How to Lay Out a Starting Line for a Plank Floor

Why this matters

A plank floor is only as straight as its first row. Start off a wall that wanders and every row after it inherits the wander, so by the far side of the room the boards run visibly out of parallel with the cabinets, the hearth or the doorway, and the last row tapers from a full board to a sliver. None of that can be fixed once the field is down. Twenty minutes with a tape and a chalk line decides how the whole room reads, and it is the same twenty minutes whether the floor is nailed, glued or floating.

What you need before you snap anything

• The room cleared and the subfloor prepped. Snapping a line over debris or high spots gives you a line that moves when you scrape it. Flatness is owned by Floor Flatness Tolerances by Floor Type; finish that work first.
• The actual plank in hand. Measure the face width (the width that shows after the joint closes, not the overall width with the tongue) on three planks from different cartons. A spec sheet number is nominal; your math runs on what is in the box.
• The maker's expansion space. Per the maker, commonly about 1/4 to 1/2 inch at every wall, hidden by base or shoe. See related: Expansion Space at Walls and Fixed Objects.
• The maker's minimum last-row width, if the sheet states one. Many click-plank sheets do.
• A 25 ft tape, chalk line with a fresh string, a framing square, a long straightedge or 8 ft level, pencil, and a helper for long pulls.

Step 1: Choose the run direction

The run direction sets the main wall, so decide it before measuring anything.

1. Follow the longest sightline. Planks running the long way of the room, or toward the main window, make the room read longer and hide end joints in the light. A room entered through one wide opening usually runs away from that opening.
2. Check the structure for nail-down solid. Solid hardwood nailed over joists should run perpendicular to them where possible; running parallel usually calls for extra subfloor build-up. This is the one case where structure can overrule looks. See related: How to Nail Down Solid Hardwood Over a Wood Subfloor.
3. Check the connected rooms. A plank that runs continuously through a hall and two bedrooms has one direction for all three. Choose it in the room with the most visible wall, then carry the line through.

Skip this step and you find out in the second room that the run you chose in the first one sends boards across a narrow hall the short way.

Step 2: Pick the main wall and measure off both ends

The main wall is the longest wall that runs parallel to the planks and is fully visible, usually the one the room is entered along or faces. It is not necessarily the straightest wall, but it is the one the eye checks the rows against.

1. Measure out from the main wall at both ends of the room, about 6 inches in from each corner, to a mark that equals the first row's planned face width plus the expansion space.
2. Pull a third measurement at the middle of the wall and write all three down. The middle tells you whether the wall bows.
3. Do not set the marks off the baseboard if the base is coming off; measure from the wall framing surface the floor will actually run to.

Two end measurements are the whole method. A line measured off one end and squared off a corner inherits the corner's error, and corners in houses are rarely square.

Step 3: Snap the line and read the wall against it

Snap the line between the two end marks. Then go back along the wall with the tape every 2 to 3 feet and read the distance from the line to the wall.

• If the readings agree within a small fraction of the expansion space, the wall is straight enough and the first row runs at its full planned width.
• If the wall bows in toward the line, the expansion space at the bow shrinks. When the bow eats more than about half the gap, the first row gets scribed and ripped to follow the wall so the gap stays even, and the line, not the wall, sets the row's leading edge.
• If the wall bows away, the gap grows at the middle. Check that base or shoe will still cover it.

The line is the reference for every row that follows. The wall only sets how the first row is cut.

Step 4: Check the line against the opposite wall and the doorways

Measure from the line to the opposite wall at both ends. The difference is how far the two walls are out of parallel, and it all shows up in the last row as a taper unless you move it.

Then walk every doorway, closet and opening the run passes through:

• Where a row will cross a doorway, mark where its edges land against the jambs. A row edge that lands within about an inch of a jamb leaves a sliver in the opening that is hard to fit and easy to see.
• Where a hall continues the run, extend the line through the opening with the straightedge and measure it off the hall wall too. A line that is parallel to the room's main wall but 3/4 inch out over the hall's length puts a taper in the hall's last row that every visitor walks past.

Step 5: Calculate the last row before you commit

This is the step that saves the room. Work it on paper:

1. Usable width = room width at that end minus the expansion space at both walls.
2. Divide the usable width by the face width. The whole number is the full rows; the remainder is the last row.
3. If the remainder is under the maker's minimum, or under about a third of a board (a shop default for appearance), rip the first row narrower so the first and last rows come out equal: add one face width to the remainder and split it in two.
4. Re-run the arithmetic at the other end of the room and confirm the taper still leaves a last row above the minimum.

Step 6: Move the line if the math says so, then lock it in

If Step 5 changed the first-row width, re-measure from the main wall at both ends to the new first-row width plus the gap, and snap again. Pull the first line out with a damp rag or mark the correct one so nobody works off the wrong string. For a nail-down or glue-down floor, screw a straight board along the line as a starter fence; for a floating floor, the first row is set to the line and held with spacers.

Worked example: a living room with a wandering main wall

The room is 19 ft long with the main wall along the long side, the entry and a front window on it. Planks are a click-lock product with a 7-1/2 inch face width (checked on three cartons), and the sheet calls for 3/8 inch expansion at every wall and states a 2 inch minimum last row.

Measurements across the room (main wall to opposite wall, framing surface to framing surface): 152 inches at the left end, 153 inches at the right end. The two walls are 1 inch out of parallel.

Last-row arithmetic at the left end:

• Usable width: 152 minus 3/8 minus 3/8 = 151-1/4 inches.
• 151-1/4 divided by 7-1/2 = 20 full rows (150 inches) with 1-1/4 inches left over.
• A 1-1/4 inch last row is under the 2 inch minimum. Fail.
• Balance it: 7-1/2 plus 1-1/4 = 8-3/4 inches, split in two = 4-3/8 inches for the first row and 4-3/8 inches for the last row.
• Check: 4-3/8 + (19 x 7-1/2 = 142-1/2) + 4-3/8 = 151-1/4 inches. It closes.

At the right end the usable width is 152-1/4 inches, so the extra inch lands in the last row: 4-3/8 plus 1 = 5-3/8 inches. The last row tapers from 4-3/8 to 5-3/8 inches along 19 ft, both above the 2 inch minimum. That wall is behind the sofa, so the taper is left there rather than split between two walls.

Line position: first-row face width 4-3/8 plus 3/8 gap = 4-3/4 inches from the main wall, measured at both ends and snapped.

Reading the wall: at mid-length the line is 4-1/2 inches from the wall, a 1/4 inch bow toward the room. The gap there would drop from 3/8 to 1/8 inch, under half the expansion space, so the first row gets scribed to the wall, not set at a straight 4-3/8.

            MAIN WALL (entry side)
  +----------------------------------------------+
  |   4-3/4 in    bow: 4-1/2 in    4-3/4 in      |
  |      |            |               |          |
  | - - -+- - - - - - + - - - - - - - +- - - -   |
  |      CHALK LINE = first row leading edge     |
  |                                              |
  |   19 full rows x 7-1/2 in = 142-1/2 in       |
  |                                              |
  |   last row 4-3/8 in        last row 5-3/8 in |
  +----------------------------------------------+
     left end: 152 in        right end: 153 in
            OPPOSITE WALL (behind sofa)

Doorway check: the hall opening is a 36 inch cased doorway in the left end wall, its near jamb 48 inches in from the main wall, with a transition under the door. Each row's leading edge sits at 4-3/4 inches plus 7-1/2 inches per row after the first: the 6th row edge lands at 4-3/4 + (5 x 7-1/2) = 42-1/4 inches from the wall, and the 7th at 49-3/4 inches. The jamb at 48 inches falls 1-3/4 inches short of the 7th row's edge, more than the inch that makes a sliver, so the 7th row gets a full-width piece notched around the jamb with 1-3/4 inches of it running into the opening. The far jamb, at 84 inches, falls inside the 12th row (79-3/4 to 87-1/4 inches), 4-1/4 inches past one edge and 3-1/4 inches short of the other, so it notches cleanly too. No line move needed.

What changes the call

• A room with a dominant feature perpendicular to the run, such as a fireplace hearth or a long island. Square the line to that feature instead of the wall, and accept tapers at both side walls, because the eye reads rows against the feature first.
• Starting mid-room. Glue-down floors and long open plans are often started from a center line and worked both ways with a spline or reversed tongue. The balancing arithmetic still applies, done from the center out to each wall.
• Herringbone or chevron. Layout runs off a center line along the pattern's axis, a different method entirely; this card covers straight-lay planks.

How to verify you got this right

Before any adhesive goes down or the first row clicks together:

• Equal reveals at both ends. Measure from the line to the main wall at both ends: both read the planned figure (4-3/4 inches in the example) within 1/16 inch. Measure from the line to the opposite wall at both ends and confirm the difference matches the taper you planned for, not a new number.
• The first-row piece fits the scribe. Dry-lay three first-row pieces along the bowed section and check the gap to the wall reads the expansion space all along.
• The last row clears its minimum at both ends on paper, and the plan for which wall takes the taper is written on the subfloor in pencil so the next installer knows it was a decision.

After five or six rows are in, pull the tape from the leading edge back to the main wall at both ends again. If the readings have drifted apart, the rows are walking, and it is cheap to correct now and impossible later.

References

• The flooring maker's installation instructions (face width, expansion space, minimum last-row width, run limits)
• See related: Expansion Space at Walls and Fixed Objects
• See related: Floor Flatness Tolerances by Floor Type
• See related: Measuring Rooms and Ordering Hard-Surface Flooring
• See related: How to Fit the Last Row and Door Jambs When Floating