Common quantity units for wood-framed projects are thousand board feet (MBF). A board foot is a volume of wood, 1 foot x 1 inch x 1 inch, or 144 cubic inches. Board-foot quantities are generally calculated using nominal material dimensions - dressed sizes are ignored.
Board foot per linear foot of any stick of lumber can be calculated by dividing the nominal cross-sectional area by 12. As an example, 2,000 lineal feet of 2 x 12 equates to 4 MBF by dividing the nominal area (2 x 12) by 12 which equals 2, and multiplying by 2,000 to give 4,000 board feet. This simple rule applies to all nominal dimensioned lumber.
Note that not all rough carpentry items are listed or noted in construction documents. Protective treads, inserts, and rails are examples of necessary but not listed items that the contractor must provide. The search for carpentry items must include roofing sections, wall sections, and all detail drawings.
Lumber - Lumber is a traded commodity and therefore is sensitive to supply and demand in the marketplace. Even in budgetary estimating of wood-framed projects, it is advisable to call local suppliers for the latest market pricing.
Treated Lumber - Treated lumber should always be used when the lumber will come in direct contact with concrete, masonry, or earth.
Bridging - Even when bridging is not shown on joist drawings, always include it, as it helps to distribute concentrated loads to the adjacent joists.
Blocking - One of the most overlooked areas of wood blocking is at roof edges. Almost always, a built-up roof or membrane roof system will require some sort of blocking and/or cant strip system.
Accessory Connector ItemsCommon to any wood-framed structure are the accessory connector items such as screws, nails, adhesives, hangers, connector plates, straps, angles, and hold-downs. For typical wood-framed buildings, such as residential projects, the aggregate total for these items can be significant, especially in areas where seismic loading is a concern. For floor and wall framing, the material cost is based on 10 to 25 lbs. per MBF. Hold-downs, hangers, and other connectors should be taken off by the piece.
Waste - Waste is an issue of concern at the quantity takeoff for any area of construction. Framing lumber is sold in even foot lengths, i.e. 10', 12', 14', 16' and depending on spans, wall heights, and the grade of lumber, waste is inevitable. A rule of thumb for lumber waste is 5%-10% depending upon material quality and the complexity of the framing.
Wood in various forms and shapes is used in many projects, even where the main structural framing is steel, concrete or masonry. Plywood as a back-up partition material and 2x boards used as blocking and cant strips around roof edges are two common examples. The estimator should ensure that the costs of all wood materials are included in the final estimate.
Short of time? Many lumber yards retain competent estimators who will provide material lists/estimates from your plans for little or no cost. This is also a good method for checking your own takeoff.
2011 Building Construction Cost Data Book
Thousands of unit costs for building components, arranged in the new CSI MasterFormat® 2010 classification system
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