How to Estimate Materials for Additions

Rough Construction

• 1

  Multiply the width by the length to determine the total floor area of your addition in square feet. Call your local concrete supplier to get an estimate in cubic feet of how much your foundation will cost.

• 2

  Determine the total square footage of the walls for the addition. Measure the length of all planned outside walls. Multiply the total length by the height of the walls to determine the total square footage of wall area.

• 3

  Determine how many studs you will need. Measure the length of each wall in feet and multiply it by 12 to get the total length in inches. Since vertical wall studs are placed 16 inches apart, divide the total number of inches by 16. This will tell you how many studs you will need.

• 4

  Estimate how many studs you will need for bottom and top plates of walls. Dimensional lumber comes in lengths from 6 feet to 16 feet. Determine the best lengths and how many are needed to complete the walls for your project. Plan to buy the longest studs available to fit your walls. Two layers of studs are necessary to create a top plate.

• 5

  Repeat steps 1 through 3 for each room, subtracting the lumber for outside walls and adding three 8-foot studs for each door.

• 6

  Add the total number of studs together. Contact your local building supply store or go to its website to determine lumber pricing. Multiply the total number of studs by the cost per unit to determine the total lumber cost.

• 7

  Multiply height times length of each wall to get square footage. Add the total square feet of all walls. Find the cost of drywall in your area. Drywall sheets are typically 32 square feet. Divide the square footage of the walls by 32. Multiply that number by the cost per drywall sheet.

• 8

  Estimate the amount of insulation you will need. Shop around for the best price on insulation that fits your needs, and add that cost to the total.

• 9

  Follow steps 1 through 6 to determine roof costs, eliminating bottom and top plates, adding lumber for a ridge pole and replacing drywall with oriented strand board.

• 10

  Estimate wiring costs. Wiring comes in rolls of varying length. Ask the contractors' department of your local supplier for information on local electrical codes to determine how much wiring and how many outlets and wall switches you will need.

• 11

  Determine a ballpark amount of fasteners, such as nails, screws, drywall mortar, drywall tape and staples. Add the costs of each to get a total.

Finishes

• 12

  Visit your supplier in person to select finishes such as flooring, paint, doors, cabinets, appliances and hardware. Get the cost per unit for your desired finishes. Choosing your finishes in person helps ensure that they will be exactly what you want.

• 13

  Choose your flooring. To estimate how much the flooring will cost, multiply the price per square foot by the number of square feet to be covered.

• 14

  Select your cabinets. To determine the cost of cabinets, multiply the price per linear foot by the length of the cabinets. Do the same for counter tops. Add in the price of hardware for each cabinet.

• 15

  Pick out doors. Multiply the cost per door by the number of doors you will need.

• 16

  Continue multiplying cost by quantity for each interior finish item you will need.

• 17

  Select your exterior siding. Multiply the square footage of the exterior walls by the cost per square feet for siding. Follow the same process for roofing material, including roof felt and shingles.

Totals

• 18

  Get bids from three contractors for each aspect of the construction, such as electrical, carpentry and finishes. Choose a contractor that fits your budget. Make sure to check references before signing a contract.

• 19

  Total up the costs of all materials to get the subtotal. Figure the amount of tax you will have to pay on this amount, and add it to your subtotal to get the total cost of materials.

• 20

  Add together the cost of materials, the contractor fees, permit and delivery fees and inspection charges to get the final estimate for the project.