Framing a House in Three Days: Optimization Is a Key Component

Arriving onsite at BCMC Build, framing an entire house in just three days looks like a daunting task. How did we do it? Obviously, using what we know best—structural building components. They are optimized to reduce the required time to frame a structure through labor and material efficiencies. They also, by definition, markedly reduce jobsite waste.

Labor

When designed and installed correctly, components can greatly reduce the time required to frame a structure. Arriving preassembled, components require less lumber on the jobsite to finish the construction process, which results in fewer connections. In the Framing the American Dream project, two identical houses were constructed simultaneously—one using stick framing and one using structural building components. Stick framing took 401 hours compared to 148 hours with components—63 percent less time! See Photo 1.

However, in order for those time savings to be realized, it is critical the components are placed on a square and level foundation. Further, they need to be designed and installed correctly, which is often easier than getting an ideal foundation. Without these conditions being met, it’s difficult for framers to gain the maximum benefit from using components.

In the case where components are not designed or installed correctly, it may actually increase the amount of time to frame a structure because of the needed modifications and potential redesign and reshipment of the components. Therefore, it is essential in the design process to ensure that components are designed from the framer’s perspective and that unbuildable plans are not created. If done properly, using components results in less labor than stick framing because less material needs to be assembled and connected, and the connections themselves are much less complicated.

Material

Trusses use triangulation, which optimizes the transfer of forces (compared to stick framing). Truss designers then optimize layouts to further reduce the number of trusses needed. This decreases the number of trusses that are built, and thus also the number of trusses that need to be installed on the jobsite. Less material also results in less dead load in the structure, which has a trickledown effect on the overall load the structure, and especially the foundation, has to resist. In order to evaluate exactly how much material is saved by using triangulation compared to stick framing, check out the subsequent analysis that was completed using the following parameters and assumptions:

Loading and deflection conditions:

• Top Chord / Rafter
  • Live Load = 20 psf (snow = 20 psf)
  • Dead Load = 10 psf
• Bottom Chord / Ceiling Joist
  • Live Load = 10 psf
  • Dead Load = 5 psf
• Roof Pitch = 6/12
• Deflection = L/240 (Live load deflection limit)
• Deflection = L/180 (Total load deflection limit)

Stick framing (rafter and ceiling) conditions:

• SP visually graded lumber design values using the SPIB effective date of June 1, 2013.
• Collar tie located ¹/₃ of the way down from the top of the rafter. (See section 4.7.6.1. of TER No. 1204-02)
• Collar tie spaced not more than 4' on center. (See section 4.7.6.1. of TER No. 1204-02)
• Rafter span is half the total span.
• Spans and on-center spacing obtained from Southern Pine Council span tables.

(Editor's Note: TER No. 1204-02 details the requirements for conventionally framed roofs and roof truss construction per IRC Section 802.)

Truss conditions:

• SP visually graded lumber design values using the SPIB effective date of June 1, 2013.
• Bearing condition: pin, roller, roller for the three span conditions.
• No repetitive member design factor is used due to larger on-center spacing, and to ensure a more apples-to-apples type comparison.
• Truss on-center spacing was optimized 1" at a time until the maximum allowable CSI was reached using standard industry truss design software.
• Top chord lumber sizes and grades for a particular span were selected based on the lumber sizes and grades of the rafters (per span tables).
• Bottom chord lumber sizes and grades for a particular span were selected based on the lumber sizes and grades of the ceiling joists (per span tables).

Additional assumptions:

The number of truss versus stick frame placements (i.e., instances of use) to achieve span was determined by dividing the length of the structure (same as the span) by the on-center spacing. The location of shear walls and end conditions was not evaluated to determine if additional instances would be required.

The goal of using these assumptions was to keep all the variables of design the same for both the trusses and the roof stick framing, and then only vary the spacing needed to resist the applied load. This provided, on an equivalency basis, the differences in the board footage used to resist identical assumed loads. See Figures 1 and 2 below.

Tables 1-4 provide the results of this analysis.

At a glance, it is easy to see the truss configuration is always able to achieve a better LF / SF ratio than the stick framing (rafter and ceiling joist) configuration. By utilizing triangulation, trusses have an optimal system to distribute forces. Through the truss design process, an optimized configuration of that system results in a lesser number of trusses needed to frame the same roof area, on an apples-to-apples basis.

On an equivalency basis, Table 4 illustrates clearly that trusses use significantly less lineal and overall board footage to frame the same roof area. One would then assume the speed of installation should be faster and the cost of lumber used should be less for the truss roof system.

It should be noted, the framing reality of applying the sheathing system over the trusses with a wider on-center spacing does potentially reduce the overall labor time savings. However, this approach is focused on an analysis that keeps all the variables the same except for truss or stick frame spacing. Effectively, it provides a good basis for evaluating the efficiencies that can be realized using trusses. It is up to the component manufacturer to decide how to take advantage of these inherent capabilities. 

Waste

Components also generate less waste than framing using traditional methods. Starting with fabrication, component manufacturers want to produce the most trusses from their lumber supply, and thus they optimize the amount of board feet they have available to produce the most trusses. Then, arriving preassembled, there is less required cutting and assembly onsite, which reduces the amount of scrap lumber, clean up time, costs for waste disposal, and promotes a safer jobsite. Furthermore, using wood components is environmentally responsible, since wood is the only renewable building material with nearly 5 million trees planted daily.

In the Framing the American Dream project, the house built with stick framing generated 17 yards of wood waste, while the house built with components only generated 4 yards—that’s less than a quarter of the waste created by stick framing.

Concluding Thoughts

We were able to frame an entire house in three days because we used structural building components. They were designed and installed correctly, which allowed us to benefit from using components and greatly reduce the amount of time needed to frame the house compared to traditional stick framing methods. In addition to the savings associated with labor costs, less material overall was used, which shows how components are able to maximize material utilization and reduce the amount of required lumber. The value engineering provided by components makes them environmentally responsible as well, since it ensures that the building industry gets more bang for their buck from the amount of raw material used to resist loads. Ultimately, through triangulation and the principles of engineering, components are able to more efficiently transfer forces than traditional stick framing, which reduces the amount of material, labor, waste, and thus the amount of time necessary to frame a structure.