Why dRMM’s new knuckle joints using homegrown hardwood are game-changing for engineered timber

Author:

Flo Armitage-Hookes

Published:

11 Dec 2025

The use of tougher species of wood eliminates the need for metal fixings and reduces the overall size of a post and beam structure

Renewable, lower-waste and aesthetically appealing: engineered wood structures are rightly lauded. However, often requiring metal fixings and oversized elements, they have their shortcomings.

dRMM, working closely with manufacturers, innovation labs and universities, has been researching ways to unlock the full potential of cross-laminated timber (CLT).

Building from Forests, funded by Forestry Commission England, has developed a series of new engineered wood products, including a hardwood knuckle joint.

The oak CLT knuckle joint removes the need for metal fixings | Credit: Alex de Rijke

Joint installed as part of a glulam portal frame | Credit: Alex de Rijke

A softwood CLT knuckle had already been prototyped, conceived and developed by Ecosystems Technologies, Edinburgh Napier University, and BE-ST, as part of research project Transforming Timber.

Building upon this, the switch to stronger species has proved a game changer. The hardwood transfers forces more effectively, eliminating the need for metal flitch plates and bolts and reducing the overall size of a post and beam structure.

“What’s really smart about the knuckle is that by tapering it, you can brace the frame so you don’t need cables or a wall panel,” says Finbar Charleson, research leader at dRMM.

The knuckles are made from British oak, which was readily available to manufacturers at the time. However, in theory they could be made from any homegrown hardwood – drawing on strength, stiffness and density data generated by the research project.

Infographic comparing the strength of seven different types of UK hardwood with Sitka Spruce. Research courtesy of Edinburgh Napier University | Credit: V&A

Although still “an involved piece of carpentry”, dRMM plans to demonstrate the knuckle in a building and hope that it will become more widely available, or even a standard product, with a growth in demand.

This is not just wishful thinking – the project’s 45mm CLT sheets are already available for furniture applications from manufacturer Highland Heritage Woodworks.

dRMM: Building from Forests is on display at V&A South Kensington until October 2026

Read the Transforming Timber research outcomes