Short answer. Roofing materials differ not in looks but in three quantities you can calculate: mass, minimum pitch and whether there is a module along the length. Mass spans a factor of twenty — from 3.4 kg/m² for bitumen corrugated sheet to 74 for heavy clay tile — and that is what drives the rafters and the noise. Pitch eliminates half the list before budget is even discussed. We sell steel, so the figures for other materials come from published sources, not from our price list.
Mass per m² of roof
| Material | Mass | On a 4 × 9 m slope | Noise vs profiled sheeting |
|---|---|---|---|
| Bitumen corrugated sheet (Onduline type) | 3.4 kg | 122 kg | −1.6 dB |
| T35 profiled sheeting, 0.45 mm | 4.1 kg | 148 kg | — |
| Metal tile, 0.45-0.50 mm | 4.1-4.5 kg | 148-162 kg | +0.4 dB |
| Asphalt shingles, 3-tab | 9.5 kg | 342 kg | +7.3 dB |
| Asphalt shingles, architectural | 14.9 kg | 536 kg | +11.2 dB |
| 8-wave asbestos-cement slate | 16.6 kg | 598 kg | +12.1 dB |
| Clay tile | 29-74 kg | 1,044-2,664 kg | +17 to +25 dB |
The noise column comes from the mass law: 20 · log(m₂ ÷ m₁). It is the theoretical ceiling for a solid barrier; a real roof build-up delivers less, but the order is right.
The main lesson from the table is not about noise but about rafters: clay tile loads a slope 7 to 18 times harder than steel. That is not “a slightly dearer frame”, it is a different roof structure. Which is why choosing the material after the rafters are up is usually too late.
Minimum pitch
| Material | Minimum pitch |
|---|---|
| Bitumen sheet on solid decking | from 5° |
| Bitumen sheet on purlins | from 10° |
| T57 profiled sheeting | from 6° |
| T45 / T35 / T20r | from 8° / 9° / 12° |
| Classic metal tile | from 14° |
| Asbestos-cement slate | from 22° |
For asphalt and clay tiles the minimum pitch is set by the individual manufacturer’s instructions — there is no universal figure here, and we are not going to invent one.
In practice it works like this: at 8° the choice has narrowed to two steel profiles and bitumen sheet on solid decking. Everything else dropped out before price was mentioned.
The module along the length
The third quantity, almost never discussed: can you get a sheet the length of the slope?
| Material | Module | Transverse joints on a 4 m slope |
|---|---|---|
| Profiled sheeting | none, any length | none |
| Metal tile | 350 mm step | none if the length is a multiple |
| Bitumen sheet | 2 m sheet | two lines |
| Asbestos-cement slate | 1.75 m sheet | two lines |
| Any tile | the tile itself | joints across the whole plane — by design |
Every transverse joint is an extra row of battens and a place where water stands in the lap. On tiled roofs that is built into the system and compensated by the shape of the tile. On sheet roofs it is a cost you can avoid.
Bitumen sheet or metal tile
This is the commonest head-to-head, and the answer is not the usual one. By mass they are practically equal: 3.4 against 4.1-4.5 kg/m². So by the mass law bitumen sheet is not quieter — the difference is 1.6 dB, and it favours steel.
But rain on bitumen sheet really does sound softer, and the reason is the material rather than the mass: a bitumen-impregnated cellulose sheet damps the impact through internal friction, while steel rings. That is a real advantage — it just does not come from the mass law. How noise is treated on a metal roof is covered separately.
Against bitumen sheet: bitumen softens in heat, which is exactly why the manufacturer splits the pitch into 5° on solid decking and 10° on purlins — without continuous support the sheet moves. And a bitumen-cellulose sheet is combustible, unlike steel.
What we do not do
We do not sell bitumen sheet, asphalt or clay tile or slate, we do not strip old roofs and we do not design rafters. We roll steel sheet to size and fold flashings from the same coil.
How to order
Step 1. Measure the pitch
That eliminates half the list before you look at any prices.
Step 2. Work out what the rafters will carry
Mass from the table times the area of the slopes. For clay tile that is a question for the structural design, not for colour choice.
Step 3. Order sheet to the slope length
Call (067) 077-56-77, Mon-Fri 08:00-17:00. Production 1-2 days, delivery another 1-5 days.
FAQ
What is cheapest? It depends on the slope and the region, and the material price is not the whole sum. A light material saves on rafters; a heavy one adds. Compare complete roofs.
What lasts longest? Clay tile, if the rafters can carry it. Steel lasts as long as its polymer coating — warranties by coating class.
Can a new material go over the old one? Sometimes. Worked through for slate here.
What really separates profiled sheeting from metal tile? Only the module: metal tile has a 350 mm step and therefore offcuts, profiled sheeting has no period at all. Mass and coating are the same.