Concrete and Framing Estimation in Construction

Estimating Concrete Volume in Slabs

• A 4in slab gets 80 square feet out of one yard of concrete.
• A 6in slab gets 50 square feet out of one yard of concrete.
• Memorizing these numbers allows for quick estimation on the job site.

Estimating Framing Material

• Lineal feet of wall multiplied by 1.2 gets you close to the number of studs needed.
• Pre-cut studs are a little more expensive but are handier.
• For plate stock, multiply the lineal feet of wall by 5, and then divide by 16 (assuming 16ft boards).

Calculating Roof Sheeting (Plywood)

• The steeper the roof, the greater the amount of roof sheeting needed.
• Use the hypotenuse of a triangle to calculate layout: A² + B² = C².
• For an 8/12 pitch, it takes about 14 1/12 inches of roof sheeting to cover one foot of horizontal distance.
• For a 4/12 pitch, it takes about 12 3/4 inches of roof sheeting to cover one foot of horizontal distance.
• For a 12/12 pitch, it takes about 17 inches of roof sheeting to cover one foot of horizontal distance.
• Don't forget to add 10-15% for waste due to cuts, overhangs, and other factors.

Using the Pythagorean Theorem

• A² + B² = C² describes the relationship between the sides of a right triangle.
• This formula can be used to calculate the exact length of a line or distance.
• Practice using this formula to improve your estimation skills.

Cutting Hip and Valley Rafters

• Memorize that the hip or valley rafter cut is always the pitch over 17, not 12.
• For example, if the common pitch is 6/12, the valley or rafter cuts are 6/17.
• This is derived from the secant function in trigonometry.

Bonus: Accounting for Waste

• Always provide 10-15% extra material for waste due to cuts, overhangs, and other factors.
• Keep the material clean and in good condition to return it for credit if needed.