First fix: electrics, plumbing, heating and ventilation before the walls close

First fix is the hidden half of the services: the cables, pipes, ducts and boxes that run inside walls, floors and ceilings. Once plasterboard goes up, you cannot see them again, so this is the stage where a few hours of checking and photographing saves you the most trouble. It is also where the trades overlap most, and where a missed detail causes expensive rework.

What happens, in order

1. Planning the layout. Before anyone cuts or drills, walk the house with the electrician, plumber and heating installer and mark sockets, switches, lights, radiators, outlets, the cylinder, the boiler or heat pump position and the ventilation unit. Changes are free on paper and expensive on the wall.
2. Electrical first fix. Back boxes are fixed, cables run to every socket, switch and light, and the consumer unit position is prepared. Cables for a doorbell, data, aerial and any smart controls are run at the same time.
3. Plumbing first fix. Hot and cold pipes are run to every tap, shower, bath, toilet and appliance, with isolating valves. Waste pipes connect to the drainage.
4. Heating first fix. Radiator or underfloor heating pipes are laid and connected to the manifold. Heat pump pipework and cylinder positions are set.
5. Ventilation ducting. Ducts and extract points for a ventilation system are fitted, with the right size and fall.
6. Testing. Pipes are pressure-tested, and electrical continuity is checked.
7. Closing up. Insulation, vapour or airtightness layers and plasterboard follow. See insulation and airtightness.

Who does what

• Electrician: a registered electrical contractor does the work and issues the completion certificate. ESB Networks requires a certificate as part of the connection process, and it is a long lead item if the electrician is late. Check the requirement on the ESB Networks certification page.
• Plumber and heating installer: may be the same firm. For gas or oil heating, use an installer registered for that fuel.
• Ventilation installer: often supplied with the unit, with commissioning to follow.
• Certifier and designer: the inspection plan normally includes a stage inspection of first fix, mainly for fire stopping, penetrations and ventilation.
• You: decide the layout and the extras. This stage rewards decisions made early.

Decisions to make before the trades start

Put these decisions in writing, with a marked-up plan, and have each trade confirm it. A verbal “that will be fine” at the stud wall is the commonest source of dispute later.

• Socket and switch positions. Walk each room with furniture in mind. Add sockets where a TV, desk, bed, worktop and charger will be.
• Electric vehicle charger. Run the cable and plan the consumer unit capacity now, even if the charger arrives later.
• Lighting plan. Number and position of ceiling lights, and what controls them.
• Heating zones and controls. How many zones, what thermostats and where.
• Future-proofing. Spare ducts, a cable to the attic or garage, and a place for solar equipment.
• Water. Position of the stopcock, outside tap and any softener.
• Internal doors and bathroom layout. The sanitaryware you choose changes pipe positions.

What to photograph and check

The aim is a record you can read in five years’ time. A photograph of a bare stud wall with a tape showing “1.2 m” beside a cable tells a future electrician exactly where it is safe to drill. A photograph without scale, or taken after the insulation is in, tells them very little.

Take a photograph of every wall and ceiling run with a tape in view before it is closed. Label them by room. At minimum:

• Each wall with pipes and cables, including heights from the floor.
• Pipe and cable penetrations through floors and walls, and how they are sealed.
• Pressure test gauges and the test duration.
• Fire stopping where pipes or ducts pass through walls or floors that need it.
• Positions of the manifold, cylinder, consumer unit and ventilation unit.
• Any bend or drop in ducts. Sharp kinks reduce airflow.

Check the following with the trades:

• Cables are in safe zones. Runs follow the usual vertical and horizontal routes from sockets and switches, so someone drilling for a shelf later is less likely to hit them. Ask for as-built drawings.
• Pipes are insulated where they could freeze, or lose heat, or sweat.
• Plumbing is pressure-tested and the result recorded.
• Penetrations through the airtightness layer are sealed with the right tapes or grommets. See insulation and airtightness.
• Ducts are the right size and have access for cleaning or filter changes.

Heat pumps and renewable energy

A new home built to the nearly zero energy building standard (nZEB) typically has a renewable energy source, and a heat pump is a common way to meet it. A heat pump works best with low-temperature emitters such as underfloor heating or larger radiators, and with good insulation and airtightness. Decide the position of the outdoor unit, the cylinder and any buffer tank at this stage. See nZEB and Part L. Check the VAT treatment of the installation with Revenue before you agree the contract.

What goes wrong, and what it costs

First-fix problems are cheap to fix on the day and expensive three weeks later. The pattern is nearly always the same: a trade works from an old drawing, a change is agreed on site and not passed on, or one trade cuts through another’s work.

• Changes after plastering. Chasing a wall to move a socket costs more and may breach the airtightness layer.
• Untested pipes. A leaking joint found after the screed or plasterboard is a flooded floor.
• Crossed trades. A pipe through a joist that was cut for a cable, or a duct blocked by a beam.
• Cables in the wrong zones. Later drilling hits live cable.
• Insulation gaps at pipes and cables. A thermal bridge or a draught source.
• Late electrical certificate. A delay with the connection means no power for second fix or drying out.

Payments, site risks and cover

Keep the order of work in mind when you ask for a payment to be released. Some builders bill first fix as one lump when the electrics, plumbing and heating are all in, others bill each trade separately. Agree this in the contract rather than when the first invoice arrives.

First fix is sometimes a separate stage payment, often tied to completion of services before plastering. Check with your builder and lender. See staged drawdown explained.

By now the house contains valuable copper, cable and pipework, and electrical work is an ignition risk if left unfinished. Check that contract works cover includes materials stored on site and not yet fitted, and that your liability cover continues. A leak during testing can damage finished surfaces if some are already in place. Look at insurance when you project manage and the cover checker.

Before insulation and plaster

• You have a dated, written list of any changes made on site, so the as-built drawings can be corrected.

• The electrician has said what the consumer unit capacity is and whether it has room for a car charger or solar later.

• Every run photographed and, ideally, drawn.

• Pressure tests and electrical checks recorded.

• Certifier or designer has inspected the stage.

• The next stage: insulation, airtightness and the air test.

Choosing the heating system comes first: see the heat pump guide and the solar PV guide.