|
 |
The use of Southern Pine lumber can result in significant material and cost savings for component manufacturers. To demonstrate this, the Southern Pine Council asked a third-party consulting company1 to formulate a direct comparison between Southern Pine and another lumber species. A component manufacturer2 ran the comparison for a typical construction project, an actual townhome development called Victory Lakes in Prince William County, Virginia3. One set of designs used Southern Pine lumber. An identical design used Spruce-Pine-Fir. The truss designs were optimized based on the truss manufacturer's typical design and manufacturing process4.
The Victory Lakes townhome designs with Southern Pine used 14% less total lumber board footage and required 39% less total square inches of truss plates overall compared to the same designs with Spruce-Pine-Fir (See Figures 6 and 7).
The use of Southern Pine netted a cost savings of 26% for a typical roof truss design, and a cost savings of 12% for a typical floor truss design (See Figure 8). The overall cost savings using Southern Pine was 18%. These results are based on lumber costs for both species of $400 per thousand board feet, and truss plate costs of $0.70 per pound. Cost savings will vary depending on a component manufacturer's actual raw material costs.
This comparison demonstrates the superior performance of Southern Pine for roof and floor trusses, and how component manufacturers that choose strong Southern Pine lumber as their preferred raw material can realize significant cost savings.
The following discussion provides details on the design comparison for Victory Lakes townhomes, typical three-story townhome construction. Figures 9 and 10 show truss placement diagrams, while Figures 11 through 14 illustrate critical information from the truss design drawings.
The floor truss comparisons are shown in Figures 9, 13, and 14. Figure 9 shows a standard floor truss layout for the second floor of a townhome unit, highlighting two primary floor trusses — a common floor truss and a girder truss. Species comparisons of the truss design details for these two primary floor trusses are shown in Figures 13 and 14.
The roof truss comparisons are shown in Figures 10, 11, and 12. Figure 10 shows a standard roof truss layout for an interior townhome unit, highlighting two primary roof trusses — a vaulted truss and a flat truss. Species comparisons of the truss design details for these two primary roof trusses are shown in Figures 11 and 12.
Figure 11 provides design details for Truss T1A, the vaulted roof truss. The first truss in Figure 11 is designed exclusively with Southern Pine (SP or SYP for Southern Yellow Pine) lumber, while the second truss is designed exclusively with Spruce-Pine-Fir (SPF). Note the SPF roof truss requires two additional webs, plus double top chords for the top center panels and the right heel panel. In addition, the SPF truss requires significantly larger plates.
Figure 12 provides design details for Truss T1, the flat roof truss. The first truss in Figure 12 is designed exclusively with Southern Pine chord and web lumber except for four webs where SPF was the optimal lumber choice due to the low lumber design stresses required to carry the axial forces. The second truss is designed exclusively with SPF. Note the SPF roof truss requires two additional webs, plus a double top chord for the right heel panel. In addition, the SPF truss requires significantly larger plates.
Figure 13 provides design details for Truss J1, the common floor truss. The first truss in Figure 13 is designed exclusively with Southern Pine lumber, while the second truss is designed exclusively with SPF. Note the SPF floor truss requires a double bottom chord in addition to significantly larger plates.
Figure 14 provides design details for Truss J1A, the girder floor truss carrying a heavy concentrated load. The first truss in Figure 14 is designed exclusively with Southern Pine lumber, while the second truss is designed exclusively with SPF. Note the SPF floor truss requires a double top chord and triple bottom chord, as compared to a single top chord and double bottom chord for Southern Pine. In addition, Southern Pine's high strength and stiffness allows a chase opening which is not possible with the SPF truss. Finally, the SPF truss requires significantly larger plates.
Footnote:
1. Qualtim, Inc. — Madison, Wisconsin
2. Shelter Systems Limited — Westminster, Maryland
3. Miller and Smith Homes, Inc. — McLean, Virginia
4. In this specific case, the component manufacturer minimizes their lumber inventory by keeping only 8' to 16' lengths in two grades for each species.
For SPF, they use No.2 for chord material and Stud grade for web material to yield the most favorable costs.
For Southern Pine, they use Dense Select Structural and No.2 as their two lumber grades.
|
|
Previous
