An Estimators Guide to Frame Take-Off in Australia

If you're new to the world of building estimation, fear not! We've got you covered with this step-by-step guide on frame take-offs. Whether you're an experienced estimator or just starting out, this guide will give you the basics you need to get started.

A frame take-off is a critical part of the building design and construction process. Essentially, it involves estimating the amount and size of timber members required to construct a building frame. So, let's take a look at the frame take-off process from an estimator's point of view.

The level of detail portrayed in this example is based on first principle estimating.  Presently, this distinctive method of conducting quantity surveying and estimation is dwindling, as numerous companies opt for pre-established templates, averages, or guesswork instead of meticulously calculating individual components.  The method outlined below has been prepared by Pekaj Group Pty Ltd. a Melbourne based quantity surveying and estimation service firm who specialise in residential construction.

Understanding the Building Codes

If you're planning a construction project in Australia, it's crucial to understand the building codes that regulate the industry. The National Construction Code (NCC) is a comprehensive set of guidelines that outlines the minimum standards for construction across the country, including Victoria. The NCC includes the Building Code of Australia (BCA), which covers specific requirements for building design and construction.

When it comes to timber framing, the AS1684 standard provides guidance on design and installation. By following these codes and standards, you can ensure that your construction project is safe, sustainable, and compliant with Australian regulations.

Understanding the Materials

Building a new structure can be an exciting time, but it's important to remember that the process can be quite involved. Before any construction begins, careful planning is required to ensure the success of the project. One critical step in this process is reviewing the building plans and identifying the frame components that need to be measured.

Typically, this information can be found within the engineering plans. The plans will state or list the sizes that should be used on the specified project. This is essential information to have, as it will guide the carpenter in the measurement process.

In most cases, roof trusses will be prefabricated and delivered to the site for the carpenter to install. However, unless the walls are ordered prefabricated, they will need to be measured manually. This is where a carpenter, or in this case, an estimator, earns their keep.

There are several components that need to be measured to complete the frame take-off, including.

• Plates (Ribbon, Top & Bottom)
• Studs (Common, Jamb and Jack)
• Junctions (External and Internal)
• Header/Ledger and Sill Trimmer
• Temp Bracing
• Noggings
• Lintels based on window and door openings
• Bracing (Plywood, Speed, Angle or Hoop Iron)
• Bolts, screws and ancillaries

Figure 1.  Framing Members - Floor, Wall and Ceiling as per AS1684

Plates

To accurately determine the appropriate plate length for each wall, it is necessary to measure the timber walls. All walls require top plates, including those over openings, while bottom plates are required for all walls except those with door openings.  

If trusses do not sit directly over a stud, a ribbon plate is necessary to simplify the carpenter's task and avoid potential difficulties arising from roof design or underlying structures. The ribbon plate also prevents the bottom chord of the truss from resting on internal walls, which would render the truss ineffective. It is important to note that the external walls provide the load-bearing capacity of the structure, and as such, there is no ribbon plate required for the internal walls unless load bearing.

When consulting the example below, take note of the pink line to indicate external walls (top and bottom plates), and the blue line for internal walls (top and bottom plates).

Figure 2.  External and Internal Plates

The measurements attained from the aforementioned example include:

External Wall: 67.35m (Pink) - deducted garage door opening for bottom plate.

Internal Wall: 95.30m (Blue) - no deductions for internal doors.

Plates are commonly provided by suppliers in lengths of either 5400mm or 6000mm. In this case, we will be using the 5400mm length to compute the overall material required. If you desire to understand the size of the wall plates for a single or double storey, the span tables in AS1684 can guide you through the basics. Nevertheless, it is important to note that this information should be included in the engineering plans.  Since the wall frames measure 90mm, the chosen material for the construction will be 90 x 45 MGP10.

Figure 3.  Top and Bottom Plates

To ascertain the necessary number of plates, the ensuing computations are necessary:

Thus, to complete this project, a minimum of 81 plates measuring 90 x 45 MGP10 in size and spanning 5400mm in length (equivalent to 437.40m) are necessary.

Studs

The primary element of a timber frame is the stud, positioned between the top and bottom plates, studs are evenly spaced to ensure strength and endurance for walls, window frames and even doors. Essentially, they serve as the groundwork of the timber frame, regulating and safeguarding the integrity of your home while providing effective lateral support.

Typically, timber wall frames are made up of either 70mm or 90mm depths, with stud thicknesses of 35mm or 45mm. The choice of stud thickness and spacing, which usually falls between 450mm to 600mm, depends on the load requirements (concrete tiled or metal roof). A variety of studs are necessary to complete the wall frame, such as the common stud, jamb stud, secondary jamb stud (supports lintel above window) and jack stud.

The common stud is a vertical member that bears the weight of the structure and transfers loads vertically to the bottom plates. Jamb studs are positioned immediately adjacent to an opening, and thus they bear a greater portion of the load than a common stud. Jack studs are shorter studs that are cut down to fit above and or below an opening.

To make the following calculations, we will assume a wall height of 2700mm and a stud spacing of 600mm for both internal and external walls.  It is common practice for builders to use 90 x 45 MGP10 for external walls with 450mm stud spacings and 90 x 35 MGP10 for internal walls with 600mm stud spacings.  However, for the purposes of this example, we will be using 90 x 45 MGP10 for both internal and external walls.

Thus, to finish the frame, a total of 469 studs measuring 90 x 45 MGP10 and spanning 2700mm in length (equivalent to 1266.30m) are necessary.

It could be argued by some that certain aspects of construction, such as the jack studs or junctions, may lack sufficient material. In theory, this assertion could be true, and it will be necessary to rely on feedback from carpenters and trial and error in future projects to correct any deficiencies.

Numerous skilled carpenters would confirm that after studs are cut, the leftover pieces are often not suitable for reuse as studs and are typically cut down further for blocking or temporary bracing purposes. So, you always have to be weary if your stud count is adequate and as no two jobs are build the same.

Figure 4.  External Junctions

Figure 5.  Internal Junctions

Figure 6.  Jamb Studs (Window and Door Openings)

Ledger / Header and Sill Trimmers

Header and sill trimmers are used above and below windows and above door openings to support the jack studs. Typically, window trimmers shall be same size and grade as the common studs up to openings of 2400mm as per AS1684, for bigger windows you may need to increase the trimmer size, but it is advisable to consult with an engineer for any specific guidelines or instructions.

Figure 7.  Ledger /Header and Sill Trimmers

Based on the calculations above, we obtained measurements of 42.70m for external windows and doors and 15.60m for internal door openings. As a result, the total length required is (42.70 + 15.60) / 5.40 = 64.10m, which is equivalent to 12 lengths of 90 x 45 MGP10 measuring 5400mm in length.

Temporary Bracing

Temporary bracing provides stability to the timber frame during the construction process, preventing it from collapsing due to wind loads, accidental impact, or uneven loading during construction. This type of bracing is necessary to distribute the lateral loads that the frame is subjected to during construction, ensuring that the frame remains plumb and square. In addition, temporary bracing maintains the integrity of the timber frame by holding pre-fabricated and on-site elements together until permanent connections can be made. This ensures that the frame remains stable and secure during the building process, safeguarding the safety of workers on site.

To ensure accurate estimation, it is necessary to allocate a specific amount of material for temporary bracing until the roof trusses are securely installed. For a typical 200m2 single storey project, approximately 10 pieces of 5400mm in length would be required. It is recommended to use the same size material, specifically 90 x 45 MGP10, to prevent breakage.

Therefore, in this case allow 10 lengths of 90 x 45 MGP10 measuring 5400mm in length.

Noggins

Noggings are a critical component in timber-framed construction and play an important role in ensuring the stability and strength of a building. According to AS1684, the Australian Standard for timber-framed construction, noggings are horizontal pieces of timber that are installed between the vertical studs in a wall frame. They serve to provide lateral support to the studs, preventing them from buckling or twisting under load, and help to distribute loads more evenly across the frame.

Noggings also help to maintain the correct spacing between studs, ensuring that the frame is dimensionally stable, and that fixtures and fittings can be securely attached. Without noggings, a timber-framed structure may not meet the required performance standards for strength and stability and could be more susceptible to damage from external forces such as wind, earthquakes, or heavy loads.

Wall studs must have continuous rows of noggings, which can be located either on flat or on edge, at maximum 1350mm centres, wherever necessary. The noggings do not require stress grading. Unless stated otherwise, the minimum size of nogging must be 25mm thick and 25mm less than the depth of the stud.

Common nogging sizing is 70 x 35mm Merch Pine for walls up to 2700mm high.  For walls over 2700mm high it is recommended to allow for 2 rows of noggings.

In order to determine the number of noggins required, we add the external and internal walls together (67.35 + 95.30) = 162.65m and then divide by 5.4 meters.  Resulting in 31 lengths of 70 x 35 Merch Pine.  

Subtracting the measurements of the window and door openings can further reduce the answer, but it's not recommended since the leftover material may be needed for other purposes, such as completing the frame or securing the structure.

Lintels

According to AS 1684, a timber lintel is necessary over an opening in a load-bearing wall to provide structural support and distribute the weight of the building above. The lintel acts as a beam, transferring the weight of the wall above the opening to the supports on either side. Without a lintel, the wall above the opening would be unsupported, leading to structural failure and potentially causing damage or injury.

Timber lintels are commonly used because they are strong, readily available, and can be easily cut to size and shape on-site. It is important to follow AS 1684 guidelines to ensure that the lintel is designed and installed correctly, and that it is able to support the load it is intended to carry.

According to AS1684, the minimum overhang for a timber lintel should be at least 50mm on each end. This means that the lintel should extend at least 50mm beyond the edge of the supporting wall on either side.

When estimating the size of lintels, whether made of timber or steel, it's customary to round up to the next incremental size, which is typically 300mm. For example, if your opening measures 950mm wide, you would order a lintel that is 1200mm long and then cut it down to the correct size on site.  

In case the engineering drawings don't specify the lintel sizes, you have two options: you can refer to AS1684 to determine the appropriate sizes, or you can discuss with a carpenter who can suggest some of the commonly used sizes for standard openings. However, if the lintel is longer than 3600mm, it will require engineering.

Bracing

Plywood and metal are two common types of bracing materials used in timber-framed buildings, and they both have their own unique advantages and limitations.

Plywood bracing is often used because it is a cost-effective and readily available material. It can be easily cut to size and shape, and it can be installed quickly. However, it is not as strong as other bracing materials and may need to be thicker to provide the required level of resistance.

Metal bracing, on the other hand, is highly durable and strong, making it ideal for buildings in high-wind or earthquake-prone areas. It is also resistant to moisture and can be installed in a variety of configurations to suit different building designs. However, it is often more expensive than plywood and may require specialist installation.

Regardless of the type of bracing used, it is essential to follow the guidelines set out in AS1684 to ensure that the bracing is installed correctly and provides the required level of stability. Failure to do so can result in structural failure, which can have severe consequences for the building and its occupants.  If you are unsure where bracing is required consult an engineer or an experienced carpenter on site.

Figure 8.  Bracing

Bolts and Screws

In building construction, bolts, screws, and straps play a critical role in ensuring the structural integrity and safety of a timber frame structure and as such should be included in the estimate.  Typically, estimators will allocate a dollar allowance (ranging from $250 to $500 per floor) for carpenters to purchase the appropriate types of fasteners and joist hangers required for the project. If uncertain about where to place these elements, it is advisable to visit a job site at the framing stage to observe their placement.

Conclusion

If you have managed to read through this entire passage, you deserve a round of applause. Framing and concrete work are the most intricate and time-consuming areas for most estimators, demanding meticulous attention to detail as they constitute a significant portion of the total project cost.  Hopefully this guide is useful in better understanding the life of carpenters and estimators alike when tackling a frame take-off.