Spruce-Pine-Fir (SPF) refers to White Spruce, Engelmann Spruce, Lodgepole Pine and Subalpine Fir, all having common characteristics and properties. SPF’s strength, light weight, ease of handling and woodworking properties has made it a popular wood for all types of framing applications in construction. SPF has great dimensional stability and strength making it a popular choice for pre-fabricated eco homes.