Solar-Ready Steel Roofs: Structural Check, Strengthening and Mounting Structures
Solar panels stay on a roof for twenty years or more, and they add weight and wind load the roof was not designed for. Before the panels go up, the roof structure has to be checked. Bongshai Steel surveys your steel roof, checks it by calculation, strengthens it where the numbers ask for it, and fabricates the mounting structure in its own factory.
What solar panels do to a steel roof
A rooftop array adds permanent weight to every purlin under it. Published engineering guidance puts a typical array on a metal roof at roughly 10 to 25 kg per square metre, and more where ballast is used. That figure is only a starting point: every roof gets its own calculation.
Weight is often not the governing load. Panels catch wind, and wind uplift at the fixing points can be the larger force, above all in coastal districts with the highest cyclone wind speeds under BNBC 2020. A roof that carries its own sheet comfortably can still be short of capacity at the purlin connections once panels are fixed to it.
Installed without a check
Sagging purlins, leaks at the fixings and sheets working loose in a storm show up later, when the panels have to come off to repair the roof.
Checked before installation
Any weak purlin, rafter or connection is found on paper, strengthened once, and the array stays in place for its full life.
From survey to a roof that is ready for panels
Six steps. You can stop after the report if the roof needs nothing.
Site survey
We measure the purlins, rafters and columns, their spans and spacing, and record the connections, the sheet and its fixings, and any rust or damage.
Structural check
We check the roof for the panel weight, wind uplift and wind pressure together with its existing loads, following BNBC 2020 and AISC 360.
Written report
You get one of three answers in writing: safe as it is, safe with the strengthening listed, or not suitable for panels.
Strengthening
Where the check asks for it, we fabricate the extra steel in our factory and fix it on site: added purlins, stiffened members, stronger connections.
Mounting structure
We fabricate the steel structure the panels sit on, for metal roofs, concrete roofs and ground-mounted arrays.
Hand over to your solar company
The roof and the mounting structure are ready for the panels, inverters and wiring your solar company installs.
What the structural check covers
Send these if you have them. If the drawings are lost, we measure the building on site.
Purlins
Section, thickness, span and spacing. Purlins carry the panels first, so they are checked first.
Rafters and frames
The main frames take the added load from every purlin along the building.
Connections and bolts
Purlin cleats, frame joints and base plates, where uplift forces concentrate.
Roof sheet and fixings
Sheet thickness and condition, and how the mounting clamps or brackets will be fixed without leaks.
Wind zone
Basic wind speed for your district under BNBC 2020. Coastal sites have the highest.
Age and corrosion
Rusted or damaged steel has less capacity than the drawing says. We check the steel that is really there.
When rooftop solar is required in Bangladesh
Under the Net Metering Guidelines 2025 and the Power Division circular of December 2025, industrial and commercial consumers with an approved load of 10 kW or more must install rooftop solar of at least 20% of the approved load when they take a new electricity connection or increase their load. The rule applies to buildings with 1,000 sq ft or more of roof that can be used for at least 20 years.
So a new factory, or a factory raising its load, needs a roof that can carry panels for those 20 years. Check the current text of the rule with your distribution company before you decide; rules and tariffs change.
Building a new factory?
Tell us at the design stage. A roof designed for solar load from day one costs little extra and needs no strengthening later.
We do the structure. Your solar company does the panels.
Bongshai Steel designs, fabricates and erects steel buildings and structural steel from its own factory, following AISC 360, BNBC 2020 and AWS D1.1. For rooftop solar we do the structural side: the check, the strengthening and the mounting structure. Panels, inverters and the net-metering application stay with your solar company, and we work alongside them.
Frequently asked questions
Can my existing factory roof carry solar panels?
Many can, some need strengthening and a few are not suitable. It depends on the purlins, the frames, the connections and the wind zone, so the answer comes from a survey and a structural calculation, not from the age or look of the building.
How much weight do solar panels add to a roof?
Published engineering guidance puts a typical array on a metal roof at roughly 10 to 25 kg per square metre, and more for ballasted systems on flat roofs. Wind uplift on the panels is often the larger load, so both are checked.
Is rooftop solar mandatory for factories in Bangladesh?
Under the Net Metering Guidelines 2025 and the December 2025 Power Division circular, industrial and commercial consumers with an approved load of 10 kW or more must install solar of at least 20% of the approved load when they take a new connection or increase their load. Check the current rule with your distribution company.
Do you supply and install the solar panels?
No. We do the structural work: the roof check, any strengthening, and the steel mounting structure. Panels, inverters and the net-metering application are done by your solar company.
What do you need to start?
The roof drawing if you have it, or four photos of the roof from inside and outside, with the building length, width and location. If drawings are lost we measure the structure on site.
Can you check a building that Bongshai did not build?
Yes. The check uses the steel that is really in the building, measured on site, whoever built it.
What does the structural check cost?
It depends on the size of the roof and whether drawings exist. We give the fee in writing before the survey.
More from Bongshai Steel
Ask for a roof check
Send the roof size and location. We reply with what we need to see and a written fee for the survey and report.
- Survey and structural calculation
- A written report you can give your solar company
- Strengthening and mounting structure quoted separately