Drywall and plaster takeoff

Drywall takes the partition on the face of framing, the stud face the board fastens to, where framers instead use the centerline. The run starts where the boards begin and stops where they end. Where a partition's board butts the finished face of another wall, the line stops there and the through-running wall keeps the continuous sheet, so the T-junction is counted once. This convention follows gypsum board application practice in ASTM C840 and the Gypsum Association GA-216.

Almost every interior partition is boarded on both faces, so the single length feeds twice the area: length times height times two. One-side conditions are the exception and must be identified: shaft and elevator walls, board over furring on an existing wall, area separation and party walls, and finishing only the exposed side of a chase. Openings are never taken out of the linear length, since plates and track, header and sill framing, and the board above and below an opening all still exist. The one exception is RICS NRM2, where the measured length excludes a void that runs the full height of the partition, such as a full-height door or glazed panel.

Drywall is measured gross over the wall, then qualifying openings are deducted from the area. Small openings are intentionally kept, because the scrap from cutting around the hole offsets the board the opening would have saved. The size at which deductions begin is the single biggest regional fork in the trade, and the two thresholds differ by roughly three times.

In North American practice the Gypsum Association convention deducts openings larger than one full 4 by 8 sheet, about 32 square feet, and ignores those of 32 square feet or less, so a standard door of roughly 21 square feet is not deducted. Under metric methods, RICS NRM2 section 28 finishings and section 20 proprietary linings and partitions, the cut point is the void rule: no deductions for voids not exceeding 1.00 square metre, about 10.76 square feet, so a normal door is deducted and a small window is not. Both are area rules, and neither shortens the linear length. The metric 1.00 square metre rule is the global default, with the 32 square foot figure applied as the regional convention in the United States and Canada. Net measurement is the basis everywhere; the metric regime is strictly net, deducting every void over 1.00 square metre.

Two assembly attributes multiply the work without changing the measured area: the level of joint finishing and the number of board layers per face. Both are attached to a surface as a factor, not a quantity change. GA-214, mirrored in ASTM C840, defines six finish levels, 0 through 5. They run from no treatment at Level 0, through tape and successive coats, to Level 4, the most common finish and the right default, with two additional joint coats, additional fastener coats, and a smooth sanded surface for flat paint. Level 5 adds a full-surface skim coat for gloss finishes and severe lighting. The level multiplies finishing labor and joint compound, not the board area.

Single layer per face is the default. Fire-rated and acoustically rated assemblies, such as corridor, demising, shaft, and stair walls, commonly carry two layers per face, with the base layer typically taped only and the face layer fully finished. Layer count multiplies board, screws, and outer-layer finishing, and each distinct wall type is taken as a separate run even on the same plan line, so a two-hour corridor wall at two layers each side is four times the base area. Layer count is driven by the assembly specification, not by region.

Corner bead protects outside corners only and is taken in linear feet as the count of outside vertical corners times the wall height, plus horizontal beads at soffits and bulkheads; inside corners take tape, not bead. Joint tape scales with board area and joint density, a common rule of thumb being about 38 linear feet per 100 square feet of board. Control and expansion joints follow the maximum spacings in ASTM C840, restated by the Association of the Wall and Ceiling Industry. On walls and furring, a control joint is required at any uninterrupted plane exceeding 30 feet. Ceilings have two cases: with perimeter relief detailed, joints at 50 feet on center each way and the area between joints not exceeding 2,500 square feet; without perimeter relief, the common case, joints at 30 feet on center each way and the area not exceeding 900 square feet, so the no-relief ceiling triggers far sooner and both cases must be carried.

Furring, resilient, and hat channel are a linear quantity derived from the boarded area and the channel spacing, commonly 16 or 24 inches on center, with edge and perimeter channel added; the spacing follows ASTM C840 and ASTM C841, and resilient channel is typically one side only. Screws are derived from board area at the ASTM C840 fastener spacing, closer at edges: roughly 12 inches on center in the field for ceilings and 16 inches for walls, with the maxima varying by single versus multi-layer and by fastening method.

Board count is net area divided by sheet coverage. A 4 by 8 sheet covers 32 square feet, a 4 by 10 covers 40, and a 4 by 12 covers 48, with 54-inch-wide board available for tall walls. These coverage figures are arithmetic, while the choice of sheet size is a craft decision: larger sheets reduce butt joints, so commercial work often uses 4 by 12 and residential often 4 by 8. Metric regions use 1200 mm wide plasterboard in lengths from 2400 to 3600 mm, the same size classes in square metres.

A gypsum ceiling is measured to the interior finished face of the perimeter walls, the same plan boundary as the net floor, bridging straight across doorways. A flat ceiling's plan polygon is its true area; a sloped, vaulted, or cathedral ceiling is flagged for the slope factor, where the true area equals the plan area times the square root of the rise over run squared plus one, and is never priced as a flat projection. Soffits and dropped bulkheads add three surfaces, not one: a reduced main ceiling, the soffit underside, and the vertical drop faces, which are the commonly missed quantity. Light fixtures, diffusers, and sprinklers are not deducted.

Net board area is grossed up for scrap, breakage, and offcuts before ordering, commonly about 10 percent for simple open rooms, 12 percent as a standard figure, and 12 to 15 percent for cut-heavy work with many corners, openings, or soffits. Joint compound scales with both area and finish level, a Level 5 skim coat using far more than a Level 1 tape-only finish, rather than a single per-square-foot number. Waste applies to the material, the sheet count, never to the measured boundary.

Lath and plaster uses the same boundaries and the same regional opening rules as board, since plaster is taken to the finished face; only the material and labor scaling changes. Lath, the plaster substrate, is taken by area to the board-face boundary and ordered by weight class: diamond-mesh expanded metal lath at 2.5 or 3.4 pounds per square yard, with rib lath for open soffits and spans. Interior lathing and furring to receive gypsum plaster follows ASTM C841, and metal lath for portland cement plaster follows ASTM C1063.

Plaster over metal lath is a three-coat system. Under ASTM C926 the basecoat is built up from a 3/8 inch scratch coat and a 3/8 inch brown coat to a nominal 3/4 inch, plus a finish coat; two-coat plaster is used over solid and masonry bases. Interior gypsum plaster follows ASTM C842, where the full thickness depends on the base: about 3/4 inch over metal lath, about 1/2 inch over gypsum lath, and about 5/8 inch over masonry or monolithic concrete, each plus the finish. Thickness does not change the measured area; it drives material volume, which is area times thickness.

Portland cement plaster, stucco, carries linear accessories required by ASTM C1063, each measured in linear feet: a weep screed as a continuous run along the base of framed walls a minimum distance above grade; corner reinforcement at external and internal corners, taken as the corner count times the height; and casing beads and control joints at terminations and openings. Lath and plaster carry higher waste than board, on the order of 5 to 10 percent or more for lath, and about 15 percent for plaster from scratch-coat keys, mixing loss, and thickness overrun.

The reporting unit follows the region's measurement system. United States practice reports board area in square feet, often grouped per 1,000 square feet for pricing, and rounds material up to whole sheets. Metric standard method practice reports area to two decimal places in square metres and orders whole boards. Plaster was historically taken in square yards, dividing square feet by nine, and that legacy unit still appears in older specifications. Procurement always rounds material up to whole units.

The same surface yields different reportable quantities by purpose. A bid estimate, a progress billing, and cost control use the net measured area. Procurement grosses that net up to whole sheets at the chosen coverage plus a waste percentage and rounds accessories to stock lengths, so the ordering quantity is always at or above the net. Reporting the ordering quantity as the bid over-bills, and reporting the net as the order under-buys.

Exayard reads the drawings and applies these rules automatically, tracing each partition on the face of framing by wall type, cutting out the openings that cross the chosen deduction threshold, applying the slope factor and soffit faces on ceilings, and converting the net result into sheets, compound, tape, bead, control joints, and fasteners for the region in use.