Estimating how much siding you'll need to complete your project can be confusing when you're trying to figure out where you'll have waste and where you'll need to order extra. Vinyl siding comes in 12-foot-long strips that are about 1 foot wide, depending upon the style. A box of vinyl siding will cover a larger square feet area on the rectangular side of a house, where the walls are straight, than it will on a gable.
A box of vinyl siding contains two "squares." A square in construction lingo equals 100 square feet, so a box of vinyl siding will cover 200 square feet. That's only a starting point, however. Houses are not smooth rectangles. They contain windows, doors and gables, which alter the amount of coverage you'll get from a single box of vinyl siding.
Areas of Waste
Gables are the biggest areas of waste because the ends of each siding strip must be cut on an angle. When you're estimating vinyl siding for a gable, a general rule is to multiply the width by the height of the gable and then multiply that number by 0.75. For instance, if your gable is 12 feet wide and 12 feet high at the peak, you would multiply 12 times 12 for a total of 144. Then, you would multiply 144 by 0.75, giving you 108. Estimate 108 square feet of siding for that gable. You would need a little more than one box of vinyl siding to do two gables of this size.
Buying Vinyl Siding
Lumberyards and do-it-yourself-type centers usually stock the most common types of vinyl siding. If you're not picky about color or lap width, you can purchase the number of boxes you think you'll need to side your house and then buy a few extra pieces from an open box. If you want a custom color or style, however, the lumberyard will have to order it, and it's unlikely that you can buy a few extra pieces. You'll have to order another full box. Returns work on the same principle. If you open a box of custom vinyl siding, and use only one piece, you probably can't return what's left over. If you have a few pieces of common stock vinyl left over, however, the lumberyard might take them back.
Adjusting for Windows and Doors
When you're estimating how much siding you'll need, the natural tendency is to subtract the square foot area for windows and doors. Unless you have a lot of large picture windows or patio doors, however, just figure the square feet without subtracting for one or two small windows or a standard door. This gives you a little leeway in case you make a cutting error during installation.
Siding contractors typically install vinyl siding strips so the ones closest to the front of the house overlap the ones farther away. This reduces the visibility of the siding seams. For prominent walls less than 12 feet wide, you may want to install whole pieces to eliminate seams. For instance, if the wall is 10 feet wide, you might want to figure it as if it were 12 feet wide, if you don't want seams.