Light Earth Infill
Straw or woodchip coated in a thin clay slip and packed by hand into temporary shuttering around a frame, then left to dry and finished with a breathable render. Known in Germany as Leichtlehm. The clay is the adhesive; the trapped air in the fibre does the insulating.
Carbon and evidence
How This Is Made
An Environmental Product Declaration is issued by a manufacturer against a declared unit. This record has neither, so it states sourced facts about process and provenance instead of a carbon figure.
German Leichtlehmbau, carried into UK and Irish natural-building practice; documented for UK use by Gaia Group
Process
Feedstock
Plant fibre
Straw or woodchip as the bulk, coated in a clay slip made from subsoil — a clay fraction around 30% is generally taken as the working target
Process heat
No heat
Binder
Clay
Fabrication
Site-formed
Sourcing: site-won subsoil with local fibre, where the ground allows it
Who Builds It
Trained contractor
Rare in the UK
Drying is the binding constraint, not the mixing — roughly eight weeks for a 300 mm wall in warm weather and considerably longer for a thicker one or a wet autumn. The wall cannot be closed up or rendered until it is dry
End Of Life
Separable
Broken out of the frame; the material composts or returns to subsoil with nothing to separate
Maintenance: Breathable render or limewash only; patched in place with fresh mix
Specification Risk
What a specifier has to resolve before this can be built.
- Certification
- No Agrement and no declared U-value; thermal performance follows from the density achieved on site and has to be argued case by case
- Fire
- No standard reaction-to-fire classification is held. UK testing has been undertaken in research contexts — confirm what actually applies to your buildup rather than assuming it transfers
- Warranty
- Contractor workmanship warranty only; there is no product to warrant
- Insurance
- Confirm warranty-provider acceptance early; it sits outside standard guidance
- Supply
- Very few UK contractors have built it. Secure the trade before the design is fixed
Read This Honestly
- •Not structural. The frame carries the load; this is insulating infill packed around it.
- •Density sets the performance, and density is a site decision. A heavier mix behaves as thermal mass, a lighter one as insulation, and neither is declared anywhere.
- •The drying programme is measured in months, not days. On a fixed contract programme this is the reason it gets value-engineered out.
- •Trapping it behind a cement render or an impermeable membrane will rot the fibre.
Design & Specification Notes
Straw or woodchip coated in a thin clay slip and packed by hand into temporary shuttering around a frame, then left to dry and finished with a breathable render.
Material Note
The clay is a binder, not the insulant — it coats the fibre and holds it in place, and the air trapped in the fibre does the work. Density is the whole trade-off: more clay means more mass and less insulation.
Typical Uses
- •Facade cladding
- •Weather protection
- •External accents
Key Performance
Weather-resistant finish for facade exposure.
Specification Actions
- •Establish whether the subsoil is site-won and have its clay fraction tested; the mix is designed to the soil, not to a recipe.
- •Agree the target density before mixing — it sets both the thermal performance and the drying time, and neither can be adjusted afterwards.
- •Record it as separable — the infill is broken out and composts or returns to subsoil, releasing the frame intact.
Indicative Health & Indoor Air
Subsoil clay and untreated plant fibre. Vapour-open and hygroscopic, and must stay that way to remain sound.
Products in this category
6 products from 4 manufacturers · 343 in this category. Ordered by the evidence each record holds, never by commercial standing.
Specification
- Finish
- Clay-slipped fibre, packed and rendered
- Service life
- 60 years