Short answer. The pitch of a mono-pitch roof barely affects how much steel you buy, but it fully determines the height of the frame and which profile you may use. On a 6 m span, going from 6° to 14° adds just 2.5% to the sheet and 137% to the rise. So the pitch is chosen from the profile and the snow, not from saving on metal.
The formulas behind it
A mono-pitch roof is a right triangle. Two quantities follow from the span and the angle:
| Quantity | Formula |
|---|---|
| Rise | h = B × tan(α) |
| Slope length | L = B ÷ cos(α) |
| Slope area | S = L × building length |
B is the span, the width of the building across the slope. α is the pitch angle. Below is the same table in numbers for a 6 m span and a building 10 m long.
| Pitch | Rise h | Slope length L | Slope area | L exceeds the span by |
|---|---|---|---|---|
| 6° | 0.63 m | 6.03 m | 60.3 m² | 0.6% |
| 8° | 0.84 m | 6.06 m | 60.6 m² | 1.0% |
| 9° | 0.95 m | 6.07 m | 60.7 m² | 1.2% |
| 12° | 1.28 m | 6.13 m | 61.3 m² | 2.2% |
| 14° | 1.50 m | 6.18 m | 61.8 m² | 3.1% |
| 20° | 2.18 m | 6.39 m | 63.9 m² | 6.4% |
| 30° | 3.46 m | 6.93 m | 69.3 m² | 15.5% |
What the table actually says
Read the last two columns together. From 6° to 30° the rise grows 5.5-fold — from 0.63 to 3.46 metres. Over the same range the slope length grows by less than 15% — 14.8%.
So a steep roof costs more not because of the metal but because of the frame: a taller back wall, longer posts, more tube or masonry. The steel barely figures in that sum. “I will make it shallower to save on sheet” saves a couple of per cent and imposes hard limits on which profile you may use.
What the pitch really decides
| Pitch | Profiles you may lay | Snow behaviour |
|---|---|---|
| from 6° | T57 only | snow sits, load at maximum |
| from 8° | T45, T57 | slides poorly |
| from 9° | T35 and above | slides poorly |
| from 12° | T20r and above | begins to slide |
| from 14° | all roofing profiles, including Classic | slides noticeably better |
| from 20° | all | clears itself during a thaw |
The minimums in the left column are not advice but the limit for that profile. Below them water climbs the horizontal overlap by capillary action whatever the quality of the installation.
Why a shallow roof needs a stronger profile
Two reasons compound. First, on a shallow roof snow does not slide and sits until the thaw, so the design load is higher. Second, a shallow roof cannot take a low wave because of the capillary effect, and T57 with its 57 mm wave is at once tighter at the overlap and stiffer across the span.
So “an almost flat roof in a cheap profile” does not work: the cheap profile leaks at that pitch, and the one that does not is dearer per square metre.
How to order
Step 1. Work out the rise and slope length
Use the formulas above, or give the manager the span and the pitch you want and we will do it together.
Step 2. Choose the profile by pitch
From the table. If the pitch is already fixed by the structure, the choice narrows automatically.
Step 3. Order sheets to the slope length
Call (067) 077-56-77, Mon-Fri 08:00-17:00. Production 1-2 days, delivery a further 1-5 days.
What we do not do
We do not design roofs, calculate the snow load for your area or size rafters. We give you the profile geometry, the minimum pitch and sheets cut to the slope.
FAQ
What is the lowest pitch possible at all? For our range, 6°, and only with T57. Below that you need a different material, not profiled sheet.
Can I do 5°? Not with our profiled sheeting. That is flat-roof territory with a different type of covering.
How much dearer is the steel on a steeper roof? On a 6 m span, moving from 9° to 20° adds 3.1 m² per 10 metres of length — about 640 UAH in T35.
Do shallow roofs need closer battens? Yes, and precisely because of snow. The spacing comes from the designer; we do not name it — details in a separate article.
How long is the wait? Production 1-2 working days, delivery a further 1-5 days.