Estimating Your Needs
Figuring the amount of siding you will need to cover your house is usually just a matter of measuring exterior walls, calculating the square footage, and adjusting the resulting figures for waste. A easy way to do this is to divide the surfaces to be covered into rectangles, and calculate the area of each by multiplying its length by its width.

Add together all the areas you have computed. Then (except for sheet sidings, such as plywood), subtract the areas of windows, doors, chimneys, and other places the new siding will not cover. The result is approximately how many square feet of siding you need; add 10 percent for waste. If your house has steep angles at its gables or other features that will necessitate a lot of cutting, add another 15 percent to the total amount.

Be sure to take into account the overlap of most board sidings. It takes about 1,240 square feet of 8-inch horizontal bevel siding, for example, to cover 1,000 square feet of wall space. Manufacturers offer charts, based on their specific patterns, to help you estimate your needs.
Vinyl and aluminum sidings are usually sold by the number of square feet a given amount covers. When ordering, you must also estimate how many linear feet of various trim pieces you need.
Plywood and hardboard sheets are sold in sizes that correlate directly with square footage. Add 10 percent for normal waste and, if your house has sharply angled walls, another 15 percent for extra cutting.

Preparing the Walls
If you are siding over an existing wall that is flat and sound, you may be able to nail new siding directly over it. On the other hand, if the existing siding is metal, vinyl, or masonry, or is irregular, you must either strip it off or provide a nailing base of furring strips on top of it (click here for more information).

For siding removal, use a claw hammer and a flat prybar for prying, and a "cat's paw" and a pair of locking pliers for pulling nails. When removing most types of siding, start at the top and work your way down.

If you want to avoid marring the wood, use the cat's paw on the first board, and then use a prybar to pry up subsequent boards and pull the nails.

To remove shingles and shakes from a wall, insert a square-bottom shovel underneath them, lift them up, and pull them off, working from the top down on the wall. Pull out any remaining nails.

Removing stucco is hard work; if at all possible, apply new siding over the old surface. For an extensive removal job, call a demolition contractor.