Boxing Up Aircon Trunking
Bulkheads, Casing & Ceiling Drops

This is a finishing and buildability guide. A standalone bulkhead has no published Klang Valley rate that we are willing to quote as fact, so its cost is given here as drivers and quotation lines rather than a number — the only two figures on this page are our own published ceiling rates, attributed where they appear. WhatsApp us for a fixed quote.

What boxing up actually is

When a split aircon is installed, three services leave the indoor unit together: the insulated copper refrigerant pair, the condensate drain hose, and the interconnecting cable. On a back-to-back installation they exit straight through the wall behind the unit and you never see them. On every other installation they run along the wall or ceiling to reach the point where they can, and the installer covers that run in a plastic casing — trunking. Trunking is a tidy cover, not a finish. It is grey or white plastic on a painted wall, and in a room anybody cares about, it shows.

Boxing up is the follow-on trade that makes it disappear. It is plaster or carpentry work, not aircon work, and it is a different contractor on a different day. That split is worth understanding before you ask for it, because the aircon installer will usually agree to “box it up” and then either sub it out or do a rough job with the wrong materials. If the aircon is not yet installed, the cheapest bulkhead is the one you never need — ask about the pipe route at quotation stage, when it is still free to change (our aircon installation cost guide covers how the route affects the install price).

Boxing up does not stop a leak — read this first

This page is asked for in two very different situations, and only one of them belongs here. If the trunking bothers you because it is ugly, read on. If there is a damp patch, a drip, a stain or a tide-mark anywhere near it, stop: boxing up will hide the symptom and leave the cause running behind a sealed board, where it will quietly ruin the new bulkhead, the wall behind it and eventually the ceiling below.

Water at an aircon run has several causes that look identical from inside the room, and they need diagnosis before anything is closed up:

• Water at the wall penetration itself — rain tracking in through the sleeve, condensate backing up out of the drain hose, or the refrigerant line sweating inside the wall. That is a distinct job with a distinct fix: see water leaking from the aircon hole in the wall.
• Water appearing in the ceiling below — which may not be the aircon at all. Telling an aircon leak from a pipe leak is the first step.
• Stains without an obvious drip — see what ceiling stains are actually telling you.
• Surface wetness that is not a leak at all — condensation and seepage look the same and are not.

Fix the water, let it dry, then box up. In that order, a bulkhead is a permanent improvement. In the other order it is an expensive lid.

The four ways to hide trunking, compared

The two built options are the ones that need thinking about. A bulkhead is a local box following the pipe; a ceiling drop is a planned architectural line that happens to contain the pipe. Where a room is getting a new ceiling anyway, the drop is almost always the better answer — it reads as design rather than as concealment, and it costs less as part of a package than as a separate visit. See our false ceiling cost guide and plaster ceiling guide for how those packages are put together.

The access trap: a bulkhead you cannot open

This is the mistake that turns a good-looking job into a bad one, and it surfaces years later. Everything inside that box needs to be reachable one day. The condensate drain hose blocks with slime and dust — it is the single most common aircon service call, and clearing it means getting at the hose. The refrigerant joints can weep. The interconnecting cable can be damaged. Sealed inside a skimmed and painted bulkhead, none of that can be touched without cutting the board open and repairing it afterwards.

The fix is neither difficult nor expensive if it is decided before the board goes up:

• An access panel at the drain end, where the hose meets its outlet or its trap. That is where the blockage will be.
• A removable section under the indoor unit, so the unit can be dropped for a chemical overhaul without demolishing the box.
• A screwed-and-filled section rather than a skimmed one where a joint sits inside. It is marginally less perfect and enormously more practical.
• A photograph of the run before boarding. Take it yourself, on your own phone, and keep it. In five years it is the only record of what is behind the plaster.

Routine servicing is unaffected by a bulkhead — see what servicing costs — but a drain clear or a joint repair is not, and that is exactly the work an inaccessible box makes expensive.

Sequencing — who has to finish before the box closes

Boxing up sits between trades, and getting the order wrong means doing it twice. The rule is simple: nothing that will ever need to move goes in after the board goes up.

Step 2 is the one that gets skipped, and it is the one that matters. A drain fault found after painting costs the bulkhead, the paint and the goodwill; found in week one it costs an afternoon.

Which board belongs in this location

A bulkhead over an aircon run is not an ordinary ceiling detail. It encloses a cold pipe in a hot, humid country, and the material has to suit that:

• Standard gypsum board — the default for a living room or bedroom bulkhead. Takes a skim coat beautifully and gives an invisible finish. It has no tolerance for repeated wetting, so it depends entirely on the run being dry and staying dry.
• Moisture-resistant board — the right call anywhere humid or outdoor-adjacent: wet kitchens, service yards, balconies, bathrooms. The cost difference over a short bulkhead run is small; the difference in outcome is not. Our plaster ceiling guide covers where each board belongs.
• Cement board — for genuinely exposed or wet locations. Heavier, harder to finish smooth, and unnecessary indoors.
• PVC panel — not a skimmed finish, but unaffected by moisture and demountable, which makes it a sensible service-area answer. See PVC ceiling.
• Timber or plywood casing — a carpentry approach that can look excellent when it is designed as joinery rather than as a hiding place, and poor when it is not.

Whatever the board, the frame under it should be metal furring rather than timber battens. Timber in a warm humid cavity next to a cold pipe is the one combination worth ruling out.

Condensation inside a sealed bulkhead — the failure mode

Here is what goes wrong in the boxes that fail. The refrigerant pair running to the indoor unit is cold. It is insulated for exactly that reason. If that insulation is thin, taped rather than continuous, split at a bend, or stops short at the wall face, the pipe sweats — and now it is sweating inside a sealed cavity with no airflow. The water has nowhere to go except into the board above it and the wall behind it. The first sign is a shadow on the paint months later; by then the board is soft.

Three things prevent it, and all three are decided before boarding. First, inspect the insulation along the whole run and insist it is continuous — every joint sleeved, nothing bare, nothing stopping at the wall face. That inspection is free while the trunking is off and impossible afterwards. Second, confirm the drain falls continuously to its outlet, with no dip holding water inside the box. Third, do not seal the cavity airtight; a boxed run benefits from being able to breathe, which is a further argument for the access panels above.

If a bulkhead has already failed this way, the repair is a ceiling repair as much as an aircon one — see ceiling repair.

How boxing-up work is priced

A bulkhead is normally absorbed into a ceiling package rather than sold on its own, which is why there is no reliable standalone rate to publish. Where the room is getting a ceiling anyway, the published ceiling rates are the honest reference point: our false ceiling cost guide puts a false ceiling at RM8–RM22 per sq ft installed in the Klang Valley, and our plaster ceiling guide puts a simple one-tier drop or cove at RM15–RM22 per sq ft including the framing. A bulkhead following a pipe is built the same way, out of the same materials, by the same trade.

Sold on its own, the price moves on drivers rather than on a rate card, and these are what a surveyor is actually looking at:

• Run length and how many corners it turns. Corners are slow: each one is framing, board cutting, two corner beads and a skim detail.
• Section size. A box tight to a single trunking run is quick; one sized to swallow a drain fall or a second service is a bigger frame.
• Height and access. Work at ceiling level over furniture, or up a stairwell, is slower and needs protection.
• Whether skimming and painting are included or handed to a separate painter — the single most common gap between two quotes for the “same” job.
• Access panels. Cheap to include, disproportionately expensive to retrofit.
• Making good where the old trunking clips came off the wall.
• Furniture protection and clean-up — skim sanding puts fine dust through a whole floor if the room is not sheeted.

What the quotation must itemise

A quote that names the board and the panel positions has been thought about. One that says “box up aircon piping” and a lump sum has not, and the gaps in it will surface as extras.

Mistakes to avoid

• Boxing up over an unresolved leak. The one mistake on this list that keeps costing after the job is done.
• No access panel at the drain end. The blockage will happen; the only question is what it costs to reach.
• Boarding before the unit has run under load. A week of proving the drain is worth more than any warranty wording.
• Standard board in a wet kitchen or service yard. Moisture-resistant board costs a little more and is the difference between ten years and two.
• Timber battens in the cavity. Warm, humid, next to a cold pipe — use metal furring.
• Letting the aircon installer do the plastering. Different trade, different tools, and the finish shows it.
• Forgetting the electrical work. Any point or cable route on that wall has to be finalised first — a wall behind a bulkhead cannot be chased afterwards.