Aerated Concrete House — Does 300mm of Block Actually Meet LBN 002-19?

Aerated concrete (autoclaved aerated concrete, often sold as gas silicate or under brand names) has become the dominant material for new private houses in Latvia over the last two decades. It's light, easy to cut and lay, and has a genuinely good baseline thermal conductivity compared to solid brick or dense concrete. What's less often checked is whether a typical wall build-up actually meets today's standard on its own.

Density classes and thermal conductivity

Aerated concrete is sold in density classes, and density is the main driver of thermal performance — lower density means more air, better insulation, but lower structural strength:

Sources: EN ISO 10456:2007 (D400, D600); D500 interpolated from manufacturer datasheets consistent with both standards.

A typical wall, checked against LBN 002-19

Take a common build-up: 300mm D500 block with a thin cement render on both faces. Using R = d/λ + R_si + R_se per EN ISO 6946:

Only the roof passes. The wall is roughly 1.6× worse than required, the floor 1.4×, and standard double glazing 1.3×. A 300mm D500 block on its own, regardless of how solid it feels, does not meet the current standard — it needs either more thickness, a lower density class, or supplementary insulation.

How thick would block alone need to be?

If you wanted to hit U = 0.23 using only aerated concrete (plus thin render, no extra insulation layer), here's what each density class would require:

D600 is structurally strong but never really works as a single-leaf solution at current standards — the wall would need to be two-thirds of a metre thick. This is exactly why real construction rarely relies on block thickness alone.

The more efficient fix: a thin supplementary layer

Instead of going thicker, adding a modest external insulation layer to a standard 300mm D500 wall closes the gap far more efficiently. Adding ~60mm of EPS or mineral wool to the same 300mm D500 + render build-up brings U to ≈0.22 — inside the 0.23 requirement, without touching the block thickness at all. A few centimetres of insulation does more than doubling the block ever could, because insulation materials (λ ≈ 0.032–0.038) conduct roughly 3–4× less heat than even the best aerated concrete.

What this means if you're building or buying

• A house advertised as “300mm gas silicate walls” is not automatically LBN 002-19 compliant — ask for the actual U-value or check it yourself
• Floor and window specification matter as much as the walls; both failed in this typical build-up
• A thin external insulation layer is usually a more cost-effective fix than upgrading block thickness or density class