Insulating an existing patio roof

Moreton Bay Insulated Patios is an independent referral service; quotes come from an independent, QBCC-licensed builder who services your area (how it works).

Option 1: replace the sheets with insulated roof panels

An insulated (sandwich) panel has a Colorbond steel top skin, a foam core and a steel ceiling liner in one piece. It replaces the existing sheet and gives you a finished ceiling at the same time. Points to know before you get quotes:

• Weight. Bondor lists typical masses for SolarSpan of 10.9 kg/m² at 75 mm and 11.3 kg/m² at 100 mm. A 0.42 mm Colorbond Custom Orb sheet is 4.35 kg/m² (Lysaght). So the new roof is about two and a half times as heavy as the one it replaces.
• Roof pitch. SolarSpan (a trapezoidal rib profile) can go down to 2°. InsulRoof (corrugated) needs at least 5°. On a near-flat patio roof, that rules out the corrugated look.
• Spans. Panels span further than sheets, so some purlins may no longer be needed. But span limits depend on the panel thickness, how open the patio is and your site's wind classification. That calculation belongs to the builder or engineer, using the manufacturer's tables.
• Lights and fans. Use only downlights approved for the panel system, and a licensed electrician. Rewiring the ceiling is easiest while the roof is off.

Comparing brands? See SolarSpan vs Cooldek and insulated vs Colorbond roofs.

Option 2: insulation under new roof sheeting

Foil-faced blankets such as Bradford Anticon are laid directly under metal roof sheeting as it goes on. CSR Bradford describes Anticon as suitable for new builds and re-roofing, with thermal, acoustic and condensation benefits. On a patio that means the existing sheets come off, the blanket goes over the purlins, and new (or the old) sheets go back on.

This keeps the look of a conventional sheeted roof. You don't get the flat steel ceiling of a sandwich panel, though, and you still pay for a full re-sheet. Ask the builder how the blanket will be supported and finished at the edges.

Structural and engineering checks

Bondor's patio design guide is blunt: it is the licensed builder's responsibility to make sure any existing structure is adequate before a SolarSpan or InsulRoof roof is attached. Where the panels connect to existing framing, the members and connections below must be assessed and strengthened if required. In practice, a builder or engineer will look at:

• Beams and posts. Are they sized for the heavier roof and the new span between supports?
• Connections. How the patio fixes to the house fascia or wall, and post-to-beam brackets. They have to resist wind uplift as well as carry the added weight.
• Footings. If the footing details aren't documented, an engineer may need to investigate them.
• Wind classification. Most South-East Queensland suburban sites are N2, while exposed coastal or elevated sites are N3 or higher. A higher class means shorter spans and stronger fixings.
• Condition. Rusted bases, rotten timber or sagging beams usually tip the decision toward a rebuild.

Does it need approval?

Schedule 1 of the Building Regulation 2021 lets you carry out repairs, maintenance and alterations without a building permit only if the work does not change the floor area or height and does not affect a structural component (section 8 allows some minor structural items). Swapping light sheets for heavier panels changes the loads on the beams, posts and connections, and often means removing or changing purlins. So expect a panel retrofit to need a building development permit from a private certifier, and get the certifier's view before you sign.

If you're not sure the original patio was ever approved, raise it at the start. The certifier has to be satisfied with the whole structure the new roof sits on. See the Moreton Bay patio approval guide and how private certifiers work.

Retrofit or rebuild?

A simple area × rate comparison for a 24 m² patio, using WhatsTheDamage's Brisbane rows (indicative, excluding strengthening, electrical and approval):

A retrofit wins when the frame is sound and only needs modest strengthening. Once new beams, extra posts and new footings are needed, the gap narrows quickly. A rebuild also lets you fix a low ceiling height (for example with a flyover), add size (see patio extensions) or change the roof style. Ask each builder to price both options so you can compare them properly. Full price detail is in the insulated patio cost guide.