Home Insulation Guide: Improve Comfort & Lower Energy Costs

Insulation is one of the cheapest things you can put in a new home, and one of the hardest to fix later. Once the plasterboard is on, missing or badly fitted batts are out of sight and out of reach, quietly costing you money every time the air conditioner runs.

In Queensland, insulation is mostly about keeping heat out. Our roofs bake for most of the year, and the ceiling is where the biggest share of unwanted heat gets in. Get the ceiling and roof right, then the walls, and you've done most of the work.

This guide covers what Queensland home owners need to know: how R-values work, what your climate zone means, which products go where, and what to check on site before it all disappears behind the plasterboard.

What insulation does

Insulation resists the flow of heat. In summer it slows heat getting into the house. In winter it slows heat getting out. It also helps with:

Noise, by reducing sound transfer through walls and ceilings
Comfort, by keeping ceiling and wall surfaces closer to room temperature
Condensation, when it's designed together with ventilation and the right membranes

That last point matters more than most people realise. Better-insulated, better-sealed homes can trap moisture if the design doesn't let it escape. The scoping study below on condensation in Australian homes is worth a look. Simply doing it "the way we've always done it" isn't good enough any more.

And yes, I do rant about this—because no one else seems to be talking about it, despite the fact that it’s costing the country billions in health expenses!

R-values explained

An R-value measures resistance to heat flow. The higher the number, the better the insulation.

There are two kinds you'll see:

Material R-value: the rating of the product itself, printed on the bag. An R2.5 wall batt is rated R2.5.
Total R-value: the combined rating of the whole roof, wall or floor system, including the cladding, air gaps, foil, framing and plasterboard. This is what actually matters for the house.

Insulation Rating Chart — Different materials have different R Values

For roofs and ceilings, total R-values are given for the direction of heat flow:

Downward R-value (summer): resistance to heat coming down through the roof into the house. This is the one that matters most in Queensland.
Upward R-value (winter): resistance to heat escaping up through the ceiling.

Three things kill R-values on site: gaps, compression and dust on foil surfaces. More on those below.

What R-values does a Queensland home need?

Under NCC 2022, which Queensland adopted for energy efficiency from 1 May 2024, most new homes need a 7-star NatHERS rating. Most builders use the NatHERS pathway, which means your insulation R-values are set by your energy assessor, not by a fixed table. The assessor models your design on your lot and specifies the insulation, glazing and roof colour needed to reach 7 stars. Those values should then appear on your plans and specification.

The minimum also depends on your climate zone. Queensland covers several:

Zone 1: hot humid summers, warm winters (including Cairns and Townsville)
Zone 2: warm humid summers, mild winters (Brisbane, the Gold and Sunshine Coasts)
Zone 3: hot dry summers, warm winters (much of the inland west)
Cooler zones on the Darling Downs and the Granite Belt, where winter heating matters too

Simplified map of Australia divided into mild tropical, mild arid and mild temperate climatic zones, with major cities marked and a note that the boundaries are indicative only. — There are different climate zones around Australia which determine minimum design requirements and material selections. Identifying which zone your site is in is required before selections are made.

As a rough guide, many south-east Queensland project homes end up with around R3.5 to R4.0 ceiling batts plus roof sarking or a foil blanket, and R2.0 to R2.5 wall batts. Your energy report is the final word, so ask for a copy and check the insulation installed matches it.

In New South Wales, BASIX sets its own requirements. If you're reading advice written for Sydney or Melbourne, remember the climate and the rules are different.

My advice: treat the energy assessment as the floor, not the target. Upgrading ceiling batts at build stage costs very little compared with the comfort and running-cost gains, and it's far easier now than crawling through a roof space later.

Types of insulation

Bulk insulation

Bulk insulation traps tiny pockets of air to resist conducted and convected heat. It works the same in either direction of heat flow.

Glasswool batts: the most common and cheapest option. Non-combustible, often with high recycled glass content. Itchy to install.
Rockwool (mineral wool) batts: denser, very good fire and acoustic performance, and easier to cut neatly. Usually dearer.
Polyester batts: made from recycled PET, non-itchy and easy to handle.
Wool batts: natural, good acoustic performance and handles moisture well. Expensive.
Loose-fill (cellulose or glasswool): blown into ceilings. Good for retrofits, less so for new builds (see below).
Rigid boards (EPS, XPS, PIR): high R-value for the thickness. Used under slabs, around slab edges, in raked ceilings and as continuous insulation outside the frame.

A person in a blue shirt installing electrical wiring in pink fiberglass wall insulation — Photo by Erik Mclean on Unsplash

I'm not a fan of installing glasswool. It makes my eyes and skin itch, so I prefer Rockwool or wool batts. Rockwool is also much easier to cut and fit neatly, which helps with gaps.

Inside of an attic with insulation and wood beams — Photo by Brett Jordan on Unsplash

Make sure the batt suits the frame. A 70mm stud wall needs a batt designed for a 70mm cavity. Stuff a 90mm batt into a 70mm wall and you compress it, lose R-value, and push the plasterboard out so the linings bow or pop.

Reflective insulation

Reflective insulation is shiny aluminium foil laminated to paper or plastic. It works by reflecting radiant heat, which makes it very effective in Queensland roofs.

The catch: it only works next to an air gap of at least 25mm, and dust on an upward-facing shiny surface ruins it. A downward-facing or vertical foil surface stays effective much longer.

Roof sarking: foil laminate under metal or tiled roofs. It reflects radiant heat and acts as a secondary barrier against water and condensation.
Wall wrap: foil or vapour-permeable membrane wrapped around the outside of the frame.

Section down a tiled roof at the eave: the membrane lies over the rafters with the higher run lapped over the lower, battens hold it down, and it runs into the gutter. — Sarking installed under a tile roof - the 40mm sag is a point to note.

Composite insulation

Composite products combine bulk insulation with a foil face:

Foil-faced blankets under metal roofs, which add R-value, reduce rain noise and help control condensation
Foil-backed batts
Foil-faced rigid boards

The foil orientation and air gaps need thinking about at design stage to make sure the product performs and doesn't create condensation problems.

Where it goes in a Queensland home

Roof and ceiling

The roof is your biggest heat source. The best-performing combination for most Queensland homes is:

Sarking or a foil blanket under the roof to reflect radiant heat, and
Bulk batts on the ceiling, laid tight with no gaps

A lighter roof colour also makes a big difference to summer heat gain.

Raked (cathedral) ceilings have little space, so they typically use rigid boards or high-density batts, and need careful design for ventilation and condensation.

Flat or skillion roofs have little or no ventilated space. Get your designer to check the condensation risk.

Ventilating the roof space

A well-ventilated roof space lets hot, humid air escape, which helps prevent condensation and reduces heat build-up. It also helps your plasterboard and paintwork last.

I'm a big fan of fixed roof vents rather than whirlybirds. Moving parts are a point of failure. Hot air rises, so as long as it has a way out, a fixed vent does the job without the risk of a seized bearing.

Walls

Brick veneer is the most common wall type in Queensland project homes. The cavity between the brickwork and the frame must stay clear so any water that gets through the bricks can drain away through the weep holes. Never fill it with insulation.

In brick veneer, insulation goes between the studs, with wall wrap or foil on the outside face of the frame.

Lightweight-clad walls (weatherboard, fibre cement, panels) also take batts between the studs, with wall wrap behind the cladding. Some designs add a rigid board over the frame to reduce thermal bridging.

Floors

Slab on ground: the most common floor in Queensland. Slab-edge insulation can help in cooler zones but is rarely needed on the coast.
Suspended timber floors: batts between the joists, supported so they don't sag, or foil under the joists in warmer climates.

Garages, bathrooms and laundries

Insulate the walls between the garage and the house, and the ceiling of the garage if there's a room above it. A hot garage cooks the rooms next to it.
In bathrooms and laundries, use products that cope with humidity and make sure exhaust fans are ducted outside, not into the roof space.

Thermal bridging

A thermal bridge is a path where heat bypasses the insulation, usually through something more conductive than the insulation around it:

Steel frames, which conduct heat far better than timber
Aluminium window frames without a thermal break
Gaps and compressed areas in the insulation

Ways to reduce thermal bridging:

Thermal breaks between steel frames and cladding (often required by the NCC for steel-framed walls and roofs)
Rigid insulation boards over the frame
Thermally broken window frames or better glazing

Thermal bridges also create cold spots where condensation can form, which is how mould starts.

Common installation mistakes

Most insulation underperforms because of how it's installed, not what it is.

Gaps. Even small gaps let a surprising amount of heat through. Batts should be cut to fit snugly between studs, joists and trusses, with no uncovered strips at corners, junctions or around windows and doors.
Compression. Squashed batts lose R-value. Don't stuff oversized batts into small spaces, and don't let other trades store materials or walk on ceiling batts.
Disturbed batts. Electricians, plumbers and air conditioning installers often move batts and don't put them back. This is the most common problem I see.
No air gap for foil. Foil pressed hard against another surface is almost useless.
Sagging sarking. Sarking should be installed with only a small sag between supports so water can drain to the gutter, and extended into the gutter or fixed at the fascia as the manufacturer specifies.
Insulation over downlights. See the safety section below.

Section across the rafters under a tiled roof: the membrane drapes between rafters with a sag of 40 mm max, so water drains down the slope beneath the battens. — Any more than the maximum renders diminishes the insulation performance

Section across a tiled ridge: the top run of membrane on each side is carried over the ridge and lapped onto the other side, held down by the top battens; the ridge capping sits on bedding with pointing troweled off in the gap each side. — Sarking overlaps ridge by 150mm to each side.

A word on loose-fill

Loose-fill can be great for retrofits, but it has a downside in new homes. It drifts and packs into gaps between ceiling joists, truss chords and plasterboard. If a ceiling ever needs re-fixing or levelling, the loose-fill packed into those gaps gets in the way.

Safety: downlights, wiring and foil

Downlights

Insulation must keep its clearance from light fittings unless the fitting is rated to be covered. Older halogen downlights need large clearances. Many modern LED downlights are IC-rated, meaning insulation can be laid over or against them, which gives you better coverage and fewer gaps. Ask your electrician for IC-rated fittings.

Where fittings aren't rated, AS/NZS 3000 (the wiring rules) sets default clearances, as shown below.

Section through a ceiling at a recessed downlight, with clearances lettered A (above, to the roof framing), B (side, to the joist), C (side, to the insulation) and D (to the driver), and a key table giving 200, 200, 50 and 50 mm. — Default minimum clearances between insulation and light fittings - luminaries (fancy word)

Foil and electricity

Foil is electrically conductive. AS/NZS 4200.2 requires care where foil membranes may contact wiring, and non-metallic fixings should be used near electrical work. In new homes, foil is usually installed before the electrical rough-in, which keeps the risk low.

Clearances to flues and fans

Keep insulation clear of hot flues, exhaust fans and other heat sources as the manufacturer requires.

If you're installing it yourself

Wear gloves, long sleeves, eye protection and a P2 mask, especially with glasswool or loose-fill. Don't step between ceiling joists. Use boards to walk on. And don't work in a hot roof space alone, or in the middle of a Queensland summer afternoon.

Australian Standards that apply

AS/NZS 4859.1: thermal insulation materials and how R-values are tested. Make sure your product is certified to it.
AS 3999:2015: installation of bulk thermal insulation.
AS/NZS 4200.2: installation of pliable membranes (sarking and wall wrap).
AS/NZS 3000: the wiring rules, including clearances around electrical equipment.

The Insulation Council of Australia and New Zealand (ICANZ) handbook below pulls the key standards into one guide. It's well worth reading.

What to check on site

You can't check insulation after the plasterboard goes on. The time to look is the frame and pre-plasterboard stage.

C10 - Rough In Stage Inspection Checklist

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Last updated 5 Oct 2026 · Revision 1 · Free updates for life

Checklist Type: Minor

Form Factor: Fillable, print-ready PDF (A4, 25 pages)

When to use: Rough-in stage: after services are installed, before cladding and linings go on

A 200-point rough-in checklist. Check electrical, plumbing, gas, solar, membranes and air-conditioning ducts before cladding and linings hide them, while changes are still easy.

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At frame stage

Wall wrap or sarking installed, lapped and taped correctly, and not torn
Sarking under the roof with the right sag, lapped at the ridge and finished at the gutter or fascia properly
Roof ventilation installed as designed

Before plasterboard

Wall batts in every external wall cavity, including garage-to-house walls
Batts the right size for the frame, with no compression or bowing
No gaps at corners, around windows and doors, or behind services
The R-value on the bags matches your energy report
Batts put back after the plumber and electrician have been through

After ceiling insulation is laid

Even coverage over the whole ceiling, with no missing sections
Batts butted tightly together, without overlaps or gaps
Correct clearances around downlights that aren't IC-rated, and around flues and fans
Insulation over the garage ceiling if there's a room above

Our C11 Enclosed Stage Inspection Checklist covers wall insulation before plasterboard goes on, and the C10 Rough In checklist covers the frame-stage items.

Get the paperwork

Your insulation installer should provide an installation certificate stating the product, R-values and areas covered. It's usually provided to the building certifier as part of the final inspection paperwork. Ask for a copy for your records. Here's an example of an older version:

And here's an example of the calculation sheet I've used on past jobs to work out insulation quantities:

The bottom line

In Queensland, focus on the roof and ceiling first: sarking or a foil blanket, plus generous ceiling batts and good roof ventilation.
Your energy assessment sets the minimum R-values. Treat it as a floor.
Never fill a brick veneer cavity. Insulation goes between the studs.
Installation matters more than the product. Gaps, compression and disturbed batts are the common failures.
Check before the plasterboard goes on. Once it's covered, it's too late.

Frequently asked questions

What's the best insulation for a Queensland home?

A combination: reflective sarking or a foil blanket under the roof to deal with radiant heat, plus bulk batts in the ceiling and walls.

What's the difference between R-value and total R-value?

R-value is the rating of the product alone. Total R-value is the rating of the whole roof, wall or floor system, including all the other layers. Total R-value is what determines how the house performs.

Can I install insulation myself?

Bulk batts in an accessible ceiling are a reasonable DIY job if you follow the manufacturer's instructions and safety advice. Leave foil products, spray foam and anything near electrical work to professionals.

Should I upgrade beyond what the energy assessment says?

Usually yes, especially the ceiling. It's one of the cheapest upgrades at build stage and among the most effective in a Queensland climate.

Insulation for Your New Home: What You Need to Know to Improve Comfort and Reduce Energy Costs

What insulation does

R-values explained

What R-values does a Queensland home need?