New Equation Could Turn Crooked, Forked Logs Into Building Columns

At a Finnish sawmill, a felled tree gets sorted in seconds. The straight, fat trunk becomes saw logs, the good stuff, the boards and beams that hold up our buildings. Everything else, the bent tops, the forked bits, the awkward curves, gets shunted toward a different fate: pulped into paper, or burned for energy. Centuries of timber practice have run on this one quiet assumption, that the best wood is the wood that looks like a plank waiting to happen.

Jaakko Torvinen reckons that assumption is costing us. The Aalto University architect has spent years trying to normalise what he calls “misfit wood,” and his latest research takes a swing at the technical objection that has always stopped designers cold: nobody could say how much weight a crooked log would actually bear.

Turns out you can just calculate it. Torvinen and his colleagues have published the first structural load tests on organically shaped roundwood columns, curved, double-curved, and forked logs of the sort that normally never make it near a building site. And the headline result is almost anticlimactic in its simplicity. The standard, business-as-usual equations engineers already use for ordinary timber columns work fine on the weird stuff too.

“It’s actually a pretty simple equation that can be used to gauge its load-bearing capacity,” says Torvinen. What surprised him was that nobody had bothered to try it before.

Why so? Because the entire industry has been looking the other way. “We’re so used to thinking in terms of standardised planks or beams,” Torvinen says. “This explains why nobody has ever looked at a tree trunk and come up with an algorithm to gauge its strength.” The waste this creates strikes him as faintly absurd. “If it’s not suitable as saw logs, it goes to pulpwood or energy wood,” he explains. “But our assumption that ‘generic is best’ is old-school thinking, and we’re wasting way too much good wood.”

Twenty Logs Between Two Concrete Walls

The experiments themselves were satisfyingly physical. Twenty logs, harvested from a continuously managed forest north of Tampere, mostly the top segments of trees that would otherwise have been written off. Scots pine and silver birch, between roughly 2.4 and 2.5 metres long, with diameters running from a slim 96 millimetres to a chunky 187. The team wedged each one horizontally between two reinforced concrete walls and squeezed, a hydraulic press bearing down along the log’s length until something gave.

And things gave in interesting ways. The pine columns tended to fail brutally: substantial bending, then a series of crackling sounds, then a sudden tensile failure with a resounding bang, sometimes splitting the entire cross-section clean through. The birch was gentler, bending further and buckling more gradually on its compression side. The forked specimens always snapped in the thicker of the two fork stems.

The numbers spanned an enormous range, from a feeble 19.2 kilonewtons to a hefty 214. That spread is exactly the problem misfit wood has always posed; every log is its own special case, geometry all over the place. But here’s the clever part. When the team ran their measured curvatures and diameters through second-order theory calculations, the same code-based methods used for normal columns, the predictions held up. Using the maximum bow imperfection, the bend at a log’s worst point, the equations consistently underestimated the real strength. Conservative, in other words. Which is precisely what you want when lives sit on top of the column.

The Curve That Helps

One quirk genuinely delighted the engineers in the data. Logs with an S-shaped bow, curving one way then back the other, carried more load than logs with a simple C-shaped curve. The secondary bend works against the main one, sort of cancelling out some of the stress, and earlier work on timber trusses had hinted at exactly this effect (up to 30 per cent more capacity in some cases). A defect, behaving like a feature.

None of this means crooked columns are about to flood the market. Torvinen is careful to call this a preliminary study, feasibility and pattern-spotting rather than a finished design code, and the sample was small and shaped by whatever the forest happened to yield that December. Plenty of work remains before a building inspector signs off on a forked pine pillar.

Still, the direction of travel feels clear, and the climate maths gives it urgency. Wood locks up carbon for as long as it stays in a building; pulp it or burn it and that carbon is back in the air within a year or two. Redirecting millions of tonnes of so-called inferior wood from the scrap heap into long-lived structural use would substitute for far more emissions-heavy concrete and steel, all while putting a genuinely beautiful material on show. Torvinen’s own buildings, the haunting Pikku Finlandia pavilion in Helsinki, a slow-living sauna that won a 2026 Wallpaper* Design Award, already hint at what knotty, charred, whole-tree architecture can look like.

“Using standard timber only is something that cash-strapped consumers are ready to abandon,” Torvinen says. “So I want to clear the path to industry embracing the possibilities of misfit wood too.” The dream is modest enough, and quietly radical. “In future projects, when a designer or client wants misfit wood in a building, it won’t be laughed at as an icebreaker, but considered as a legitimate design proposal like any other.”

Source: Wood Material Science & Engineering, DOI 10.1080/17480272.2026.2679658

Frequently Asked Questions

What is “misfit wood,” and why does so much of it go to waste?

Misfit wood is timber that fails the shape and size standards for saw logs, mainly because it is curved, forked, or otherwise irregular. Because the timber trade has long assumed straight logs make the best material, this wood is usually pulped into paper or burned for fuel rather than used in construction. Researchers now estimate millions of tonnes are discarded this way each year, which is what makes finding a structural use for it so appealing.

How can engineers tell whether a crooked log is strong enough to hold up a building?

It turns out the standard equations already used to size ordinary timber columns also work on irregular logs, provided you measure the wood’s diameter and the size of its curve. When researchers fed those measurements into the usual code-based calculations, the predictions reliably came in below the log’s true strength, erring on the safe side. That means designers may not need exotic new tools to work with naturally shaped wood.

Is it true that a more twisted log can actually be stronger?

Counterintuitively, yes, at least for one type of bend. Logs with an S-shaped curve carried more load than logs with a simple single curve, because the second bend works against the first and partly cancels out the stress. Earlier studies on timber trusses found a similar effect of up to around 30 per cent extra capacity, suggesting the geometry of a defect can sometimes work in your favour.

Why does using this wood matter for the climate?

Wood stores carbon for as long as it remains in a structure, whereas pulping or burning it releases that carbon back into the atmosphere within a year or two. Putting otherwise-wasted logs into long-lived buildings keeps the carbon locked away and can substitute for concrete and steel, both of which carry far heavier emissions. Scaling that swap across the construction sector could make a meaningful dent in building-related emissions.

What’s stopping forked and curved logs from being used in buildings tomorrow?

This was a small, preliminary study built around whatever logs a single forest happened to yield, so it proves feasibility rather than delivering a finished design standard. Building codes, classification systems, and larger test datasets all still need developing before inspectors will routinely approve an irregular column. The work charts a path toward that goal rather than completing the journey.