Turret and cantilevered stairs

Enclosing wall

Enclosing wall

Figure 9.1e Principles for stonework stairs: Tapered threads with central column and enclosing wall

Enclosing wall can be a square/OR rectangular shell

Open well

built into n.

Cantilever treads, resting on their front edges on the steps below

Figure 9.1f Principles for stonework stairs: Cantilevered stone stairs within a drum

One source for these dramatic structures of turret and cantilevered stairs is the influential writing of Andrea Palladio. The text from 1570 I Quattro Libri del Architettura (The Four Books of Architecture) devotes significant illustrations and text to the advantages of open well stairs constructed with stone cantilevers. The designs of Vignola's Palazzo Farnese, Caprarola, and Palladio's staircase in the Carita Monastery, Venice (Figures 9.2a-c), were both seen by Inigo Jones. In his sketchbooks, Jones records details of these stairs with notes as follows, 'They succeed very well that are void in the middle, because they can have light from above, and those that are at the top of stairs see all those that come up or begin to ascend, and are likewise seen by them'.

Inigo Jones certainly drew upon the inspiration of Andrea Palladio in the 'Tulip' staircase in the Queen's House, Greenwich (Figures 9.2d and 9.2e). A technical refinement occurred whereby the treads were rebated at the front bearing edge on the step below. The rebating prevented slipping in the building stage and improved the bearing from one tread to the next as compared with the

Open well

built into n.

Enclosing wall

Enclosing wall

Cantilever TurretCantilever Turret

Figure 9.2b Turret and cantilever stairs: section plan of stairs at the Carita Monastery, Venice, 1560-61, Architect: Palladio simple bed joint illustrated by Palladio (Figure 9.2c). Other notable English stairs built on the cantilever principle in the seventeenth or early eighteenth centuries are the open spirals at The Monument, City of London (Figure 9.2f), and the great stairs at Chatsworth (Figures 9.2g and 9.2h). Wren and Hooke deployed at The Monument a moulded riser, which features in full at the tapered end, while a blocked end to the nosing gives the necessary rebate at the tail of each tread. This detail is abandoned in the lower parts where a supporting wall exists towards the open well. A further development in

Figure 9.2c Detail of steps, Carita Monastery (from Ackerman, James S., Palladio, Penguin Books Ltd, 1979)

scale occurs with the geometrical stairs below the south-west tower stairs at St Paul's Cathedral, constructed by the master mason W. Kempster in 1706-8.

The most courageous cantilevers were made under Talman's direction at Chatsworth House, Derbyshire. The geometry follows a multiple-turn staircase within a square shaft. The cantilever dimension of 2 464 mm implies the cutting of vast blocks of sound local sandstone, the quarter landing slabs having sizes of around 2 600mm2. Each step weighed around 500 kg, the design above the first floor being reduced to more modest sizes of around 1 600 mm together with the introduction of carriage pieces. Talman was also involved with work at Hampton Court and it is thought likely that the mod-illion profile (Figure 9.2i) can be attributed to that source.

Figure 9.2d General view, Tulip staircase, Queen's House, Greenwich, 1629-35, Architect: Inigo Jones

Figure 9.2e Detail of treads, Tulip staircase

Cantilever Turret

Figure 9.2e Detail of treads, Tulip staircase

Figure 9.2f Details from cantilever steps, The Monument, City of London, circa 1671, Architects: Sir Christopher Wren and Robert Hooke

Figure 9.2g General view, The Great Stairs, Chatsworth House, Derbyshire, 1689-90, Architect: William Talman, balustrade by Tijou

The tailing-in of the tread ends is critical in terms of tightness of fit, the depth of bearing varying between 110 mm and 152 mm. The lesser dimension is common in nineteenth-century domestic work while Wren used 150 mm for the south-west tower stairs at St Paul's and 152 mm at Hampton Court. The crucial stabilizing role of the metal balustrade needs to be taken into account. Dismantling the balusters will often destabilize the treads. Such

Concrete Cantiliver Spiral Staircase
Figure 9.2h Detail of cantilever treads, The Great Stairs

strengths may not be calculated but there is little doubt that stone cantilevers, and side-mounted balusters, act together once assembled with leaded joints from metal to stone (refer back to the Queen's House details, Figures 9.2d and 9.2e).

The moulding of the underside of the tread gives interest to the stair when viewed from below, as in the Da Costa House (Figure 9.2j). This is particularly important where both the up and down flights join a landing.

The beauty of the final example (Figure 9.3) is the sweeping soffit of the stair which gives a sculptural design to the entrance hall of this small house.

SECTION

AT WALL

enrichment

2160 mm and

1650 mm wide carving

ELEVATION

AT STRING

Pictures Stair Turret

Figure 93 Stair showing sculptural form

SECTION

AT WALL

enrichment

2160 mm and

1650 mm wide carving

ELEVATION

AT STRING

Figure 93 Stair showing sculptural form

Figure 9.2i Modillion profile to stairs at Hampton Court, circa 1700

Figure 9.2j General view, Da Costa House, Highgate, 1990, Architect: Russell Taylor, Engineer: Sam Price of Price and Myers

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Responses

  • arja
    How to show the cantilever staircase on the floor plan?
    1 month ago

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