TMBR_WIKI

simplified mass timber research

As mass timber continues to grow in popularity, so too does the amount of information. This website is a prototype to provide designers a platform for simplified timber research. Allowing those wanting to utilize timber to easily make informed decisions early in the design process.

MASS TIMBER RULES OF THUMB

Outlined below are rules of thumb for 6 major categories that influence mass timber projects. It is important to be aware of the parameters that can influence your projects so that one can design more consciously in the beginning, rather than having to make major corrections when it comes time to prepare your project for construction. These rules of thumb are intended to make more informed decisions during preliminary design, ultimately making the following design development and construction document phase easier later on.

Within the 6 major categories; manufacturing, transportation, assembly, structure, fire and acoustics. There are 3 sub-categories ( or 'systems') for mass timber which include 1D, 2D and 3D systems.

manufacturing

The process of making / fabricating timber elements to be utilized in construction. It is important to note that there are general constraints and processes for timber manufacturing that one should be aware of as it can influence the overall feasibility and aesthetics of a project. It is also very helpful to be aware of CNC practices and how the tools used can dictate the form

Learn more about manufacturing

  • Typical Beam Depths: 114mm - 2128mm
  • Typical Beam Width: 365mm
    • However, if a greater width is desired, then it can be manufactured in 50mm increments, i.e. 415mm, 465mm, etc... Members then become exponentially more expensive
  • The length is determined by the desired span from the designer. However, it is important to also take transportation and assembly rules of thumb into consideration when determining the length of beam.
  • Typical Depth of CLT for commercial and educational projects: 500mmmm
  • The typical total depth of Assembly: 60mm-215mm.
    This includes insulation, raised floor system, etc.
  • Typical Width: 3500mm Maximum
  • Typical Length: 16500mm Maximum
  • Typically CLT panels with a depth from 60mm100mm consist of 3-layers
  • Where as CLT panels with a depth from 120mm180mm consist of 5-layers.
  • Note that CLT panels are always comprised of an odd number of layers.
  • In order to attain its structural properties, CLT panels always need to have an odd number of layers. i.e) 3-Layers, 5-Layers, 7-Layers, etc...
  • H = Height: ±3000mmmm typ.
  • The width is Dependent on transportation and assembly rules of thumb
  • Length: 16500mm Maximum
  • Note that the 2D manufacturing of CLT panels also has an influence on the dimensionality of 3D modules.
  • Within the ‘wet’ module, the red represents finishing for wet conditions and below the ceiling CLT member is a drop ceiling for mechanical installations. Alternatively this can be located against one of the walls of the module or in the raised floor system

transportation

Once you have decided the sizing and the process of making your timber components. How do you get them to your project site? It is important to know the constraints of transportation as it will further influence the sizing of components which may in turn influence the overall aesthetics of your project.

Note that these rules of thumb are currently based off of Ontario Standards.

learn more about transportation

  • Transporting a 1D system is most cost effective if they are stacked regularly and compactly with no wasted space and no requirements for wide or long loads
  • The same rule applies to 2D panels as well.
  • To ensure transportation is most effective, prefabricated members should be as typical as possible, avoiding custom or one -off members
  • Transport Sizes with no additional requirements:
    • H = Maximum Height: 4m
    • W = Maximum Width: 2.55m
    • L = Length of Rigid lorries: 12m
  • Transport Sizes if there is an escort vehicle on Urban and country roads:
    • H = Maximum Height: 4m
    • W = Maximum Width: 3m
    • L = Length of Articulated Lorries: 16.5m
  • Transport Sizes if there is a Police escort vehicle on Urban and country roads:
    • H = Maximum Height: 4m
    • W = Maximum Width: 3.5m
    • L = Length of Road Trains: 18.75m
  • Transportation of 3D modules follows the same size conditions as 2D systems. However, since 3D modules contain a lot of dead space within themselves while being transported, as opposed to stack panels, beams and columns. Depending on the size of the 3D module, the more trips are required to bring everything to site, affecting overall construction time. However, this is to be balanced with assembly rules of thumb.

assembly

The sizing of the parts have been chosen based off of manufacturing and transportation parameters, but what about assembling those components on site? Assembly rules of thumb provide ideas on how to design components so that timber construction can be as optimized as possible.

learn more about assembly

  • Try to use standard sizing for all components wherever possible in order to simplify on site assembly, resulting in faster construction.
  • Requires simple lifting equipment.
  • Simplify connection details bet ween elements.
  • Typically uses wrap around straps for beams.
  • The large format components enable a fast assembly and ensure the building is well braced
  • Avoid custom sizes or one-off cuts to ensure fast construction.
  • Depending on the final design. The pick points used to life the panels into place may be exposed. The designer should then take this into consideration into the final design.
  • However, if the facade and other final finishing are completed on site, then these pick point will be hidden within the assembly.
  • The larger the modules, the more cost-effective this structure will be.
  • In some cases, the ceiling can be completely omitted from the module so that when stacked, the underside of the floor becomes the ceiling. The same idea can be applied to the walls of the module. i.e) Two 3m wide modules come together to create a 6m room.
  • It is ideal to separate ‘wet’ modules from ‘dry’ modules to increase construction speed.
  • • To optimize the use of the factory setting, integration of technical installation can increase on site construction speed.

structure

It is important to note that a CLT solution that is 4 storey’s or less would use more CLT than required. Therefore it is recommended to go 5 storey’s or higher when proposing an engineered timber project that utilizes CLT. However, this is purely from an optimization perspective.

Another aspect of timber structures is that mass timber structures prefer to be stacked, avoiding cantilevers and 'transfer slab' like conditions although it can be done.

Note that the following rules of thumb are geared towards educational and commercial mass timber buildings
Learn more about timber structures

  • Glulam Beam Depth calculation for Office/ Education Program:
    • One can use the calculation L/16 = D to determine the depth of a beam. Where L = the span in millimeters
  • One can use the calculation L/47 = D to determine the thickness of a panel.
    • Where L = the span in millimeters
  • For determining spans of 3D modules, it is recommended to reference the rules of thumb for 2D Spans as well as 2D manufacturing and transportation to ensure an easy combination of 2D and 3D systems
  • For 3D modules, use 2D rule of thumb to calculate for the floor panel first
  • To determine the ‘ceiling’ depth of a CLT panel in a 3D Module:
  • The ceiling panel is typically ±25% thinner than that of the CLT Floor panel in a residential module

fire

In the case of educational typologies, typically a fire rating of 30 - 60 minutes is required. Of ten time, educational buildings will also add sprinkler installations to help improve their fire rating. For the purposes of combining residential and educational typologies, a fire rating of 60min or greater will be attained.
Learn more about fire

  • As a result of Glue laminated timber being rarely used in multi-storey residential units, there are no specific fire rules of thumb for this condition. As stated previously, it is recommended to utilize 2D, 3D or a combination of both for residential units.
  • The required corridors and staircases must be kept free of fire loads by means of paneling with non-combustible cladding.
  • If the ceiling and floor are made of visible wood, the walls should be paneled with a noncombustible material, or if t wo walls are not lined, then either the ceiling or floor may be made of visible timber
  • In principle, increased requirements for fire resistance can be compensated by the following measures:
    • Increase the thickness of the CLT element
    • Increase the number of layers of the CLT element
    • Clad CLT member with fire rated gypsum board
  • For 3D systems, follow the rules of thumb stated for 2D systems. However, for 3D systems:
    • The double stacking of CLT panels increases the fire resistance rating of the project
    • Resulting in the potential for thinner CLT Panels
  • Important to keep in mind of the double stacking of floor to ceiling and wall to wall

acoustics

For acoustic rules of thumb, the research was based on German context as it currently has the highest level of sound requirements for residential typologies. Resulting in these requirements becoming the typical rules of thumb for projects going forward to attain the most optimum acoustic conditions.

It is important to note that impact sound can be understood as the sound generated from foot fall, moving furniture or anything that makes direct contact with a floor slab that in turn generates sound. While airborne sound is generated from things like conversation, music and other audible sources and it has a significant impact on flanking.

Flanking sound is an essential consideration and should be addressed through detailing of components by providing acoustical breaks where timber members meet and should be considered for 1D, 2D, and 3D systems. Subsequently, there are two methods to minimize this which include, vibration damping using flanking transmission barriers and separate inner cladding of load-bearing elements.

learn more about acoustics

  • Mitigating impact sound as much as possible with assembly
  • Use of acoustic breaks
  • Accommodating for Airborne sound is achieved through the infill of insulation between members
  • Utilizing acoustic tiles or drop ceiling in a beam system
  • For 2D systems, in both residential and educational typologies it is imperative that the detailing of CLT panels takes flanking into consideration during the design. To mitigate this, there must be an acoustical break bet ween CLT panel members. Typically 5mm-10mm thick.
  • On average, 2D floor assemblies utilize 7mm30mm of impact sound insulation in addition to thermal insulation
  • Providing an airspace bet ween the wall finish and the CLT member helps to mitigate impact and airborne sound reverberations
  • 3D module provides the opportunity to develop airtight details
  • Use of insulation to separate modules
  • Acoustic breaks/ seals where modules connect to mitigate impact sound
  • Double stacking of CLT walls helps to improve the acoustical rating

MASS TIMBER RESOURCES:

The following list has proven to be extremely beneficial when researching the application of timber in architectural projects: