Blocks compared

Key issues

For:
• Durability
• Strength
• Thermal mass
• Accoustic mass
• Insulation capability

Against:
• Often high levels of embodied energy
• Energy used in transportation
• Non renewable resources
• Effects of quarrying and extraction of clay and shale
• Use of cement in assembly

Types of blocks:

Hollow clay blocks (for monolithic construction)
	Hollow clay blocks are made from common brick clay often admixed with industrial wastes such as flyash and cinder ash. The blocks are fired in a similar way to bricks.
	Can contain recycled materials (check)
	Reuseable
	Materially efficient compared to solid clay bricks
	Large reserves
	Durable
	Low toxicity
	No greenhouse gases
	High natural content
	Contribute to better U-Values
	No UK manufacturer (imported - adding to embodied energy)
	High embodied energy

Aereated concrete blocks ('Aircrete')
	Aircrete is made from various materials including ground sand, PFA (more...) cement, lime, aluminium powder and water. They are blended together into a mixture which foams to create an exceptionally strong and light cementitous matrix with high thermal insulation.
	Recycled content - most blocks use fly ash, a waste product
	High weight/strength ratio results in less material than aggregate blocks
	High level of thermal insulation
	High embodied energy (the aluminium and cement components)
	Low thermal mass

Aggregate concrete blocks
	Aggregate concrete blocks are made from cement, sand and aggregates. The mix is moulded and then cured in heated chambers. Lightweight blocks differ in the weight and nature of the aggregate component. Conventional lightweight aggregates (eg shale and clay) are expanded in kilns using considerable energy. Using ‘Slag’ (a re-cycled bi-product of the steel industry- more...) obviates the need to produce artificial lightweight aggregates thus dramatically reducing the embodied energy.
	DENSE AGGREGATE CONCRETE
	Durable
	High thermal mass
	Resource depletion - virgin aggregate, sand
	Greenhouse gases
	LIGHTWEIGHT AGGREGATE CONCRETE
	Durable
	Resource depletion - virgin aggregate, sand
	Greenhouse gases
	HIgh embodied energy
	DENSE AGGREGATE (using SLAG aggregate and cement) CONCRETE
	Recycled content
	High thermal mass
	Durable
	LIGHTWEIGHT AGGREGATE (using SLAG aggregate and cement) CONCRETE
	Recycled content
	Durable
	Not airtight (no fines)

Interlocking wood blocks (for monolithic construction)
	Timber blocks are made from cross-glued boards, studs and rails and have horizontal and vertical interlocking parts. ‘Dry’ assembly, interlocking wood block systems are a fast alternative to timber frame structures.
	Reusable and recyclable
	Made from timber offcuts from forest thinnings
	Renewable resource
	Non-toxic
	Low embodied energy at the factory gate
	No greenhouse gases
	High natural content
	Hollow core allows for added thermal and accoustic insulation and services distribution
	Mortar-free dry construction
	Loadbearing up to 7 storeys (manufacturers provide design service)
	Lower thermal mass than concrete and clay
	Lower insulation capability than concrete and clay
	No UK manufacturer (imported - adding to embodied energy)

We would specify:

First Choice: • Dense aggregate blocks using slag • Aereated blocks • Hollow clay blocks • Wood blocks
Mortar: • Use lime mortar - try to avoid cement mortar

Block products:

• L322 Blocks