Before solar panels go on a roof, someone needs to confirm the structure can carry them through decades of storms. For most houses the extra weight is modest and well within what a sound roof was built to hold. The more demanding question is usually wind, because a strong gust pulling upward tries to lift panels, rails and fixings together. A proper roof assessment therefore looks at the added dead load, the wind forces acting in both directions, and whether each fixing reaches structure strong enough to resist them.

The loads a solar array puts on a roof

Engineers separate the forces on a building into load types, check each one, then combine them in design calculations with safety factors. For a rooftop array the relevant loads look like this.

Dead load is lighter than most people expect

A typical residential panel weighs roughly 20-25 kg and covers a little under two square metres. Once rails and brackets are included, a flush-mounted array commonly adds somewhere around 10-15 kg for each square metre of roof it covers, spread fairly evenly across many fixings. A tiled roof already carries a considerable permanent weight in its tiles, and its framing was designed with that in mind, so a structurally sound tiled or metal roof on a house built to modern codes can usually accept a flush-mounted array without reinforcement.

The picture changes for tilt frames on low-pitch roofs, ballasted systems on flat concrete roofs that rely on added weight to stay put, large arrays on lightweight commercial roofs with little spare capacity, and any roof whose framing has been weakened or altered. Panel construction matters too. As explained in what solar panels are made of, glass-glass modules are generally heavier than panels with a polymer backsheet.

Wind uplift is usually the load that governs

When wind flows over a building it speeds up around the roof and creates suction across much of the surface, strongest near ridges, edges and corners. A panel mounted a short distance above the roofing feels a pressure difference between its top face and the air gap beneath, and the result is a force trying to peel the array away. In a severe storm that force can far exceed the array's own weight, so it normally determines how many brackets are needed and how far apart they can be.

The design wind force on a particular roof depends on several site factors:

• Wind region. Australia is mapped into regions, and cyclonic regions in the north carry much higher design wind speeds than most of NSW.
• Terrain. Open farmland, beachfront sites and exposed ridgelines see stronger wind than sheltered suburban streets.
• Topography and shielding. Hills and escarpments accelerate wind, while neighbouring buildings can shield a roof.
• Building height and roof shape. Taller buildings and some roof pitches attract higher pressures.
• Position on the roof. Edge and corner zones see the highest suction, so arrays are set back from edges.

For houses these factors are often summarised as a wind classification, for example N1 to N6 in non-cyclonic areas. Mounting systems come with engineering documentation, based on the Australian wind actions standard AS/NZS 1170.2, that sets maximum bracket spacing and rail spans for each classification and roof zone.

Rafters, battens and purlins: where the load actually goes

Roofing is a weather skin, not something an array can hang from. Tiles are held mainly by their own weight and clips, and thin metal sheeting is designed to span between supports rather than resist concentrated pull-out forces. Every bracket therefore has to pass its load into a framing member underneath.

• Tiled roofs. Tile hooks are generally screwed into rafters, the sloping members that carry the battens. The hook passes between tiles, and the tile above it is often ground slightly so the hook cannot press on it and crack it.
• Metal roofs. Brackets are fixed through the sheeting into battens or purlins with screws of the type and length the mounting documentation specifies, or clamped to the ribs of concealed-fix profiles without penetrating the sheet.
• Flat and low-pitch roofs. Tilt frames catch more wind, so fixing capacity and the waterproofing of each penetration get extra attention.

Rafters in Australian houses are commonly spaced around 600 or 900 millimetres apart, which dictates where brackets can land, so the rail layout is adjusted to suit the framing. Screw embedment depth, edge distance and the condition of the timber around each fixing all affect how much pull-out force a connection can resist.

Why older roofs deserve a closer look

A roof that has stood for fifty years has shown it can carry its own weight, but that says little about spare capacity or how well new fixings will hold. A careful assessment looks for:

• sagging ridgelines or rafters, which can point to undersized framing or struts removed during past renovations
• timber affected by rot, leaks or termites, which reduces the holding power of screws
• brittle terracotta or weathered concrete tiles that crack under foot traffic
• rusted metal sheeting or corroded fixings that will not last as long as the panels
• roofing that may contain asbestos, which must not be drilled or cut and generally needs removal by licensed specialists before an array is considered

Panels can be expected to operate for 25 years or more, so repairing a tired roof section first is often cheaper than removing and refitting the array later.

When a structural engineer gets involved

For a typical house with a sound roof, the accredited designer relies on the mounting system's certified tables and an in-person inspection. A separate engineering check is more likely for large or commercial arrays, ballasted or tilted systems, heritage or unusual structures, sites in higher wind classifications and roofs showing the warning signs above. The engineer reviews framing sizes and spans, calculates combined loads, checks fixing capacity and may specify reinforcement, closer bracket spacing or a different mounting method.

None of this is do-it-yourself work. Roofs carry serious fall risks, penetrations must be sealed correctly, and solar design and installation must be carried out by an accredited installer, with electrical work done by a licensed electrician. Fixings and roof penetrations generally fall under the installer's workmanship warranty, which is separate from the manufacturer cover described in solar panel warranty types explained.

Next steps

If your roof is older, exposed to strong wind or built from lightweight materials, ask for its structure and fixing method to be checked before any system is designed. The energy market lists Structural Engineering Certification from $690 per roof and Roof Repairs Before Solar from $490 per repair; both prices are indicative and confirmed after a site assessment. To have your roof inspected in person rather than judged from satellite images, request a free assessment from Blue Energy Solar.

Frequently asked questions

Can solar panels make a roof leak?

A correctly installed array should not cause leaks. Tile hooks pass between tiles rather than through them, and screws through metal sheeting use sealing washers placed where the profile sheds water. When leaks do appear, they usually trace back to tiles cracked by foot traffic, poorly sealed penetrations or cable entries. If you notice water stains after installation, ask the installer to inspect the roof rather than climbing up yourself.

Should I replace my roof before installing solar?

If the roof is likely to need replacing within the next several years, doing it first is usually the better sequence. Removing and refitting an array later adds labour cost and leaves the system out of action for a period. A roof in fair condition with isolated problems can often be repaired under the array area instead of being fully replaced.

What are the options if a roof cannot carry panels?

The answer depends on the problem. Framing can sometimes be reinforced, a different roof face may be stronger, or a lighter mounting approach may work. Where there is space, a ground-mounted array or a solar carport avoids the roof altogether, although each of these needs its own structural design, footings and, in some cases, council approval.