Siding and Cladding: Measure Your Project and Order the Right Quantity

Understanding Siding and Cladding Units

Siding and cladding materials are typically sold by the linear foot (LF) or by the square foot (SF), depending on the product and profile. It is essential to confirm the unit of measure for the specific product you intend to use before beginning your calculations. Linear footage usually applies to individual boards of a consistent width, while square footage often applies to panels or systems where the width is integrated into the coverage area.

When dealing with linear foot products, the quoted length often refers to the nominal length, and actual usable lengths may vary slightly or require trimming. Always clarify the actual dimensions and usable lengths when ordering to avoid surprises on site. For square foot products, the manufacturer will typically provide a coverage area per piece or bundle, which accounts for any necessary overlap or joint details.

Step 1: Measure Your Wall Surfaces

Begin by accurately measuring all wall surfaces that will receive siding or cladding. For each distinct wall section, measure its width and height. Note down these dimensions. If a wall has varying heights, such as a gable end, break it down into simpler geometric shapes (rectangles, triangles) and measure each one individually.

Crucially, measure the actual surfaces to be clad. Do not rely on architectural drawings alone, as field conditions can differ. Account for all openings like windows and doors. While you will subtract these areas later, it's often useful to calculate the gross area first, then net out the openings.

Step 2: Calculate Gross Area and Subtract Openings

Multiply the width by the height for each rectangular or square wall section to get its area in square feet. For triangular sections (like gables), use the formula (base x height) / 2. Sum these individual areas to get the total gross square footage of all surfaces to be clad.

Next, measure the width and height of all windows, doors, and other openings within these walls. Calculate the area of each opening and sum them to find the total area of openings. Subtract this total opening area from your total gross wall area to arrive at the net square footage requiring cladding. This net area is your starting point for material quantity.

For example, a wall measuring 20 feet wide by 10 feet high has a gross area of 200 square feet. If this wall has a window that is 4 feet wide by 5 feet high (20 square feet) and a door that is 3 feet wide by 7 feet high (21 square feet), the total opening area is 41 square feet. The net area to be clad is 200 - 41 = 159 square feet.

Step 3: Account for Profile Overlap and Waste Factor

Many siding and cladding profiles, especially those installed horizontally, feature an overlap that reduces the effective coverage per board. For example, a board advertised as 6 inches wide might only provide 5 inches of exposed face once installed. Always refer to the product specifications for the 'effective coverage' or 'exposed face' width. Use this effective coverage in your calculations.

A critical step is to add a waste factor to your net material quantity. Waste accounts for cuts around openings, mitered corners, damaged pieces, and mistakes. A typical waste factor ranges from 10% to 20%, but this can vary based on the complexity of the project, the profile of the material, and the installer's experience.

Consider a simple rectangular wall section measuring 10 feet wide by 8 feet high (80 square feet net area). If using a siding board with an effective coverage of 5.5 inches (0.458 feet), you would need 80 square feet / 0.458 feet = 174.67 linear feet of exposed width. If boards are sold in 16-foot lengths, you'd calculate how many boards are needed to cover this linear footage, considering cuts and waste. For a 15% waste factor, you would multiply your net quantity by 1.15 to get your adjusted quantity.

Worked Example: Calculating Siding for a Small Wall

Let's calculate the quantity for a small accent wall using a thermally modified Ayous cladding profile, which has an effective coverage of 5.5 inches (0.458 feet) and is typically supplied in 8-foot lengths.

Project dimensions:

Wall A: 12 feet wide x 9 feet high

Window 1 (in Wall A): 3 feet wide x 4 feet high

1. Calculate Gross Area for Wall A: 12 ft x 9 ft = 108 SF

2. Calculate Area of Openings: Window 1: 3 ft x 4 ft = 12 SF

3. Calculate Net Area to be Clad: 108 SF - 12 SF = 96 SF

4. Convert Net Area to Linear Footage based on effective coverage: 96 SF / 0.458 ft (5.5 inches) = 209.61 LF

5. Apply Waste Factor: For this project, we'll use a 15% waste factor due to window cuts and potential end trimming. 209.61 LF x 1.15 = 241.05 LF.

6. Determine Number of Boards: Since boards are supplied in 8-foot lengths, we need 241.05 LF / 8 LF/board = 30.13 boards. Always round up to the nearest whole board. So, you would need to order 31 boards of 8-foot thermally modified Ayous cladding.

This calculation assumes a horizontal installation. Vertical installations may have different waste considerations, especially with longer runs.

Considering Specific Profiles and Installation

Different siding and cladding profiles, such as tongue-and-groove, shiplap, or board-and-batten, will affect your quantity calculations. Tongue-and-groove and shiplap often have a clear effective coverage. Board-and-batten requires calculating both the wider boards and the narrower battens separately.

Rainscreen systems, which create a ventilation gap behind the cladding, do not alter the cladding quantity calculation itself, but they do require additional materials for the furring strips and other components of the assembly. Always consult the manufacturer's installation guidelines for specific profiles, as these often detail recommended spacing and cutting practices that can influence waste.

For Maximo Accoya and various thermally modified wood options, or Norx composite cladding, specific milling and available lengths may vary. Confirm these details when requesting a quote to ensure your calculations are based on the actual product you will receive.

Before you order

• Confirm the unit of measure (LF or SF) for your chosen siding/cladding product.
• Measure all wall surfaces (width and height) accurately, including gables.
• Measure all openings (windows, doors, vents) within those surfaces.
• Calculate the gross area of each wall section.
• Calculate the area of each opening.
• Subtract total opening area from total gross wall area to get net area.
• Identify the 'effective coverage' or 'exposed face' width from product specifications.
• Convert net area to linear footage if applicable, using effective coverage.
• Determine an appropriate waste factor (10-20% is common, adjust for complexity).
• Multiply net quantity by (1 + waste factor percentage) to get adjusted quantity.
• Divide adjusted linear footage by available board lengths and round up to the nearest whole board.
• Consider ordering a few extra pieces for future repairs or unexpected issues.

Confirm installation details, approved uses and warranty terms in the current instructions for the exact product and profile. Your installer should verify the substrate, structure and applicable project requirements.

Questions to help you decide

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