The Sequence of Trades on a London Building Project: What Happens and When

The sequence of trades on a construction project is not arbitrary — it follows the logic of the building process:

• •Structural works must happen before anything they support can be installed
• •First-fix mechanical and electrical (M&E) trades must happen before the surfaces that conceal them are formed
• •Wet trades (concrete, screed, plaster) need drying time before the finishes that go over them can be applied
• •Finishes must be completed in an order that doesn't damage previous work

**The cost of wrong sequence:** If electrical first-fix is not completed before plasterboard goes up, the cables cannot be run without destructive cutting and re-making of surfaces — adding cost and programme time. If screeds are laid before plumbing is complete, the plumber must cut through the screed to reach buried pipework. The whole programme is interdependent.

**Client decisions and the sequence:** Client decisions also have sequence dependencies. If the kitchen units are not specified before first-fix electrical, the electrician cannot correctly position the sockets, switches, and appliance connections. If bathroom sanitaryware is not confirmed before tiling, the tile positions (particularly around baths, shower trays, and basins) cannot be fixed. Late decisions cascade through the programme.

**Sequence: Before structural works begin**

• •Strip out and soft strip — removing floor coverings, fixtures, fittings, kitchen units, sanitary ware, and anything that needs to be disposed of
• •Asbestos survey and remediation (where required) — notifiable asbestos removal must be completed before any demolition or structural works. In London Victorian properties, artex ceilings, floor tiles, pipe lagging, and roof felt can all contain asbestos
• •Demolition of existing structures — removing internal walls, cutting out existing openings, and any structural elements that are being replaced
• •Scaffold erection (where required for external works or roof works)
• •Temporary works — installing temporary props and supports before removing load-bearing elements

**Why it must happen first:** You cannot begin foundation work, frame extension walls, or make structural alterations safely until any existing asbestos is removed, temporary supports are in place, and the stripped building reveals its actual condition.

**Sequence: After demolition, before first-fix trades**

• •Excavation — foundations for extensions, retaining walls, drainage runs
• •Drainage and below-ground services — foul drainage, surface water drainage, any services running below the ground-floor slab must be installed before concrete is poured over them
• •Foundations — concrete poured after drainage is in place
• •DPC (damp-proof course) and DPM (damp-proof membrane) installation
• •Concrete slab — ground-floor slab poured after drainage and DPM are in place
• •Structural steelwork — RSJ beams installed after temporary props are in place and openings are made
• •Masonry — extension walls built from foundation up
• •Roof structure — timber or steel roof frame, including any loft conversion structural work
• •Roof covering — tiles, slate, or flat roof membrane (to make the building weathertight before internal first-fix begins)

**The 'making weathertight' milestone:** Until the roof covering is on and windows/doors are in, the building is open to rain. All internal first-fix works must wait for weathertightness — wet electrical cabling and plasterboard are both destroyed by water. Making the structure weathertight is the most critical early programme milestone.

**Sequence: After weathertight, before plastering**

• •First-fix plumbing — supply and waste pipework run to positions of sanitaryware and appliances (the actual sanitaryware and appliances are not installed at this stage — only the pipes)
• •First-fix electrical — all cable runs, back boxes for sockets and switches, cables to positions of all light fittings, distribution board (consumer unit) roughed in
• •First-fix heating — radiator pipework runs, underfloor heating pipes or wiring laid in screed zone
• •Ductwork — MVHR (mechanical ventilation heat recovery) ducts, kitchen extract duct, bathroom extract duct runs
• •Any structural timber noggings required for fixing sanitaryware, shower rails, or heavy items to stud partitions — must be installed before boards go up
• •First-fix inspection and sign-off by Building Control inspector where required (particularly for electrical work in new extensions)

**Why this phase must precede plastering:** All first-fix mechanical and electrical work is concealed by the plaster finish. Plasterboard, screed, and wet plaster are all applied over the top of first-fix elements. If any first-fix work is missed or incorrect, it requires opening up the finished surface to correct — which is significantly more expensive than getting it right first time.

**Sequence: After first-fix, before second-fix and finishes**

• •Screeds — floor screed laid over underfloor heating pipes (where installed), drainage channels, and any service runs that will be buried in the floor. The screed must be allowed to dry before floor finishes can be applied — typically 4–6 weeks for a 75mm sand-cement screed (or 2–3 weeks for faster-drying anhydrite screed)
• •Plasterboarding — plasterboard fixed to all walls and ceilings before plaster skim coat
• •Plaster skim — wet plaster applied to plasterboard and any masonry surfaces. Must be allowed to dry before decoration — at least 2–4 weeks for skim plaster, longer in winter or poor ventilation
• •Tiling to wet areas (bathrooms, shower enclosures) can begin as soon as the surface is dry — but only after the screed has dried sufficiently for floor tiling

**The drying time constraint:** Drying time is one of the most frequently underestimated programme elements. Clients who want a project completed quickly often cannot understand why the programme shows 4–6 weeks between plastering and decoration — but rushing this stage results in paint blistering, tile adhesive failure, and moisture-related defects that are expensive to remedy.

**Sequence: After wet trades have dried, in a structured order**

• •Second-fix joinery — door linings, skirting boards, architraves, stair handrails and balusters, window boards, fitted wardrobes. Joinery is typically the first second-fix trade on site.
• •Second-fix electrical — fixing face plates, sockets, switches, light fittings, consumer unit connection. Electrical second-fix follows joinery because skirting boards conceal the bottom of the cable run to the socket back box.
• •Second-fix plumbing — fixing sanitaryware (bath, WC, basin, shower), radiators, and appliance connections. Typically follows electrical second-fix.
• •Kitchen installation — worktops, units, and appliances installed once first-fix is complete, floor finishes are laid, and decoration is at the appropriate stage (typically after walls are painted, before final coat)
• •Bathroom tiling and sanitaryware installation — second-fix plumbing and tiling often overlap in bathrooms
• •Decoration — undercoat and finish coat painting to walls and ceilings, gloss painting to joinery. Decoration typically happens in two passes: first coat before floor finishes, final coat after floor finishes and before sanitaryware.
• •Floor finishes — hardwood, engineered, or LVT/SPC flooring laid last among floor trades, typically after first-coat decoration, before final touch-up decoration
• •External works and landscaping — driveway, patio, planting. Always last — protecting them during the main build phase is impractical.

**The sequence within second-fix:** The sequence within the second-fix phase matters because each trade can damage the previous one. Decoration before floor finishes means paint drips on bare subfloor (acceptable). Decoration after floor finishes means paint drips on finished floor (not acceptable). The correct sequence minimises rework and damage.

**Sequence: After all works are complete**

• •Snagging — a systematic walk-through by the contractor to identify and record incomplete or defective items before handover. A good contractor produces a snagging list themselves before the client walk-through, not in response to it.
• •Client snagging walk-through — the client walks through the completed works with the contractor and identifies any items they wish to have addressed
• •Snagging rectification — all agreed snagging items completed
• •Building Control final inspection and completion certificate — for all notifiable works (extensions, structural alterations, loft conversions, significant electrical works). The Building Control completion certificate confirms the works comply with Building Regulations.
• •Handover documentation — warranties for any appliances or systems, test certificates for electrical installation (Electrical Installation Certificate — EIC), gas safety certificate (where new gas appliances are installed), operation manuals for systems (MVHR, underfloor heating, boiler), Party Wall Award discharge confirmation where applicable
• •Practical completion — formal handover of the completed works

**Why the completion certificate matters:** The Building Control completion certificate is a significant document — it confirms that the work was carried out in compliance with Building Regulations. It is typically required when selling the property, remortgaging, or making an insurance claim. Projects that are built without Building Control involvement (or that fail the final inspection) can cause serious problems at the point of property sale.