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Roof Types & Measuring
Single Slope Roofs
A single-slope roof (also known as a mono-pitch or lean-to roof) requires accurate length and width measurements for us to quote your sheeting needs.
- The width determines how many sheets you’ll need.
- The length determines the sheet length required.
Apex Roofs
Apex roofs meet at a central ridge. To calculate your sheeting requirements, measure from the ridge down to the eaves on both sides, as roof dimensions can vary.
If the apex is uneven, record each side separately.
Top Tip:
Take measurements in multiple places to ensure the roof is square. If dimensions differ, always order sheets to the longest measurement.
Roof Pitch & Purlin Spacing
Minimum Roof Pitch
Box profile sheets require a minimum pitch of 4°. If unsure, seek guidance from a structural engineer.
Typical Purlin Spacing
- 0.7mm sheets: up to 1.2m apart
- 0.5mm sheets (usually for cladding): no more than 1m apart
These figures are recommended guidelines – always check suitability for your project.
Commercial Buildings & Two-Sheet Runs
For commercial buildings or longer roof spans requiring two-sheet runs:
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A minimum pitch of 4° still applies.
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Ensure a purlin supports the sheet overlap.
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Follow the recommended spacing above.
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Always confirm structural suitability with your engineer.
Sheet Positioning & Laps
Side-Lap Overlaps
Before fixing, position sheets on the roof to confirm correct overlap. Sheets must overlap by at least one profile side-to-side. Colour caps can be added to match the sheet colour and cover exposed screw heads.
End-Lap Overlaps
Where two sheets meet on longer runs, allow a recommended minimum 200mm overlap.
- Ensure the overlap is supported by a purlin.
- Side overlaps must remain at least one profile.
We supply sheets up to 12m in length. Anything longer will require a two-sheet run.
Sheet Laying Order
For two-sheet runs, begin at the eaves on the corner opposite the prevailing wind to reduce the risk of side-lap water ingress.
Ensuring the first sheet is square will prevent a “saw-tooth” effect at the eaves.
Fixing the Sheets
Main Sheet Fixing Position
Fix box profile sheets through the valley of the profile. We recommend using our self-drilling, self-sealing tek screws.
Top Tip:
Avoid over-tightening or under-tightening screws, as this can affect washer performance and waterproofing.
Stitcher Screw Spacing
When fixing flashings, use 22mm stitcher screws.
Stitcher screws should be spaced no more than 400mm apart to ensure a secure, weather-resistant joint.
Ridge Fixings
When securing ridge flashings, use TEK-type stitcher screws through the highest point of each profile.
Ridge fillers can be installed to help prevent water ingress and keep out birds and vermin.
Flashings & Finishing
Flashings & Finishing Edges
Once the final sheet is installed, use flashings to seal the sides and apex. Flashings provide essential weatherproofing and a clean, professional finish.
Barge Flashings
Barge flashings help seal and weatherproof roof edges while improving the overall finish.
- Minimum overlap on barge flashings: 200mm
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Secure using stitcher screws
- Mastic lapping tape can be used for additional protection
Ridge Flashings
Ridge flashings are used on apex roofs, while single-slope roofs may require a custom design.
Fix ridge flashings using stitcher screws through the flashing into the sheets. Always install ridge flashings opposite the prevailing wind, overlapping each section by at least 200mm.
Custom Flashings
Custom flashings can be manufactured to match your steel sheeting and provide essential weatherproofing – particularly where sheet runs meet at the ridge.
Weatherproofing & Accessories
Foam Fillers
Eaves and ridge foam fillers improve weather resistance and help prevent bird and vermin entry.
Use a flexible, waterproof silicone to bond fillers continuously across the sheet width.
Colour Caps
Colour caps provide a neat finish by matching or contrasting with your chosen sheeting while concealing screw heads and washers.
Roof Lights
Roof lights increase natural light and typically offer around 80% translucency.
They can be positioned between steel sheets but must be supported on both sides and installed with correct side and end overlaps.
Completing the Roof
Finish by:
- Installing the ridge flashing where sheets meet at the apex
- Securing barge flashings
- Clearing any debris during installation to avoid damaging the sheet coating
- Installing guttering or fascia as required
Top Tip:
Always clear debris from the roof during installation to protect the sheet coating and maintain performance.