Landscape Elements refer to the variety of artefacts found in a garden. One such landscape element is pergolas. Arising from the Latin word pergula meaning projecting eave, in the 19th century pergolas were used extensively and is still in use today. A pergola is a structure used outdoors consisting of an overhead part which is open to sky and supported on pillars or columns. It is usually linear, having a narrow width. It is similar to an outdoor corridor if free-standing in a garden or acts as a verandah if adjacent to a building. In Sri Lanka, historically, pergolas were unknown until recent times. The Sri Lankan traditional use of outdoor space with structures, were in the form of pavilions in large gardens or wayside rests (ambalamas). These were covered roofs supported on columns with open sides in keeping with the climate.
Functions and materials of Pergolas
The pergola is usually an element in the larger design of the space in which it stands. It is often a connective element, either as an extension from indoors to outdoors or perhaps a threadlike connection between a covered walkway gradually peeling away its top covering exposing raw beams and revealing itself to the open space of the garden. A pergola may also serve as an entrance leading inwards or pause-point when oriented straddling the entrance. The subtle nuances of welcome invitation, or limited entry, is achieved by placement. A pergola as a mechanism for pause allowing attention to the scene ahead is also possible.
A pergola can be made of materials such as timber, concrete, or a mix of materials such as brick columns supporting an overhead structure of timber or concrete cross beams and connective lattice or lath. This we can refer to as lateral beams or laterals. Modern materials such as fibreglass and others are also used. Although de-mountable they are often permanent structures.
One may ask ‘Why have a Pergola?’ A pergola is rarely used for its own sake. Traditionally, it was a structure to display plants which required support. The vine arbour at Peradeniya Gardens comes to mind, although the structure is a somewhat different. Now, a pergola is usually used to extend living space, connect walkways, as a shade structure or as a support for plants, particularly vines or climbers. It can also be useful as a filter. Filtering unwanted views, such as a garden overlooked by high-rise structures may lend privacy, or in reverse, like a shy maiden looking through a veil can afford views of scenery upward and beyond. Dust may be filtered, as may many other pollutants. It also provides an extra perch for birds, which may be welcome to the nature lover but a nuisance if used by them as a toilet.
Concrete pergola beams are also used to secure small courtyards within homes while retaining some openness. The security afforded would allow internal spaces to flow unhindered without the need for enclosing doors.
I like to see a pergola as either naked or clothed. A ‘naked pergola’ would express its structure, while the ‘clothed pergola’ would more express the vines or creepers it would support.
The simplest pergola will have a double series of columns evenly spaced apart perhaps 8 to 10 feet to support a beams from column to column which in turn supports a series of laterals at right angles to the direction of the beam. It is the placement and size of these that create patterns. The shape and material of the supporting column, the base and head of the column all contribute to the overall appearance. Moreover, the columns may be single or double as in the arrangement of the overhead lateral beams. The laterals may be joined at the same level of the supporting beam or may be above it. They may be at right angles or even oblique. Oblique laterals will consume more material and complicate joinery perhaps to no fruitful purpose.
In pergolas, The depth and spacing of the laterals should be carefully decided. This is often dependent on many factors such as orientation, climatic requirement, the need for openness or closure to screen and aesthetic consideration. The purpose or function of the pergola must be clearly established at the outset. Of course the fundamental requirement of having a structurally stable pergola with beams that do not sag when weighted or warp with climatic conditions and laterals similarly selected with sound joinery is the basis of safety and a pleasing structure. Spacing may be uniform and single or double laterals may be used, the doubles being uniformly spaces. Other effects are possible, but if not functional and skillfully applied may result in a fussy mess.
The naked pergolas
The ‘naked pergola’ while expressing structure also provides shadow effects. A pergola in a temperate climate provides shade against day-long slanting sun-rays, but in a tropical setting only overhead sun-paths need be considered. The location of a pergola in temperate situations will favour only a particular side (South in Northern hemisphere and vice versa) unlike a tropical location.
Deep cross-section laterals will form broad bands of uniform shadows depending on orientation. The East-West pergola will give more lateral shadows than North-South orientation. A flat surface below will display the cast shadows according to the position of the light source (the sun usually) and the pattern of the laterals above. However if the surface is curved or irregular the shadow pattern will distort accordingly. Shadows can enhance the textural effect of the paving below.
Shadows cast by a pergola often give stunning photo opportunities, but may also be a disturbance if focus is on the activity below due to flicker effect.
Ornamentation of the parts often derives from the overall aesthetic of the setting. The most obvious is the treatment of the end of the laterals. These may be left raw expressing the cross-section of the lateral, say 7 inches by 1 ½ inches or so as an example which is the same cros-sectio throughout its length. Alternatively they may be tapered outwards beyond the supporting beam in a patterned form. The possibilities are many. The columns may be ornamented at base or head too. Long spans of cross beams may have extra support with cleats or angled supports. These are often found on timber structures rather than concrete pergolas. The shape of the column may have base surrounds of rings or pedestals depending on whether square or circular. The post or column may also arise simply from the ground level with its supporting foundation unseen below ground.
The clothed pergolas
The ‘clothed pergolas’ with all of the considerations above would support either awnings below the lateral beams or more usually elements above such as rush mats, fine slatted screens or what is most usual and common – plants. Having an awning or other inert see-through materials converts a pergola into a shade structure. The use of plants, particularly climbers and vines displays the pergola in its traditional functional form.
The placement of the climber is important. Obviously plants require a growing medium to provide the basic requirements of nutrients, along with sunlight, air and water. If the plant arises from ground level, either directly from the garden soil or a containerized source it requires a support to climb. Thus placement should be by a column or wall to reach the pergola beams above. Placement must also consider whether the entire structure is to be clothed or only part. The young plant may require to be assisted to the top. The climbers may twine or cling and the support should allow for this. It can be seen that the selection of type of climber should be made at an early stage.
Selection of plants for Pergolas
The plant may be heavy or light considering its weight. So while climbers of Congea tomentosa or some Jasminum species can be considerably heavy, other species of Jasmine can be very lightweight. There are several possible plants and selection is an important consideration based on many factors. Basic factors are appropriate selection for climate, soil type, light conditions and wind. Other practical factors may be whether the plant attracts particular insects, important in restaurants, or gives off pleasant scents or nasty odours.
Selection is made on many other factors. It is fashionable and useful to use edible plants contributing to urban agriculture – snake gourd, bitter gourd are pretty plants to use as climbers. Decisions based on bio-diversity, aesthetics, environment & well-being may be other considerations.
A climber may have less foliage, just barely covering the structure like a seductive covering while being integral with, yet expressive of, the pergola structure,. Full foliage or flowering Thunbergias may clothe the structure completely showing itself off rather than the supporting structure. Some plants may ‘drip’ through the open slats or laterals.
Hirsute climbers are to be avoided which may cause skin irritation. Thus while Mucuna on a pergola is a visual delight it may be a physical detriment. Mikania is considered invasive and aggressive, while Antigonon leptopus is pretty although aggressive. Jungle creepers will be appropriate depending on the environment such as clothing upper floor pergolas over balconies, such as at Heritance, Kandalama.
The choice of plants is vast but selection should be appropriate. The concept should indicate the basis for selection be it biodiversity, aesthetics or any other. Even a combination is possible.
Pergolas also provide support for accessories – Hanging pots, hanging awnings, mobiles which move with the wind and lighting fixtures find a place on a pergola.
Design – the important consideration
The most important consideration is not the pergola itself. It is the decision as to the necessity to have such a structure. Many factors then come to play. Function or purpose and placement initiate further decisions. A clever designer would be able to select just the right materials, pattern and proportions for a pergola, if required, to be seamlessly a part of the garden.
Professional in charge – Landscape Architecture
Chartered Architect / Chartered Landscape Architect
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