A1: Structural form and function
Timber is a versatile building material that has been used for centuries as a structural material. Solid timber is widely used in domestic housing but engineered products are also widely available (used mainly for engineering solutions in many buildings); products include laminated veneer lumber (LVL), parallel strand lumber, glulam, I beams, box beams, steel web beams and numerous board materials such as plywood, chip board, fibre board and orientated strand board (OSB).
The many products available give the engineer the versatility to design unique timber structures capable of meeting the client's requirements (e.g. safety, cost, functionality, fire performance, durability and aesthetic appeal). Structural forms and concepts are dictated by end use, space requirements and cost. At the preliminary design stage there are many criteria to be considered.
- Space division
- In-plan organisation
- Water supply
- Waste removal
- Fire protection
- Surrounding properties
- Dead load
- Live load
- Ground conditions
The building shape is influenced by many factors including how it fits into its surroundings, the creativity of the designer, its functionality, the economics of construction and its capability to meet the structural requirements.Timber used structurally must be strength graded by qualified personnel under the supervision of an accredited certification body such as the National Standards Authority of Ireland (NSAI) or the Timber Research and Development Association (TRADA). Timber is usually strength graded in the dry state with a moisture content of approximately 20% but its moisture content, treatment (perhaps with preservative or flame retardant) and finish (planed or sawn) can be further specified by the designer. Timber can be an efficient structural material as well as durable, fire resistant, environmentally friendly and aesthetically pleasing.
Solid timber is widely used in domestic housing mainly for roof rafter, trussed rafters, ceiling joists, purlins and floor joists. Timber frame construction has become increasingly popular in Ireland due to its thermal efficiency, rapid construction times, cost and its environmental image. Traditional timber frame construction is almost identical to masonry construction, essentially the only difference being the inner leaf of the external wall being constructed mainly of timber. The thermal insulation is contained within the external wall inner leaf and is protected and sheltered from the cavity and therefore performs extremely well. Timber frame is a system that can be designed to easily give increased performance in sound, fire and thermal parameters.
Engineered wood products, the most common ones probably being glulam, LVL, parallel strand lumber and I-beams are used in a wide range of building types; apartments, offices, factories, shopping centres, sports halls as well as housing. The engineering of the timber enhances the performance of the timber and maximises its use. Glulam can be made in almost any size and is capable of carrying heavy loads and spanning large distances. LVL and parallel strand lumber tend to go into products such as I-beams or to be used as part of an I-beam floor system. I-beams and similar engineered systems are increasingly being used especially in timber frame buildings in apartments and housing. Refer to building regulations for thermal performance.