A drawing note that simply says "40mm TRUECORE battens" leaves out the two things that actually determine whether the batten performs on this specific roof: base metal thickness (BMT) and the span it needs to carry between supports. Getting the depth right and the BMT wrong (or vice versa) produces a batten that looks correct on delivery and underperforms once loaded.
Depth, BMT and span are three separate decisions
40mm is a common commercial batten depth, but the same nominal depth is manufactured across different BMTs to suit different spans and loads. A 40mm batten at a lighter BMT spanning too far under load will deflect more than the roof system tolerates; the same depth at a heavier BMT handles a longer span or heavier roof loading. Always confirm BMT and span rating together against the actual purlin/rafter spacing on the job — not just the depth noted on a generic specification.
Coordinating batten depth with insulation thickness
Batten depth directly affects available clearance for a roofing blanket sitting between batten and sheet on some roof constructions. On jobs where a thicker ThermaRoof blanket (moving toward the higher end of the R1.3–R4.2 range) is specified alongside standard battens, check that the combined build-up doesn't create excessive compression at the batten line — this is the same compression problem spacer systems solve for purlin-direct fixing, and it applies just as much where battens are involved.
Where 40mm TRUECORE fits
- Standard commercial tiled and metal roof battening at typical purlin/rafter spacings, where 40mm depth balances cost and structural performance for common spans.
- Re-roof and re-batten jobs where existing rafter spacing is fixed and the batten needs to suit that spacing without structural modification.
- Jobs pairing standard-thickness insulation where clearance isn't the binding constraint.
Where spans are longer, loads are heavier (heavy tile, wind-exposed sites), or a thicker insulation pack is specified, a deeper batten or heavier BMT may be the correct answer even though 40mm reads as the "standard" choice on paper.
The most common batten mistake we see isn't wrong depth — it's the right depth at the wrong BMT for the actual span, which only becomes visible as deflection once the roof is loaded and the problem is a lot more expensive to fix.
Corrosion protection at cut edges
TRUECORE steel's corrosion protection performs differently at cut edges and fixing points than across the coated face — site cutting practice matters. Confirm the roofing crew is using appropriate cutting methods (avoiding excessive heat build-up that can compromise coating at the cut) and that fixings are appropriately rated and compatible, particularly in coastal or corrosive environments where mismatched fixings accelerate localised corrosion.
Before you order
Confirm actual purlin/rafter spacing on the specific roof (not assumed from a similar job), target BMT and span rating for that spacing and expected load, insulation thickness being paired with the batten system, and site environment (coastal, industrial, standard) affecting corrosion protection needs. Send us the roof plan and span details and we'll confirm the correct batten spec rather than defaulting to whatever depth was ordered last time.
