Hemp Hurd & Hempcrete

Hempcrete is hemp hurd mixed with a lime-based binder and water, then cast into formwork around a timber frame or pressed into blocks. It isn't structural; the frame holds the building up and the hempcrete fills the walls as insulation. What it does well: it's vapor-open, so walls breathe and moisture doesn't get trapped; the lime makes it resistant to fire, mold and pests; it stores carbon for the life of the building; and it insulates at a commonly cited figure of around R-2 per inch, so a 12-inch wall lands in the mid-20s. It isn't for below-grade or anywhere that stays wet.

Mixing it

A common starting mix is 4 parts hurd to 1 part binder by volume, with water added until it holds together in a fist. The hurd has to be clean and consistently sized, which is why the hempcrete hurd is screened differently from the mulch. The binder is sold by lime suppliers, not by us. Cast in lifts, tamp lightly (over-compacting kills the insulation value), and expect weeks of curing. For anything load-bearing, code-related or larger than a shed, work with a builder who has done hempcrete before.

To estimate hurd: wall length × height × thickness in feet gives cubic feet of hempcrete, and roughly four-fifths of that volume is hurd. Bags are sold by weight, and loose hurd runs on the order of 7 lb per cubic foot, so figure about 5 to 6 lb of hurd per cubic foot of finished wall and round up.

Mulch

Spread 2 to 3 inches around perennials, shrubs and on paths. Hemp hurd is pale, coarse, holds moisture and suppresses weeds, then breaks down into the soil over a season or two. Dry hurd is light enough to blow; water it in after spreading.

Animal bedding

More absorbent than pine shavings or straw, low in dust, and free of the aromatic oils in pine that bother some birds and horses. Spot-clean daily; the used bedding composts.

Soil amendment

Worked into heavy clay it opens the soil for air and roots; in sandy beds it holds water. Like any woody material, it borrows nitrogen while it breaks down, so add a nitrogen source alongside it the first season.