Hempcrete and conventional concrete are both composite building materials, but beyond that broad similarity, they behave in fundamentally different ways. Understanding those differences, including where hempcrete falls short as well as where it excels, is essential for anyone considering it as a building material.
What each material is made of
Conventional concrete is a mineral composite: cement (typically Portland cement), aggregate (sand and gravel), and water. It cures through a chemical hydration process, producing a dense, rigid matrix with high compressive strength.
Hempcrete, by contrast, is a bio-composite made from hemp shiv, the woody core of the hemp stalk, mixed with a lime-based binder and water. The binder sets through a combination of hydraulic action and carbonation. The result is a material that is lightweight, porous at a microscopic level, and structurally very different from anything mineral concrete can offer.
According to The Hempcrete Book, that microscopic porosity is the single biggest structural difference setting hempcrete apart from mineral concretes, and it underpins nearly every performance difference between the two materials.
Structural strength: where concrete wins
This is the most important distinction to get straight upfront: hempcrete is not a structural replacement for concrete.
The maximum documented compressive strength of hempcrete is 3.5 MPa. Conventional concrete typically achieves around 17 MPa, roughly five times greater. This gap means hempcrete cannot function as a primary load-bearing material in the way concrete does. It cannot form structural columns, beams, or conventional foundations.
In practice, hempcrete is used as an infill material within a structural frame, typically timber, which carries the loads of the building. The hempcrete provides enclosure, insulation, and mass, while the frame does the structural work.
How hempcrete fails differently
The structural difference isn't just about numbers. Hempcrete also fails differently to concrete and masonry. Conventional concrete fractures under excessive compression: it cracks and breaks. Hempcrete instead deforms, bending out of shape under load, with some recovery towards its original form when that load is removed.
This means current standard methods for testing masonry and mortars aren't entirely appropriate for assessing hempcrete's structural performance. It's a genuinely different class of material, and the wide range of values reported across structural studies reflects both the difficulty of testing it and the variation that comes with different mixes, binders, and production methods.
This deformability, which looks like a weakness compared to concrete, also confers resistance to cracking. Even binder-rich hempcrete mixes used in floor applications retain this quality, which rigid concrete slabs lack entirely.
Thermal, hygric, and environmental performance: where hempcrete leads
Where hempcrete diverges most favourably from concrete is in its performance as a building envelope material.
Concrete has poor thermal insulation properties and typically requires substantial additional insulation layers to meet modern energy performance standards. Hempcrete provides both structure (within its limited capacity) and insulation in a single material. In floor applications, for example, a hempcrete build-up can often be shallower than an equivalent concrete floor with added insulation, reducing excavation depth and associated waste.
Hempcrete also benefits from good flexural strength relative to its density, which has practical consequences. Unlike concrete floor slabs, hempcrete floors do not require expansion joints, simplifying construction detailing.
Environmental considerations
The environmental profile of the two materials diverges sharply. Portland cement production is a significant source of CO₂ emissions globally. Hempcrete's lime binder has a lower embodied carbon than Portland cement, and hemp shiv itself sequesters carbon during the plant's growth, carbon that remains locked in the material throughout the life of the building. See Is hempcrete carbon negative? for the fuller picture, including which mixes qualify and which don't.
The current research literature consistently identifies hempcrete as a bio-based material with strong sustainability credentials. Most studies to date, though, have been conducted in European contexts, and researchers have flagged that regional validation is necessary, particularly where hemp is to be grown and processed locally, since the properties of hemp shiv can vary with crop variety, growing conditions, and processing methods. Claims about environmental performance should be understood in that context: the picture is promising but not yet fully global in its evidence base.
Practical considerations for builders
Hempcrete cannot replace concrete structurally; a load-bearing frame is always required, with hempcrete acting as infill and insulation rather than a structural material. Mix design matters significantly too: higher-density, binder-rich mixes suit floors, lower-density mixes suit walls, and the right specification depends on the application, so builders should refer directly to their supplier or manufacturer for accurate performance data on specific products.
Hempcrete's deformability is a genuine advantage in certain applications compared to rigid mineral concrete, given its resistance to cracking and ability to accommodate building movement. Floor build-ups can also end up shallower than concrete equivalents, since hempcrete contributes insulation value as well as floor structure, with corresponding savings on excavation and spoil disposal.
Cost comparisons aren't straightforward, and the source material available for this article doesn't provide specific cost data for hempcrete versus concrete, so no direct comparison is made here; costs vary significantly by region, specification, and procurement route. See How much does hempcrete cost? for a fuller treatment. What can be said is that hempcrete's multi-functional performance, structure plus insulation in one material, means like-for-like comparisons need to account for what would otherwise be separate insulation systems.
Summary: two materials, two different jobs
Hempcrete and concrete aren't competing products in most building scenarios; they serve different roles. Concrete excels as a structural, load-bearing material. Hempcrete excels as a thermally performing, vapour-permeable, low-embodied-carbon building envelope material used within a structural frame.
The more useful question isn't which material wins, but which one, or which combination, best meets the performance, environmental, and practical requirements of a given project.
For builders and designers working towards low-carbon, high-performance buildings, hempcrete deserves serious consideration for walls, floors, and roof builds where its properties align with project goals, specified with a clear understanding of what it can and cannot do, and with input from experienced suppliers who can provide accurate data for the specific products being used.
Sources
- Stanwix, W. & Sparrow, A., The Hempcrete Book