Siding is ordered from an area, so the work is getting an honest area and then converting it to the unit you buy. Most of the judgment is in what to leave out.
Siding area = walls + gables and other area − large openings
With allowance = siding area × (1 + allowance)
Squares = with allowance ÷ 100 sq ft, rounded up
Cartons = with allowance ÷ coverage per carton, rounded up
Measuring the area
Add up the lengths of the walls that share a height and multiply by that height. Triangular gables and walls at other heights are measured separately and entered as added area. For a 120 ft run of 9 ft walls with 200 sq ft of gables the planner finds 1,280 sq ft.
Windows and doors
The installation manual cited below says windows and doors are not usually deducted, because leaving them in provides an allowance for waste, and that very large openings, such as a garage door, can be deducted. The planner follows that: it asks only for large openings, and a typical window or door stays in the wall area. The same house with and without a 112 sq ft garage door deducted:
| Openings | Net siding area | With 10% extra | Squares to buy |
|---|---|---|---|
| None deducted | 1,280 sq ft | 1,408 sq ft | 15 squares |
| Garage door deducted | 1,168 sq ft | 1,284.8 sq ft | 13 squares |
Whether to deduct a particular opening is your decision. The point is that the default is to leave ordinary openings in.
Squares or cartons
A square is 100 sq ft, and the planner rounds the area with its allowance up to whole squares: 14.08 squares, so the list says 15 squares. If your siding is sold in cartons, enter the installed coverage printed on the carton. With an example coverage of 200 sq ft per carton the same area is 7.04 cartons, which rounds to 8 cartons.
Worked example 120 ft of 9 ft walls plus 200 sq ft of gables, by the square, 10% extra
| Material | Calculated | Buy |
|---|---|---|
| Siding10% extra | 14.08 squares | 15 squares |
This example assumes
- 10% extra allowance, an editable planning default
- 200 sq ft per carton is an example: use the coverage on your carton
- A 112 sq ft garage door as the one large opening in the second row
What is not counted
Trim, J-channel, starter strip, corner posts, soffit and fascia are measured in linear feet and are separate. This estimates siding area only and says nothing about the wall behind it or how the siding is installed. For the unit itself, see what a square of siding is; for the same deduction question in a paint job, see whether to subtract doors and windows.
What changes the estimate?
- Gable and other added area
- Which openings are large enough to deduct
- The allowance for waste, which can be higher for complex walls
- Whether you order by the square or by the carton