Specifying Glulam for Your Project: What You Need to Know
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We’re seeing more and more architects, contractors and property owners eager to incorporate glulam (glued-laminated timber) or CLT (cross-laminated timber) into their projects. The sustainability benefits and aesthetics make timber an increasingly attractive choice.
But for many, this is uncharted territory – what do you need to consider BEFORE embarking on this journey?
We’ve guided countless professionals through their first glulam projects and beyond. Experience has taught us that addressing key considerations early can make all the difference between a smooth process and potential headaches down the line.
So, what should you consider when specifying glulam for the first time? Let’s examine six key areas most frequently brought up in our client conversations.
1. Do I need different insurance for glulam buildings?
One of the questions asked most often is about insurance for timber buildings. It’s not surprising that insurers frequently don’t have much experience with modern timber structures, which can lead to some hesitation or risk aversion.
The good news is that there are insurers out there with solid track records in covering timber buildings. Finding the right one is key. Getting them involved early in the design process helps you to identify any insurer-specific requirements.
For example, insurers might have requirements around fire treatment specifications. Understanding what boxes you need to tick early on allows you to build them into your design from the beginning rather than making costly changes later.
With the growing popularity of timber construction across the UK, insurance options are increasingly available. The Alliance for Sustainable Building Products (ASBP) has published an excellent guide on insuring timber buildings that we often recommend.
2. Fire Safety – addressing the elephant in the room
We mentioned fire already so let’s talk about it.
Yes, wood burns – we’re not going to pretend otherwise! But when we talk about fire ratings for timber buildings, we’re looking at two key factors:
1. First, there’s the reaction to fire. The Euroclass System (BS EN 13501-1) is a rating for the material based on three criteria:
a. its combustibility or its relative contribution to fire
b. smoke produced
c. the likelihood of producing flaming droplets.
In the UK, we are mainly concerned with the first part of the criteria, its combustibility, or the “surface spread of flame.” This is mainly about how quickly fire can spread across surfaces. Typically, large areas of exposed timber will require a treatment to help slow down any potential spread.
2. Second, the structural fire resistance. This is the structure’s ability to remain standing during a fire. This is where glulam is surprisingly high-performing. We calculate this using the charring rate method – we know glulam burns at approximately 25mm per half hour, which allows us to design beams with additional thickness to maintain structural integrity even during a fire event. Connection brackets are best embedded within the timber and protected in a similar way.
Fire ratings are typically specified in minutes – commonly 30, 60, or 120 – and are determined by qualified professionals during the design phase.
As structural manufacturers, we don’t specify what fire rating a building should have, but we design to the standards and specification provided.
3. How bad is it if glulam gets wet?
Managing moisture is critical for any timber structure, and different considerations depend on whether you’re using glulam or CLT.
For glulam, temporary exposure to moisture might cause some visible watermarks to appear, but these are generally repairable through sanding. Glulam has the advantage of allowing moisture to escape through exposed faces, meaning it can dry out naturally after getting wet. Problems typically only arise when moisture content stays above 20% for prolonged periods – we’re talking about many months or even years when rot or fungal growth might begin.
The main concern with glulam is when wet material is encased in a way that traps moisture inside, preventing it from drying out. As long as there’s a route for water to escape, most moisture issues can be easily managed.
CLT requires more careful moisture management due to its layered construction. The continuous glue lines act as barriers that trap moisture and the end grain can absorb water. If CLT gets wet and is sealed before properly drying, that moisture can remain trapped inside, potentially causing problems.
We take several protective measures with CLT, including factory-applied membranes for roofs and floors and end-grain sealers to help keep water out. We also recommend particular attention to roof details – for instance, avoiding flat CLT roofs in favour of a minimum 5-degree slope and omitting roof parapets in CLT, which can be prone to leaks if not properly detailed.
One practical tip to note – CLT isn’t recommended for consistently wet areas like shower rooms. It’s not that you can’t use timber in these spaces, but other solutions can be better due to the high moisture environment.
Moisture concerns are entirely manageable with proper design, installation, and maintenance. It’s about working with the material’s properties rather than against them.
For a thorough guide on moisture management, The Structural Timber Association’s Moisture Management Strategy is a comprehensive and thorough guide on moisture management.
If you’re planning on using glulam externally, this blog detailing tips for external glulam design helpful.
4. Is building with timber more expensive?
The honest answer is – it depends on your specific project. There’s no one-size-fits-all answer here.
Mass timber construction often (but not always) costs more than conventional methods, but we can provide early-stage cost advice specific to your project to help you understand the implications for your budget.
A CLT house will typically cost more than traditional construction methods, and glulam portal frames generally cost more than steel alternatives currently. That said, we’ve completed extensions ranging dramatically in cost – from £12,000 to £250,000 – showing the tremendous flexibility in how timber can be incorporated into projects of varying scales and budgets.
Mostyn Road in Wimbledon – design supply and fit: around £12k
Curved Oak Conservatory – Hampshire was around £150K (not including the curved double glazing!)
House for Oskar and Theo – was somewhere between the two.
The best approach is early engagement with us to understand cost implications for your specific design. We often suggest ways to achieve your vision while keeping costs manageable.
For detailed cost information, read our blog post, ‘How Much Does Glulam Cost?’
5. How long does it take to build with glulam – and will it last?
Timber construction involves multiple stages, each requiring time in your project schedule. It very much depends on the scale and complexity of your project.
1. The design phase typically takes 3-4 weeks for simple designs but can extend to many months for complex projects where the design needs to be developed from an early stage, especially with multiple parties involved.
2. Following design approval, material procurement and manufacture follows typically taking 8-10 weeks, occasionally extending to 12 weeks or more during our busiest periods or for the largest projects.
3. Installation time varies tremendously, from one week to several months, depending on the project’s size and complexity.
There is a lot to consider, which is why when we speak to someone with an enquiry, we work out WHERE in their project process they are so we can guide them from the start.
6. How long will it last?
The good news is – once installed and properly maintained, your timber structure will last for generations.
Building with glulam is relatively new, so we haven’t been around long enough to answer that question with specific numbers.
That being said, as our fungal expert colleagues like to point out – there’s wood in the pyramids that’s thousands of years old!
Keep timber dry, and it can last for millennia. The glue in modern glulam is essentially inert, like glass, and historic timber buildings standing across the UK and beyond are a testament to wood’s remarkable longevity.
Ready to Specify Glulam for Your Project?
The key to success with any timber project is early engagement with specialists like us at Buckland Timber. Our team will provide you with expert guidance through every stage of your project, from initial design considerations to installation.
Contact us today to discuss your project requirements and discover how glulam can create stunning, sustainable spaces that stand the test of time