It’s a little-understood part of the roofing process – and really, we aren’t surprised.
While crucial, it’s also somewhat… bland.
Who wants to talk about metal roof gauge when they could be talking about the more exciting stuff, like:
- What colour your brand new metal roof is going to be?
- How a new metal roof is going to increase your home’s value?
- The ease-of-maintenance that comes with metal roofing?
If you ask us, roof gauge is up there with roof plumbing, ventilation and air gaps as one of the most important criteria when planning metal roof installation in Melbourne.
And it’s also one of the least understood!
With a bit of luck however, once you’re done reading this, you’ll have a better idea about the importance of roof gauge (and more importantly, which gauge is right for you).
What is a roof gauge, anyway?
In a word: thickness.
Roof gauge plays a crucial role in how strong and durable your metal roof is. Depending on the application, one particular gauge might be more suitable given the circumstances.
Understanding which gauge your metal roofing installation in Melbourne should use is an important decision – you only get one shot at it (after all, you can’t rip up your roof and start over!)
And making that decision begins by understanding what gauge is best suited for your upcoming roofing project.
In Australia, we use BMT to measure the thickness of steel sheets for roofing.
What is BMT?
Why not just use millimetres?
Simple: because today’s metal roofing panels aren’t just a simple sheet of steel (or copper, or tin, or zinc) anymore.
Let’s look at COLORBOND metal roofing as an example. On top of a unique steel alloy optimised for strength, COLORBOND roofing is also covered with protective coatings and layers that help protect them from the harsh Australian conditions.
This is what makes today’s metal roofs considerably stronger than the roofs of old. It also makes millimetres a less-than-ideal way of gauging (get it?) thickness, as it doesn’t tell you how much is actual metal, and how much is coating.
Enter BMT, or Base Metal Thickness.
Essentially, BMT measures the thickness of the metal itself before any protective layers and paint are applied in millimetres. So 0.50BMT tells us that the steel base of this particular sheet is 0.5mm thick without coatings, primers or paint.
By contrast, we also have TCT, or Total Coated Thickness which, like the name suggests, measures the total thickness, coatings included.
When looking at roofing panels, it’s important to figure out what you’re dealing with. While the number is the same, 0.40BMT and 0.40TCT are completely different things – indeed, the first is effectively thicker (and therefore, stronger) than the second!
When planning for metal roofing installation in Melbourne, it’s important that you know the difference between these two measurements – it could save you a whole load of trouble!
The all-important question: which gauge should you use for your metal roofing installation?
The answer: it depends!
Thankfully, when it comes to corrugated metal roofing (the wavy stuff), there are 3 common gauges in use in Australia:
- 0.42 BMT
- 0.48 BMT
- 0.60 BMT
These are the gauges that COLORBOND uses for its metal roofing (and as the biggest and most reputable manufacturer in Australia, many smaller players also use these gauges).
But which one is right for you?
Should I use 0.42 BMT?
Used predominantly for domestic metal roofing installation, 0.42 BMT is the most common of the three on Melbourne homes.
For most homes, this is more than enough to deal with the types of weather conditions we experience here in Melbourne.
0.42 BMT gauge is adequate for most homes in the city, and is resistant to denting and other types of damage and wear your roof may experience throughout the year.
Of course, if you’re worried about denting and buckling, there’s nothing stopping you from upgrading to a thicker gauge!
For example, say your project also calls for a roof-mounted air conditioner, solar panels, or a satellite dish.
Work on any of these three will require someone to climb onto your roof – while it can take hailstones, 0.42 BMT has a harder time taking the full weight of a tradie and their equipment!
In these cases, our metal roofing experts recommend opting for a thicker gauge, at least for the area around your A/C or satellite dish.
What about 0.48 BMT?
Unlike its thinner cousin, 0.48 BMT is used primarily in industrial applications.
Part of this is due to the boost in strength and durability that comes from the added thickness.
Another reason for this however is that in many cases, it’s chosen to cut costs!
Metal framing is expensive – the less of it used, the better.
By choosing a thicker gauge for the roof, architects and structural engineers can get away with spacing out the roof trusses. The thicker roof compensates for the fact that trusses are further apart now.
This isn’t really a concern for homes, where roof area tends to be much smaller (not to mention, most Aussie homes use cheaper wood framing, making this less of a concern).
And what about 0.60 BMT?
One of the strengths of metal roofing is that it can be used in a much wider range of applications than tile. You have way more leeway in terms of:
- Pitch and angle
- Shape (think the wavy roof at Southern Cross Station)
- Design and appearance
That’s why metal is the roofing of choice for weird roofs, including steep, flat and curved roofs.
Here’s something you may not have known about the last one, however: while curved roofs look fantastic, bending metal can also potentially weaken it.
Hence, the need for 0.60BMT gauge!
Will your metal roofing installation look something like this? To compensate for the effect bending can have, 0.60BMT roofing can be used to increase the durability and strength of your roof.
There’s no rule saying that these are the ONLY times each gauge is appropriate…
If your budget permits, there’s nothing wrong with asking your metal roof installation team to upgrade to a thicker gauge for your roof.
Planning metal roofing installation in Melbourne?
Or metal roofing repairs? Or a gutter inspection?
If so, you’ll need to choose a gauge that’s appropriate for your home and circumstances.
Of course, that isn’t the only decision you’ll have to make when planning for metal roof installation in Melbourne – there’s also the question of metal type, installation method, fasteners and roofing product.
It’s a lot to take in – thankfully, our team of metal roofing experts can help.
We’ll work with you and your architect, answering all your questions about metal roofing and ensuring that you choose a gauge that won’t leave you with dents, leaks and other damage.
We bring 20 years of experience to bear on metal roofs all over Melbourne, ensuring that your roof is strong, durable and that it looks fantastic!