Guides · Faisalabad, Lahore, Punjab
Solar on Tin and Metal Sheet Roofs (Factory Sheds)
Short answer
Solar on a tin sheet roof works well when the panels are carried by the shed's purlins and trusses, not by the thin sheet itself, and every fixing through the sheet is sealed against water. Most factory sheds in Punjab can take a well-designed system, but the purlins' condition, the sheet's age and the fixing method decide whether it stays dry and secure for years. A survey of the shed from inside and out comes before any design.
This guide is for factory, warehouse, workshop and farm-shed owners. For roof weights and RCC slabs, see will my roof hold solar panels?
Why sheds are good places for solar
Factory sheds often have large, open, unshaded roofs and heavy daytime loads underneath: looms, motors, compressors, lighting and fans. That matches solar output well, especially under net billing, where each unit used on site is worth more than a unit exported. Our industrial and commercial solar page and our guide to solar for Faisalabad textile, dyeing and loom units cover the bigger picture.
The challenge is that a sheet roof is light, thin and full of joints. It was built to keep out rain, not to carry equipment.
Solar on a metal sheet roof
Sheet profile
Clamp or rail chosen to match
Fixing
Sealed screws into the purlins
Corrosion
Galvanised steel or aluminium parts
How panels are fixed to a sheet roof
There are three common approaches. The right one depends on the sheet profile, purlin spacing and the condition of the shed.
| Method | How it works | Best suited to | Points to check |
|---|---|---|---|
| Rails fixed through the sheet into purlins | Brackets or rails screwed through the sheet crest into the purlin below | Most corrugated and trapezoidal sheet sheds | Every screw is a potential leak; must hit the purlin; sealing washers |
| Short rails or clamps on the sheet profile | Short rails fixed to the sheet ribs, spreading load along the profile | Newer, thicker trapezoidal sheets in good condition | Sheet thickness and fixing strength; maker's approval for the profile |
| Independent elevated structure | Steel frame on its own columns, passing over the shed | Old, weak or fragile sheets; asbestos-cement roofs; sheds due for re-roofing | More steel and foundation work; column positions |
Fix into the purlins, not just the sheet
The purlins are the horizontal steel or wooden members that run under the sheet and carry it. A fixing that only grips thin sheet can pull out in a storm. In most designs, the rail brackets are fixed through the crest (high point) of the sheet into the purlin, so the load goes into the shed's frame.
That means the engineer needs to know:
- Purlin spacing and size, measured from inside the shed
- Purlin condition: rust, bending, missing bolts
- Truss condition and spacing
- Whether the shed was ever designed for extra load
If the purlins are too far apart or too weak, extra purlins can sometimes be added, or an independent structure used instead.
Panel orientation on a pitched shed
On a sloping shed roof, panels usually follow the roof pitch to keep the frame light and wind loads low. This means the tilt and direction are set by the roof, not chosen freely. A south-facing slope is ideal; east and west slopes still produce, with output spread more across morning and afternoon. North-facing slopes with a steep pitch are usually avoided. The engineer weighs this against the cost of tilt frames.
Stopping leaks
Leaks are the most common complaint after solar on a shed. They are almost always caused by poor fixing practice, and they are preventable:
- Fix through the crest, never the valley. Water runs in the valleys; a hole there sits in running water every time it rains.
- Use proper sealing washers under every screw head, and do not over-tighten, which crushes the seal and dents the sheet.
- Hit the purlin. A screw that misses the purlin leaves a hole with nothing to hold it.
- Clear metal shavings (swarf) from the sheet after drilling. Left behind, they rust and stain, and can start corrosion.
- Seal any abandoned holes properly, not just with a dab of silicone.
- Check old sheet laps and existing screws before work starts. Many "solar leaks" were existing leaks that nobody noticed.
Our guide to roof leaks and waterproofing when installing solar covers sealing methods and monsoon checks in more detail.
Corrosion: metals that do not get along
Aluminium rails, steel brackets, galvanised sheets and stainless screws can be used together safely, but only with care. When two different metals touch and stay wet, the less noble one can corrode faster. Rainwater running off panel frames onto a galvanised sheet can also leave corrosion marks over time.
Good practice includes:
- Isolating pads or tapes (EPDM, butyl) between rails and sheet
- Fasteners suited to the materials being joined
- Treating any cut or scratched galvanising with zinc-rich paint
- Protecting earthing connections from corrosion, since a rusted earth bond is a safety problem as well as a cosmetic one. See solar earthing and surge protection.
- Regular inspection at the bottom edges of panels and around fixings
Heat under the panels
Sheet roofs get very hot in a Punjab summer, and panels lose output as their temperature rises. Panels mounted close to a hot sheet with little airflow run hotter than panels with a good gap underneath. A rail height that leaves space for air to move helps. See solar panels in Punjab summer heat.
A side benefit often noticed by shed owners: panels shade the sheet, which can make the space underneath feel cooler. We do not put a number on this, because it depends on the shed, insulation and ventilation.
Wind and storms
Sheds are often in open industrial areas with little shelter. Wind can lift panels and the sheet together if fixings are weak. Edges and corners see the highest uplift. Design should allow for:
- Fixing spacing suited to the exposure, with closer fixings at edges
- Keeping arrays back from roof edges where possible
- Checking the sheet's own fixings to the purlins, which may be old
Our storm and lightning safety guide covers pre-monsoon checks.
Safety on fragile roofs
Sheet roofs, especially old cement or asbestos-cement sheets and roof lights (translucent panels), can break under a person's weight. Falls through fragile roofs are a serious risk. Safe work needs:
- Walking only on purlin lines or on boards and walkways laid across them
- Covering or marking roof lights
- Proper PPE and fall protection
- No work in rain or strong wind
The same applies to cleaning. Plan permanent walkways or access routes so panels can be cleaned without stepping on the sheet. See how often to clean solar panels.
Asbestos-cement sheets should not be drilled or cut casually, because the dust is a health hazard. On such roofs, an independent elevated structure or ground-mounted solar on spare land is often the better route.
When the sheet is too old
If the sheet is rusted through, brittle or near the end of its life, replace it before installing solar. Removing panels later to re-roof costs time, labour and lost generation. Sometimes the best plan is new sheeting and solar together in one shutdown window.
How Solar Works Pakistan approaches shed roofs
Industrial EPC is our core work. We have served 50+ industrial clients, including textile, dyeing, loom and soap units. On a shed project:
- Our engineer surveys the shed from inside and out: purlins, trusses, sheet condition, existing leaks and roof access. The site survey is normally free.
- Our in-house engineering team, including dedicated AutoCAD experts, designs the structure and fixing layout for that shed.
- Our own team fabricates and assembles the structure on site, with safe access and PPE.
- Commissioning includes the necessary safety tests before handover.
Structures carry a 3-year Solar Works Pakistan structure warranty, and service is backed by a 1-year service warranty under the applicable project terms. Large projects follow a project-specific schedule. See L2, L3 and elevated solar structures for structure options.
Get today's price or a free site survey
Send photos of the shed roof from above and below, plus 12 months of electricity bills.
- WhatsApp or call: 0336 666 4321
- Email: info@solarworks.pk
- Head office: Main Boulevard, Sargodha Rd, Block F FDA City, Faisalabad
- Lahore branch: 2nd Floor, Jeff Heights, Gulberg, Lahore
- Hours: 9:00 AM to 6:00 PM, daily
We serve factories and commercial sites across all of Punjab. See our Faisalabad and Lahore pages, or contact us.
Frequently asked questions
Can solar panels be installed on a tin sheet roof?
Yes, if the structure is fixed into the purlins and trusses and every fixing is sealed. The sheet alone is too thin to hold panels in a storm.
Will solar panels cause my shed roof to leak?
They should not if fixings go through the crest of the sheet into the purlin with proper sealing washers. Most leaks come from fixings in the valley, missed purlins or over-tightened screws.
Do I need to replace old sheets before installing solar?
If the sheet is rusted, brittle or near the end of its life, yes. It is far cheaper to re-roof before solar than to remove and refit panels later.
Can solar go on an asbestos-cement roof?
Drilling or cutting asbestos-cement sheets releases harmful dust, so they should not be fixed into casually. An independent elevated structure or ground-mounted system is usually safer.
Do panels make the shed hotter or cooler?
Panels shade the sheet, which often makes the space below feel cooler. The panels themselves run hot on a sheet roof, so a good air gap underneath helps their output.
How long does a factory shed installation take?
It depends on size and site. Small projects normally take about a week, subject to payment, stock and site readiness; larger industrial projects follow a project-specific schedule.
Sources
- fischer, mounting systems for PV on trapezoidal metal sheet roofs (short rails with EPDM layer; self-drilling screws with EPDM gaskets; butyl tape)
- SolarQuotes, "Corrosion alert: why solar panels on galvanised roofs are bad news" (galvanic and runoff corrosion; mitigation): https://www.solarquotes.com.au/blog/corrosion-solar-galvanised-roofs/
- SurgePV, rooftop solar structural assessment (load path from clamp to rail to supporting member)