Old Canaan Building Materials

Douglas fir is sold two ways: flat grain and vertical grain. They are the same species. They behave completely differently. Flat grain Douglas fir cups, checks, and splinters on a porch deck within a few seasons. Vertical grain Douglas fir on the same deck performs for decades. The distinction is one of sawing method, and it matters more than any other single factor in specifying fir for finish applications.

Vertical grain fir has a tight, parallel grain pattern on the face — the growth rings run perpendicular to the board face. The surface is smooth, dense, and accepts paint evenly. Flat grain fir has a cathedral pattern on the face — the growth rings run at an angle or parallel to the face — and the soft earlywood between the hard latewood bands wears unevenly, raises in humidity, and splinters under foot traffic.

Vertical grain Douglas fir (also called edge grain or quarter-sawn fir) is sawn so that the annual growth rings are oriented roughly perpendicular to the face of the board — within 30 degrees of perpendicular by the standard grading definition. It is available from specialty lumber dealers and some millwork suppliers as a stock item. It costs more than flat grain fir because the sawing method produces less yield per log.

Vertical grain Douglas fir is dimensionally stable — it moves very little in width with seasonal humidity changes, and when it does move, it moves in thickness rather than width. It holds paint exceptionally well because the dense, even surface does not raise or splinter under traffic. It is correct for porch decking, interior flooring, and any finish application where stability and paint adhesion are the specification.

Vertical grain fir is the historically correct lumber for porch decking and interior flooring in New England buildings from the late 19th century through the mid-20th century, when old-growth fir was available from Pacific Northwest mills as a standard material. The old-growth fir floors in well-maintained New England houses from this period are still performing correctly.

From specialty lumber dealers. Specify "vertical grain Douglas fir" or "edge grain Douglas fir" explicitly — the default at most lumber yards is flat grain. In New England, dealers that stock it include specialty hardwood dealers and millwork suppliers. Allow extra lead time — it is not a walk-in purchase at most yards.