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Thermal Bridging: Which Blocks are Best?

Thermal bridging occurs where there are breaks in the insulation in the fabric of a building and can account for up to 35% of a building’s total heat loss. Architects and designers often specify aircrete blocks, such as Mannok aircrete thermal blocks, to effectively combat this heat loss. Mannok aircrete blocks can reduce heat loss through thermal bridging by up to 80%, so it’s a very effective way of improving the overall performance of a house.

But, can Mannok aircrete blocks be replaced with an alternative block, such as a lightweight aggregate block? The blocks are very different, so it is not just a matter of switching one block for another. There will certainly be performance issues and potentially compliance issues also.

Thermal Blocks Comparison

We can see this very clearly when we look at one very common junction, the floor to wall junction as shown in Fig. 1, and compare using Mannok aircrete blocks with using lightweight aggregate blocks.

Thermal Bridging Floor to wall junction
Fig. 1: Thermal Bridging Floor to Wall Junction

To compare, we will look at three key consideration: cost, performance and compliance.

To effectively combat thermal bridging, this detail will require four lightweight aggregate blocks, whereas, when using Mannok aircrete blocks, only one block is required as shown in Fig. 2.

Fig. 2: 1 Mannok Aircrete Block Vs 4 Lightweight Aggregate Blocks
Fig. 2: 1 Mannok Aircrete Block Vs 4 Lightweight Aggregate Blocks

Cost and performance

Comparing the cost, lightweight aggregate blocks will cost around 4 times more in this detail, whereas just one Mannok aircrete block is not only much cheaper, but is also 15% more thermally efficient than the four lightweight aggregate blocks.

Durability Compliance

Blocks are located below DPC in this junction. For Mannok aircrete blocks, this is no problem as they have declared thermal performance for use both above and below DPC. Other blocks, including lightweight aggregate blocks, do not have declared performance below DPC.

In addition, there are important compliance considerations when using blocks in this location. Lightweight aggregate blocks do not meet the compliance requirements of NSAI publication SR325 for durability.

Mannok aircrete blocks, however, have been tested and are third party agrément certified as freeze thaw resistant, which makes them ideal for use in this location.

The comparison is clear. To combat thermal bridging, Mannok aircrete is the best block available in Ireland, and the only thermal block certified for use in this location, below DPC.