Coordinating an Interior With the Mechanical and Electrical Package

The interior and the services are built by different teams reading different drawings. This is the sequence of documents and hold points that keeps them from colliding.

Interior work and services work are priced separately, drawn separately and usually built by different companies, yet they occupy the same walls, floors and ceilings. Coordination is the deliberate process of resolving that overlap on paper, with named hold points that neither side may pass. Without it, the overlap is resolved by sequence, which means whichever trade arrives first wins and the other one adapts expensively.

Before stage one

Begin coordination once the layout is fixed, the furniture plan exists and the services concept is established, and well before either package is tendered. You need to know the equipment loads, the cooling strategy, the drainage positions and the ceiling void depth available. Attempting coordination after either package has been ordered converts it from a drawing exercise into a variation exercise, which is the same work at several times the price.

• Confirm the furniture and equipment layout, because loads, outlet positions and air distribution all follow it.
• Obtain the services concept with duct sizes, drainage routes, plant locations and the electrical capacity available.
• Establish who owns coordination and give that party written authority to instruct position changes.
• Agree one set of base drawings and one revision numbering convention for both packages.
• Fix the hold points in the programme now, while they are still dates rather than arguments.

Stage 1: Agree the coordination basis and the drawing discipline

Decide which drawings are the single source of truth and who issues them. Agree that both packages work on the same base plan at the same revision, that every issue carries a revision number and date, and that superseded drawings are withdrawn rather than left in circulation. Set out the file naming and the distribution list so that nobody on site is working from a drawing somebody else has replaced. This stage is administrative and it prevents the most common coordination failure, which is two correct drawings that disagree with each other.

• Deliverable: A coordination protocol naming the base drawings, the revision convention, the distribution list and the hold points.
• Owner: The coordinating party, accepted in writing by both packages.
• Approval gate: Both packages confirm in writing which revision they are working from before any detailed design proceeds.

Stage 2: Produce the load and demand schedules

The interior tells the services what it needs. Produce a schedule of electrical loads by position, covering appliances, equipment, lighting circuits and anything with a motor; a schedule of water and drainage demands by fixture; and an occupancy and heat gain schedule by room, since cooling capacity follows the number of people and the equipment in the space rather than the floor area alone. These schedules are the interior's brief to the engineer, and without them the engineer designs to an assumption.

• Deliverable: Electrical load, water and drainage, and occupancy and heat gain schedules by room and position.
• Owner: Designer compiles with the owner; services engineer reviews and sizes against them.
• Approval gate: Capacity is confirmed as available, or an upgrade is identified, before layouts are developed further.

Stage 3: Draw the coordinated ceiling and wall layouts

Overlay the interior and services information on one drawing per plane. On the ceiling, resolve lighting, grilles, detectors, sprinklers where present, speakers, curtain tracks and access panels. On the walls, resolve outlets, switch plates, thermostats, control panels, intercom and the joinery that will cover any of them. On the floor, resolve drainage positions, floor boxes and underfloor services against the finish layout and setting-out. Every clash found here is a line moved; every clash missed here is work removed.

• Deliverable: Coordinated reflected ceiling plans, wall elevations and floor service layouts, issued as one set.
• Owner: Coordinating party produces; both packages sign the set.
• Approval gate: No installation in any plane before that plane has a signed coordinated layout.

Stage 4: Issue the builder work and penetration schedule

Services need holes, chases, bases, supports and fire stopping, and those are usually built by the interior or construction package rather than the services installer. Produce a schedule listing every opening and chase with its size, position and the service it carries, every equipment base with its loading, and every penetration requiring fire stopping with the system to be used. The schedule prevents two familiar failures: openings cut on site through something that should not be cut, and penetrations left unsealed in a wall that was supposed to be fire-separating.

• Deliverable: A builder work schedule with every opening, chase, base and fire-stopped penetration listed and located.
• Owner: Services engineer specifies the requirement; the interior package builds it.
• Approval gate: No opening is cut on site that is not on the schedule, and none is formed in a rated element without an approved detail.

Stage 5: Review the clashes formally before installation

Hold a coordination review with both packages and the designer, working through the ceiling, wall and floor sets, and record every clash with a decision and an owner. Pay particular attention to the places where congestion concentrates: the zone outside a riser, the area above a wet room, the ceiling in a corridor where everything crosses, and any point where a structural element reduces the void. Record the outcome as a marked set rather than as meeting notes, because a decision that is not on the drawing will not reach the installer.

• Deliverable: A clash register with each item, its resolution, the owner of the action and the revised drawing reference.
• Owner: Coordinating party chairs; both packages commit to the resolutions.
• Approval gate: The register is closed and the drawings reissued before the installation sequence starts.

Stage 6: Test and record before anything is concealed

Pressure test pipework, test and certify electrical circuits, commission extraction and prove drainage falls before the ceiling is closed or the floor screeded. Then photograph every concealed zone with a measurement reference, because that record is the only way a future contractor will know what runs where without exploratory damage. A concealment carried out before testing converts a ten minute check into a demolition exercise, and it is one of the few project failures that is entirely avoidable by sequence alone.

• Deliverable: Test and commissioning records per system, plus dated pre-concealment photographs with references.
• Owner: Services installer tests; designer or supervising engineer witnesses; owner retains records.
• Approval gate: No void, chase or floor is closed before its contents are tested and photographed.

Stage 7: Hand over as a maintainable record

At completion, compile the as-built services drawings against the as-built interior, with the access panel positions, the isolation points, the equipment schedules, the commissioning data and the warranties. The test of this record is simple: could a maintenance contractor who has never seen the building isolate a circuit, reach a valve and replace a component without opening anything speculatively? If not, the record is incomplete regardless of how many files it contains.

• Deliverable: A combined as-built record linking services and interior, with access, isolation, commissioning data and warranties.
• Owner: Both packages contribute; the coordinating party compiles; the owner retains.
• Approval gate: Final payment released only when the combined record passes a practical isolation and access test.

Handovers between stages

Three hand-offs carry almost all the risk. The first is from the interior to the engineer, where an incomplete load and demand schedule leads to equipment sized against assumptions. The second is from coordination to installation, where a resolution agreed in a meeting never reaches the drawing the installer is holding; close it by reissuing drawings rather than circulating notes. The third is from installation to concealment, where a void is closed before testing because the finishing trade was waiting; close it by making the test record a documented hold point in the programme rather than an understanding between site staff.

How you know it is finished

Coordination has worked when no service was moved after installation, when no opening was cut that was not scheduled, when every concealed zone was tested and photographed before closure, and when the combined record lets a stranger maintain the building. Requirements for electrical and mechanical installation, fire stopping and testing are revised from time to time, so confirm the current position with a qualified engineer and the relevant municipal and civil defence authorities when you build rather than relying on earlier practice. Where a fire-separating element is penetrated, obtain written confirmation of the approved detail from a qualified engineer instead of accepting a general assurance on site.

Domira designs and delivers interiors as part of the building, not after it: the finishing schedule, the joinery and the services coordination that decide whether a space looks built or assembled. Share the space and Domira will tell you what it would specify and what it would leave out.