The carbon built in.

Double brick puts brick in every wall: two leaves outside and, as WA builds it, the internal walls too, which need footings of their own. With their footings, which are counted with the floor, the walls carry about {share} of this home’s upfront carbon.

Brick veneer keeps one leaf of brick and swaps the rest for a timber frame and plasterboard, inside and out, so its walls carry far less carbon than double brick.

Steel framing weighs less than timber but carries more carbon per kilo, so it adds a little to a brick veneer home. The brick still carries most of the walls’ carbon.

Lightweight cladding on a timber frame is the lowest-carbon wall here. With no brick, the floor, roof and windows carry most of what’s left.

Lightweight cladding on a steel frame stays far below double brick, though the steel adds more than timber would.

AAC is aerated concrete: light for masonry, and mostly sand, cement and lime. As a veneer over a timber frame, the wall carries more carbon than lightweight cladding but much less than brick veneer.

Over a steel frame, AAC veneer carries a little more than over timber, as the steel adds more than timber would.

Insulated panels are light, but their steel skins and polystyrene core carry a lot of carbon per kilo. The internal walls are panels too, as panel systems build them, so the walls, inside and out, carry about {vsBrick} of what double brick’s do. Steel-framed internal walls would save about {panelInside} t.

Without product data, the NABERS defaults apply: the highest reasonable value for each material. They lift this home from {typ} to {def} kg CO₂e/m². Specifying products with EPDs lets an assessment use their real figures.

Waffle pods save some concrete, but the polystyrene pods and extra reinforcement carry carbon of their own, so here the waffle slab carries about {floorVsSlab} what a standard slab does.

A suspended timber floor needs concrete only for its footings, so it carries about {floorVsSlab} what a slab does. Most of that is the particleboard flooring.

AAC floor panels weigh three times as much as particleboard and carry more carbon, though the floor still carries about {floorVsSlab} what a slab does.

A 50 mm concrete topping is far thinner than a slab, but it needs mesh, a sheet to pour it on and a stronger frame to carry it: the floor carries about {floorVsSlab} what a slab does.

A 50 mm concrete topping on a steel frame: the topping needs mesh, a sheet to pour it on and heavier steel to carry it, so the floor carries about {floorVsSlab} what a slab does.

A suspended steel floor needs concrete only for its footings, but its steel joists and bearers carry a lot of carbon per kilo: the floor carries about {floorVsSlab} what a slab does.

Steel joists and bearers under AAC flooring make the highest-carbon suspended floor here, at about {floorVsSlab} what a slab carries.

Brick walls can’t stand on a suspended floor, though: they run down to strip footings of their own, which add about {belowFloor} t to the floor.

Timber windows carry about half the carbon of aluminium ones, glazed the same way, and windows are one of the biggest single items in a home.

uPVC windows aren’t in the NABERS database, and no Australian EPD covers them, so this option uses the European industry EPD for a double-glazed uPVC window: the weighted mean of eleven makers’ windows, with steel-reinforced frames. Single glazed, one pane comes out.

Double glazing adds a second pane of glass, about {pane} t here, to this home and the reference alike, so the comparison stays on how the home is built. It also cuts heating and cooling energy every year, which a lab counting upfront carbon can’t show.

Single glazed, in this home and the reference alike, as most WA homes are. Double glazing would add about {pane} t up front, and cut heating and cooling energy every year.

Steel roofing weighs about a tenth as much as concrete tiles but carries far more carbon per kilo, so a metal roof carries more upfront carbon than a tiled one.

Concrete tiles weigh about ten times as much as steel roofing but carry far less carbon per kilo, so the roof carries about {roofVsMetal} what a metal sheet roof on a timber frame does.

Terracotta tiles carry about twice the carbon of concrete tiles per kilo, so they lift the roof’s share.

A steel roof frame weighs less than a timber one but carries far more carbon per kilo, so the roof carries much more than it would on timber.

A steel roof frame weighs less than a timber one but carries far more carbon per kilo, so the roof carries much more than it would on timber.

A steel roof frame weighs less than a timber one but carries far more carbon per kilo, so the roof carries much more than it would on timber.

Insulated panel roofs are usually skillions, like this one at 5°. The roof is its own ceiling and the panels span on their own, so there’s no roof frame, ceiling or batts. Even so, its steel skins and foam carry about {roofVsMetal} what a metal sheet roof on a timber frame and its ceiling do. With no ceiling, the walls run up to the roof, which adds about {rakedWalls} t to them, inside and out. At 150 mm, the panel also insulates less than the R5.0 batts of the other roofs.