Hem Fir — Density, Movement, Workability & Cost

Hem-fir is the West Coast counterpart to SPF, and it carries the identical structural logic: a grading group, not a species, built by bundling western hemlock together with several true firs that grow in the same range and share close enough mechanical properties to be sold as one interchangeable category of framing lumber.

What's actually inside a hem-fir bundle

The group combines western hemlock with California red, grand, noble, Pacific silver, and white fir — western hemlock is the dominant constituent and the species this page uses as its reference figure (29 lb/ft³, 540 lbf Janka), but the true firs bundled alongside it run measurably lower in shrinkage: FPL's Table 4-3 lists white fir at 3.3% radial / 7.0% tangential / 9.8% volumetric, grand fir at 3.4/7.5/11.0, and noble fir at 4.3/8.3/12.4 — a real spread hiding under one grade stamp.

Movement, using the dominant species as the working baseline

Western hemlock's own tangential (7.8%) and radial (4.2%) figures give a 1.9 ratio. Run that reference through an 8"-wide stud and it sheds about 0.125" (3.2mm) across its width seasoning from a wet 14% down to a drier 8%; the wood movement calculator applies the same hemlock baseline at other widths. A stud milled to actual dimension, 1.5" by 3.5" and 8 feet long, weighs about 8.5 lb on the wood weight calculator, which covers other framing dimensions too.

The discipline that actually matters with this group

Hem-fir arrives wetter than SPF typically does, since hemlock specifically holds a lot of water in its green state — hem-fir studs are genuinely notorious for continuing to shrink noticeably after a wall has already been framed and closed up, which is why experienced framers let delivered stock sit and acclimate before final trim work rather than cutting everything to a tight fit immediately. Nothing about the actual machining is difficult; the discipline is entirely about patience with moisture content rather than any working-quality issue.

Durability, cost, and the western framing trade

Hem-fir is non-durable, though it accepts preservative treatment better than SPF does — still short of southern yellow pine's treatability, but a genuine middle ground between the two. At roughly $3.50 per board foot it's inexpensive, on par with SPF. Framing lumber, trusses, sheathing, interior trim, and concrete forms round out its uses across the western lumber trade.

The two grading groups, compared

Where SPF dominates Canadian and northern US framing, hem-fir fills the equivalent commercial role across the Pacific Northwest and California — the two groups rarely compete directly in the same regional market, so which one you actually encounter usually depends more on where you're building than on any structural preference between them.

What people actually ask about hem-fir

Why do hem-fir studs seem to keep shrinking even after the wall is framed? Hemlock, the dominant constituent species, arrives from the mill wetter than many other softwoods, so a wall framed with insufficiently dried hem-fir can show continued shrinkage — visible as slightly loosened fasteners or minor gaps — as the wood keeps drying in place over the following months.

Does hem-fir carry the same structural grading stamps and span ratings as Douglas fir, or are they rated differently on a building plan? They're graded under the same structural lumber grading system and span tables generally use both, but Douglas fir typically rates somewhat higher in bending strength, so a plan calling out Douglas fir specifically isn't automatically satisfied by substituting hem-fir without checking the actual allowable span for the grade in hand.

If a deck substructure absolutely must use hem-fir because that's what a regional yard actually stocks, what's the practical mitigation? Detailing the frame to shed water quickly — sloped surfaces, gaps for airflow between members, and flashing at every horizontal joint — reduces sustained moisture contact more than the treatment itself would, since hem-fir's weaker preservative uptake means the wood's own chemistry is doing less of the protective work than it would with southern yellow pine.

If a stamp just says "Hem-Fir," is there any way to know which species is in a specific board? Not from the grade stamp alone — it certifies structural grade, not species, so telling a fir board from a hemlock board inside the same bundle comes down to visual cues like colour and knot character rather than any label on the wood itself.

This page's reference figures are western hemlock's own density, Janka hardness and shrinkage; the true-fir numbers quoted above for comparison were pulled separately from FPL's Table 4-3.