How to be 100% confident your frames and trusses are code compliant
Radiata pine varies in strength and stiffness, which means the timber used in the skeleton of a house needs to be carefully selected to ensure it meets building code standards. The same careful selection process is even more critical when it comes to the fixings and connectors.
The NZ building code sets out specific engineering standards for timber framing and trusses, based on established load calculations and formulas.
There is a range of fixed loads, forces, and variables that are taken into consideration. A lot of these depend on the exact location of the home and the purpose of the building, for example a farm shed versus a family home. Regional wind loads, snow loads and seismic activity, are all part of the equation.
Basic engineering considerations
When designing frames and trusses, here’s a summary of the key factors:
- Permanent action (dead load)
- Imposed action (live load)
- Static liquid pressure
- Ground water
- Rainwater ponding
The main timber properties used to calculate load factors are:
- Stiffness determines the span capability of a piece of timber.
- Strength and stiffness for timber are related, so a species which is stiff enough will generally also be strong enough.
- Treatment. To meet Building Code requirements for durability, treated timber is used for framing in most circumstances.
The super-strength truss
The inherent strength of trusses comes from their shape. The triangular design helps to evenly distribute the loads on the framing.
Designing and engineering trusses is an exacting science, and there are many factors to consider. For instance, the truss connections (type and capacity) need to be specified for:
- Connection to the loadbearing structure
- Connections between trusses such as girder and truncated trusses
- Lateral support to give stability to the trusses
Check the BTL
All of this information should be provided in the design statement issued by the accredited fabricator via the production of a Buildable Truss Layout (BTL).
The BTL details roof bracing, tie downs, and important truss-to-truss and truss-to-frame connections that are critical components in the completed truss and building system.
MiTek Trusses are designed to meet building code engineering standards, but just to be sure, they build in an extra safety margin for added security.
The Mitek Gang-Nail™ Truss System has a proven track record and is accepted by all building authorities.
The right connections
When pieces of timber are put together in a frame or truss design, the structural stress can be greatest at critical load transfer points (where the timber is joined).
MiTek® supports truss and frame manufactures by providing engineering software to accurately detail timber frame construction in line with the New Zealand Building Code. So you can feel fully confident that the frames and trusses you’re installing are 100% up to code.
To find out more about timber frame engineering, download the MiTek NZ Training App. It contains product installation details, tutorials and a simple video overview of timber engineering in plain speak.