choosing blockwork: Dense vs lightweight vs Aircrete

If you ask a supplier for a choice between blocks, your first decision will be between dense,

“Your structural engineer should always be used to specify the block dependent on your own home design”

Choosing between the three – or between blockwork and one of the other construction systems – often comes down to a number of factors, including strength, useability, cost, energy performance and airtightness, as outlined below.

One difference between individual block products is their strength. Clearly, the fundamental job of a building block is to hold things up – the roof, the wall above it, the floor structure, your heavy bed, gym equipment and bath. All of these things transfer their weight into a loading that is transferred to the ground through the external walling system. So your walls need to be strong.

The strength of the blocks is measured in a compressive force rating expressed in newtons per mm2. The good news is that for self-builders building houses and for extensions below four storeys (which includes almost everyone) the use of blocks in the 3-10N/mm2 range is usually more than enough for loadbearing purposes. As long as ceiling heights for two-storey houses are below 2.7m, BS103-2 suggests that both walls can be built out of aircrete achieving a minimum strength of 2.9N/mm2. This doesn’t allow for any non-standard loadings and so it’s worth saying that your structural engineer should always be used to specify the block dependent on your own home design. Clearly, with traditional blocks enjoying compressive ratings well above 5N, this isn’t a problem that users of more traditional blocks need worry about.

Dan Mutti from D&M Homes, one of the UK’s longest established and popular self-build pack- age suppliers, who specialise in masonry homes,