A cob and earth builder is a specialist craftsperson with expertise in constructing and repairing buildings using traditional earthen materials - principally cob (a mix of subsoil, straw and water), rammed earth, adobe and related techniques. Earthen construction has a long history in the UK, particularly in the South West of England, and there are estimated to be 60,000 cob buildings in Devon alone. These buildings require specialist knowledge for repair - cement-based mortars and renders will damage them irreparably, and only earth-compatible materials should be used. Earth building specialists are also in demand for new eco-construction projects.
What they do
- Repair and consolidate deteriorated cob walls using compatible earth mixes
- Apply earth-based render and plaster to cob and stone walls
- Construct new cob walls for extensions and outbuildings
- Install earthen floors using traditional compressed earth techniques
- Advise on appropriate materials for cob building repair
- Carry out condition surveys of historic cob and earth buildings
- Construct rammed earth walls for new builds
- Prepare earthen building reports for listed building applications
When you need one
An earth building specialist is needed for any work to a cob or earth building, and for new eco-build projects using earthen construction techniques.
Typical costs (UK, 2025)
| Job type | Typical cost |
|---|---|
| Day rate | £200 - £350 / day |
| Cob repair (per sq m of wall face) | £80 - £180 / sq m |
| New cob wall construction (per sq m) | £150 - £350 / sq m |
| Earth render (per sq m) | £40 - £80 / sq m |
| Earthen floor (per sq m) | £40 - £90 / sq m |
| Cob survey and assessment | £400 - £900 |
Cob repair costs depend heavily on the severity of deterioration and accessibility. Stripping damaging cement render before re-applying earth render is an additional cost. Prices are typically lower in the South West where cob buildings are most common.
Qualifications and memberships to look for
SEDA promotes earth building techniques in Scotland and maintains a network of practitioners. Active particularly in the context of rammed earth and modern earth construction as well as historic repair.
Regional cob building networks, particularly in the South West, connect practitioners and share knowledge of historic cob repair. The Devon Earth Building Association has been a significant source of expertise in cob repair and construction techniques.
SPAB and Historic England both publish guidance on the repair of earthen buildings. Practitioners who follow and reference this guidance are more likely to apply appropriate repair methods that will protect the building long-term.
How to find a cob and earth builder
Frequently asked questions
What is cob?
A traditional building material made from subsoil mixed with water, straw and sand - used for thousands of years in the UK, particularly in Devon, Dorset and East Anglia. Cob walls are typically 450-600mm thick and extremely durable when kept dry. The phrase 'all cob wants is a good hat and a good pair of boots' reflects the two critical factors: a sound roof overhang and a dry plinth or base course.
How is a cob building repaired?
Cob must be repaired using compatible materials - new cob or earth-based renders and plasters. Cement or hard gypsum plasters trap moisture and accelerate the deterioration of the cob. The repair process typically involves cutting out damaged material, re-packing with new cob mix, and applying earth or lime-based render coats that allow the wall to breathe and shed moisture.
Can you build a new cob house?
Yes - cob building is experiencing a revival for eco self-build. New cob buildings require planning permission and Building Regulations approval. Structural calculations by an engineer experienced in earthen construction are required, and the design must demonstrate adequate thermal performance and moisture management. Several specialist practices now design and build new cob homes in the UK.