Oct
Colorbond thickness is measured in BMT, or base metal thickness, which is the thickness of the steel before any coating or paint is applied. Most Brisbane homes are roofed with 0.42mm BMT Colorbond. The sturdier 0.48mm BMT suits hail-exposed sites, roofs carrying solar panels, and roofs where sheets need to span further between supports.
If you’re comparing roofing quotes, the BMT figure is one of the simplest ways to check you’re comparing like with like. This guide explains what the numbers mean, how 0.42 and 0.48 differ, and what to look for before you sign.
What Does BMT Mean on Colorbond Roofing?
BMT stands for base metal thickness. It measures the steel core of the sheet only. It doesn’t include the metallic coating that protects the steel from rust, or the primer and paint layers that give Colorbond its colour.
In Australia, Colorbond steel roofing comes in 0.42mm, 0.48mm or 0.60mm BMT, depending on the product. For residential roofing, the choice almost always comes down to 0.42mm or 0.48mm.
BMT vs TCT: Why Your Roof Sheet Measures Thicker
TCT, or total coated thickness, is the thickness once the protective metallic coating has been added. The paint layers add a little more on top of that. So if you measure a Colorbond sheet yourself, it will always read slightly thicker than its BMT figure. That’s normal and doesn’t mean you’ve been given a heavier sheet.
This matters when you compare quotes. A quote listing a thickness that’s a few hundredths of a millimetre above 0.42 can sound heavier than one showing “0.42mm BMT”, even though both could be the same sheet. If a quote lists a thickness without saying BMT or TCT, ask which one it is.
0.42 vs 0.48 Colorbond: Which Should You Choose?
| 0.42mm BMT | 0.48mm BMT | |
|---|---|---|
| Typical use | Standard residential roofs | Larger, exposed or heavier-duty roofs |
| Weight | Lighter | Heavier |
| Dent resistance | Good | Better |
| Span between supports | Standard | Can span further |
| Cost | Lower | Higher |
0.42mm BMT is the standard thickness for most residential roofing. It’s lighter to handle and install, costs less, and performs well on a typical pitched roof with standard batten or purlin spacing.
0.48mm BMT is stiffer and more resistant to denting from hail and foot traffic. Because it’s more rigid, some profiles can span further between supports, which suits large roofs, commercial buildings and roofs with regular maintenance access.
Both thicknesses come in the same Colorbond colour range. Many Colorbond colours also include Thermatech® solar reflectance technology, which helps reduce heat build-up in summer whichever thickness you choose.
What Colorbond Thickness Do Brisbane Homes Need?
For most suburban Brisbane homes, 0.42mm BMT Colorbond does the job. It’s what most residential re-roofs use, and it handles everyday Queensland conditions well.
It’s worth talking to your roofer about 0.48mm if:
- your suburb has a history of hail damage during storm season
- you’re planning to install solar panels or other rooftop equipment
- you have a large or low-pitched roof that needs longer sheet spans
- the building is commercial or gets regular roof access for maintenance
The correct thickness also depends on the roof profile and the wind rating for your site. A qualified roofer checks the manufacturer’s span and wind tables for your property, so thickness shouldn’t be a guess.
Does Thicker Colorbond Last Longer Near the Coast?
No. A thicker base steel makes a stronger sheet, but it doesn’t make the roof more resistant to corrosion. Corrosion protection comes from the metallic coating and paint system.
For homes close to the ocean, such as on the Gold Coast, the Sunshine Coast or Brisbane’s bayside suburbs, the more important choice is the product type. BlueScope’s Colorbond Ultra is designed for harsher coastal environments. Colorbond warranty terms also vary depending on how close your home is to the coast, so check which product and warranty apply to your address before you commit.
How to Check the Thickness on Your Roofing Quote
A clear roofing quote should tell you:
- The BMT of the roof sheets. Look for “0.42mm BMT” or “0.48mm BMT”, not just a thickness figure.
- The profile. For example, corrugated, Trimdek or Klip-Lok.
- The product. Standard Colorbond, Colorbond Ultra or Zincalume.
- The material and thickness of the flashings and gutters. These should be listed too, not just the roof sheets.
- The warranties. Both the manufacturer’s warranty and the installer’s workmanship warranty, in writing.
For a broader look at pricing, see our guide to Colorbond roofing costs in Australia. If you’re still deciding between finishes, read what’s the difference between Zincalume and Colorbond roofs.
Why Brisbane Homeowners Choose Roo Roofing
Roo Roofing has been replacing and restoring Brisbane roofs for more than 23 years. We’re QBCC licensed (#1147373) and Master Builders members. We work with quality Colorbond and Zincalume products and recommend the right thickness and profile for your home, not just the cheapest option.
Our metal roof replacement work comes with an installation warranty of up to 10 years, alongside manufacturer warranties of up to 36 years and our Watertight Guarantee.
Frequently Asked Questions
Is 0.42 Colorbond Thick Enough for a House?
Yes, for most homes. 0.42mm BMT is the standard thickness for residential Colorbond roofing and suits typical pitched roofs with standard support spacing. Your roofer should confirm it against the profile’s span and wind tables for your site.
Is 0.48 Colorbond Worth the Extra Cost?
It can be, if your roof is large, exposed to hail, carrying solar panels or getting regular foot traffic. 0.48mm is stiffer and more dent-resistant. For a standard suburban home in a sheltered spot, 0.42mm is usually enough.
Does Colorbond Thickness Affect the Warranty?
The manufacturer’s warranty depends mainly on the product you choose, your home’s environment (particularly distance from the coast) and correct installation. Ask your roofer to confirm in writing which warranty applies to your property.
Can You Walk on 0.42 Colorbond?
Roofers walk on Colorbond along the fixing lines, where the sheet is supported underneath. 0.48mm is stiffer and less likely to dent under foot traffic, which is one reason it’s specified for roofs that need regular access.
Book Your Free Roof Assessment
Not sure which Colorbond thickness is right for your home? Our team will inspect your roof, explain your options in plain English and give you a clear, itemised quote. Call 1300 734 148 or book your free roof assessment online, and we’ll get back to you within 24 hours.
