Heavy timber framing has been very instrumental in the building and construction industry. Over the years wood beams have been utilized to span floors and roofs of buildings since the beginning of civilization. Historic roof timbers were put together with load bearing walls of masonry to construct public building structures and houses. Starting from Britain, the entire Europe and finally North America, carpenters used hand-hewn timbers to construct buildings by means of wood-to-wood connections (Pollard and Nikolaus, 710-711). Today, heavy timber construction using exterior concrete or masonry walls are regarded as Type 4 construction in building codes (Isaacs 1-12). The development and significance of heavy timber construction has thus grown. Therefore, this essay seeks to highlight the uniqueness of heavy timber framing and the reason why it has attained a relatively preferential treatment in building codes rather than light timber framing.
Uniqueness of heavy timber framing
The usefulness of heavy timber framing cannot be over-emphasized. For instance, at times of fire, heavy timber framing catches fire gradually and not spontaneously, like in the case with light timber. Again, heavy timber framing supports building load even following serious charring. Heavy timber receives relatively preferential treatment in building codes. For one reason, code recognizes the resistance properties of fire associated with heavy timber framing that is far much better than light wood framing.
Heavy timber framing can be sandblasted after normal fires and still remain in service following an average damage by fire. This is a better property compared to unprotected steel beam which would collapse following such normal fires. Heavy timber framing constructions are given specifications of timber sizes that are bare minimum (Isaacs 1-12). The edges of the heavy timber framing must however be chamfered to make the fire resistance capability better.
Precautions with heavy timber framing
There are some special sustainability considerations with respect to timber framing that need to be taken care of. One of them is wood shrinkage. When wood is subjected to huge amounts of contraction and expansion as a result of seasonal changes in the content of moisture, specifically in the perpendicular direction to the grain fiber direction, it can fail to serve the purpose it is intended for. Such effects should be minimized through good detailing (Bailey 25-34). Girders and beams should be left to shrink without making the roof and the floors to sag.
The support of heavy timber framing to masonry walls is highly advocated. The leading beam should be covered from decay owing to the seepage of moisture via the masonry walls. This is attained through leaving an airspace ventilation of about ½ inch between the beam sides and masonry. Another option would be treating the beam chemically to avert decay. Anchorage of the beam securely to the wall is paramount so that it is protected from being pulled away from the main wall in normal services. All the same, this should be in a position to freely rotate, without interfering with that part of the wall as would be the case in a fierce fire.
The manner in which attachment is done should make it possible for rotation of the anchorage in the case when the beam will fall apart due to damage caused by fire (Harris 23-45). The means of placing a cover on the roofs and the floors with good decking is highly recommended. The decking of floors should be covered using a finish floor comprising a nominal 1 inch thick boards that are tongue-and-grooved and laid perpendicular or may be diagonally to the structural decking or by way of using particle boards or plywood.
Resisting lateral loads
Buildings lateral bracing is also recommended. Building is usually braced against seismic and wind forces through the shear wall resistance, working along with the action of the diaphragm of the floor and roof decks. In the high seismic risk areas, the walls should be both reinforced horizontally and vertically, and the decks could have had to be well nailed or may be overlaid using plywood to augment the shear resistance. Buildings with exterior walls that are framed must be provided with shear panels or diagonal bracing (Bailey 25-34). The roof should be well supported to the entire building.
The structure of a heavy timber frame differs from that of a light frame as well as the connections of heavy timber framing differ from light framing ones. Generally, in timber-framed building construction, the roof weight and the entire building are supported and carried by the frame made of timber. In heavy timber framing, the structural timber frame is developed and designed to provide anchorage to the entire load (Pollard and Nikolaus, 710-711). With the light timber framing, the structure depends on the linings and cladding together with the framing to provide anchorage to the load. Heavy timber framing needs the supply of huge timber dimensions, placing higher demand on the available forests and eventually amounting to deforestation in case that new plantings are not made.
Timber connections and pressure as a result of loading has led to more effective methods of framing other than light timber framing. Heavy timber framing has made strong connections leading to the elimination of small timber pieces (Harris 23-45). The conventional braced framing applied the commonly known mortise and tenon connections as a means of creating a very rigid structure that is in a position to counteract the roof loading levels, the contents of the house, ambient factors like the wind and any impact on the house through accidental contact. For heavy timber framing and connections the end of the floor joists are held in position by keys-like joints set in between steady joists. Diagonal braces meant to keep the building strong and steady are also applied in heavy timber framing and connections. Connections are made as each of the timber pieces is cut cautiously into the neighboring piece.
The study of timber framing has been approached differently by both western and eastern specialists in framing. Taking a simple correlation, western approaches may not assemble the whole timber framing by piece. On the contrary, the eastern approach may not eliminate everything that is not forming part of the desired goal (Elpel 3-6). Nevertheless, by means of different methods these approaches achieve a similar aim and objective. The western approach could shape the frames the whole day as the eastern builders would meditate on the construction and make a strategic move in making the desired frame and connection.
In conclusion, owing to its high quality characteristics overriding light timber framing, heavy timber framing is unique. Fire-resistance capabilities for heavy timber framing are very high and, thus, give it an upper hand in the building and construction industry. The connections and load resistance capabilities of heavy timber framing offer a strong and rigid structure to make buildings more safe and secure.