Colour coated roofing sheet
3 Rib roofing sheet, rated down to a 3° pitch
The 3 Rib is our main roofing sheet: a colour coated galvalume trapezoidal profile with 1,000 mm effective cover, four 250 mm pitches of three ribs each, and a minimum roof pitch of 3°. We roll it in 0.5 mm TCT, cut to your lengths up to 12 m.
It is the sheet we suggest for most factory, warehouse and shed roofs. The crest is domed so it can be walked on during erection and maintenance, and the side laps are formed to keep water out at low slopes.
Where it is used
Roofs of factory sheds, warehouses and pre-engineered buildings, and the walls of the same buildings where the owner wants one profile throughout. It is rated down to 3°, so it suits low-slope roofs up to 12 m from ridge to eave. A longer roof needs end laps, and then we ask for 5° or more. The domed crest suits roofs that maintenance staff will walk on.
If the roof is flatter than 3°, or you need one sheet to run more than 12 m without an end lap, look at the 4 Rib standing seam instead and talk to us about the purlin spacing.
Specifications
| Supply width | 1060 mm ± 5 mm |
|---|---|
| Effective cover width | 1000 mm ± 5 mm |
| Crest height | 30 mm ± 2 mm |
| Crest width | 25 mm |
| Profile pitch (centre to centre) | 250 mm ± 2 mm |
| Pitches per sheet | 4 |
| Ribs per pitch | 3 |
| Thickness | 0.5 mm TCT, about 0.45 mm BMT (0.3 to 0.7 mm TCT on order) |
| Minimum roof pitch | 3° |
| Side laps | Anti-capillary |
| Coating | Aluminium-zinc (galvalume) AZ150, to AS 1397 |
| Steel grade | 550 MPa |
| Top paint coat | 25 microns, RMP or SMP |
| Maximum length | 12 m |
| Also available | Crimp-curved |
Material
The 3 Rib is rolled from galvalume coil: steel with an AZ150 aluminium-zinc coating to AS 1397, in 550 MPa steel, with a 25 micron top coat of RMP or SMP paint. We buy the coil from JSW, Tata, AM/NS or POSCO, and the mill test certificate for the coil you receive comes with the consignment.
AZ150 means 150 grams of aluminium-zinc coating per square metre, counting both sides of the steel. It is the coating class to check on a quote, together with the base metal thickness, because the paint colour tells you nothing about the steel underneath.
What the profile does
- Domed crest. The top of each rib is domed rather than flat, which lets it take foot traffic during erection and later maintenance. People should still walk on the purlin lines.
- Anti-capillary side laps. The lap between sheets is formed so that water is not drawn sideways into it, which is what lets the sheet go down to a 3° pitch.
- 1,000 mm cover. Four 250 mm pitches across a 1,060 mm supply width, lapped to 1,000 mm. A shed 50 m long needs 50 sheets along each side of the roof, before allowances.
- Crimp-curved option. The sheet can be crimp-curved for curved roofs and eaves, to a minimum of 6.5°.
- Cut to length. Sheets up to 12 m, cut to your cutting list at the plant, so there is little cutting on site.
Fixing and laying
The 3 Rib is fixed through the crest to the purlins with self-drilling screws and sealing washers, 55 mm long on the roof and 25 or 35 mm on cladding. On the roof, each side lap is also stitched between the purlins with screws at 300 mm centres or closer. Wherever practicable, the sheets are laid so the exposed side-lap edge faces away from the prevailing wind, starting at the leeward end of the roof and working towards the wind. The 3 Rib has an anti-capillary side lap, so the approved MNF profile drawing and your project specification set the laying direction, and they take priority. Fit foam fillers cut to the profile at the eaves and ridge to close the rib openings.
Purlin spacing is set by our engineer against the wind and load on your site, so send the drawing or the building size and we will check it before pricing.
Limits
Two things to know before you order. Below 3° we do not recommend the 3 Rib. And the longest sheet we can send by road is 12 m, so a longer slope is covered with end laps, sealed and fixed over a purlin, and laid at 5° or more. Each end lap is at least 200 mm long, or 150 mm on a roof steeper than 15°.
Accessories for the 3 Rib
Ridges, eave and valley gutters, gable and corner flashings, drip trims and foam fillers are made to match the 3 Rib in colour and profile. For daylight we supply FRP sheets made to match the roof profile you order, and turbo ventilators with a base plate matched to the roof. See the accessories page.
Colours
Standard colours from the coil suppliers' colour-coated range; RAL shades and special colours on order with a minimum quantity. Colours on screen differ from the coated sheet, so ask for a swatch before you decide.
Send the roof area or a cutting list and the colour, and we will price the 3 Rib for you.
Get a quoteQuestions buyers ask us
What is the minimum roof pitch for a 3 Rib sheet?
3°. The anti-capillary side lap and the domed crest keep water moving at that slope. On a roof long enough to need end laps we ask for 5° or more, and a little extra pitch helps on a site with heavy rain.
What is the cover width of the 3 Rib sheet?
1,000 mm effective cover, from a supply width of 1,060 mm, both within plus or minus 5 mm. So a shed 60 m long needs 60 sheets along each side of the roof, before allowances.
Can people walk on the 3 Rib roof?
Yes. The crest is domed so it takes foot traffic during erection and maintenance. Walk on the purlin lines, and keep regular traffic to a walkway if there is one.
What thickness is the 3 Rib and what is the coating?
0.5 mm TCT as standard, in 550 MPa steel with an AZ150 galvalume coating and a 25 micron RMP or SMP top coat. That is about 0.45 mm BMT. Other thicknesses from 0.3 to 0.7 mm TCT are rolled on order, and our thickness guide gives the approximate BMT for each.
Can the 3 Rib be curved?
Yes, it is available crimp-curved for curved roofs and eaves, to a minimum of 6.5°. Send the radius with your enquiry and we will confirm it can be done.
How long can a 3 Rib sheet be?
Up to 12 m, which is the longest we send by road. Longer slopes are covered with end laps over a purlin, at least 200 mm long, or 150 mm on a roof steeper than 15°.