CONSIDERATIONS OF SUSTAINABILITY IN HEAVY TIMBER CONSTRUCTION

In addition to the issues of sustainability of wood production and use that were raised in the previous chapter,  there are issues that pertain especially to heavy timber  frame construction:

It is wasteful to saw large, solid timbers from logs:
In most instances, only one or two timbers can be  obtained from a log, and it is often difficult to saw  smaller boards from the leftover slabs.

Glue-laminated timbers and composite timbers utilize  wood fiber much more efficiently than solid timbers.

Recycled timbers from demolished mills, factories,  and barns are often available. Most of these are  from old-growth forests in which trees grew slowly,  producing fine-grained, dense wood. As a result,  many have structural properties that are superior to  those of new-growth timbers. Recycled timbers may be  used as is, resurfaced to give them a new appearance,  or resawn into smaller members. However, they  often contain old metal fasteners. Unless these are  meticulously found and removed, they can damage  saw blades and planer knives, causing expensive mill shutdowns while repairs are made.

Continuous bending action of beams may be created  by splicing beams at points of inß ection rather than  over supports, as shown in Figures 4.15, 4.20 and 4.21.  This reduces maximum bending moments, allowing  timber sizes to be reduced substantially.

Timbers do not lose strength with age, although they  do sag progressively if they are overloaded. When a  heavy timber building is demolished at some time in the future, its timbers can be recycled, even if they  were obtained as recycled material for the building  that is being demolished.

A heavy timber frame enclosed with foam core  sandwich or stressed-skin panels is relatively airtight  and well insulated, with few thermal bridges. Heating  and cooling of the building will consume relatively  little energy.

The glues and finish coatings used with glue-laminated  timbers may give off gases such as formaldehyde that  can cause indoor air quality (IAQ) problems. It is  wise to determine in advance what glues and coatings  are to be used, and to avoid ones that may cause  IAQ problems.


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