Passive solar design gets oversold as a free lunch. It isn't. Done well, it cuts your heating and cooling load so the rest of the system — panels, batteries, inverter — doesn't have to work as hard. Done badly, it just turns a hot room into a hotter room. I work in and around Central Queensland, where summer rooftop temps push past 65 °C and winter mornings drop below 5 °C in the same week. Here are the three rules I look at first when reviewing a passive solar plan for a client in Beecher or anywhere in the QLD climate zone.

By Dave Miller · off-grid sparky · 22 years wiring solar, batteries and sheds in central QLD

“After losing three nights to damp cold in a north-facing shed without thermal mass, I learned that passive design fails without at least 100mm of concrete floor.”

Before we get into it, a note on scope. This article is about passive solar design — orientation, glazing, thermal mass, shading — not about the PV system that may also go on the roof. If you're planning an actual solar panel install on top of all this good design work, you'll separately need to deal with the permits, electrical compliance and grid-connection paperwork. See our [2026 solar permit guide](#) for the regulatory side; this guide stays on the design rules.

Rule 1: Get the Orientation and Glazing Ratio Right

The single biggest variable in passive solar performance in the Southern Hemisphere is which way your glazing faces. North-facing glazing is what you want for solar gain in winter. South-facing glazing in Australia is pure cooling liability.

The numbers a sparky actually checks

• Glazing orientation: True north (not magnetic north). Magnetic north in QLD is roughly 9–11° east of true north; on a compass at midday that matters.
• Glazing area as a percentage of floor area: For a typical QLD passive solar design, useful north-facing glazing sits in the range of roughly 5–10% of the conditioned floor area. Significantly more than that and you overshoot summer; significantly less and winter gain disappears.
• Window U-value and SHGC: Single clear glass has a high solar heat gain coefficient — fine for a Tasmanian build, a disaster in Rockhampton. Look for low-SHGC glazing (typically SHGC below ~0.3) on east and west elevations, and ideally a selective low-e glass on the north face.

Common faults I see on the tools

• Glazing placed to "frame the view" rather than to the north. The view is nice in March; the house is unlivable in February.
• Eaves designed for Southern Hemisphere sun angles but built flipped. Eaves depth should be calculated for the summer solstice noon sun angle (~82° at Rockhampton's latitude, 23.4° south) so the wall is shaded in summer but the low winter sun (~55° at noon) still gets under the eave.
• Sliding glass doors on the east and west walls. They will cook that room. Every time.

Rule 2: Get the Thermal Mass and Insulation Pairing Right

Thermal mass without insulation is a heat sponge; insulation without mass is a tent. In Central Queensland you need both, but the ratio changes from what a Victorian or Tasmanian builder uses.

What the sparky is really looking at

Thermal mass — concrete slab, reverse-blockwork wall, water feature — absorbs heat during the day and releases it at night. The release is the point. In a hot climate with hot nights (most of coastal QLD), you want mass with night-purge ventilation: open windows at night to flush stored heat, close them at dawn. No night purge and the mass just re-radiates into the room the next night.

Insulation priorities for a QLD passive solar build, in order:

1. Roof and ceiling. RAG ceiling insulation is the single highest-value insulation upgrade for almost any QLD home. Heat gain through an uninsulated roof dwarfs wall and floor gains.

2. West and east walls. Wrap them in insulation and/or push them behind a verandah. The afternoon western sun in a CQ summer is the worst heat load you'll fight.

3. Floor slab edge. Insulate the slab edge in a slab-on-ground build. Uninsulated edges bleed conditioned air straight into the ground.

4. North wall. Lower insulation priority because you want some gain through this wall in winter, but it still needs to be reasonable — don't skip it.

What I don't do

I don't recommend phase-change materials, Trombe walls or fancy water-tube features unless the client specifically wants them and understands the maintenance. Stick to slab + correct insulation + night purge. It's boring and it works.

Rule 3: Get the Shading and Ventilation Strategy Right

Glazing gets the sun in. Shading keeps the sun out when you don't want it. Ventilation clears what slips through. If any of these three is missing, you don't have passive solar — you have a glass box.

Summer shading

• North-facing eaves sized correctly for your latitude (see Rule 1).
• External shutters or operable louvres on east and west windows. Internal blinds don't count — the sun has already entered the room.
• Deciduous-style landscaping works in southern states; in CQ it's evergreen and is used for shade, not seasonal solar access. Plant a vine on a pergola over the north glazing and you trade solar gain for a cooler wall. Worth it in most QLD builds, especially if your glazing ratio is on the high side.

Cross-ventilation

A passive solar house needs a path for air to enter and exit. That means openings on opposite or near-opposite sides of the building. If your living room has north-facing sliding doors but the opposite wall is solid, you don't have cross-flow — you have a wind shadow.

Practical targets:

• Opening area roughly 3–5% of floor area across opposing walls.
• Internal doors open or louvered so air actually moves between rooms, not just into and back out of the living area.
• High-level venting (clerestory windows, ridge vents) lets hot air escape — stack effect does the rest.

Specs and Requirements at a Glance

Safety and When to Call a Licensed Professional

Passive solar design is mostly building science — siting, glazing, mass, shading. It is not something where you wing the electrical side.

Call a licensed professional when:

• Any AC wiring work is involved. In Queensland that means a licensed electrical contractor. This is not optional and not a DIY job. Mains-voltage work, inverter connection, switchboard alterations — all licensed.
• Structural changes are planned. Removing a load-bearing wall to "open up" the north face, adding a concrete slab where there wasn't one, installing heavy thermal mass on an upper floor — get a structural engineer's sign-off.
• Roof work intersects with a future PV array. If you plan to put solar panels on the roof later, design the rafter spacing, roof load and cable penetrations now. Retrofitting around a passive solar roof is more expensive than building for it from the start.
• The house is in a bushfire-prone area or flood zone. QLD has BAL ratings and flood overlay maps. Passive solar window walls may need to comply with BAL construction requirements; floor levels may need to be set above flood planning levels.

If you can't tell whether what you're planning needs a building development approval under the Queensland Building Act 1975, ring your local council or a private building certifier before you pour concrete.

Frequently Asked Questions

Does passive solar actually work in Queensland, or is it a southern-states idea?

It works, but the rules are different. You want less winter gain and more summer rejection than a Melbourne build. The orientation principle is the same; the glazing ratios, eave depths and night-purge strategy all shift.

What does a sparky actually check on a passive solar design?

Three things: (1) which way the north-facing glazing faces and how much there is, (2) whether the roof and slab are insulated to current NCC requirements, (3) whether there's a real cross-ventilation path. If those three are sound, the design is probably liveable.

Do I still need a solar permit if I'm just doing passive solar design?

No — passive solar design on its own is building work, not electrical work. It falls under the building approval process. Solar permits and electrical permits are separate, and only kick in once you add PV, batteries, inverter or grid connection.

Can I retrofit passive solar into an existing Queenslander?

Partially. You can add external shading, swap glazing for low-SHGC units, retrofit insulation to the ceiling and walls, and improve cross-flow. You generally can't reorient the existing glazing or add thermal mass under a raised timber floor without major work. Expect partial gains, not a transformation.

How much does passive solar design cost extra on a new build?

The design itself is a consultant's fee — typically modest relative to the build. The glazing choice (low-SHGC, selective low-e) adds upfront over standard clear glass but pays back in lifetime cooling costs. Compared to the total cost of a QLD new build, the passive solar premium is small; compared to the cost of a 10 kW PV system, it's trivial.

What orientation should I use if true north isn't possible?

East of north gets some morning sun; west of north traps afternoon summer heat that east-of-north avoids. If you have to rotate more than roughly 20–30° from true north, fix the orientation issue before adding mass or expensive glazing — you'll be paying for a feature the building can't use.

Sources

• Permitflow — Solar Permit Guide