Lacuna: thermal modification boosts timber utility

This article was originally published in issue 52 of Passive House Plus magazine. Want immediate access to all back issues and exclusive extra content? Click here to subscribe for as little as €15, or click here to receive the next issue free of charge

When Viking ships are recovered from the bed of Roskilde Fjord in Denmark, it is usually the keel that survives intact. To form the curved bow and stern, the Vikings heat-treated timber in hot embers, using water to prevent it catching fire. Once warm and pliable, the wood was bent into shape. The process burned away the sugars, lactose, glucose and the like, that decomposition bacteria would otherwise feed on, achieving, as an unintended consequence, a lifespan measurable in centuries.

Heat treatment not only increases natural durability; it also confers exceptional dimensional stability, making the timber resistant to moisture absorption. The practical result is that U-values do not rise as humidity increases.

These properties suit cladding well, but they are arguably essential for folding doors, where multiple panels in sequence must hold their dimensions reliably throughout the year: neither swelling and binding in winter nor contracting and becoming draughty in summer.

Lacuna UK and Ireland Ltd has used thermally modified timber (TMT) for bifolds for the past 15 years and has recently refined its door design further by combining different heat-treated species in a laminated build-up, each chosen for a distinct property.

Internally, TMT beech provides a smooth, refined surface finish, comparable in quality to a grand piano. In the middle layer, the low density of TMT pine contributes good insulation properties. Externally, TMT ash, being exceptionally hardwearing, offers a robust and natural face.

The result, the company says, is a bifold that performs consistently across climates and seasons, combining Scandinavian material intelligence with the dimensional precision that passive house construction demands.