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In general 
The simplest lucarne is no more than the extension of a roof beyond a gable wall, with a ridge timber strong enough to support a hoist. A gin wheel on this beam can provide a simple rope hoist, sufficient to lift a sack of grain. Any greater weights than this are likely to need either a pulley block with multiple advantage, or a geared 
Mills may only require loading to a single floor, but warehouses will require access from each floor. Each hoist accesses all of the floors beneath it, through their prominent doors. These doors often provide a modern indication of an old warehouse building's original purpose. These doors sometimes have an iron fold-down flap outside them, as a short loading step, giving clearance for the hoist away from the wall.
Some large examples are multi-storey.
Where multiple vehicles could be alongside a building at once, there could be multiple closely spaced lucarnes in use simultaneously.
Many surviving warehouses are now converted as multiple flats. The large loading doorways on each floor are often converted with large windows and sometimes a balcony. The lucarne is now superfluous and may be either preserved as a decorative feature, or (often for wooden examples in poor condition) removed. Some remain in a vestigial form, where they must still complete a roof, but the structure below has gone.
In general architecture
Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing building ...
a lucarne is a term used to describe a dormer window
A dormer is a roofed structure, often containing a window, that projects vertically beyond the plane of a pitched roof. A dormer window (also called ''dormer'') is a form of roof window.
Dormers are commonly used to increase the usable spac ...
. The original term french: lucarne
In general architecture a lucarne is a term used to describe a dormer window. The original term french: lucarne refers to a dormer window, usually set into the middle of a roof although it can also apply to a façade lucarne, where the gable of t ...
refers to a dormer window
A dormer is a roofed structure, often containing a window, that projects vertically beyond the plane of a pitched roof. A dormer window (also called ''dormer'') is a form of roof window.
Dormers are commonly used to increase the usable spac ...
, usually set into the middle of a roof although it can also apply to a façade lucarne, where the gable
A gable is the generally triangular portion of a wall between the edges of intersecting roof pitches. The shape of the gable and how it is detailed depends on the structural system used, which reflects climate, material availability, and aesth ...
of the lucarne is aligned with the face of the wall. This general meaning is also preserved in British use, particularly for small windows into unoccupied attic or spire
A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spires are ...
spaces. Nikolaus Pevsner
Sir Nikolaus Bernhard Leon Pevsner (30 January 1902 – 18 August 1983) was a German-British art historian and architectural historian best known for his monumental 46-volume series of county-by-county guides, ''The Buildings of England'' (1 ...
gives its meaning as "a small gabled opening in a roof or a spire".
In industrial architecture the term lucarne is used to describe a feature of a warehouse
A warehouse is a building for storing goods. Warehouses are used by manufacturers, importers, exporters, wholesalers, transport businesses, customs, etc. They are usually large plain buildings in industrial parks on the outskirts of cities ...
, mill
Mill may refer to:
Science and technology
*
* Mill (grinding)
* Milling (machining)
* Millwork
* Textile mill
* Steel mill, a factory for the manufacture of steel
* List of types of mill
* Mill, the arithmetic unit of the Analytical Engine early ...
or factory
A factory, manufacturing plant or a production plant is an industrial facility, often a complex consisting of several buildings filled with machinery, where workers manufacture items or operate machines which process each item into another. T ...
where a window or opening high up on an outside wall supports a hoist above doors on the floors below.
The simplest lucarne is no more than the extension of a roof beyond a gable wall, with a ridge timber strong enough to support a hoist. A gin wheel on this beam can provide a simple rope hoist, sufficient to lift a sack of grain. Any greater weights than this are likely to need either a pulley block with multiple advantage, or a geared chain hoist
A hoist is a device used for lifting or lowering a load by means of a drum or lift-wheel around which rope or chain wraps. It may be manually operated, electrically or pneumatically driven and may use chain, fiber or wire rope as its lifting med ...
.
Some lucarnes are enclosed, and are often wooden-clad structures cantilever
A cantilever is a rigid structural element that extends horizontally and is supported at only one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a canti ...
ed out from the wall. For strength though, the hoist is often carried by a steel girder or reinforced concrete structure. These enclosed lucarnes may act as a loading dock for that floor, with a trapdoor beneath, or they may be simply weather housings for a hoist serving the floors beneath. They are commonly a small housing high in the eaves, above the main working floors.
Mills may only require loading to a single floor, but warehouses will require access from each floor. Each hoist accesses all of the floors beneath it, through their prominent doors. These doors often provide a modern indication of an old warehouse building's original purpose. These doors sometimes have an iron fold-down flap outside them, as a short loading step, giving clearance for the hoist away from the wall.
Some large examples are multi-storey.
Where multiple vehicles could be alongside a building at once, there could be multiple closely spaced lucarnes in use simultaneously.
Repurposed buildings
Many surviving warehouses are now converted as multiple flats. The large loading doorways on each floor are often converted with large windows and sometimes a balcony. The lucarne is now superfluous and may be either preserved as a decorative feature, or (often for wooden examples in poor condition) removed. Some remain in a vestigial form, where they must still complete a roof, but the structure below has gone.
References
{{Reflist, refs= {{Cite book , title=The Railway Goods Shed and Warehouse in England , first1=John , last1=Minnis , first2=Simon , last2=Hickman , publisher=Historic England , year=2016 , isbn=978-1-84802-328-4 , page=62 {{Cite book , title=Victorian and Edwardian British Industrial Architecture , first=Lynn , last=Pearson , publisher=Crowood Press , year=2016 , isbn=978-1-78500-189-5 , page=7 Architectural elements Warehouses