First Fix vs Second Fix: What's Included in Each Stage?

Summary

First fix and second fix are the two main internal work stages in UK construction, separated by the plastering milestone. First fix takes a building from bare structure to plaster-ready by installing all the hidden elements — timber framing, pipework, cable runs, insulation, and ventilation ducting. Once first fix is complete and signed off (including a building control pre-plaster inspection), the plasterer boards and skims the walls and ceilings. Second fix then covers every visible, finished element: hanging doors, fitting skirting and architrave, connecting sockets and switches, installing sanitaryware, hanging radiators, and commissioning all services. Getting the sequencing right between trades at both stages is one of the most common sources of delay on domestic projects, particularly at the handover from first fix to plastering.

Key Facts

• First fix = all work before plastering; second fix = all work after plastering — this applies across carpentry, plumbing, electrical, and heating trades
• First fix work is almost entirely hidden in the finished building — it sits behind plasterboard, under floors, and above ceilings
• Second fix items are deliberately held back until after plastering to avoid damage from wet trades
• Building control will typically carry out a pre-plaster (first fix) inspection to check hidden work before it gets covered up — this is the last chance to inspect wiring, pipework, insulation, and fire-stopping
• All trades must complete their first fix before the plasterer can start — if one trade overruns, the entire programme slips
• First fix typically takes longer than second fix on a standard domestic project (new build or extension)
• Plumbing and electrical first fix must include pressure testing and cable integrity checks before sign-off
• The terminology is standard across the UK construction industry and is used in contracts, pricing schedules, and building control documentation

First Fix vs Second Fix Overview

Detailed Guidance

What's included in first fix carpentry?

First fix carpentry is the structural and framing stage. It covers all the timber work that forms the skeleton of the internal spaces before the plasterer arrives:

• Stud wall construction — Timber or metal stud partitions to create room layouts, including head plates, sole plates, and studs at standard centres (typically 400mm or 600mm)
• Door linings — Fitted plumb and square into stud or masonry openings, packed and fixed before boarding. These must be set to the correct finished floor level
• Floor joists — Trimming around openings (stairwells, loft hatches), strutting between joists (herringbone or solid), and decking with structural boards
• Roof structure — Trussed rafters or cut roof construction, including ridge boards, hip and valley rafters, purlins, and ceiling joists
• Noggins — Short horizontal timbers fitted between studs to provide fixing points for wall-hung items (radiators, kitchen units, TV brackets, grab rails). Critical for plumbing and heating trades
• Boxing in — Framing around soil pipes, waste pipes, and service risers to allow boarding and plastering over
• Window boards — Fitted to internal cills before plastering
• Staircase carcass — Strings, treads, risers, and newel posts (balustrade and handrail are typically second fix)
• Joist hangers and structural metalwork — Installed as part of the timber frame-up

What's included in second fix carpentry?

Second fix carpentry is the finishing stage — the visible joinery that gives rooms their completed appearance:

• Skirting boards — Fitted tight to plastered walls and finished floor level, scribed at internal corners, mitred at external corners
• Architrave — Fitted around door linings with consistent margins (typically 5-7mm reveal)
• Door hanging — Fitting internal doors with correct clearances (2-3mm sides and top, 8-10mm bottom for carpet), including handles, latches, and hinges
• Kitchen fitting — Base units, wall units, worktops, plinths, cornice, and end panels. Requires precise coordination with plumbing and electrical second fix
• Staircase finishing — Balustrade, handrail, spindles, and cappings
• Built-in joinery — Wardrobes, shelving, window seats, alcove units
• Flooring — Timber or engineered board installation (though this often falls to a specialist)
• Finishing hardware — Door stops, coat hooks, toilet roll holders, towel rails

What's included in first fix plumbing?

First fix plumbing installs all the hidden pipework that will later be plastered or boarded over:

• Hot and cold water supply pipes — Run from the mains entry point to every draw-off position (kitchen, bathrooms, utility, outside taps). Typically 15mm copper or plastic push-fit, with 22mm feeds to baths and combination boilers
• Waste pipes — 32mm for basins, 40mm for baths/showers/sinks, 110mm for WCs. Waste runs need correct falls (minimum 18mm/m for 32mm, 9mm/m for 40mm)
• Soil stack — 110mm SVP (soil and vent pipe) connecting WCs and sometimes other waste to the below-ground drainage
• Central heating pipework — Flow and return pipe runs from the boiler position to each radiator location, including drop points (tails) left ready for second fix connection
• Hot water cylinder position — Pipework connections for the cylinder, including primary flow and return from the heat source, cold feed, and hot draw-off
• Gas supply pipe — From the meter to the boiler position (must be installed by a Gas Safe registered engineer)
• Pressure testing — All pipework should be pressure tested before being concealed. Typically 1.5x working pressure for a minimum of one hour

What's included in second fix plumbing?

Second fix plumbing connects all the visible fittings and appliances to the pipework installed at first fix:

• Sanitaryware — WC pan and cistern, wash basin and pedestal/wall bracket, bath, shower tray, shower valve and head
• Taps and mixers — Basin taps, bath taps, kitchen mixer
• Traps and waste connections — Bottle traps, P-traps, shower wastes
• Appliance connections — Washing machine valve, dishwasher valve, outside tap
• Silicone sealing — Around baths, shower trays, basins (waterproofing critical)
• Testing and commissioning — Run all taps, check for leaks at every joint, flush WCs, verify hot water temperatures, check waste drainage

What's included in first fix electrical?

First fix electrical installs the hidden wiring infrastructure before plastering:

• Cable runs — Twin and earth cables routed through joists (drilled through the centre third) and chased into masonry walls. SWA (steel wire armoured) for external runs
• Back boxes — Metal or plastic boxes sunk into walls for sockets, switches, and fused spurs. Depth must suit the finished plaster line
• Consumer unit positioning — Main board located (typically near the meter), with circuits wired back to the board
• Ceiling rose points — Loop-in wiring run to each light position
• Smoke and heat detector cabling — Interlinked detectors are a Building Regulations requirement (Approved Document B). Cable runs installed at first fix
• Data and TV cabling — Cat 6 data runs, coaxial TV points, and speaker cables if specified
• Bonding — Supplementary and main bonding conductors to gas, water, and oil pipes as required by BS 7671 (18th Edition Wiring Regulations)
• Conduit and trunking — Where surface-mounted second fix is not acceptable, or for future flexibility

What's included in second fix electrical?

Second fix electrical connects the visible components and certifies the installation:

• Socket faceplates — Single and double sockets, USB sockets, fused connection units
• Switch faceplates — Light switches, dimmer switches, fan isolators, shaver sockets
• Light fittings — Pendants, downlights, wall lights, external lights. Downlights in fire-rated ceilings need fire-rated housings
• Consumer unit cover and labelling — Circuit labels must be clear and accurate
• Extractor fans — Bathroom and kitchen extract fans connected and tested
• Smoke and heat detectors — Units fitted and interlink tested
• Electrical Installation Certificate (EIC) — Issued on completion of a new circuit. Includes schedule of inspections and test results
• EICR (Electrical Installation Condition Report) — For existing circuits that have been modified. Required for Part P compliance
• Part P notification — Notifiable electrical work (new circuits, consumer unit changes, work in bathrooms/kitchens) must be notified to Building Control or carried out by a registered competent person (NICEIC, NAPIT, ELECSA)

What's the correct sequencing between trades?

Getting the sequence right is the single most important factor in avoiding delays on a domestic project. The standard sequence for a new build or major extension is:

Phase 1 — First Fix (all trades, before plastering)

1. Carpenter first fix — Stud walls, door linings, floor joists/decking, noggins. This must happen first because plumbers and electricians need the framing in place to route their services
2. Plumber first fix — Hot and cold pipe runs, waste pipes, soil stack, heating pipework, cylinder position. Plumber needs stud walls up to know exact positions. Requires noggins in place for pipe clips and valve positions
3. Electrician first fix — Cable runs through joists and studs, back boxes, consumer unit. Electrician works around plumber's pipework to maintain safe separation distances. Runs cables through noggins and joists after carpenter has drilled or notched them
4. Heating engineer first fix — Often the same person as the plumber. Central heating pipe runs, gas supply, boiler flue hole, underfloor heating loops (if applicable). Must coordinate with the electrician for boiler and thermostat wiring
5. Ventilation first fix — MVHR or extract ducting installed. Coordinated with the electrician for fan power supplies
6. Insulation — Fitted between and around all services once first fix is complete
7. Building control pre-plaster inspection — Inspector checks all hidden first fix work, insulation, fire-stopping, and structural elements before they are concealed

Critical coordination points at first fix:

• Carpenter must install noggins at radiator, kitchen unit, and wall-hung basin positions before plumber arrives
• Plumber must pressure test before boarding starts — a leak found after plastering is extremely expensive to fix
• Electrician must confirm back box depths with the plasterer so faceplates sit flush with finished plaster
• All fire-stopping around service penetrations through party walls and fire compartments must be completed before boarding

Phase 2 — Wet trades

8. Plasterboarder — Boards walls and ceilings, covering all first fix work
9. Plasterer — Skim coat over plasterboard. Walls need approximately 3-5 days to dry before second fix begins (longer in cold or damp conditions)

Phase 3 — Second Fix (all trades, after plastering)

10. Electrician second fix — Faceplates, light fittings, consumer unit completion. Usually goes first in second fix because sockets are needed for other trades' power tools
11. Plumber second fix — Sanitaryware, taps, appliance connections. Needs finished walls for accurate fitting. Must coordinate with tiler in wet rooms
12. Heating engineer second fix — Hang radiators, fit boiler, connect controls, power flush, fill, and commission. Radiators go on after decorating is complete (or protected during decorating)
13. Carpenter second fix — Skirting, architrave, door hanging. Goes after plumber and electrician so that skirting can be scribed around pipework and faceplates. Kitchen fitting is a separate phase requiring coordinated plumbing and electrical
14. Tiler — Coordinated with plumber for bathroom/kitchen sequencing. Usually after sanitaryware is positioned but before final plumbing connections
15. Decorator — After all second fix carpentry is complete. Radiators removed or protected

Common sequencing mistakes:

• Fitting skirting before radiator pipes are connected — leaves the carpenter having to cut around pipes instead of the plumber notching the skirting
• Hanging doors before the finished floor is down — results in incorrect bottom clearances
• Plastering before the pre-plaster building control inspection — means ripping off plasterboard to show hidden work
• Installing sanitaryware before tiling is complete — much harder to tile neatly around a fitted WC or basin

How do I price first fix and second fix separately?

Pricing first fix and second fix as separate line items is standard practice for new builds, extensions, and major renovations. Here is how to approach it:

Day rates (2026 guide figures):

Second fix day rates tend to be slightly higher because the work requires more precision, is visible in the finished building, and any mistakes are immediately obvious.

Pricing structure options:

1. Day rate — Most common for first fix carpentry and plumbing. Straightforward but gives the customer less cost certainty
2. Price per unit — Common for second fix items. For example, door hanging (£40-£80 per door), skirting (£3-£6 per linear metre fitted), radiator hanging (£80-£150 per radiator)
3. Fixed price per stage — Quote a lump sum for "first fix carpentry" and a separate lump sum for "second fix carpentry". Requires an accurate specification up front
4. Measured rates — Used on larger projects. Rates per metre run of pipework, per socket installed, per metre of skirting, etc.

Tips for accurate pricing:

• Always price first fix and second fix on separate lines in your quote — it gives the customer transparency and protects you if the specification changes between stages
• Include for return visits — second fix happens weeks or months after first fix, so factor in mobilisation time
• Price contingency for first fix discovery work (rotten joists, unexpected service routes, non-standard wall constructions)
• For plumbing, include materials on first fix (pipe, fittings, clips) and sanitaryware on second fix — these are usually supplied separately
• Kitchen fitting is typically priced as a standalone item rather than lumped into second fix carpentry

Frequently Asked Questions

Can first fix trades work at the same time?

Yes, and on larger projects they usually do. Carpenters, plumbers, and electricians can overlap in different rooms or zones, but there is a natural dependency — the carpenter's stud walls must be up before the plumber and electrician can route services through them. On a small extension, trades typically follow sequentially. On a new-build house, they can work in parallel across different floors or rooms.

How long does first fix take on a typical extension?

For a single-storey rear extension (roughly 20-30m2), first fix carpentry takes 3-5 days, plumbing 2-3 days, and electrical 2-3 days. These overlap partially, so the total first fix period is typically 5-8 working days. Allow an additional 1-2 days for building control inspection and any remedial work before the plasterer starts.

Does building control need to inspect first fix?

Yes. Building control will normally carry out a pre-plaster inspection (sometimes called a first fix inspection) to check all hidden work before it is covered by plasterboard and plaster. This includes structural timber, insulation, fire-stopping, pipework, and electrical runs. You must give building control notice before covering up this work — failing to do so can result in them requiring you to open up finished walls for inspection, which is costly and disruptive.

What happens if I skip the pre-plaster inspection?

Building control may refuse to issue a completion certificate. In the worst case, they can require you to remove plasterboard to expose hidden work for inspection. This is expensive and time-consuming. Always book the pre-plaster inspection in advance and do not allow the plasterboarder to start until it has been passed.

Is underfloor heating first fix or second fix?

Underfloor heating pipe loops are first fix — they are laid before the screed is poured. The manifold, pump, mixing valve, and controls connection is second fix. The screed itself is a wet trade that sits between first and second fix, similar to plastering for walls.

Who is responsible for fire-stopping at first fix?

Every trade is responsible for fire-stopping their own penetrations through fire-rated walls and floors. In practice, the main contractor or site manager should coordinate this and carry out a final check before the pre-plaster inspection. Intumescent collars around plastic pipes, fire-rated sealant around cable penetrations, and cavity barriers in timber frame are all first fix items.

Regulations & Standards

• Building Regulations Approved Document A (Structure) — Governs structural timber elements including floor joists, roof structures, and load-bearing stud walls

• Building Regulations Approved Document B (Fire Safety) — Fire-stopping requirements at service penetrations, fire-rated construction, smoke detector requirements

• Building Regulations Approved Document L (Conservation of Fuel and Power) — Insulation standards that must be met at first fix before boarding

• Building Regulations Approved Document P (Electrical Safety) — Notification requirements for electrical work in dwellings

• BS 7671 (IET Wiring Regulations, 18th Edition) — The UK standard for electrical installations. Governs cable sizing, protection, earthing, bonding, and testing

• BS EN 806 / BS 8558 — Design, installation, and testing of water supply systems

• Gas Safety (Installation and Use) Regulations 1998 — All gas first fix and second fix work must be carried out by a Gas Safe registered engineer

• Water Supply (Water Fittings) Regulations 1999 — Requirements for plumbing installations to prevent contamination and waste

• First Fix vs Second Fix: A Complete Guide - Creation Construction

• First Fix vs Second Fix Building Work Stages - Self Build

• First Fix and Second Fix - Wikipedia

• First Fix - Designing Buildings Wiki

• First and Second Fix Plumbing Explained - MML Plumbing

• First and Second Fix Plumbing - Build It

• Difference Between First Fixing and Second Fixing - Ligna Carpentry

• Building Control Inspection: Quick Guide to UK Compliance

• Carpentry Prices Guide - Checkatrade

• Average Plumber Hourly Rates in the UK 2026 - Gas Engineer Software

• First Fix vs Second Fix: A Complete Guide for Contractors - Priceworx

• timber spans — Timber sizing for structural first fix

• bathroom refit — Bathroom renovation scope

• building control — Inspection stages and building control