Architect
A qualified design professional responsible for producing architectural drawings, planning applications, and Building Regulations submissions. On construction projects, an architect may also act as contract administrator, issuing instructions, certifying payments, and managing the design process through to practical completion.
Air Source Heat Pump (ASHP)
A low-carbon heating system that extracts heat energy from outside air to warm a building. Increasingly specified on UK new builds and retrofits to meet energy efficiency targets. Covered by Part L of the Building Regulations. Eligible for the Boiler Upgrade Scheme government grant. Requires oversized radiators or underfloor heating for efficient operation.
Architect's Drawings
Scaled technical drawings produced by an architect or architectural technician, showing the layout, dimensions, elevations, and construction details of a project. Required for planning permission and Building Regulations applications. Also used by contractors and quantity surveyors as the basis for estimating and tendering.
Asbestos Survey
A mandatory survey of any pre-2000 building before refurbishment or demolition work begins. Required under the Control of Asbestos Regulations 2012. Identifies the presence, type, condition, and location of asbestos-containing materials. Must be carried out by a qualified surveyor. Asbestos removal requires a licensed contractor.
Bill of Quantities (BoQ)
A structured document listing every item of work on a construction project, with quantities, units of measurement, rates, and totals. Prepared by a quantity surveyor from architect's drawings and specifications. Used to obtain competitive tenders on a like-for-like basis. Forms part of the contract documents once work is awarded.
Full guide: What is a Bill of Quantities?Building Control
The regulatory function responsible for ensuring that building work complies with the Building Regulations. Building Control officers inspect work at key stages and issue a completion certificate on satisfactory completion. Required for most structural, electrical, and plumbing work. Can be provided by a local authority or an approved inspector.
Building Regulations
Statutory minimum standards for the design and construction of buildings in England and Wales, covering structural safety, fire, energy efficiency, ventilation, drainage, accessibility, and more. Separate from planning permission. Building Regulations approval is required for most building work. Non-compliance creates legal liability and problems when selling the property.
BIM (Building Information Modelling)
A digital process in which a three-dimensional model of a building is created and shared across all project stakeholders — architects, engineers, contractors, and clients. BIM Level 2 is mandatory on UK government projects. The model contains not just geometry but also data about materials, costs, and programme. Increasingly adopted on commercial and larger residential projects.
Defects Liability Period (DLP)
A contractual period — typically 6 or 12 months after practical completion — during which the contractor is required to return and remedy any defects that become apparent. During the DLP, a portion of the retention money is withheld. At the end of the DLP, a defects inspection is carried out and the final retention is released once all items are resolved.
Dayworks
A method of valuing construction work that cannot be priced in advance. The contractor records the labour hours, plant, and materials used each day, at agreed rates from a dayworks schedule in the contract. Used for unforeseen or very small items of work where a fixed price is impractical. Requires client signature on daywork sheets to be valid.
CDM (Construction Design and Management Regulations)
The Construction Design and Management Regulations 2015 set out the legal duties of those involved in construction work to plan, manage, and coordinate health and safety. Applicable to all construction projects. On notifiable projects (more than 30 working days or 500 person-days), a Principal Designer and Principal Contractor must be appointed, and a Health and Safety Executive notification submitted.
CIS (Construction Industry Scheme)
A UK tax scheme under which contractors deduct money from subcontractor payments and pass it to HMRC as an advance payment towards the subcontractor's tax and National Insurance. Standard rate is 20%; higher rate 30% applies to unregistered subcontractors. Contractors must verify subcontractors with HMRC and submit monthly CIS returns.
Contingency
A sum included in a construction estimate or budget to cover unforeseen costs. Typically expressed as a percentage of the overall contract value — 5% to 10% on a straightforward renovation, 10% to 15% on a refurbishment of an older property. Not a profit allowance; specifically reserved for work that was genuinely impossible to foresee at pricing stage.
Cover Letter (Quote)
An introductory document accompanying a construction quote or tender, addressed to the client and summarising the scope of work, the price, and the terms on which the quotation is made. A professional cover letter increases credibility and reduces the chance of misunderstandings about what is and is not included in the price.
Contract Administrator (CA)
The person appointed under a building contract to administer it on behalf of the employer — typically the architect or project manager. Responsibilities include issuing instructions, certifying progress payments, assessing variations, granting extensions of time, and issuing the practical completion certificate and defects completion certificate.
Cost Plan
A structured budget prepared at design stage, breaking the total projected cost of a project into elemental sections — substructure, superstructure, finishes, services, and so on. Updated at each design stage as more information becomes available. Used by clients and quantity surveyors to control costs against budget before work begins on site.
Cladding
An external covering applied to the structure of a building for weather protection, insulation, or aesthetics. Materials include timber, brick slip, render, metal, composite panels, and fibre cement. Post-Grenfell, combustible cladding systems above 18 metres on residential buildings are prohibited. Requires Building Regulations approval and must comply with Part B (Fire Safety).
Day Rate
A method of pricing work where a tradesperson charges a fixed daily rate for their labour, without a fixed total price. Common for smaller jobs, maintenance work, and situations where the full scope cannot be determined in advance. Clients pay for actual time spent. Risk of cost overrun sits with the client rather than the contractor.
Full guide: What is a Day Rate Builder?Defect
Work that does not comply with the contract or building specifications. A defect may be discovered during the contract, at practical completion, or during the defects liability period. The contractor is obliged to rectify defects at their own cost. Persistent or serious defects may entitle the employer to engage another contractor and deduct the cost from the original contractor's final account.
DPC (Damp Proof Course)
A horizontal barrier built into a wall to prevent rising damp from the ground. Typically a layer of impermeable material — bitumen felt, polythene, or engineering brick — installed at least 150mm above external ground level. Required by Building Regulations. An injected DPC can be retrofitted to older walls using chemical injection to manage rising damp.
Dry Lining
A method of finishing internal walls and ceilings using plasterboard fixed to a timber or metal frame, rather than traditional wet plaster. Faster and less disruptive than wet plastering. Standard in new builds. The plasterboard joints and screw fixings are finished with jointing compound and skim coat plaster for a smooth finish.
Demolition
The controlled dismantling or removal of structures or parts of structures. On refurbishment projects, selective demolition (strip-out) removes specific elements — walls, ceilings, floors — while retaining the main structure. CDM Regulations apply. Notifiable demolition requires prior notification to the HSE. Asbestos surveys and removal must precede any demolition of pre-2000 buildings.
EPC (Energy Performance Certificate)
A certificate rating the energy efficiency of a building from A (most efficient) to G (least efficient). Required when a property is built, sold, or let. From 2025, rental properties in England must achieve EPC band C or above. The certificate is based on a SAP calculation and is valid for 10 years. Improvements to insulation, heating, and windows raise the rating.
Extension of Time (EOT)
A formal contractual mechanism allowing the completion date to be extended where delays are caused by events beyond the contractor's control — such as exceptionally adverse weather, client-instructed variations, or late information. Must be applied for in accordance with the contract. Grants relief from liquidated damages but does not automatically entitle the contractor to additional payment.
Final Account
The agreed financial settlement at the end of a construction contract, reconciling the original contract sum with all additions and deductions — variations, provisional sums, fluctuations, and any claims. Agreed between the contractor and the contract administrator or quantity surveyor. Must be agreed before the second half of the retention is released.
First Fix
The stage of construction work carried out before plastering — typically the installation of structural timbers, pipework, cable routes, and ductwork that will be concealed within walls, ceilings, and floors. First fix electrics involves running cable; first fix plumbing involves running pipework. Inspected by Building Control before being covered over.
Foundations
The below-ground structural elements that transfer the load of a building into the ground. Types include strip foundations (most common in UK residential), raft foundations (for poor ground conditions), pad foundations (for columns), and piled foundations. Foundation design is specified by a structural engineer based on soil conditions and the load to be supported.
Groundworks
The below-ground and ground-level work that forms the foundation of a construction project — including excavation, drainage, foundations, service ducting, and oversite concrete. Usually the first trade on site. The quality and accuracy of groundworks determines the accuracy of everything built above. Poor groundworks are one of the most common causes of programme delay and cost overrun.
Gross Internal Area (GIA)
The total floor area of a building measured to the inside face of external walls, including internal partitions, stairwells, and all internal spaces. The standard measurement basis for commercial property and residential construction estimating in the UK. Distinct from Net Internal Area (NIA), which excludes structural elements and common areas.
Insulation (Wall / Floor / Roof)
Thermal insulation materials installed in walls, floors, and roofs to reduce heat loss and meet Building Regulations Part L. Common types: rigid foam boards (PIR/PUR), mineral wool batts, blown fibre, and spray foam. External wall insulation (EWI) adds insulation to the outside of a building. Internal wall insulation (IWI) is used where external application is not possible.
Interim Certificate
A payment certificate issued at regular intervals during a construction contract — typically monthly — showing the value of work properly completed to date, less retention and any previous payments. Issued by the contract administrator or quantity surveyor. The employer is obliged to pay the certified amount within the period stated in the contract, typically 14 days.
Instruction (Architect's Instruction / AI)
A formal written instruction issued by the contract administrator directing the contractor to carry out a change to the works, omit work, or address a specific issue. Contractors should not carry out additional work without a written instruction. If an AI involves a change to the scope, it becomes a variation and the cost is assessed for inclusion in the final account.
Labour Only
A contract arrangement where the subcontractor provides labour only — the main contractor or client supplies all materials. Common in plastering, tiling, and painting. Simplifies material procurement for the subcontractor but requires the main contractor to manage material deliveries, sequencing, and quality control. Labour-only rates are lower than supply-and-fix rates for the same trade.
Lintel
A horizontal structural element installed above a door, window, or opening in a wall to carry the weight of the structure above. Steel lintels are standard in modern UK cavity wall construction. Concrete lintels are used in blockwork. The correct specification — span, load, and thermal performance — is determined by the structural engineer or lintel manufacturer's selection guide.
Liquidated Damages (LD)
A pre-agreed sum stated in the construction contract that the contractor must pay to the employer for each day or week the project runs beyond the agreed completion date. Must represent a genuine pre-estimate of loss, not a penalty. The contract administrator issues a non-completion certificate as the basis for deducting LDs from the contractor's final payment.
Main Contractor
The company or individual holding the primary contract with the client for a construction project. The main contractor is responsible for the overall execution, management, and coordination of the project — including engaging and managing all subcontractors. Carries legal responsibility for the works, health and safety, and meeting the contract programme and quality standards.
Materials on Account
A credit account arrangement with a builders' merchant or material supplier, allowing materials to be ordered and delivered on account, with invoices paid monthly. Standard practice for established contractors. Requires a credit application and account approval. Monthly statements are reconciled against delivery notes and invoices. Enables cash flow management without upfront payment for every delivery.
Method Statement
A document describing how a specific piece of construction work will be carried out — the sequence of operations, the plant and equipment to be used, the materials required, and the health and safety precautions to be taken. Required for high-risk activities under CDM Regulations and increasingly expected by clients as part of tender submissions.
Full guide: What is a Method Statement?MVHR (Mechanical Ventilation with Heat Recovery)
A whole-house ventilation system that extracts stale air from wet rooms and simultaneously supplies fresh filtered air to living and sleeping spaces, recovering up to 90% of the heat from the outgoing air. Required in highly airtight new builds to comply with Building Regulations Part F. Increasingly specified on Passivhaus and high-performance residential projects.
Measured Works
Work that can be accurately quantified from drawings and specifications, and priced at agreed rates. Contrasted with provisional sums and dayworks, which cover work that cannot be measured in advance. Most of the work in a standard BoQ is measured work. The accuracy of the measurement directly determines the accuracy of the tender price.
Parge Coat
A thin coat of mortar or plaster applied to the internal face of a masonry wall — typically in a cavity — to seal the surface and improve airtightness. Used in party wall cavities and around structural openings to prevent air leakage. Increasingly specified in airtightness-focused new builds and retrofits. Also used historically as a flue liner in chimney stacks.
Party Wall
A wall shared between two properties — typically between semi-detached or terraced houses. Work that affects a party wall — including excavation near a shared boundary — requires a Party Wall Agreement under the Party Wall etc. Act 1996. Neighbours must be served a Party Wall Notice at least two months before work begins. A party wall surveyor may be appointed to agree an award.
Performance Bond
A financial guarantee provided by a surety company on behalf of the contractor, assuring the employer that the contractor will fulfil their contractual obligations. If the contractor defaults, the employer can make a claim on the bond — typically 10% of the contract value. Common on larger public sector and commercial contracts. Adds a cost for the contractor, typically 0.5%–1% of the contract value.
Permitted Development (PD)
Certain types of building work that are allowed without requiring planning permission under the Town and Country Planning (General Permitted Development) Order. Covers extensions, loft conversions, outbuildings, and other works subject to size limits, material restrictions, and boundary constraints. PD rights can be removed by a local authority in conservation areas or via an Article 4 direction.
Piling
A foundation system using long columns driven or bored into the ground to transfer building loads to deeper, more stable soil or rock strata. Used where ground conditions are poor, where the building is heavy, or where settlement risk is high. Types include driven steel piles, bored concrete piles (CFA or rotary), and screw piles. Designed by a structural engineer and carried out by specialist piling contractors.
Practical Completion
The stage at which the main contractor's works are complete for all practical purposes — the client can occupy and use the building, even if minor outstanding items remain. Triggered by the architect or contract administrator issuing a Practical Completion Certificate. Starts the defects liability period, releases the first half of the retention, and transfers risk back to the employer.
Practical Completion Certificate
A formal certificate issued by the contract administrator confirming that practical completion has been achieved. Marks the end of the contractor's liability for liquidated damages, triggers the start of the defects liability period, and releases the first tranche of retention money. Essential in dispute resolution as it defines the dividing line between contractor and employer liability for risks such as damage and insurance.
Prelims (Preliminaries)
Project-wide costs that cannot be attributed to a specific trade or element — including site management, scaffolding, temporary facilities, site security, welfare provisions, health and safety compliance, insurance, and small plant. Typically expressed as a percentage of the works cost, or priced separately as a BoQ section. Often 10%–15% of the overall contract value on a well-managed site.
Prime Cost Sum (PC Sum)
An allowance included in a Bill of Quantities or quotation for a specific item where the actual product has not yet been selected — such as kitchen units, sanitaryware, or floor tiles. The contractor adds their profit and attendance on top of the PC sum. When the client selects the actual item, the PC sum is adjusted up or down in the final account.
Full guide: What is a Prime Cost Sum?Project Manager
A professional responsible for managing the delivery of a construction project on behalf of the client — including programme, cost, quality, risk, and stakeholder management. On smaller residential projects, the main contractor often acts informally as project manager. On larger schemes, an independent PM is appointed alongside the architect and quantity surveyor to represent the client's interests.
Provisional Sum
An allowance included in a Bill of Quantities or contract for work that cannot be fully defined at tender stage — such as groundworks in uncertain soil conditions or specialist subcontract work. Defined provisional sums (where the work is known but not fully designed) and undefined provisional sums (where the work is genuinely unknown) are treated differently under JCT contracts.
Full guide: What is a Provisional Sum?Quantity Surveyor (QS)
A construction cost professional who manages the financial aspects of a building project — including cost planning, procurement, contract management, valuation of work, and final accounts. Employer's QS acts for the client; contractor's QS manages the commercial aspects from the contractor's side. The profession is regulated by the Royal Institution of Chartered Surveyors (RICS).
Full guide: What is a Quantity Surveyor?Quote vs Estimate
A quote (or quotation) is a fixed offer to complete a defined scope of work at an agreed price — once accepted, the price is binding. An estimate is an approximate calculation of likely cost and is not legally binding. In common usage, the terms are often used interchangeably, but the legal distinction matters: a client who accepts a quote cannot be charged more without agreeing a variation.
Full guide: Quote vs Estimate — What's the Difference?Rendering
The application of a cement-based or polymer-based mortar coat to the external face of a masonry wall, providing a weatherproof and decorative finish. Traditional sand-and-cement render is applied in two or three coats and finished by scraping, wood-floating, or roughcasting. Modern thin-coat silicone renders are applied over a carrier board system and offer improved flexibility and self-cleaning properties.
Retention
A percentage of each payment — typically 3%–5% — withheld from the contractor by the client under the construction contract as security for the contractor's performance. The first half of the retention is released at practical completion; the second half at the end of the defects liability period. A long-standing source of cash flow pressure for contractors and subcontractors in the UK.
Full guide: What is Retention in Construction?Retention Bond
An alternative to cash retention, where a financial institution provides a guarantee to the employer in lieu of withholding money from the contractor. The contractor maintains full cash flow while the employer still has security against non-performance. Retention bonds are increasingly advocated as a fairer alternative to cash retention following several high-profile contractor insolvencies.
Roughcasting
A traditional external render finish in which gravel or small aggregate is thrown onto the final wet render coat to create a textured, weather-resistant surface. Common in Scotland and Northern England. Also known as pebbledash where larger pebbles are used. Provides excellent weatherproofing and durability, though it traps dirt more than smooth finishes.
RSJ / Steel Beam
A steel I-section beam (Rolled Steel Joist) used to carry loads across openings — such as where a load-bearing wall is removed to open up a space. The beam size, grade, and bearing length are calculated by a structural engineer. Installation requires a Structural Engineer's calculation pack and Building Control approval. RSJ is an older term; Universal Beam (UB) is the current standard section.
SAP Calculation
The Standard Assessment Procedure — the UK government's method for assessing the energy and environmental performance of new dwellings, as required by Building Regulations Part L. Carried out by an accredited SAP assessor using approved software. Produces the energy rating (EPC band) and demonstrates compliance with CO2 emission targets. Required before a completion certificate is issued on new builds.
Scaffold
A temporary access platform erected alongside or above a structure to allow safe working at height. Must comply with the Work at Height Regulations 2005 and the NASC guidance document TG20. Erected and inspected by a competent scaffolding contractor. Scaffold hire is costed as a preliminary item — the period on hire and the complexity of the access design determine the cost.
Schedule of Works
A document listing all the work to be carried out on a project, broken down by trade or work package, in the sequence it will be executed. Used in place of a full BoQ on smaller projects. Sets out what will be done, by whom, and in what order. Provides the framework for a programme of works and is an important reference document for both contractor and client throughout the job.
Full guide: What is a Schedule of Works?Screed
A layer of cementitious or anhydrite material applied to a concrete floor slab to create a smooth, level surface for the floor finish. Sand-and-cement screed (typically 75mm thick) is the traditional type. Liquid anhydrite (calcium sulphate) screeds are self-levelling and increasingly used over underfloor heating systems. Drying time must be observed before laying floor coverings.
Second Fix
The stage of construction work carried out after plastering — including the installation of visible fittings, fixtures, and finishing elements. Second fix electrics includes fitting sockets, switches, light fittings, and consumer unit connections. Second fix plumbing includes fitting sanitaryware, taps, and radiators. The final visible quality of the work is largely determined at second fix stage.
Skip Hire
The rental of a metal waste container for the removal of construction debris and spoil. Skips are priced by size (2 to 12 cubic yards typically) and duration of hire. A permit is required from the local council if the skip is placed on a public highway. Costs vary significantly by region and waste type — certain materials (plasterboard, asbestos, soil) require separate disposal arrangements.
Snagging
The process of identifying and listing minor defects, incomplete items, and finishing issues — typically at or just before practical completion. A snagging list (or snag list) is compiled by the client, architect, or project manager and handed to the contractor for rectification. On new builds, snagging surveys are increasingly carried out by independent specialists before legal completion.
Full guide: What is Snagging?Structural Engineer
A qualified engineer who designs and assesses the structural elements of a building — foundations, beams, columns, floor structures, and roof structures. On residential renovation projects, a structural engineer is typically required to specify steel beams (RSJs), assess the capacity of existing elements, and sign off structural alterations for Building Control. Qualified through the Institution of Structural Engineers (IStructE).
Subcontractor
A specialist contractor engaged by the main contractor to carry out a specific trade package — such as plumbing, electrics, plastering, or groundworks. Subcontractors are directly employed by the main contractor, not the client. The main contractor remains responsible to the client for the subcontractor's work. CIS deductions apply to most subcontractor payments in the UK.
Supply and Fix
A contract arrangement where the subcontractor supplies both the materials and the labour to install them. The subcontractor takes responsibility for material quality, procurement, and delivery. Typically priced at a higher rate than labour-only. Simplifies main contractor procurement but places the subcontractor at risk from material price fluctuations on longer contracts.
Tanking
A waterproofing system applied to below-ground or below-water-table walls and floors to prevent water ingress. Cementitious tanking slurry is applied to the inside face of masonry. Membrane tanking systems use a bonded or cavity drainage membrane. Required on basement conversions and below-ground structures. Must be designed and installed in accordance with BS 8102.
Tender
A formal offer to carry out a specified scope of work at a stated price and within a stated programme. Submitted in response to an invitation to tender (ITT) from the client or their representative. On competitively tendered contracts, multiple contractors price the same BoQ to allow a like-for-like comparison. The lowest compliant tender is not always accepted; quality, programme, and experience are also assessed.
Timber Frame
A construction method using a structural timber frame to carry the loads of the building, rather than masonry blockwork. Common on new builds in Scotland and increasingly throughout the UK. Timber frame panels are typically factory-fabricated and erected on site. Faster to erect than masonry construction. Must comply with Building Regulations for structural performance, airtightness, and fire.
UFH (Underfloor Heating)
A heating system in which heat is distributed through pipes or electric elements embedded in or beneath the floor surface. Water-based (wet) UFH uses hot water from a boiler or heat pump circulated through plastic pipes in screed. Electric UFH uses resistive heating elements. UFH suits low-temperature heat sources such as heat pumps and provides even heat distribution without radiators.
Underpinning
The process of strengthening or deepening an existing building's foundations — typically to allow a basement conversion, to address subsidence, or to build an extension with deeper foundations adjacent to an existing structure. Mass concrete underpinning (needle-and-pit method) is the traditional approach. Mini-piled underpinning offers a less disruptive alternative. Structural engineer design and Building Control approval are required.
Variation Order (VO)
A formal instruction to change the scope of work from that originally contracted — adding, omitting, or altering work. The contractor prices the variation and the cost is agreed before the work is carried out, or assessed after on a fair valuation basis. Variation orders must be in writing to be valid. The cumulative value of variations is reconciled in the final account.
VAT in Construction
Value Added Tax applies to most construction services in the UK at the standard rate of 20%. However, certain works attract a reduced rate of 5% — including energy-saving materials installation and residential conversions from non-residential use — or zero rate, including new-build residential construction. The domestic reverse charge mechanism applies to B2B construction services, shifting VAT accounting responsibility to the customer.
Void (Construction)
A cavity or open space within a building structure. In floor construction, a void formed between the structural slab and a raised access floor allows services (cables, pipes, ducts) to be routed beneath the floor. In cavity wall construction, the void between the inner and outer leaves provides thermal and moisture protection. Floor voids must be sealed at compartment boundaries for fire compliance.