Structural checks before fixing rooftop solar frames

A rooftop solar array looks light, and once it is fixed it is largely out of sight. The panels are thin, the rails are slender and the installer often arrives with a standard kit that has worked on many roofs. Underneath, though, the array adds a permanent load to the roof and a wind load that acts through every fixing on the frame. Those forces have to be carried by rafters, trusses and the walls below them, and most existing roofs were designed for their covering and their own weight, not for a rail system and a field of panels.

The risk is not that every roof will fail. It is that the assumption that an old roof will carry anything placed on it goes untested. A roof that has kept the weather out for decades has proved that it can carry its covering, but it has not proved that it can carry a new concentrated load at the points where the rails are fixed. A check before the rails go on is the only way to know the difference, and it is far cheaper than a repair after a storm.

This article is about existing roofs, where the frame is already built and the question is whether it can take a solar array. It is distinct from the design of a new home that is made ready for solar, which is covered in the article on solar ready design for new homes. The checks below apply to the retrofit job a builder is most likely to be asked to carry out.

What a solar array asks of an existing roof

Two forces matter most. The first is the permanent weight of the array, the panels, rails, brackets and inverter fixings, which is carried into the frame at every point of attachment and stays there for the life of the system. The second is the wind. Wind pushes on the face of a panel and, because the array sits above the roof surface, it lifts the array as well. That uplift is transferred through the brackets into the frame, and it is greatest where the wind is strongest, at the edges and corners of the roof.

The combination is the reason a frame that is adequate for the roof alone may not be adequate for the array. The weight is added evenly across a surface, but the fixings concentrate load at points. The uplift acts in the opposite direction to the gravity load that the roof was designed to resist. A roof that is sound in service can therefore be overstressed at a single fixing, and the first sign of that is often a crack in the covering, a lifted tile or a bracket that works loose months later.

The documents to find before anyone climbs up

The first step is to gather what already exists. Look for the original frame design, whether it is a set of truss design documents or a set of construction drawings for a conventional framed roof. Find the roof covering and confirm what it is, because the fixing method for a tile roof and for a metal sheet roof are different. Record any previous alterations to the roof, including added skylights, extensions, new insulation and any earlier solar installation, because each of them may have changed the load path.

Ask the owner for any engineer’s report or certificate relating to the roof, and for any records of past repairs. A report prepared for an earlier job may answer part of the question, and a past repair may show a weakness that the new array must not aggravate. Gather what you can before the assessment is commissioned, because a practitioner who has the history of the roof will give a sharper answer than one who has to work it out from the ceiling.

When a structural assessment is needed

A structural assessment of the frame, the covering and the proposed fixings should be made before the rails are fixed to an existing roof. The assessment is not a formality. It is the professional opinion that the frame can carry the array under the loads it will meet, and it should be specific to the roof in question rather than a general statement about solar installations. The assessor should be a qualified practitioner, and the work should be documented in writing.

Where the assessment relates to structural design, the Design and Building Practitioners Act governs who may prepare and certify that design for building work in New South Wales. A builder who engages an engineer should confirm that the engineer is registered to do the work, and should ask for the registration to be recorded in the job file. The assessment should name the roof it covers, state the assumptions made, and say what must be done before the array is loaded. An assessment that does not do those things will not protect the builder or the owner when the question is later asked.

Fixing into the frame, not just the covering

The fixings must reach the structure. A bracket that is screwed only into the battens, or only into the tiles or the sheet, is held by whatever that material can offer, and the frame beneath may never receive the load at all. The brackets should be set to the rafters or trusses at the positions the assessment specifies, and the spacing of the rails should follow the frame rather than the panel layout alone. Where the frame members are not where the installer expected, the layout should change to suit the structure, not the other way round.

The method differs by covering. The comparison below sets out the general differences, and the assessment and the manufacturer’s instructions must govern each specific job.

Every penetration through the roof covering is a route for water, and it must be flashed and sealed in the order the covering requires. A bracket set into the frame with a sealant bead alone will fail as the roof moves, and a penetration that is not flashed to the profile will carry water into the roof space. The flashing and sealing are part of the structural fixing, not an afterthought to it.

Wind, exposure and the edges of the roof

Wind does not act evenly across a roof. The edges and corners see greater uplift than the middle of the roof surface, and a roof that is exposed to the coast or to open country sees more than one that is sheltered by trees or neighbouring buildings. The engineer takes account of the wind conditions at the site, and the layout of the array should respond to that assessment. Placing panels at the edges or corners because they receive the best sun is a common mistake, and it can be the single decision that overloads a fixing.

The energy design of the array and its structural design are two separate questions, and the structural answer must come first. Orientation and shading influence how much the panels produce, and the general passive design guidance on the Your Home website is a useful background to understanding why orientation matters. But a panel that produces well and sits on a fixing that cannot carry its uplift is not a good installation, and the builder must make that clear to the owner and the installer before the layout is fixed.

Sequencing the fixing work safely

The sequence matters as much as the fixings. Survey and assess the frame before any material is ordered, because the assessment may change the layout or require strengthening that has to be done first. Strengthening is then carried out before the array load is applied, and the rails are fixed only after the frame is confirmed. Working on the roof itself needs the same care as any roof job: fall protection, safe access and a plan for the weather, with the roof kept covered whenever work pauses.

A common failure is to fix the brackets and then load the frame with the panels in one day, because the crew is on the roof and the materials are at hand. The assessment should be checked against the actual positions of the frame members on the day, not against the drawing. Where a position differs, stop, mark the variance, and confirm the revised fixing with the assessor before the bracket goes in.

Underground services and cable routes

Solar installations often involve more than the roof. Cables run down walls, through roof spaces and sometimes into the ground, and any trench for a cable, an earth or a ground mount can meet services that were not on the plans. Before any excavation, use Before You Dig Australia to find the underground services that may be affected, and keep the response with the job file. Striking a buried service is a safety event and a delay, and it is the sort of incident that can make a simple solar job expensive very quickly.

Electrical work on the array and its connection to the building must be carried out by a licensed electrician. The builder’s role is the structure, the fixings, the penetrations and the coordination between trades, and the job runs better when each party knows where its responsibility ends and the next one begins.

A worked example: a builder in the Hunter

Consider a builder in the Hunter who was asked by a homeowner to fix a solar array to an older tile roof. The installer had proposed a layout with the panels along the roof edge, where the sun was strongest, and wanted to fix the rails to the battens. The builder asked for a structural assessment before any rails were ordered, and the engineer examined the frame, the covering and the existing repairs.

The assessment found that the rafters at the proposed edge fixings were smaller than the spacing required for the uplift, and that a previous repair near the eaves had already loosened some tiles. The engineer required the rafters to be strengthened at the edge positions, the damaged tiles to be replaced, and the layout to be moved inboard where the frame could take the load. The fixings were made to the rafters, each penetration was flashed to the tile profile, and the builder photographed each one before the panels went on.

The owner received a slightly smaller array in a position the engineer had cleared, and a file that showed the frame had been checked. The installer had to revise the layout, and the owner accepted a modest cost for the strengthening. The useful point is that the structural answer determined the layout, not the other way round.

Records and the handover to the owner

The job file for a solar frame should contain the documents that show the roof was checked and the fixing was made properly. That means the survey, the structural assessment, the layout as approved, the strengthening drawings where they apply, photographs of each fixing and penetration, and the manufacturer’s instructions. Give the owner a copy of the assessment and the fixing record, because the owner will need them if the roof is repaired, sold or assessed for insurance in the years ahead.

Be clear in the written contract about who engaged the assessor, who is responsible for the frame, and who is responsible for the electrical work and the array. Where the solar installer is a separate business, the builder should confirm the division of responsibility in writing before the work starts. The NSW Government guidance on contracts for home building work is the reference point for what a written residential contract should cover, and it is worth checking the contract against it before the fixings are made.

Keeping the structural question at the centre

The structural check is the one step on a solar job that cannot be recovered later. A panel that is wrongly oriented can be moved, and a poorly chosen inverter can be replaced. A frame that has been overloaded at its fixings is a structural problem that may not show until a severe wind event, and by then the cost of finding and repairing it is much higher than the cost of the assessment. The builder who makes the assessment a fixed part of the job, rather than an option the client can decline, protects the owner, the installer and the builder’s own position.

If you want to build your understanding of roof structure and fixings, the PointCPD course catalogue lists the NSW builder CPD courses available.

The PointCPD guide to how NSW builder CPD works explains how that learning is recorded for a licence holder.

The related article on roof truss bracing and tie-down checks covers the permanent forces a frame must already resist, which is the starting point for any question about adding weight to it.

Questions builders ask

• Roofing
• Solar
• Structure

Published 15 October 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.