An office on the floor above a gym, a bar or a restaurant takes much of its layout from the business underneath, because that business decides where the noise and the cooking smells come up. The main sources, from dropped weights to the kitchen exhaust, are best dealt with in the tenancy below, so the office fitout concentrates on what can be built on its own side of the slab.
That work decides where the quiet rooms sit and how they are built, and it seals the gaps in the slab and risers before any wall goes up. We can build it as part of a whole corporate fitout or as a single scope of quiet rooms and sealing, and the order is the same either way.
Visiting When the Floor Below Is Busiest
Before we draw a layout, we visit the office floor at the hours the business below is busiest, such as an evening class at the gym or a dinner service at the restaurant. Standing on the office floor at those times shows where the noise comes up and how strong it is, which a quiet mid-morning inspection cannot show.
Where the business below allows it, we also walk its floor and mark on our own floor plan what sits under each part of the office. That means the free-weight area and the class studio, the speakers, the kitchen line and dish wash, the cool room and its compressor, and the riser carrying the kitchen exhaust. The building manager may also hold that tenancy's fitout drawings, which show the same items to scale.
The hours go on the plan as well. A bar that is busiest late at night may barely overlap an office that closes at six, while lunchtime classes or a lunch service fall inside the working day. Where the office needs a measured target, an acoustic consultant can record the noise on the floor during those busy hours, and the floor and wall build-ups are set from that recording.
Placing Quiet Rooms over the Quiet Parts Below
With the floor below marked up, the rooms that need quiet go over its quietest parts. Boardrooms, meeting rooms, phone rooms and private offices sit over storerooms and back offices, while the open office, corridors, the print area, the kitchenette and storage sit over the class studio, the free weights, the bar or the kitchen line.
A room moved on the plan needs no extra material, and every layer added to a wall or floor does, so we settle the layout against the floor below before pricing any acoustic upgrade. Stores and corridors placed over the loudest zones also put distance between that noise and the rooms that need quiet.
Some rooms cannot move, such as a corner office that needs the view or a boardroom beside reception. Where one of those lands over a loud part of the floor below, it becomes the room we build with isolation on every side, and the rest of the floor can stay a standard office build.
Impact and Bass Through the Concrete
Sound from the floor below reaches the office in two ways. Voices and the higher notes of music travel through the air and find their way up through gaps around services, risers and the stair. Dropped weights and the vibration of compressors and fans travel through the concrete itself, and the floor, columns and walls of the office give that vibration off again as sound.
Amplified music arrives both ways. Walls and floors hold back low notes far less well than high ones, so the bass line of a class playlist or a bar's music is the part most likely to be heard upstairs.
A wall or ceiling on its own does little against sound carried by the structure. It is reduced by isolating the vibration where it enters the building, and that point is in the tenancy below. Impact from dropped weights is reduced by the isolated floor that a commercial gym fitout lays under the free-weight area, and plant noise by rubber or spring mounts under the compressors and fans. Those belong to the other tenant's fitout and are settled between that tenant and the building.
The Australian Building Codes Board's sound handbook notes that structure-borne sound cannot be removed from a building entirely, only reduced by isolation. Isolation on the office side lowers the thumps and the bass inside a room without removing them, and some of both will usually still be heard in a room built over the free weights or a bar's speakers.
Carpet, Insulated Walls and Isolated Rooms
Carpet laid over an underlay absorbs more sound than a hard floor or carpet tiles glued straight to the slab, so the voices and music that do come up do not build up in the room. It makes an open office quieter overall but does little against a thump or a bass note, which thin soft finishes barely absorb.
We can build meeting rooms and offices with insulated plasterboard partitions taken full height to the concrete above, sealed along the top and at each end. Those walls keep out the sound reaching the open office around them, through the riser, the stair or the floor beyond the room. They do not stop sound rising through the room's own floor.
For a room that has to be quieter again, such as a boardroom over a loud zone or a recording room, an acoustic consultant can specify isolation on every side. The floor is floated on rubber or spring mounts, the walls go up on two frames that do not touch, and the ceiling hangs on isolating hangers, so the space becomes a room within a room standing apart from the slab. The floated floor finishes higher than the floor around it, so the level at the door is planned with the room.
Any rigid fixing that crosses from the inner room to the building, such as a duct bracket or a conduit screwed to both, carries vibration past the mounts. Ducts and conduits therefore join the room through flexible connections, and the joints around the room's edges are closed with a flexible sealant.
A Kitchen Exhaust Shaft Through the Office Floor
Air from the canopy over a commercial kitchen is ducted up through the building to the roof, so a restaurant on a lower floor sends its duct through every floor above it. Through an office floor the duct usually runs inside its own fire-rated shaft, which takes a block of floor area out of the plan and is drawn in before any room around it.
Where the shaft is new or being rebuilt, we can build its walls in a tested plasterboard shaft wall system, which goes up from the office side at each floor without anyone working inside the shaft. The certifier and the mechanical engineer confirm the fire rating and the shaft size, and the shaft walls go up before the office partitions that meet them.
Kitchen exhaust ducts need cleaning hatches at each change of direction. Where the duct turns on our floor, the shaft wall takes an access panel opposite the hatch, and a panel in a fire-rated shaft usually needs a fire rating of its own. We keep furniture and storage clear of that panel so the duct cleaner can reach it.
The duct carries the rush of exhaust air and the sound of its fan, so on the plan we can place a store or the print area against the shaft rather than a meeting room. Where a room has to adjoin it, we can add a lining and insulation on the room side, and we keep power, data and shelving off the shaft wall so its fire rating is never cut into.
Sealing the Slab and the Riser Against Cooking Smells
Cooking smells reach an upper floor along the same routes as airborne sound, through gaps around pipes and cables in the slab, through risers and shafts, and up the stair and lift. Air drifts between floors through those openings, so sealing them on the office floor cuts the smell and the noise together.
We seal while the slab is bare, after any strip-out and before a wall or carpet goes down. Every hole through the slab is found and marked, and each one carrying a pipe or cable is sealed around it with a tested fire and smoke sealing system. Holes no longer in use, such as the cores of old floor boxes, are filled with a fire-rated mortar. Where a seal is also needed on the underside, it goes in from the ceiling of the tenancy below, booked through the building manager outside that business's trading hours.
The riser cupboard on the office floor belongs to the base building and is usually closed by a fire door that shuts on its own. We seal around the services where they pass through its floor, check that the door closes fully against its frame, and keep stores and shelving clear of it so it is not propped open.
Floor boxes are the other route. A box set in a hole cored through the slab draws its cables up from the gym's or the restaurant's ceiling underneath, so on this kind of floor we can bring desk power down from our own ceiling in power poles or along the walls instead.
Outside Air and Air Pressure on the Office Floor
AS 1668.2, the Australian ventilation standard, asks for kitchen exhaust to discharge upward from above the roof and to be kept further from outdoor air intakes than ordinary exhaust. Where the office has its own air conditioning with an outside air intake, the mechanical trade places that intake away from the restaurant's discharge, and the position is agreed with the building before any opening is cut.
Which way air leaks through a gap depends on the pressure either side of it. An office that takes in a little more outside air than it exhausts sits slightly above the pressure of the riser and the stair, so air leaks out through any gap left instead of being drawn in. A kitchenette or toilet exhaust fan running without matching supply does the opposite, so the mechanical trade balances the two in its design.
We can build what that system needs inside the office. That covers the bulkheads carrying the outside air duct across the ceiling, framed and sealed openings where ducts pass through our walls, and panels in the ceiling wherever a damper or fan has to be reached.
When we price an office above a gym or a restaurant, we visit while the business below is at its busiest, then build the quiet rooms over the quietest parts of its floor.
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