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Roofing guide

TCT vs BMT — Reading Roofing Sheet Thickness Correctly

Why two roofing sheet quotations at "0.50 mm" can contain different amounts of steel, and how to compare them.

Roofing and colour-coated sheet thickness is quoted in one of two ways:

TCT — total coated thickness: base steel plus metallic coating plus paint layers.
BMT — base metal thickness: the steel substrate alone.

For the same stated number, a TCT sheet has less steel than a BMT sheet, because part of the TCT figure is coating and paint. Structural performance and weight depend on the base steel.

How to compare quotations

Confirm whether each quotation is TCT or BMT.
Confirm the metallic coating (for example AZ150) and paint system (RMP, SMP, PVDF).
Compare on the same profile and effective cover width.
Compare the price per running metre or per square metre of cover, not per tonne alone.

What to write in the BOQ

State "0.50 mm BMT" or "0.50 mm TCT" explicitly, with coating and paint system. If a consultant's specification says only "0.50 mm", ask which basis is intended before ordering.

Related: Profiled roofing sheets · PPGL sheets · IS 15965

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