Hemp Building Materials & Hempcrete: A Buyer’s Guide

The main product types

• Hemp-lime (hempcrete): hemp hurd mixed with a lime-based binder and water. It is cast or sprayed in place, or made into precast blocks and panels. It is a non-structural insulating infill. A timber or other frame carries the loads.
• Hemp fiber insulation: batts and boards made from bast fiber, usually with a binder fiber, installed much like other batt insulation.
• Panels and composites: boards and panels using hemp fiber or hurd with a binder, for sheathing, interior finishes or prefabricated wall systems.

Hempcrete in the building code

The 2024 International Residential Code (IRC) added Appendix BL, Hemp-Lime (Hempcrete) Construction, which sets minimum requirements for hemp-lime wall systems in one- and two-family homes and townhouses. IRC appendices apply only where a state or local jurisdiction adopts them, so ask your building official whether Appendix BL is in force before you design around it.

Updates adding fire-resistance-rated hemp-lime wall assemblies were approved at the ICC hearings for the 2027 IRC. Projects outside the IRC’s scope, such as commercial buildings, follow the International Building Code and usually need an engineer’s or code official’s approval of the system.

Thermal performance (R-value)

Hemp-lime’s insulating value depends on its density. Table BL106.2 of Appendix BL lists these per-inch R-values, and permits project-specific lab test results (ASTM C177, C518, C1114 or C1363) instead:

That is lower per inch than foam or fiberglass, so hemp-lime walls are thick, often around 12 inches. Their thermal mass, vapor-open behavior and fire and pest resistance are why builders choose them.

What to ask a supplier

• Binder type and mix design, and the in-place density the product achieves.
• R-value test reports by an accredited lab, with the test standard named.
• Fire, moisture and surface-burning test data relevant to your assembly.
• Installation method, drying time and installer training or certification.
• Code documentation: Appendix BL compliance, evaluation reports or engineering letters.
• Lead time, minimum order and delivered freight cost.

Quick checklist for suppliers

• Material composition, dimensions and thermal or acoustic test data
• Applicable building codes, certifications and installation requirements

Confirm local approvals and qualified design guidance before specifying products.