First Fix vs Second Fix — What Each Stage Means and What It Includes

First fix is all the work carried out before plastering — the work that is hidden within the structure of the building (behind walls, within floor and ceiling voids, in roof spaces) and cannot be accessed once plasterboard is fixed and plaster is applied.

• **First fix electrics**:
• •Installing the consumer unit (fuse board) position and main cable run
• •Running cables throughout the building to every socket, light, and appliance position
• •Positioning back boxes (the metal or plastic boxes that the switches and sockets will fix to)
• •Running cables for mains-wired smoke alarms at each level
• •Cables for heating controls, extractor fans, and any specialised circuits (electric shower, cooker, EV charger)
• •First fix does NOT include fitting switches, sockets, light fittings, or connecting the consumer unit — those are second fix

• **First fix plumbing**:
• •Installing the new pipework runs for hot and cold water throughout the building
• •Installing soil and waste pipes for new bathrooms, WCs, and kitchen sinks
• •Positioning the boiler location pipework and connections (boiler is not fitted at first fix)
• •Installing central heating flow and return pipework to radiator positions throughout the building
• •Radiator valves and tails at each radiator position
• •First fix does NOT include fitting sanitaryware (bath, basin, WC), radiators, or the boiler

• **First fix carpentry**:
• •Stud wall framing (where stud walls are part of the new layout)
• •Window and door lining installation
• •Floor joist installation (in new structures)
• •Stair string and newel post installation (the structural elements of the staircase)
• •Plasterboard fixing (boarding the stud walls and ceilings)
• •First fix does NOT include skirting boards, architraves, doors, fitted furniture, or stair treads — those are second fix

Between first fix and second fix, the plastering phase takes place. This is when:

• •Plasterboard is skimmed with a thin coat of finish plaster (traditional wet plaster)
• •OR dry lining compound is applied over taped plasterboard joints (drylining/tape and joint system)
• •Render is applied to external walls
• •Floor screeds are poured (liquid screed or traditional sand/cement screed) over underfloor heating pipes or to level uneven floors

• **Why plastering is the dividing line**:
• The plastering phase is the dividing line between first and second fix because:
• •Once plaster is applied, the cables and pipes are fully concealed — any changes require cutting into the finish
• •The plaster must fully dry (minimum 3–4 weeks for traditional plaster, faster for drylining compound) before second fix decoration
• •The plaster provides the smooth surface onto which skirting boards, architraves, and other second-fix elements are fitted

**Plastering programme**: For a typical extension (4m x 5m footprint, with first-floor bathroom above), plastering typically takes 1–2 weeks for a small team of plasterers. Drying time before decoration adds a further 2–4 weeks.

Second fix is all the work carried out after plastering — the visible, finished elements that are installed to complete the space.

• **Second fix electrics**:
• •Fitting all switches and socket faceplates
• •Fitting light fittings and pendants
• •Connecting and commissioning the consumer unit
• •Connecting and testing all circuits
• •Part P certification and Building Control notification
• •Installing and testing the mains-wired smoke alarms

• **Second fix plumbing**:
• •Fitting the boiler and commissioning the heating system
• •Installing radiators and connecting to the flow and return tails
• •Fitting the bath, basin, WC, and shower in each bathroom
• •Fitting taps, valves, and waste connections
• •Connecting and testing all water supply and waste connections
• •Commissioning the boiler and full heating system pressure test

• **Second fix carpentry**:
• •Installing skirting boards and architraves throughout
• •Hanging internal doors on their linings
• •Installing door furniture (handles, hinges, locks)
• •Stair treads, risers, and balustrading
• •Fitted wardrobe installation
• •Any other joinery elements (window boards, bespoke shelving)

**Decoration (separate from second fix carpentry)**: Decoration (painting and decorating) typically follows second fix carpentry. The sequence is: plaster dry → first coat of paint → skirting and architrave installation → final coat of paint (cutting in around the new joinery).