Where pipework is exposed, an upright sits on the branch out of harm's way and needs no drop.

A pendent in an open space hangs below the pipe, exposed to forklifts, stored goods and personnel.

Every pendent also needs a drop pipe, which in a large warehouse is a great deal of additional pipework and fittings.

Uprights can also spray over the top of beams and ducts, which a pendent below the pipe cannot.

Warehouses, plant rooms, car parks and roof voids are the usual applications.

Where a finished ceiling exists, the argument reverses and a pendent is preferred.

Water is thrown upward onto the deflector, which redistributes it downward and outward.

That detour is what produces a usable floor pattern from a head pointing the wrong way.

The deflector geometry is designed for water arriving from below and differs from a pendent's.

It also means the head needs clear space above it for the pattern to develop.

Roof structure, decking or ductwork too close above interferes with the distribution.

The permitted distance to the ceiling above is specified in the same way as for a pendent below one.

No - the deflector is designed for one orientation and produces an untested pattern in the other.

Water arriving from above strikes the deflector completely differently.

Heads are marked with their orientation, and installing one wrongly is a defect found at inspection.

A small number of heads are listed for both orientations and are marked accordingly.

Those are the exception, and the marking is what permits it rather than the physical fit.

Mixed orientations within one design area also complicate the hydraulic calculation.

Because an upright does not trap water, so the pipework drains completely after operation or testing.

In a dry system, water left standing in the pipe after a trip can freeze - which is the condition the dry system existed to avoid.

A pendent drop is a low point that holds water regardless of how the main pipe is graded.

Some standards restrict dry systems to upright heads for exactly this reason, unless dry pendent sprinklers are used.

Pipework in dry systems is also graded to drain, and the head orientation is part of that.

Residual water is one of the main causes of internal corrosion in dry systems as well.

Less so than pendents in the same space, but they still need guards in high-traffic areas.

Sitting on top of the branch pipe puts them above most handling activity.

Forklift masts, crane hooks and long loads still reach them in warehouses.

Sprinkler guards are wire cages fitted over the head and are listed components rather than generic cages.

A guard that alters the spray pattern is worse than none, which is why they are listed with specific heads.

Accidental operation from mechanical damage is a significant cause of unwanted discharge.

Spacing is set by hazard classification and head listing, and the two are treated separately in the standards.

Both are subject to the same maximum coverage area per head for a given classification.

Obstruction rules differ because the spray develops in a different direction.

Distance to the ceiling above is specified for uprights as distance below is for pendents.

Sloped roofs and deck structures introduce their own rules for upright installations.

The design standard in force locally governs all of it, and figures differ between markets.

Routinely - most buildings use both, chosen per area rather than per building.

Finished areas take pendents and back-of-house or exposed areas take uprights.

Within a single design area, consistency matters more, because the hydraulic calculation assumes a pattern of operating heads.

Spares stock has to cover every type installed, including orientation, rating, response and finish.

Recording which head goes where is part of the as-built documentation.

Replacing a failed head with the wrong orientation is a common maintenance error in buildings using both.