Glulam and fire safety: The burning questions you’re right to ask
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What’s the risk?
You don’t need to be a safety expert to see a possible link between timber and fire and then have questions about a building’s safety. You’re right to do so, and it’s one of the most often asked questions.
With over ten years of project experience, we can often be a valuable resource if you have questions not directly related to glulam. When it comes to fire, you want to be sure, firstly, that your building is safe and secondly that you’re not going to get tripped up by any regulatory-type building control issues, insurance, or problems in the future.
So, what are the steps to follow to achieve these points?
Get expert advice
While we’re experts in the design, manufacture and construction of your glulam for timber projects, we’re not fire experts. We take it seriously, though, and always advise you to engage with a fire consultant early on for your project.
There are many aspects of building design involving fire that we have little involvement with, but which may affect your design. Practical considerations, such as fire escape routes, fire alarms, and sprinkler systems, are all vital safety considerations when turning your concept into reality.
There are also regulations governing the design of buildings with timber. For example, there are regulations restricting the use of combustible materials in multi-storey residential buildings that must be followed. The key for you to understand is that once a fire consultant has been engaged, they will specify some fire ratings for your structure. It is only after this stage that we can offer further advice.
Broadly speaking, the specified fire ratings for your project that we can help with will deal with two things:
- How long can the structure stand up in a fire and
- How the material reacts when it is burnt
In-house glulam fire testing
1. Fire resistance: Keeping structures standing
The first way we can help is with structural fire resistance. This is about how long a building’s load-bearing structure can continue to carry weight during a fire, allowing people time to escape. In other words, if the worst happens, how long will the building stay standing?
Fire resistance is usually specified in minutes and is set by a qualified fire engineer, not by us. Independent eyes are essential here, and you may come across 30-, 60-, or 90-minute fire ratings.
The good news is glulam structures perform well in this area. So, how do we do it? We design glulam and CLT elements to meet these durations using the charring rate method.
What is the charring rate method?
Timber chars at a predictable rate, at around 25mm every 30 minutes. Knowing this lets you build allowances into your designs, like extra thickness to meet the higher fire ratings.
For example, if you need a beam to resist fire for 60 minutes, we allow for a 50mm char layer on exposed faces, making sure the remaining section is still strong enough to do its job.
We also look at the connections of the design – after all, a structure is only as strong as its joints, which is why we take extra care with all connections in our manufacturing process.
The connections can be checked using the charring rate method or by using available fire sealant materials.
- Metal brackets and fixings should be concealed inside the timber, where the surrounding wood protects them.
- We also sometimes use fire stop materials in connection gaps to prevent fire from tracking through joints and weakening the structure.
2. Designing for reaction to fire
The second way we can help is when you have a surface spread of flame or reaction to fire rating requirement for the CLT or glulam elements of your project.
We don’t specify fire ratings but we can share a little more information about what fire ratings mean.
A ‘Reaction to Fire’ rating is based on how fire behaves on timber surfaces. This is rated using the Euroclass system (BS EN 13501-1), and looks at:
- How easily the material ignites (A1 to F in the table below)
- How much smoke is produced (S1-S3, table below)
- Whether it makes flaming droplets (d0-d2, table below)
| A1 | The product is classed as a Non-Combustible |
| A2 | Limited Combustability |
| B | Combustible materials - Very limited contribution to fire |
| C | Combustible materials - Limited contribution to fire |
| D | Combustible materials - Medium contribution to fire |
| E | Combustible materials - High contribution to fire |
| F | Combustible materials - Easily flammable |
| s1 | Emissions absent or very little |
| s2 | Emissions with average volume intensity |
| s3 | Emissions with high volume intensity |
| d0 | No burning droplets |
| d1 | Slow dripping droplets |
| d2 | High/intense dripping droplets |
Table showing Euroclass ‘Reaction to Fire’ ratings (BS EN 13501-1) for timber surfaces
Slowing fire spread – applying a treatment
So how does glulam typically perform against these ratings, and what can be done to improve it?
A typical example would be where a project requires a reaction to fire rating of, say, B, S1-d0. So based on the table above this translates to:
B = Combustible materials – very limited contribution to fire
S1 = Emissions absent or very little
d0 = No burning droplets
Our glulam has a reaction to fire class D-s2, d0, and at Buckland, we are often asked to supply a reaction to fire class B-s1, d0 rated product. To bring it to the required class, the glulam requires an additional treatment.
In the UK, we mainly focus on the surface spread of flames (the combustibility). For large, exposed areas, such as CLT panels or structural roof decking, the solution is typically a fire-retardant coating that slows the spread of fire.
If you or your fire engineer requests fire treatment for your glulam, it can be applied during manufacture or on-site – we tend to apply it only in the factory.
While we don’t recommend or specify a specific coating to use, we ensure its applied in accordance with the manufacturer’s guidance. A factory application makes this process much easier to achieve and document. Of course, we’ll then provide you with the records to trace what has been done, so you can give evidence to whomever needs to know.
Buckland recently used Nordtreat, specified by the client for two rail station projects. We know the specific requirements for the application of Nordtreat finishes, and we’re confident in the finish they give. They’re also low in volatile organic compounds, which is important for us, as it keeps things environmentally friendly.
Want to read a bit more about fire treatment? Do take a look at our blog post for more information about the work involved: “The full treatment with Buckland Timber – Why choose Nordtreat flame retardant protection?”
Charred glulam
Fire safety: Never “one and done”
When it comes to fire, you can’t rest on your laurels and trust everything will be fine. That’s true for brilliant timber design and manufacturing, full stop. It’s also true for fire safety and evolving best practice, so we always choose to work with companies that share our approach.
We’re also currently carrying out our own in-house testing on treated glulam.
With glulam, we want to investigate how the more frequent glue lines (compared to CLT) can be best protected using a fire treatment. There’s some evidence to say that fire can track up the glue lines in glulam and we have commissioned some of our own testing to investigate this. While it is up to the treatment manufacturers to provide their own certifications, we’re interested in being as well informed as possible so we can give the best guidance.
So, what can you expect from Buckland?
As we’ve outlined here, we can explain the process, how we can help, and when to bring in expert advice, but we can’t determine the specific requirements you need – we leave that to the fire experts.
We also can’t tell you what fire rating a beam or frame has if it is retrospective for buildings we’ve not been involved with. This question usually comes from insurers, and we get it, but we can’t provide those ratings ourselves, it has to come from the original building designer.
It’s good for everyone that fire safety standards are independent, what we can do is ensure you get detailed design drawings, calculations, and materials used, and records of any treatments applied. You’re then in a strong position to pass everything on to the fire engineer and sign things off – one less thing to worry about!
For more details on what you need to know when specifying glulam for your project, check out our blog here, or if you’re thinking about your next project and would like to talk it through with one of the team, get in touch!