Everyone talks about the timber. Almost nobody photographs the connections.
But the screws, brackets and plates between the panels decide how a mass timber building carries load, handles fire, keeps sound down and stays dry. If you want one place to put your attention before tender, mass timber connections are it.
We'd love to give you a percentage for how much they drive cost and programme. We can't, and you should be wary of anyone who does. What the industry does say is that connections are cost drivers, and that bringing the fabricator in early cuts late changes. Here's what we'd settle first.
Mass timber connections carry the whole building
Inside a cross-laminated timber (CLT) panel or glulam beam, the layers are glued. Between products, the connections are mechanical: screws, bolts, nails and brackets. The Mass Timber Institute puts it plainly: how well the connectors transfer load determines how much of each element's benefit you get.
Connections also set how the structure moves. In research on a seven-storey modular CLT building, the racking stiffness of a panel was significantly influenced by the connectors fixing it. In small-scale US tests, nailed steel-plate connections were more ductile than lag-screwed ones, and some timber-only joints failed suddenly. Ductile means able to deform without breaking suddenly, which is what you want when a structure is pushed hard. New Zealand researchers combined screws at different angles to get a hold-down connection that is strong, stiff and ductile at once: screws at 45 degrees give strength and stiffness, and screws at 90 degrees give ductility.
In Australia, engineers design these connections with AS 1720.1 and often draw on Eurocode 5 as well.
The common connection types
These are the connections you'll meet most. The table describes what they do. It isn't a design guide: connection design is project-specific, and engineers decide.
Connection | What it does | Where it appears | Resolve early |
|---|---|---|---|
Self-tapping screws (screws that cut their own thread, often long) | Join panels, beams and walls; a US design guide calls them the most common and versatile CLT fastener | Panel-to-panel joints, panel-to-beam and wall junctions | Screw type and length; long fully threaded screws can restrain timber as it moves with moisture |
Metal angle brackets | Connect walls, floors and other supports | Wall-to-floor and floor-to-floor junctions | Fire protection of exposed steel; effect on flanking sound |
Hold-downs (anchors that resist uplift at wall ends) | Hold shear walls down so they resist sideways loads | Bases and ends of CLT walls | Stiffness and ductility; access to install |
Concealed steel plates and dowels | Join beams to columns with the steel hidden inside the timber | Beam-to-column joints | Fabrication tolerances; fire protection from the surrounding timber |
Fire: protect the connection, not just the timber
Thick timber chars and protects itself. Steel in a connection doesn't. BRANZ reported tests on LVL beam-column joints that found more charring where exposed steel touched the timber and where gaps opened as the joint deformed. It also listed failure modes that lead to earlier failure: bent brackets, stripped screw threads and buckled screws.
Charring matters at the joint too. US guidance explains that char shrinks, so steel can be exposed sooner than a simple char depth calculation suggests. Common ways to deal with this include concealing steel inside the timber, covering it with timber or fire-rated lining, and using sealants and connection geometry. Your fire engineer chooses. The point is to ask early.
Sound and moisture: two things connections change
Sound first. CLT is light and stiff, so noise can travel through the structure around a floor or wall, which is called flanking transmission. Recent research from Empa, the Swiss materials laboratory, found that fastener configuration significantly influences flanking sound at CLT junctions, and that brackets can't be treated as simple rigid points. Isolating brackets and resilient layers exist, but a 2024 Chalmers thesis notes that predicting low-frequency transmission across CLT joints is still hard. So acoustic engineers test and detail junctions rather than assume.
Now moisture. End grain and joints are where water is most likely to get trapped and dry slowly, according to FPInnovations. And long fully threaded screws can restrain timber as it swells and shrinks with moisture. Connection details matter on site as well as in service.
Why connections affect cost and speed
A WoodWorks structural design presentation lists connections among the cost drivers in mass timber. Beyond that, the evidence is about coordination. The Canadian Wood Council says mass timber needs more coordination than traditional structural systems, because prefabricated components and tight tolerances call for early planning.
Tolerance is how far a built element can vary from its drawn size. CNC machines cut timber panels to within millimetres, while some trades work to 6 to 12 mm, so the joint between them needs room for the difference. Engineers at Thornton Tomasetti say bringing a supplier in during schematic design helps align the design with available products, fabrication methods and erection sequences, and cuts late changes.
Most of this guidance comes from North America, Europe and New Zealand. Treat it as a guide to what to ask, not a rule for your Australian project.
Resolve before tender: eight questions
Connection design is project-specific, and your engineer decides. These are questions to settle before documents go out.
Who designs and details the connections: the engineer of record, or a specialist engaged by the contractor?
Are the connections detailed so that any qualified supplier can bid?
Have we talked to a fabricator or supplier before the documents are final?
What tolerances do the steel, concrete and other trades achieve at timber interfaces, compared with CNC-cut timber?
Which connections are exposed, concealed or protected, and has the fire engineer reviewed them?
Which junctions affect sound, and how will they be detailed and tested?
How are end grain and joints protected from moisture, and do the screws allow for timber movement?
How will each connection be installed, in what order, and with what access?
See it for yourself
Connections are easier to understand when you can hold them. Mass Timber Central, Australia's first dedicated mass timber collaboration and education space, is at 8 Bank Place in Melbourne's CBD. It's open Monday, Tuesday and Thursday, 10am to 3pm. Rothoblaas, SPAX and Eurotec are display partners, so you can handle real screws and brackets and talk through details with our engineers. For any capacity or rating, read the manufacturer's own technical document: self-tapping screws from these makers come with European Technical Assessments.
Frequently asked questions
What are mass timber connections? The screws, bolts, brackets and plates that join mass timber panels and beams. Inside each product the layers are glued. Between products, the connections are mechanical.
Why do mass timber connections matter? They shape how loads move through the structure, how it behaves in fire, how sound travels and where water can collect.
What should be resolved on connections before tender? Who designs and details them, whether any qualified supplier can bid, tolerances with other trades, and how fire, sound and moisture are handled at each joint.
Who is responsible for designing mass timber connections? It varies by project, so settle it in writing before tender. In North American practice, the structural engineer of record customarily designs and details them, and brings in a timber specialty engineer if they lack the experience.
Let’s keep in touch.
Discover more about what we are up to. Follow us on Linkedin and Instagram.
