Why wall weight matters in taller buildings
In a building of three or more storeys, the walls usually sit on a frame of concrete or steel columns and beams. Every kilogram of wall has to be carried by that frame and its foundations. AAC blocks weigh about a third as much as red bricks, so a frame filled with AAC needs less steel and concrete, and the building weighs less in an earthquake.
In a single-storey house the walls can carry the roof themselves. Here weight matters less, and local, low-energy blocks such as stabilised earth blocks or fly-ash bricks are often the cheapest low-carbon choice.
Where the carbon savings come from
- No kiln firing: red clay bricks are fired with coal or wood. AAC, fly-ash bricks and earth blocks are cured with steam, or simply in the air.
- Less cement: blended cements (PPC, PSC, LC3) replace part of the clinker with fly ash, slag or clay, and clinker is where most of cement's CO₂ comes from.
- Plants that store carbon: hemp, straw, bamboo and timber keep the carbon the plants took from the air for as long as the building stands. Ask for FSC or PEFC certified timber.
To compare your own house, put the quantities into the building materials carbon calculator.
Frequently asked questions
Can I build a two-storey house with AAC blocks?
Yes. The usual way is a reinforced concrete frame with AAC walls filling the gaps. Load-bearing AAC walls are possible for one or two storeys, but they need stronger blocks and a structural engineer's design, especially in earthquake zones.
Are lightweight bricks strong enough?
AAC blocks are usually 3 to 5 N/mm² in compressive strength, similar to ordinary red bricks, which is enough for walls. Heavy shelves, water heaters and TV mounts need anchors made for AAC.
What should I use for a tall building?
A concrete or steel frame using blended cement (PPC or PSC), with AAC or fly-ash infill walls. Where the building code allows it, cross-laminated timber can carry the whole structure of mid-rise and some high-rise buildings.
Do green materials cost more?
AAC and fly-ash bricks often cost about the same or less per square foot of finished wall, because they need less mortar and plaster and a lighter frame. Hemp, straw and engineered timber usually cost more today, but save on heating or cooling.
Sources
- Autoclaved aerated concrete (Wikipedia) ↗ – density and use of AAC
- Cross-laminated timber (Wikipedia) ↗ – CLT in multi-storey buildings
- Auroville Earth Institute ↗ – compressed stabilised earth blocks