Planning Service Routes Through Floors and Structure

Across the floor structures in the library, a horizontal route has three legitimate homes: inside the structural depth between members, beneath the soffit in a hung or suspended zone, or within voids formed in the units themselves where the maker permits it. A solid panel removes the first of those, which is why a battened or suspended zone has to be added deliberately.

The fourth outcome is not a home. It is what happens when none of the three was planned: material removed from a member, a sheet or a unit, by someone who needed the route to exist.

In a joisted floor the space between deck and ceiling is used for pipework, cabling and sometimes ducts, and the entries describe it as the part of the assembly that takes most of the pressure from later work. Whether services pass between the members or through them is named as the single coordination decision that most often turns into structural damage.

The member type governs what is possible, and the manufacturer's information for an engineered product is the document that answers it.

In a composite deck floor, distribution below the floor is fixed to the deck, and deck direction, rib positions and the reinforcement above all constrain where a hanger may go. Coordination is far easier before the deck is set out than after. In a precast plank floor, services are usually hung beneath rather than buried within, so the soffit becomes a fixing plane — and what may be drilled into a prestressed unit is defined by its manufacturer rather than judged on site.

The hanging itself has a constraint the surface hides. A deck presents a continuous face downward while being made of different things at different points, so what a fixing lands in cannot be read from the soffit.

A crossing through a floor is not just a hole. The element it crosses was built to be continuous: it may carry structure, and it may be relied on to resist the passage of air, moisture, sound, smoke or heat, or several of those at once. Every layer interrupted there has to be brought back together around whatever passes through, and each layer is returned by a different means.

The entries separate three things that get run together. A builders work opening is provision made in advance of the service. A pipe sleeve is a lining that keeps the crossing and the structure independent, and it creates a gap rather than closing one. The penetration is the position itself, which exists whether or not anything has yet been done about it.

In a precast plank floor, the pattern of units and the position of openings are settled before manufacture rather than during the work. In a mass timber structure, openings, service holes, recesses and connection preparation are part of the manufacturing information, so late service coordination is a structural change rather than a variation of finish. In a post-tensioned plate, every hole, sleeve, drain, socket and fixing belongs to the pre-pour coordination, because afterwards the slab contains no area that can be assumed to be free of a tendon.

The composite deck sits alongside them with a slightly different deadline: penetrations are located before the deck is set out. In each case the point at which a services drawing becomes a structural drawing arrives earlier than most programmes assume.

Forming an opening while an element is being built is a different operation from cutting one into a finished element, and the difference shows in the material around it: reinforcement arranged for the opening, support provided over it, edges formed rather than broken.

It carries its own consequence, though. The opening exists, open and oversized, for as long as it takes the service to arrive, and an opening that was formed and never used is far more often covered by a finish than properly closed.

The whole subject reduces to one question asked early: who is agreeing the route, against which structural information, and by what date. Asked at the right moment it is a coordination task. Asked afterwards it becomes a request to alter a structure that has already been built to a different assumption.