Siding is ordered by the square — 100 square feet — and bought in cartons of vinyl panels or in fiber cement planks, and the makers do not agree on the one thing that changes the order most: what to do about the doors and windows.
- Vinyl makers leave them in. The Vinyl Siding Institute’s installation manual says windows and doors are “not usually deducted”, because counting them gives an allowance for waste; its worksheet, like CertainTeed’s, takes off half of a large opening such as a garage door or a sliding door, and then adds 10 per cent to every material. A carton of double 4 inch or double 5 inch panels covers two squares.
- James Hardie takes them out. Its HardiePlank chart counts 12-foot planks on the wall area less the openings, and leaves waste out. The page counts each plank as its length times the exposure you choose, which is what the chart’s figures are; Hardie gives no figure for waste, so the 10 per cent the page starts from is its own.
Walls are length times height, and a gable end is half its width times its height. The trim runs along the edges: starter strip around the base, J-channel round the doors and windows and up the rakes, and a corner post down every corner, in the 12 ft 6 in and 10 ft lengths CertainTeed sells them. House wrap covers every wall, openings and all, in DuPont’s 9 × 150 ft rolls laid with the laps DuPont asks for, and the fasteners come by weight, by the institute’s rule.
While the siding is off is the time to fill empty wall cavities, ENERGY STAR says — the page hands the walls to the insulation calculator.