Anyone who chooses hemp and lime today is usually looking for more than just an insulation material. The demand is for materials that have proven themselves in practice. Hemp blocks (hemp-lime) are increasingly coming into focus. They combine thermal insulation with high capillary activity and thermal mass – a combination that has often been lost in modern solid construction.

Why hemp? The material properties in detail

Hemp blocks are essentially a composite of Hemp shives and lime as a binder. Designed as non-load-bearing masonry, they enclose a load-bearing structure (e.g. made of timber, sand-lime brick or concrete). According to the FDES, a 36 cm wall achieves a phase shift of 23.6 hours and a thermal resistance of R = 5.07 m²K/W.

At the same time, the blocks can buffer fluctuations in indoor humidity (µ = 2.8).

Hemp blocks in practice: three approaches

1. Urban densification in Berlin

In a vacant lot in Berlin, a three-storey townhouse is currently being built that relies entirely on hemp building materials. Situated between two fire walls, the project shows how Hemp blocks also work in tight urban spaces. Alongside the CO₂ stored in the hemp (according to the FDES around 62 kg per m² at 36 cm wall thickness, life cycle A–C overall +58.9 kg CO₂e per m²), sound insulation is the key argument here (Rw 44 dB at 36 cm). You can find out more about this project at Hemp! there it is and on urbancleanbuilding.de, the website of architect Michael Bader.

2. Commercial and residential combined: Halle (Saale)

For the new build of a horticultural business in Halle, the priority was cost-effectiveness combined with high standards in the choice of building materials. Here, 15 cm thick hemp blocks were placed as an outer envelope in front of a calcium silicate masonry structure. This combination makes use of the load-bearing capacity and mass of the calcium silicate masonry on the inside and the insulating performance of the hemp on the outside. This system is particularly interesting for you as a self-builder: the large-format blocks can be cut precisely with hand-held tools and are easy to work with.

3. Renovating existing buildings: half-timbered house on Fejø

The fact that Hemp blocks can be combined with historic structures, as a project on the Danish island of Fejø shows. During the renovation of an oak timber frame, the infill panels were filled with 9 cm thick hemp blocks. On the inside, an additional hemp lining was added. What matters in projects like this is the system: a mineral Lime base plaster (like the HP 9) and a mineral paint (e.g. titanium dioxide-free silicate paint BEECKOSIL) finish the wall.

What matters during installation

If you are planning, Hemp blocks to use it, you should bear three points in mind:

• The first course is crucial: as with any thin-bed block masonry, a perfectly level first course determines the success of the entire wall.

• System consistency: hemp works best in combination with mineral plasters. Clay plasters indoors can additionally buffer fluctuations in indoor humidity.

• Structural protection: when planning, pay attention to details such as roof overhangs and roof underlay boards in the roof area, to protect the structure from the weather in the long term.

Hemp blocks are not a “trend product” but a logical answer to the question of how we can build solidly today with hemp and lime.