice 708, the route by which a person converting a non-residential building to dwellings can sell or grant a long lease at the zero rate rather than merely paying 5% on the works. Paragraph 5.3.2 carries the 10 year rule: a building that has been used as a dwelling in the 10 years before the sale is not treated as non-residential for these purposes, so the conversion of a house that has simply stood empty for a few years does not qualify here. The section also sets out who may zero rate (a person converting, which HMRC defines narrowly), what counts as a first grant of a major interest, the certificate requirements, and the interaction with the reduced rate at section 7. Distinguish this from section 8, which reduced rates renovation of dwellings empty for two years, and from section 7, which reduced rates a changed number of dwellings conversion.
- very strong RN-TQUASW cited
HM Treasury
HM Treasury's supplementary guidance to the Green Book on optimism bias (2013), which tells appraisers to make explicit, evidence-based upward adjustments to estimates of cost and duration.
Cited in How Cost Estimates Work: Levels, Accuracy and Error Margins, Renovation Contingency: How Much to Allow.
- very strong RN-UVW6H5 cited
Infrastructure and Projects Authority
The UK Infrastructure and Projects Authority's cost estimating guidance for major projects. Its principles tie an estimate's class and confidence level to the evidenced maturity of the scope, not to reaching a gate.
Cited in How Cost Estimates Work: Levels, Accuracy and Error Margins, Renovation Contingency: How Much to Allow.
- very strong RN-1DLUIJ cited
Infrastructure and Projects Authority
The IPA guidance's figure of estimate accuracy by stage gate: SOC (class 5, under 5% maturity, -20% +50%), OBC (classes 4 to 3, 30%, -15% +30%) and FBC (classes 3 to 2, over 60%, -10% +10%).
Cited in How Cost Estimates Work: Levels, Accuracy and Error Margins.