Measuring a House for an Exterior Repaint

Why this matters

An exterior bid is two different products sold on one page: siding, which is area and mostly material, and trim, which is length and mostly labor. Estimators who measure the whole house as one square-foot number end up pricing a plain ranch and a gingerbread Victorian of the same footprint the same way, and lose money on one of them. The measurement also sets the gallon order, so a missed gable or a forgotten bump-out shows up as a short order on the second day, not on paper. This card is the house-specific layer; the general method lives in The Measure and Takeoff Basics, and the triangle math in Area of Triangles, Gable Ends and Sloped Walls.

Measure from the ground, in three passes

Everything here can be taken from the ground with a measuring wheel, a laser, and a pitch gauge or phone level. Nobody climbs to measure for a bid; if a dimension truly cannot be read from below, estimate it from course counts and say so on the takeoff.

Pass 1, the footprint. Walk the foundation with a wheel and sketch every wall, bump-out, bay and chimney chase as you go. Write each length on the sketch, not on a list: a sketch shows the jog you forgot, a list does not.

Pass 2, the heights. For each wall, the height that matters is the painted siding: bottom edge of the siding to the underside of the soffit. A laser does it in one shot. Without one, count siding courses and multiply by the exposure, which you can measure on a course you can reach. Exposed foundation is a separate line if it gets painted, and left out if it does not.

Pass 3, the gables and the linear-foot items. Read the roof pitch at a rake with a pitch gauge, compute each gable's rise from it, then walk the house again for fascia, soffit, gutters, downspouts, corner boards and openings.

 PLAN, wall lines, two story
   +------------- 40 ft --------------+
   | eave side: fascia, soffit and    |
   | gutter, 42 lf with overhangs     |
 28 ft        perimeter            28 ft  <- gable ends
   |    2 x (40 + 28) = 136 ft        |
   +------------- 40 ft --------------+

 GABLE END ELEVATION, 28 ft wall
               /\
     rake     /  \     rake 18.0 lf each,
     fascia  /    \    4 rakes = 72 lf
            / 9.33 \   gable rise, 8 in 12
           /   ft   \
          +----------+  <- soffit line
          |  siding  |  18 ft, bottom of siding
          |  28 ft   |  to soffit: 36 courses
          +----------+  at 6 in exposure

Body area: perimeter times height, plus gables

For a house whose walls share a height, body area is perimeter x siding height. Where heights differ (a one-story wing, a walkout basement side, a sloping lot), measure each wall's height separately and add wall by wall; a sloping wall averages its two end heights.

Gables are triangles on top of the end walls: half the wall width times the rise. The rise comes from the pitch: on an 8 in 12 roof, the roof climbs 8 in for every 12 in of horizontal run, and the run to the ridge is half the wall width.

Openings

Deduct doors and windows at their size including casing, the same way the interior takeoff does, and count their trim separately. Some estimators skip window deductions to cover waste; if your shop does, do not also add a waste factor on the body, or the waste gets bought twice. Garage doors, large sliders and big picture windows always come out, because they are large enough to move the gallon count.

Trim is counted in linear feet, not area

Fascia, rake boards, soffit edges, corner boards, frieze boards, gutters and downspouts are long and narrow. Their area is small, so material barely moves, but every foot is ladder work with a brush, so labor scales with length. Count each item separately:

• Fascia: along the eaves, including the overhang past the gable wall, and up each rake. A rake board is longer than its horizontal run; compute it from run and rise or read it with the laser.
• Soffit: linear feet times the soffit depth gives an area for material; the length drives labor.
• Gutters and downspouts: linear feet, faces only unless the scope says inside the gutter.
• Corner boards: one per outside corner, length equal to the siding height there.
• Windows and doors: many shops count trim per unit (each window, each door) with a size class, because a casing, sill and apron is one job however you measure it.

Worked example: a two-story colonial

A rectangular two-story, 40 by 28 ft, smooth fiber-cement lap at a 6 in exposure, gables on the 28 ft ends, 8 in 12 roof, 1 ft overhangs at eaves and rakes. The siding height on all four walls is 18 ft: the estimator counts 36 courses from the bottom course to the soffit on the back wall, and 36 x 6 in = 216 in = 18 ft. The laser agrees.

Body walls. Perimeter 2 x (40 + 28) = 136 ft. Body = 136 x 18 = 2,448 sq ft.

Gables. Run to the ridge is 28 / 2 = 14 ft; rise = 14 x 8 / 12 = 9.33 ft. Each gable is 0.5 x 28 x 9.33 = 130.7 sq ft; two are 261 sq ft. Gross siding = 2,448 + 261 = 2,709 sq ft.

Openings. Sixteen windows at 3 by 5 ft = 240 sq ft; two entry doors at 3 by 6.67 = 20 sq ft each, 40. Total 280. Net siding = 2,709 - 280 = 2,429 sq ft.

Fascia. Each eave runs the 40 ft wall plus the 1 ft rake overhang at each end, 42 ft; two eaves are 84 lf. Each rake covers a horizontal run of 14 ft plus the 1 ft eave overhang, 15 ft, rising 15 x 8 / 12 = 10 ft over that run, so its length is the square root of (15 x 15 + 10 x 10) = the square root of 325 = 18.0 ft. Four rakes are 72 lf. Fascia total 84 + 72 = 156 lf.

Soffit. Eave soffit 84 lf at 1 ft deep, 84 sq ft. Gutters 84 lf along the eaves; downspouts four at 18 ft, 72 lf. Corner boards four at 18 ft, 72 lf. Openings 16 windows and 2 doors, counted per unit.

The takeoff that leaves the driveway reads: 2,429 sq ft of body, 156 lf fascia, 84 lf of 1 ft soffit, 84 lf gutter, 72 lf downspout, 72 lf corner board, 16 windows, 2 doors.

Two checks before it goes to the estimate. First, the gables are 261 of 2,709 gross sq ft, about 10 percent; an estimator who measured "perimeter times eave height" and stopped would have priced a tenth of the siding as free, and that tenth is the part needing the tallest ladder. Second, the trim list totals 156 + 84 + 84 + 72 + 72 = 468 lf before a single window, which on a two-story is days of ladder work that the body area does not reveal.

Where field measurements drift

• Height read to the wrong line. A laser shot to the gutter top instead of the soffit adds the fascia and gutter depth, often most of a foot, to every wall. On this colonial an extra 0.75 ft is 136 x 0.75 = 102 sq ft of phantom siding.
• The wheel rounding corners. A wheel run around the outside of shrubs reads long; one run tight to a bump-out reads short. Wheel each straight wall separately and add them, and check the sum against the opposite walls on a rectangle: front and back should agree, and so should the two ends.
• Course counts across a band. Many colonials have a frieze board or belly band between floors. Count courses above and below it separately and add the band's own height, or the count comes up a band short.
• Garage and porch faces. The wall behind a porch roof is still siding, usually a story lower than the rest; it is the face most often left off a sketch drawn from the street.

Texture and substrate change the material, not the measurement

Measure the same way on any siding; adjust the material afterwards.

• Rough-sawn wood, shakes and split-face block carry more true surface than the flat area, and drink more. If the data sheet gives a rough-surface spread rate, use it for those areas. If it does not, apply a shop allowance; 20 percent more material is a common starting point, to be tuned from your own reconciliations. Had this colonial been rough-sawn cedar, the body would be ordered as 2,429 x 1.20 = 2,915 sq ft of coverage.
• Lap siding's bottom edges are real surface that the flat measurement does not include, roughly one edge per course. On smooth lap the reconciliation history usually absorbs it; on deep-butt shakes it is worth noting.
• Mixed substrates (fiber-cement body, cedar trim, a stucco chimney chase) get measured as separate lines, because they may take different primers and different spread rates. See The Exterior Primer Map, Substrate by Substrate.

What changes the measurement method

• Hip roofs have no gables; the walls stop at the soffit, and the body is perimeter times height alone.
• Dormers are their own small walls and triangles, usually measured as count plus a typical size, priced for access.
• Porches and decks are separate scopes: ceilings in area, railings and balusters in linear feet or per section, floors in area.
• Sloping lots need each wall's height at both ends; a walkout side may be 24 ft tall at one corner and 18 at the other, averaging 21 ft across that wall.
• Pre-1978 houses get measured the same way, and the takeoff flags every surface where paint will be disturbed, because that work is RRP work and the area totals feed the 20 sq ft exterior threshold. See Lead Paint RRP Protocol Reference.

References

• See related: The Measure and Takeoff Basics
• See related: Area of Triangles, Gable Ends and Sloped Walls
• See related: The Exterior Primer Map, Substrate by Substrate
• See related: Lead Paint RRP Protocol Reference
• Coating manufacturer product data sheets for rough and smooth surface spread rates