Reclaimed Ulin Ironwood for Structural Timber & Architecture Bali, Indonesia
Naturanexa manufactures structural timber, building components, outdoor elements and architectural joinery from 100% reclaimed Indonesian Ulin — one of Southeast Asia's most durable heavy hardwoods.
One species with many names and a long history in tropical construction.
Ulin is the Indonesian name most commonly associated with Eusideroxylon zwageri, a heavy tropical hardwood in the Lauraceae family native principally to Borneo and Sumatra.
It is internationally known as Borneo ironwood and is also called Belian or Billian in parts of Southeast Asia. Indonesian regional names include Ulin, Belian, Tebelian and related local variations.
The term “ironwood” or “kayu besi” is broader and may be used for several exceptionally hard local timbers. For architectural specifications where species identity matters, the botanical name Eusideroxylon zwageri provides the clearest reference.
Why Ulin became a heavy-construction timber.
Ulin combines high density with strong natural durability. Those characteristics explain its historic use in bridges, piles, house posts, marine structures and other applications where timber is expected to tolerate demanding conditions.
Is Ulin one of the hardest and densest woods?
There is no single universal ranking for the “hardest wood in the world”. Hardness, density, compression strength and impact resistance measure different properties.
Ulin is nevertheless recognised in technical literature as one of Southeast Asia's heaviest and most durable commercial timbers. Its density can approach or exceed that of water, which is why particularly dense pieces may sink rather than float.
Existing timber given another architectural life.
Naturanexa does not need a newly harvested tree to manufacture an Ulin beam, rafter, screen or door. Our approach is based on recovering existing Ulin timber and preparing it for a new project.
Reclaimed material may carry evidence of its previous life: colour variation, old fixing marks, weathered surfaces or changes in patina. Depending on the intended product, some of this character can remain visible or the timber can be re-machined toward a cleaner architectural finish.
For a slow-growing species with a long history of intensive use, extending the service life of existing material is central to the way Naturanexa works with Ulin.
From heavy timber to finished architectural details.
Beams & Posts
Large reclaimed Ulin sections for structural frames, pavilions, villas and visible heavy timber architecture.
Rafters
Structural roof members and exposed timber components used where the roof structure remains part of the architecture.
Joists
Repeated structural components for floor, subframe and outdoor support systems.
Battens
Smaller calibrated sections for screens, framing, architectural slats and repeated timber details.
Pergolas
Posts, beams, rafters and associated components for exposed outdoor shade structures.
Fences & Screens
Exterior boundaries, privacy screens, kisi-kisi and architectural slatted systems.
Doors & Windows
Reclaimed Ulin frames and architectural joinery manufactured around project openings and dimensions.
Balustrades & Stairs
Timber components for stairs, railings, handrails, terraces and other visible architectural details.
Ulin was a construction timber long before it became an architectural material.
Technical references document Ulin across an unusually wide range of heavy-duty applications, helping explain why reclaimed structural sections remain valuable today.
Heavy Construction
Bridges, piles, house posts, structural supports, masts, poles and other large timber members are among the historic applications documented for Ulin.Marine & Wet Environments
Ulin has historically been used for wharves, docks, sluices, marine structures and ship components where timber is exposed to demanding moisture conditions.Traditional Architecture
House posts, structural frames and Ulin roof shingles known as sirap form part of the timber's architectural history across Borneo and Indonesia.
Dense timber changes the way it must be machined.
High density is an advantage in service but it also affects production. Ulin can be successfully sawn, planed, drilled, mortised and sanded, but tooling and machining methods need to account for its hardness.
This is one reason project preparation matters: repeated structural sections and detailed components are easier to control when material selection and machining happen before installation.
Start with the function, then define the timber.
Reclaimed timber projects work best when the intended application, dimensions, quantities and level of processing are clear before production begins.
01 · Define the Application
Tell us what the component must become and where it will be used.
- Beam or post
- Joist or rafter
- Batten or screen
- Pergola component
- Door or window
- Fence or balustrade
- Custom architectural element
02 · Define the Dimensions
Reclaimed stock varies, so dimensions and quantities help determine what material can be selected and how it should be processed.
- Section width
- Section thickness
- Required lengths
- Number of pieces
- Repeated or unique components
03 · Define the Preparation
The same reclaimed timber can be supplied at different levels of preparation depending on the project.
- Raw structural timber
- Resized sections
- Planed surfaces
- Custom machining
- Joinery preparation
- Architectural finish
One reclaimed material, two dedicated areas of expertise.
Our businesses work with reclaimed Ulin in complementary ways. Naturanexa concentrates on structural timber, building components, outdoor elements and architectural joinery.
For dedicated reclaimed Ulin decking and flooring expertise, our sister company Kaltimber focuses specifically on those products.
Reclaimed Ulin beams, posts, battens, joists, rafters, raw structural timber, pergolas, fences, screens, doors, windows, balustrades and custom architectural components.
Explore Naturanexa Structural Timber →Dedicated reclaimed Ulin decking and flooring manufactured in Bali for residential, hospitality and architectural projects.
Visit Kaltimber →Need something other than Ulin?
Our partner Kitaru Lumberyard in Bali complements Naturanexa's reclaimed Ulin production with other reclaimed tropical hardwoods, Ulin roofing shingles and professional timber hardware.
Common questions about reclaimed Ulin ironwood.
What is Ulin wood?
Ulin is the Indonesian name commonly used for Eusideroxylon zwageri, a very dense and naturally durable tropical hardwood native principally to Borneo and Sumatra. It is internationally known as Borneo ironwood.
Is Ulin the same as Borneo ironwood?
Yes. Borneo ironwood is a common English name for Eusideroxylon zwageri. Belian or Billian are other regional names associated with the same species.
Is every timber called “ironwood” actually Ulin?
No. “Ironwood” and the Indonesian expression “kayu besi” can be used as general names for several very hard local timbers. When species identification is important, specify Eusideroxylon zwageri.
Is Ulin one of the hardest woods in the world?
There is no single universal definition of the world's hardest wood, because hardness and density are different measurements. Ulin is, however, recognised as one of the heaviest and most durable construction timbers of Southeast Asia.
Does Ulin sink in water?
Very dense Ulin can approach or exceed the density of water, so some pieces can sink rather than float. Density varies according to the individual piece and moisture condition.
Is Ulin suitable for structural timber?
Ulin has a long history in heavy construction including bridges, posts, piles, structural frames and other demanding timber applications. Naturanexa processes reclaimed Ulin into beams, posts, joists, rafters and other structural components.
Can Ulin be used for beams and posts?
Yes. Large reclaimed Ulin sections can be supplied and processed as beams, posts and other heavy structural timber, subject to available reclaimed stock and the dimensions required by the project.
Can Ulin be used for rafters and joists?
Yes. Naturanexa manufactures reclaimed Ulin joists and rafters as project-specific repeated structural components.
Is Ulin suitable for outdoor architecture?
Ulin's historic use in exposed tropical construction makes it particularly relevant to pergolas, fences, screens, balustrades and other exterior timber components.
Is reclaimed Ulin different from newly harvested Ulin?
Reclaimed Ulin has already been used in a previous structure before being recovered for another use. Naturanexa selects and reprocesses this existing timber rather than depending on newly harvested Ulin for its building components.
Is reclaimed Ulin always rustic?
No. Reclaimed character can be retained when desired, but the timber can also be resized, machined and sanded toward a cleaner and more precise architectural appearance.
Is Ulin difficult to machine?
Its density requires appropriate tools and machining methods. Cutting edges can wear faster than with lighter timber and pre-drilling is recommended for many fixing applications. Despite its hardness, Ulin can be successfully planed, mortised and sanded.
What is Sirap Ulin?
Sirap Ulin are traditional roof shingles made from Ulin ironwood. Timber shingles have a long history in Indonesian and Bornean architecture. Sirap is available through our partner Kitaru Lumberyard.
Does Naturanexa supply Teak or Bangkirai?
Naturanexa specialises in reclaimed Ulin. For reclaimed Teak, Bangkirai and additional species including Meranti and Kapur, clients can work with our Bali partner Kitaru Lumberyard.
Where should I go for reclaimed Ulin decking or flooring?
Reclaimed Ulin decking and flooring are the specialist focus of our sister company Kaltimber. Naturanexa focuses instead on structural timber, building components, outdoor elements and architectural joinery.
What should I send Naturanexa for a structural or architectural quotation?
Send the required dimensions, lengths, quantities, application, drawings or BOQ, along with any machining, joinery or finish requirements relevant to the project.
Further information about Eusideroxylon zwageri.
Need Ulin beyond decking and flooring?
Send Naturanexa your dimensions, drawings or BOQ for reclaimed Ulin beams, posts, battens, joists, rafters, outdoor elements, architectural joinery or custom building components.