A guide to glulam connections and when to use them

1.  Bolted connections

Bolted connections are the classic glulam connection. You can probably imagine chunky steel, big washers and visible engineering.

They suit projects where an industrial aesthetic is wanted, where the visible fixings become part of the glulam feature.

Why you’ll use them – advantages

• Strong, reliable, and your contractors will be used to working with them.
• Good installation tolerance, coming from a 2 mm bolt‑hole tolerance, which helps if things aren’t perfectly lined up on site.
• Can be used for moment or pin joints (see below)

What you need to think about

• To get maximum fire resistance, you need to plug them, but this limits bolt length.
• Some movement occurs because of the hole size.
• Do visible bolts match the look you’re after? Because you have to cover the washer and the bolt head, the plugs can be quite big, so it may not be the right choice if you don’t want that aesthetic as part of your design.

Where these connections work

Think about exposed office structures, industrial conversions and simple connections in portal frames. Strength and visual impact are where bolted connections excel.

Trenders Avenue bolted connections

2.  Dowelled connections

This joint sees smooth steel dowels pass through steel plates in the glulam.

The hidden connection gives a cleaner, neater, more minimal look than bolts, and they’re a good option when you want tight, stiff joints.

Why you’ll use them – advantages

• Very stiff, thanks to minimal movement or play.
• Good fire performance when plugged.
• Discrete, even when you’ve got loads of fixings.
• Can be used for moment or pin joints (see below)

What you need to think about

• Harder to install due to zero tolerance, giving less margin for error if holes don’t line up perfectly.
• Risk of damaging timber when hammering dowels and plugging holes, if not done expertly.

Where these connections work

Think about clean, simple interiors, including projects with high‑load joints where stiffness matters, as well as when connections need to be hidden for fire safety.

Dowelled connections during manufacture

3. Resin‑anchored connections

Epoxy-bonded rods are popular as a really neat way to connect glulam.

They’re completely hidden, passing through the two connecting pieces of glulam, forming super-strong bonds on either side of the join.

Why you’ll use them – advantages

• Fully hidden connections with no visible steel give you a clean timber look.
• Very strong when correctly installed.
• Fast and often cost-effective to install on your project.

What you need to think about

• Expert installation is required as bad drilling or preparation weakens bonds.
• Specific testing is needed to ensure a good bond.
• We’d generally advise to avoid these for critical connections, unless the joint can be tested prior to install.

Where these connections work

Think about feature beams and columns in galleries or homes where a high load-bearing capacity is needed. When looks matter, you’ll get the clean lines you’re after with no visible fixings.

Hertfordshire House, which used resin-anchored connections

4. Skew Screwed connections

You can use only screws, without any bracketry, to form connections in glulam structures.

Modern fully threaded timber screws can generate very high load capacities, more than you might think!

Why you’ll use them – advantages 

• Concealed – so no visual fixing
• Low cost
• No machining or bracketry required
• Good for fire performance – screws can be hidden within the timber

 What you need to think about

• Requires expert installation as these are quite easy to get wrong!
• Strength capacity is limited – they won’t do the highest load connections without a bracket

Where these connections work

These are useful connections for areas of a project where you have lots of members, relatively low load.

If you don’t want to see fixings, for example purlins between roof trusses, these are a good option.

Skew Screwed connections – credit Rothoblaas

Skew screw connection example in the purlin connection above, Able Canopies project

There is also a type of skew-screwed connection that can be used in conjunction with a special washer and thick steel plates (see diagram below).

These can generate very high load capacities, but you need to be careful not to let the timber get too wet. This can cause the timber to swell and apply large forces to the screw heads, which can break them off.

Fig 1 – skew-screwed connection and steel plates

5. Proprietary brackets

Proprietary brackets are specialised, manufactured, and often patented steel connections used to join beams. These brackets are often used as angle brackets for framing, joist hangers, and truss connectors.

We’ve included some of the more common ones below.

Simpson Joist Hanger – credit Simpson

5.1. Simpson joist hanger

 Why you’ll use them – advantages

• Cost effective
• Easy to install
• No machining of the glulam needed to use them

What you need to think about

• Not aesthetically pleasing  – hangers are fully on show and
• No fire resistance as no protection from being covered by timber

Rothoblaas alumidi

5.2 T plate type connections

As the name suggests, these are a “T” shape and used to connect beams at a 90-degree intersection, often used to create sturdy joints in frameworks. Examples of these include Simpson TU connectors or Rothoblaas Alumidi (pictured above)

 Why you’ll use them – advantages

• Simple, easy to specify and clear load capacities
• Can be concealed
• Can have fire rating
• Not expensive
• A bit flexible on tolerance

What you need to think about

• More machining required to conceal than other connectors
• Need to be dowelled – so dowels need to be plugged and sanded which adds another process on site

Pitzl brackets

5.3 Interlocking concealed hanger type connections

Interlocking concealed hanger-type connections are high-strength, steel, or aluminium connectors designed to join beams such as secondary beams to main beams, or beams to columns. They use a dovetail-like or tongue-and-groove mechanism that allows the components to slide and lock together.

Examples of these include Rothoblaas UVT or LOCKT, SIHGA and Pitzl (pictured above) and Simpson ETB hangers.

Why you’ll use them – advantages

• Look smart and nice to fiddle with
• Can be fully concealed within timber and therefore easily designed for fire resistance.
• Fire test results are available for some

What you need to think about

• Very tight machining tolerances required to be fitted easily.*
• Less popular with installers due to difficulty fitting sometimes.

*It’s worth noting that CNC cut pockets need to be very accurate, otherwise the bracket cannot be fitted – e.g., a lot of them are designed to a 10mm recess in the supporting beam, if this is machined to 12 or even 11mm, the bracket cannot be fitted. Also, especially the bigger connectors are difficult to fit if the beam is not 100% level when lowered onto the connection.

Simpson etb (left) and Rothoblaas LockT (right)

6. New and bespoke connectors

We’ve been increasingly using more bespoke connectors like the Rothoblaas ring connector pictured below.

There is an expanding range of screw-in options available from companies like Rothoblaas and SIHGA IDEFIX that can be used to make these connections.

They work well as they have a single bolt to install on site, but the structural work is done by screws into the timber which means the brackets can be installed off-site, then bolted together on-site easily.

Why you’ll use them – advantages

• Not much steel required – efficient use of the high tensile capacity generated by screws into timber
• High load capacities
• Recessed installation so visually good and easy to design for fire
• Quick to install

What you need to think about

• Can still be expensive, but prices will come down as they increase in popularity
• Skilled installers are needed – there is a danger of over-torquing screws for example, which could result in reduced load capacity

Where these connections work

Bespoke and ring connectors are helpful for projects where you need to significantly increase the load-carrying capacity of joints – structural framework where high lateral loads are expected, large frames and span lengths in particular.

Ring connectors in an oak structure

SIGHA IDEFIX Bracket

7. Moment and pinned connections

Here’s one for the engineers reading!

Moment joints in timber are common in glulam, but it’s good to be aware that they do add cost to a project because of their complexity.

Most of them are bespoke-designed and don’t use off-the-shelf components. These joints are used where the joint needs to stop rotation, so they would be used in a cranked beam, a splice in a beam or an eaves connection in a portal frame for example.

Pinned connections on the other hand are used when you don’t need to give the joint a rotational stiffness, which means they only need to take shear forces. These are used more widely than moment joints, and are cheaper as they can be made using any of the connection types listed and are generally smaller.

Making the right connection – What to do next?

While a connecting piece might not be the first thing you think about when designing a build, the more you know, the more likely you are to make the right choice and build brilliantly with glulam. It’s a bit of a taste of what it’s like working with us at Buckland Timber.

Two things to remember:

• It’s all about making the right connection for the right installation, so make sure you’re clear and confident, and if you’re not sure, ask.

• Don’t worry if your project requirements fall outside these. This is just the tip of the iceberg! At Buckland, we’ve got the expertise to work with you on all project scopes, including where bespoke connections are needed.