How to Calculate Treehouse Siding in Five Simple Steps

Treehouse siding in one line

Treehouse siding is simple: wall perimeter, times wall height, divided by the sheet size, plus waste, rounded up. A 10 ft by 8 ft treehouse with 6 ft walls is 36 ft of perimeter and 216 square feet of wall — 6.75 sheets exact at 32 square feet per sheet, 8 sheets with 10% waste. The rest of this guide is about getting those inputs honest: the length, the width, the height, and the sheet size.

Step 1: Measure the treehouse, length and width

Measure the treehouse in feet, length and width, on the outside of the wall frame, since siding covers the outside, not the inside. The worked example is 10 ft long and 8 ft wide. Measure each side where the wall will actually run, not where the platform extends past it: a platform overhang is deck, not wall, and siding bought for the platform over-orders. If the treehouse is not a rectangle, measure each wall separately and add the wall areas.

Step 2: Work out the wall perimeter

Add the length and the width and double the sum, since siding runs around all four walls, not across one side. The example is 2 times 10 plus 8, or 36 ft of perimeter. Every foot added to the length adds 2 ft of perimeter, since the length appears on two opposite walls, and the same holds for the width: a foot wider is another 2 ft of perimeter, or 12 square feet of wall at 6 ft high.

Step 3: Multiply perimeter by wall height for the wall area

Multiply the perimeter by the wall height for the wall area, since every foot of perimeter carries a full strip of wall that high. The example is 36 times 6, or 216 square feet. Measure the height from the platform to the top of the wall, not to the roof peak: the gable triangle above the wall is not wall area, and a height read to the peak over-orders. If the walls are different heights, work out each wall separately and add the areas.

Step 4: Divide by the sheet size for the exact count

Divide the wall area by the sheet size for the exact count, since sheets are sold by the sheet and cover a fixed area each. One 4 ft by 8 ft sheet covers 32 square feet, so the example is 216 divided by 32, or 6.75 sheets exact. If your sheets are a different size, divide by their area instead: a 4 ft by 10 ft sheet covers 40 square feet and would take the same walls to 5.4 sheets exact. The exact count is almost never whole, and that is normal — the waste step, not the division, settles the order.

Step 5: Add waste and round up

Add the waste for cuts around the door, the window and the tree opening, then round up to whole sheets, since sheets are sold by the sheet. Ten percent on the example is 6.75 times 1.10, or 7.425, rounded up to 8 sheets, and the spare sheet is not wasted — it is the sheet the door, the window and the tree opening consume. Round up at the end, not at the start. Then cut, fit, and keep the offcuts for patching.

Treehouse siding in numbers

Suppose the treehouse is 10 ft long and 8 ft wide, the walls are 6 ft high, the sheets are 4 ft by 8 ft, and the waste is 10%. Wall perimeter: 2 × (10 + 8) = 36 ft. Wall area: 36 × 6 = 216 sq ft. Sheets exact: 216 ÷ 32 = 6.75. Sheets with waste: 6.75 × 1.10 = 7.425. Sheets to buy: 8, rounded up. Order: 8 sheets.

Common mistakes

The most common mistake is counting one wall instead of all four, which buys a quarter of the siding. The second is forgetting to double the length and width, which buys the perimeter of half a treehouse. The third is measuring the height to the roof peak, which buys siding for the gable as if it were wall. The fourth is dividing by the sheet length instead of the sheet area, which turns 216 square feet into 27 sheets. The fifth is rounding down, which buys a treehouse one sheet short at the last wall.

Worked example, start to finish

A treehouse, 10 ft long and 8 ft wide, 6 ft walls, 4 ft by 8 ft sheets, 10% waste. Wall perimeter: 36 ft. Wall area: 216 sq ft. Sheets exact: 6.75. Sheets with waste: 7.425. Sheets to buy: 8. Result: buy 8 sheets, and keep the offcuts for the door trim and the tree opening. If the same treehouse were 12 ft long instead, the need would rise to 9 sheets, but the height would be unchanged.

What changes the answer most

The height changes the answer most, because it is the figure most often guessed and it multiplies the whole perimeter: moving from 6 ft to 5 ft cuts the order from 8 sheets to 7 sheets, while the treehouse never changes, and moving to 7 ft lifts it to 9 sheets. The length is second: every foot at 8 ft wide and 6 ft walls is another 12 square feet. The width is third, and it moves the order exactly like the length. The sheet size is fourth: it changes only the sheet count, never the wall area. The waste is fifth, and it changes only the top of the sheet order, never the walls themselves.

Frequently asked questions