Bio-aggregate: workshop

Energy-retrofitting the traditional hygrothermal envelope. Preparation, mixing and casting bio-aggregate hemp lime onto existing masonry.

When: Monday 24th – Wednesday 26th October, 10 – 5pm
Where: Bristol
Cost: £240

Open days

Drop in, come take a look and maybe have a go!

When: Wednesday 26th October 1 – 4pm
Where: Bristol
Cost: Free

When: Saturday 29th October 1 – 4pm
Where: Bristol
Cost: Free

Plaster: workshop

Energy-retrofitting the traditional thermal envelope. Preparation, mixing and applying coarse base-coat and fine top-coat Lime plaster.

When: Monday 21st – Wednesday 23rd November, 10 – 5pm
Where: Bristol
Cost: £240

When: Thursday 24th – Saturday 26th November, 10 – 5pm
Where: Bristol
Cost: £240

Open days

Drop in, take a look and have a go!

When: Wednesday 23rd November, 1- 4pm
Where: Bristol
Cost: Free

When: Saturday 26th November, 1- 4pm
Where: Bristol
Cost: Free


Monday 28th – Thursday 31st March
Hemp Lime contractors

Thursday 28th – Saturday 30th April
Lime plaster basecoat

Thursday 5th – Saturday 7th May
Lime plaster topcoat

Thursday 30th June – Saturday 2nd July
Lining paper


The refurbishment model being applied to our existing housing stock is falling short of predicted energy savings and is causing damp. It overlooks no cost and low cost interventions such as occupant behaviour and air movement, and doesn’t understand the traditional thermal envelope. In preference, an industry-led, product based, systemised approach to wall insulation is being applied. The cost versus savings are upside down, the building physics are back to front and our understanding of architectural detailing is inside out. Add to this hidden layers of cement render, vinyl paint and polyvinyl acetate it’s no wonder buildings don’t perform as predicted, let alone as they were intended. The existing model is Static, considering only the thermal and vapour resistivity to predict how the building will perform and when damp will occur. Improved loft insulation and glazing make walls the coldest surface in the room, increasing risk of condensation. External insulation is costly, complex, unsympathetic and retrofitting leaves cold spots internally. Walls insulated internally with foam board lose their capacity to buffer temperature, humidity and when incorrectly installed, cause interstitial condensation. Breathable insulation boards are mechanically fixed over layers of historical unknowns. Are they the right type of breathable or are they vulnerable to degradation?

Traditional construction has a Hygroscopic thermal envelope and interiors which act as a reservoir, buffering peaks in humidity avoiding moisture drop out and reducing heat loss. ‘Decorative’ cornice and wallpaper have a purpose, by adding thermal inertia and hygroscopic capacity the thermal envelope can respond sympathetically to both the changes in external and internal weather. Thermal inertia and hygroscopic reservoirs buffer peaks preventing the storms that cause condensation.

This paper presents the case for using hygroscopic Hemp and Lime to solve damp problems with the secondary effect of improving the thermal efficiency of older buildings. The author draws on over 25 years of observations, remediating damp and calls for a better understanding of traditional construction. A knowledge-led approach to refurbishing our existing housing stock, that understanding how it was originally intended to perform and how what we now do in them and to them affect how they behave, causing damp. People, air movement and a lack of understanding of the traditional thermal envelope.

Hemp and Lime internal wall insulation and hygroscopic interiors build on the knowledge of the past, employing traditional, simple but innovative techniques developed specifically for the preparation, mixing and casting of Hemp and Lime in damp remediation, general repairs and refurbishment. Resurrection of a unique surface preparation method, the timber ‘Dochan’ quickly flattens out any uneven surface for a true, flat, vertical finish that holds together rather than disturbing old lime mortar and loose brickwork. A small scale mixing process for safe clean material handling making domestic projects accessible and affordable. Casting that connects and engages with the wall even when challengingly thin layers are applied.

Using case studies the principle of the hygroscopic reservoir is tested to the extreme with a condensation proof, hygroscopic bathroom and with the problematic north facing ‘decorative’ façade of an archetypal Victorian terraced house. Over a century of bad practice put right in a couple of weekends. No specialised equipment just low cost knowledge-led renovation. The author calls for a more sympathetic and democratised approach to retrofitting that’s healthier for our buildings, the occupants and their bank balance.

Damp pathology, renovation and refurbishment consultant.

Architectural detailing, the purpose behind the decorative façade.

Hygrothermal passive heat recovery, resurrecting, reinventing and reinstating the traditional thermal envelop.

Neighbourhood construction, peer to peer practitioner support.


Damp remediation
No cost and low cost interventions. From source to symptom.

Hemp and Lime
Resolving damp whilst reducing both the need and consumption of household energy.

Talks and workshops
Come along to one of our free events or arrange a  group tutorial.

Advice and consultancy
Buildings pathology, Hemp Lime, energy, damp, renovation and refurbishment consultancy.