Short answer. Steel thickness does not solve noise. Going from 0.45 to 0.50 mm adds 0.9 dB of sound insulation — below the threshold at which the ear notices any difference at all. Noise under a metal roof is fixed by the build-up beneath it, not by the sheet. And there are actually two noises — rain and thermal ticking — and they are fixed by different things.
Why thicker steel does not help
The sound insulation of a uniform panel is governed by its mass: doubling the mass buys roughly 6 dB. The formula is simple — gain = 20 · log(m₂/m₁). Put our thicknesses into it:
| Change | Mass ratio | Insulation gain |
|---|---|---|
| 0.45 → 0.50 mm | 1.11 | 0.9 dB |
| 0.45 → 0.70 mm | 1.56 | 3.8 dB |
| 0.40 → 0.70 mm | 1.75 | 4.9 dB |
| doubling the mass (for reference) | 2.00 | 6.0 dB |
Even the thickest steel in our range does not reach one doubling of mass. A 0.9 dB difference is inaudible. To be clear: steel thickness is chosen for load and stiffness, not for noise — different problems.
The same logic kills profile choice as a noise measure. T57 instead of T20r is about pitch and batten span, not about how loud the rain is.
What actually reduces rain noise
| Measure | What it does | How important |
|---|---|---|
| A cold attic | decouples the roof from the living space with an air volume and a floor | the most effective, and usually free — you either have one or you do not |
| Insulation in a habitable loft, 150-200 mm | absorbs and adds mass to the build-up | the main measure where there is no attic |
| Thermal and acoustic insulation under the sheet | damps the sheet’s own ring at the moment a drop lands | audible, works together with the insulation |
| A lined ceiling below | adds mass on the other side of the build-up | cheap and underrated |
| Closer batten spacing | shortens the free span of the sheet, so the amplitude drops | a side effect; nobody does it for noise alone |
One logic runs through all of it: the sheet is a membrane. Either press something absorbent against it or separate it from the living space. Neither has anything to do with which steel you ordered.
One exception: a gazebo is the one place where none of these work, because you sit directly under the sheet with no build-up at all. That is covered in the gazebo article.
The second noise: ticking with no rain
A metal roof ticks in the evening after a sunny day and again at dawn. That is not rain and not wind — it is thermal expansion. Steel expands at 12 · 10⁻⁶ per degree, and on a long sheet that comes to measurable millimetres.
| Sheet length | 50 °C swing | 80 °C swing |
|---|---|---|
| 3 m | 1.8 mm | 2.9 mm |
| 6 m | 3.6 mm | 5.8 mm |
| 9 m | 5.4 mm | 8.6 mm |
An 80 °C swing is not an exaggeration: in winter the sheet sits at −20, and in summer a dark surface in the sun runs well above air temperature. Six metres of steel travel almost a centimetre over the year, and every movement happens in jerks as the metal breaks free of friction against the batten and the screw. That is the ticking.
What to do about it: do not overtighten the screws. The washer should press the sheet, not clamp it — otherwise the expansion has nowhere to go and a quiet slide becomes a sharp snap. Lengths and tightening rules are in the fixings article.
What we do not do
We do not design roof build-ups, calculate acoustics or visit sites. We sell the sheet and the materials that go under it, insulation included.
How to order
Step 1. Decide what is under the roof
A cold attic or a habitable loft. Everything else follows from that, not from the sheet.
Step 2. Choose the profile by pitch
Not by noise. Minimum pitches by profile are in the roof installation article.
Step 3. Order the sheet and the layer under it together
Call (067) 077-56-77, Mon-Fri 08:00-17:00. Production 1-2 days, delivery another 1-5 days.
FAQ
Is metal tile quieter than profiled sheeting? No. Mass per square metre is of the same order, and noise is set by mass and build-up, not by the pattern.
Does an anti-condensation backing help? Partly: the fleece damps the ring and holds condensation, but it does not replace insulation.
Why is my neighbour’s roof quieter? Usually because they have a cold attic and you have a habitable loft. The material is not the reason.
Can anything be done on a roof that is already built? From below, yes: insulation between the rafters and a lined ceiling. From above, nothing without taking the sheet off.