India has a long and rich history of use of timber across various regions of the country. Historic timber structures, as defined in the Wood Committee’s Principles
The short and robust variety of timber found in India is generally sourced from deciduous trees found in all regions of the country except the north, northeast and Himalayan ranges where a softer variety of timber is found. In areas where access to timber was limited, its usage has been restricted to decorative elements, reserved for the buildings of royalty and rich merchant classes
Historic timber structures were often constructed of old growth indigenous timber and the scarcity of quality timber and lack of tradesmen with traditional carpentry skills pose challenges to timber heritage conservation in India
The International Wood Committee’s Principles states that the preservation of historic timber structures starts in the forest and thus it establishes a link between cultural heritage preservation and the conservation and sustainable use of forest resources
- CONSTRUCTION QUALITIES OF TIMBER
Factors that influence the properties and longevity of timber include the growing condition of the tree, the way the wood is cut, the seasoning method, its use and surface finishes (e.g. axed vs. sawn surface, the application of protective coatings)
The following are some properties that qualify wood as a versatile building material:
- Wood has great strength to weight relationship.
- Timber has relatively good compression, tension, bending and torsion strengths.
- It can provide long spans with single pieces or can be built up with systems of bits.
- It can provide a total structural mechanism or can be part of a combined system.
- It is relatively easy to mend or add to the timber structure.
- It can be manipulated with precision cutting for structure and ornamentation.
- Wood can be driven into the ground for displacement and skin friction piles.
- It can be nailed and glued as per requirement.
- Timber considerably dampens the effects of impacts, vibrations and noises and does not easily chip and small scale denting can be ‘ironed-out’.
- Wood has longevity comparable with stone and brick and generally better than soil.
- STRUCTURAL USE OF TIMBER
Timber, in India, has been extensively used in roofing, especially in the timber rich southern parts of the Peninsula and is still much in use in the west coastal regions, right from Kerala to Konkan
Wood is the only one of the common traditional building materials that consistently comes in long lengths – promoting its use for monolithic posts, plates, beams, braces, struts and planks. When shaped and jointed or glued the lengths together form frames and trusses
- DECAY OF TIMBER
Wood as an organic material may decay and degrade rapidly compared to stone, brick or other major historic building materials, as a result of moisture, fungi, insect attack or fire.
- Wood, being an organic material, is actively affected by relative humidity, which causes it to expand and contract. These result in organic decay of the timber caused by fungi resulting in dry rot, wet rot, heart rot, brown rot, insects like beetles and termites, and marine borers
- Defects in wooden structural members, whether at the joints or elsewhere, are more critical to a structure’s load-bearing capacity than other primary building materials
(Larsen & Marstein, 2016).
- Timber decay is usually caused by a common set of conditions (e.g. moisture, insects, ultraviolet [UV]), but decay manifests itself in different ways due to variable factors such as timber species and site conditions
- Other risks such as natural disasters, fire, vandalism and theft are also factors of deterioration.
- Building extensions or modifications that block off ventilation could result in the rapid deterioration of original building fabric
- Issues such as changes in use, redundancy of buildings due to socio-economic developments, the use of substitute modern materials in repairs, and appropriate interpretation/ reconstruction approaches also affect the structural integrity of timber structures
- Often roof is the most distressed part of any heritage building in India and depleting roof maintenance skills add to this broad issue. Decay is more pronounced and difficult to address in abandoned historic buildings with no human activity. Extreme fluctuations in temperature and moisture lead to alterations in the moisture and oil content within timber, further accelerating its decay
- ECOLOGICAL APPROACH OF TIMBER PRESERVATION
Whenever historic timber structures are repaired, some decayed and damaged parts must be replaced by new timbers. Nowadays, the quantity of replacement timbers is minimized as much as possible, but it is indispensable to replace timbers to some extent. In order to secure future supply of replacement timbers, saving forests is of urgent importance. Therefore, protecting cultural property buildings and saving forest reserves are closely linked
One should look at the possibility of preserving or repairing a timber structure using techniques and construction technology which correspond to those used originally. This also includes the use of the traditional dressing tools or machinery
An ecological approach to timber conservation is one which has its roots in respect for the crafts and craftsmanship is required for the preservation of timber structures. Larsen and Marstein recommend that preservation work or repair of historic timber structures should be duplicated, as far as this is possible, the choices that previous generation made, out of respect for their insight, wisdom and knowledge
- When replacement of a member in a timber structure is necessary, replacement timber of the same species of wood and of a similar quality should be used;
- Tools and techniques identical or similar to those used by previous generations of craftsmen to convert and dress the timber and to assemble the various members should be used.
The reason for this approach is that it is the insight, wisdom and knowledge of previous generations as represented in the structure handed down to us, that constitute the authentic historic document. Only in cases where the original choices have not proved to be durable or sustainable should we opt for modern solutions
- REPAIR OF TIMBER STRUCTURES
New building materials have gradually replaced wood where the material has demanded labor intensive maintenance, such as on roofs and foundations
Traditional methods of repair of timber buildings presuppose
- The availability of timber of the same species, grading and scantling as the old, decayed timber which is to be replaced;
- That forest owners are interested in keeping forest reserves with old-growth, ‘mature’ trees;
- The availability of craftsmen, in particular carpenters who are familiar with the handling of traditional tools; and
- The availability of traditional tools.
Physical defects in timber can be verified using a set of Non Destructive Tests (NDTs) using an experienced specialist. Globally used non-destructive tests for timber include
- Visual inspection and species identification
- Pin driving and screw withdrawal method
- Stress wave and ultrasound methods
- Ultrasonic Pulse Velocity (UPV)
- Resistance drilling
- Digital radioscopy
Most factors that cause wood to deteriorate can be effectively controlled or eliminated. The fundamental principle is to minimize contact with water, as this would eliminate fungal attack and significantly minimize opportunities for insect infestation. This is commonly achieved by applying surface treatment such as paint, oil and tar
The guiding principle is to “do as much as necessary but as little as possible”. Non-invasive, reversible techniques are favored
- Repair of the local failures (of members, units and connections) is the first step to be taken.
- Second step is to ensure the stability of the structure by means of shoring, loosening the connections and reducing the displacements.
- If the timber is partly damaged or decayed, as in the end of the joists, beams, columns, struts, purlins, they can be reused on site by metal capping or even providing new timber using different types of joinery available for taking different types of loading patterns, such as, compression, tension, sheer, bending or torsion. Replacement of timber is best done with recycled timber from dismantled buildings as it would be the best selected timber at that time and assuredly well-seasoned too
- The integration of the bracings or the application of a systematic bracing is generally fundamental to prevent further displacements and deformations.
- Lastly, the replaced timber has to be treated against potential termite attack and other agents of decay before being placed in the building
Various circumstances might arise during the repair which affects the success of conservation work. Change of ownership may diminish the sense of attachment to and responsibility for the property; a change of function may result in misuse, or the ageing of the residents could mean that maintenance and repairs become neglected. In consideration of such possibilities, routine maintenance work should be conscientiously enforced
 ICOMOS (International Council on Monuments and Sites) is an international non-governmental organization of professionals, dedicated to the conservation of the world's historic monuments and sites.
 In general, timber performs remarkably well within the Indian sub-continent. This is partly attributed to the climatic conditions prevailing in most of the countries that are conducive to its growth. Most parts of India do not undergo as severe a wet and dry cycle as seen in other parts of the world. The predominance of a hot and arid type of climate ensures the longevity of timber in the plains and deserts while the perennially wet and humid coastline also maintains a constant environment for timber to thrive in
 In the southern states of Kerala and Tamil Nadu, timber, particularly in the form of coconut palm wood, is available in abundance and is used widely in construction
 Widely used in the coastal states, such as Kerala, coastal and south interior Karnataka, parts of Tamil Nadu and Andhra Pradesh, it continues to be an integral part of the building vocabulary in some of these areas, particularly, Kerala. In Andhra Pradesh, one can find widespread usage of Burma teak that was brought in through British trading posts along the sea. The architectural language of the vernacular in the Central Provinces, namely Madhya Pradesh and Chhattisgarh, as well the north-east and the Himalayan belt have evolved around the extensive use of timber
 The word “dhajji” has its roots in the old Farsi word for ‘patchwork quilt’, for which this traditional building technique bears a great likeness with its latticework of timber frames filled in with earth or stone masonry. Dhajji construction has also proven its earthquake resistance over the centuries in Northern India and Pakistan
 The constructions built in the seismic areas are generally made according to a few principles selected over the time by practice, these are appropriate geometry of the building, may be symmetry of the shape, a larger and heavier ground floor in comparison with the upper ones, presence of connecting members in every principal direction, efficient but ductile connections, bracings in the horizontal and, more, in all the vertical planes; good sizing and strength, of course, is a fundamental requisite
 A big difference between stone and wood is the time-dimension in the ageing process. The ageing and deterioration of wood is more rapid and is also of another character than that of stone: in stone, the deterioration moves from the outside towards the inside; in wood, decay and deterioration caused by fungi and insects may start from within and move outwards
 While preservation primarily prevents further deterioration and retains an object in its found condition, restoration aims to reinstate a significant aspect of an object, which may be desirable to enhance an understanding or appreciation of an object.
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