Siding takeoff from aerial imagery: how to calculate siding square footage without a ladder

Roof takeoffs went remote years ago, because a roof is the one surface an overhead image sees perfectly. Siding is harder for exactly the opposite reason: walls are vertical, and a top-down photograph shows you almost none of them.

You can still get most of the way there, because the two hardest inputs for a siding takeoff — perimeter and gable widths — are derived from the roof and footprint, which aerial imagery does capture precisely.

The arithmetic

Wall area breaks into two parts, and both come off measurements you can take remotely.

Rectangular wall area

Perimeter × wall height. The building footprint gives you perimeter directly. Wall height is the one figure that needs a human: storey count from street imagery, then roughly 9–10 feet per storey including the floor assembly, or your local norm.

Gable triangles

Each gable end adds a triangle: ½ × width × height. Width is the building dimension, which you have. Height comes from the roof pitch: height = (width ÷ 2) × (rise ÷ 12). A 30 ft wide gable at a 6/12 pitch is 15 × 0.5 = 7.5 ft tall, so 112.5 sq ft of extra wall per gable.

Openings: subtract less than you think

The usual convention is to subtract only openings larger than about 30 sq ft — garage doors, sliding doors, picture windows. Standard windows are left in.

That is not sloppiness. Siding around a window generates offcuts that cannot be used elsewhere, plus trim work that costs labour, so the material you “saved” largely evaporates. Deducting every window produces a takeoff that is arithmetically tidy and short on site.

Waste factor

• 10% — simple rectangular elevation, few corners
• 15% — multiple corners, dormers, or more than two gables
• 20% — lap siding on a cut-up elevation, or anything with a strong pattern to match

A worked example

A 40 × 30 ft two-storey house, 6/12 pitch, gables on the two short ends, one 16 ft garage door:

• Perimeter: (40 + 30) × 2 = 140 ft
• Wall height: 2 storeys × 9.5 ft = 19 ft
• Rectangular area: 140 × 19 = 2,660 sq ft
• Gables: 2 × (½ × 30 × 7.5) = 225 sq ft
• Less garage door (16 × 7): −112 sq ft
• Subtotal: 2,773 sq ft, plus 15% waste = 3,189 sq ft

Every input there except wall height came from the footprint and the roof — both measurable from an aerial in seconds.

What still needs eyes on the building

• Substrate condition. Rot behind the existing cladding is not visible from anywhere but arm's length.
• Existing siding type, which decides removal and disposal cost — and whether asbestos testing applies on an older property.
• Obstructions: meters, service entries, AC units, decks that have to come off or be worked around.

Why bother

The same address lookup that produces a roof number produces the footprint, perimeter and pitch a siding takeoff needs. If you already quote roofs remotely, siding is mostly a second rate card — and it lets you answer “can you do the siding too?” with a number instead of another appointment.