How many boards, cuts, hinges and steps?

Divide the deck width by the board face width plus the gap to get the number of rows, then divide the deck length by the board length to get pieces per row, and multiply. A 16 by 12 ft deck with 5-1/2 in boards and a 3/16 in gap needs 26 rows; with 16 ft boards that is 26 boards plus waste. The most common mistake is using the nominal size: a 5/4 × 6 board is 5-1/2 inches wide, so assuming 6 leaves you about 8% short.

About 3/16 inch for kiln-dried lumber, which will move only slightly. Wet pressure-treated lumber is different: lay it tight, because it will shrink as it dries and open its own gaps, often to a quarter inch or more. Composite decking follows the manufacturer, and the required gap usually varies with the installation temperature, since composites expand more than wood. Gaps matter for drainage and drying, not just looks — a deck with no gaps holds water and rots from the top down.

It depends on the orientation and the saw kerf. For a 30 by 15 inch part with a 1/8 inch kerf, laying the length along the sheet gives 3 columns by 3 rows, or 9 pieces; rotated it gives 6 by 1, or 6. So the first orientation wins with 9 pieces and about 88% yield. The kerf is not negligible: nine cuts across a sheet consume over an inch of material, which is exactly the amount that turns four pieces into three.

Above 80% is good for straight guillotine cutting. Between 65 and 80% is typical. Below 65% means the part size and the sheet size are fighting each other, and you should look at rotating the parts, mixing different part sizes on the same sheet, or buying a different sheet format if one is available. A CNC nest can beat guillotine cutting by several points because it is not limited to cuts that go all the way across.

IRC R311.7.5 sets a maximum riser height of 7-3/4 inches and a minimum tread depth of 10 inches for one- and two-family dwellings. Within a single flight, the risers may not vary by more than 3/8 inch from largest to smallest, and neither may the treads. Minimum headroom is 6 ft 8 in measured vertically from the tread nosing line, and minimum stair width is 36 inches above the handrail. Commercial stairs under the IBC are stricter: 7 inch maximum riser and 11 inch minimum tread.

Measure the total rise from finished floor to finished floor. Divide by a target riser of about 7.5 inches and round up to get the number of risers. Divide the total rise by that number for the actual riser height, which will be identical for every step. The number of treads is one less than the number of risers, because the top riser arrives at the floor above. Then check that the tread depth you can fit in the available run is at least 10 inches, and if it is not, the stair needs more horizontal space or a landing.

It is an eighteenth-century French comfort rule: the tread depth plus twice the riser height should fall between 62 and 64 centimeters, which is 24.4 to 25.2 inches. It captures the fact that a normal stride shortens as you climb. It is a good sanity check and it is genuinely useful, but it is not US code. The IRC governs, and the equivalent American shorthand is the rule of 25 — riser plus tread between 17 and 18 inches. A stair can satisfy Blondel and still fail the IRC riser limit, so check the code first.

One per 30 inches of door height, rounded up, with a floor set by the weight: two for a light hollow-core, three for a standard solid-core, four for an exterior or fire-rated door, and five for anything oversized. Take whichever number is higher. A standard 80 inch interior door works out to three by the height rule, which matches the weight-based minimum for solid-core. A 96 inch tall door needs four by height regardless of what it weighs.

Screws per hinge are the number of holes per leaf times two leaves — four for standard residential hardware, six for heavy-duty. So three hinges with four-hole leaves is twelve screws per door, plus a buffer for the ones you strip or drop. Size goes with the weight: #6 by 5/8 in for light doors, #8 by 1-1/4 in for standard, #8 by 1-1/2 in for exterior, #10 by 2-1/2 in for oversized. On the jamb side, at least one screw per hinge should be long enough to reach the framing behind the jamb.

Add the outer frame perimeter, twice width plus twice height, to the perimeter of each sliding sash, allowing about 1-1/4 inches of overlap per sash. Add a contraframe perimeter if one is set into the masonry, and one rail equal to the window width for a transom. Then add 10 to 15% for miter waste and divide by the stock bar length. US aluminum extrusion is generally stocked in 16 ft bars, while metric markets use 6 meter bars, which is 19 ft 8 in — so a cut list optimized for one stock length will not be optimal for the other.

Because the nominal size refers to the rough green dimension before it is dried and surfaced. A 2 × 4 finishes at 1-1/2 by 3-1/2 inches, a 2 × 6 at 1-1/2 by 5-1/2, and 5/4 decking at about 1 inch thick by 5-1/2 wide. The convention is standardized in the US Department of Commerce voluntary product standard PS 20. It matters for every take-off: a wall of 2 × 6 studs is 5-1/2 inches thick, and a deck of 6 boards is 33 inches wide before you count the gaps.

The ones used here: a 2440 by 1220 mm sheet is 96.06 by 48.03 inches, which is within 1.5 mm of a US 4 by 8 sheet; a 3 mm kerf is 0.118 inches against a US 1/8 inch blade; a hinge every 0.75 m is a hinge every 29.5 inches, effectively the US 30 inch rule; a 3 cm sash overlap is 1.18 inches; and a 6 m stock bar is 19 ft 8 in against a US 16 ft one. The Blondel range of 62 to 64 cm is 24.4 to 25.2 inches, and the metric riser target of 18 cm is 7.09 inches — noticeably lower than the 7.5 inch US design target.