‘It’s a No-Brainer’ – Biobased is Best

CPD Presentations By Dermot Moore

Graham Durrant, Founder of Hemp-Lime Spray Ltd., has over 30 years of building and design experience, focusing on environmentally friendly methods. In 2013 Graham completed an MSc Architecture Degree in Advanced Environmental and Energy Studies. He wanted to ‘champion a green building material’ during this time.

Referring to three key issues: embodied carbon, anticipated thermal performance and moisture regulation, Graham looked at hempcrete as a solution. In short, his goal was to find ‘the most environmentally sane way of getting a comfortable building’. 

The Carbon Question

Graham began his presentation with a comparison of conventional and biobased walls. Without a shadow of a doubt, this showed that biobased is far superior where embodied carbon is concerned. Graham informed us that even though there are massive fluctuations in carbon footprint figures, we are still far better off using biobased materials. Comparing hempcrete and conventional builds, Graham calculated for every hempcrete home built, ‘we are fifty-three and a half tonnes better off… It’s not even close, the carbon footprint’ (1.20 – 2.40).

Personal Journey with Hempcrete

Graham then described different ways of casting hempcrete, hand cast and spray cast. Most of the work Graham does involves the spray technique, the process he guided us through. Two key differences he noted between hand cast and sprayed are the ‘much better adhesion’ of sprayed hempcrete and the requirement of fewer people for the task (5.32 – 5.50). 

Retrofits and Monoliths

The versatility of hempcrete spray was made proven by Graham and his team’s work on a home. They resurfaced dilapidated, uneven walls. The hemp spray had no problem, as Graham demonstrated with video footage of its application. The spray is particularly great for old buildings with uneven surfaces, as varying lines can be quickly followed and filled in by spraying (6.40 – 9.03). Another fine example was an old church Graham renovated, where the spray was used to fill in the long, oblong alcoves without causing a drastic reduction in depth (16.16 – 17.08).

The following job Graham presented was the largest monolithic hempcrete build at the time. Like Jeremy Blake and Tom Woolley, Graham demonstrated how a hempcrete build can easily gain bad press.

Graham had warned the contractors that the walls were not in line and, therefore, not ready to apply hempcrete. Unfortunately, the contractors chose not to go with his recommendations. This decision caused disruption when glazers for the building arrived. The glazers said the wall was not straight enough to install the glazing. In their efforts to align the walls, the hempcrete was torn.

Eventually, this worked out in the more extraordinary tale of hempcrete’s versatility, as Graham’s team could fill in the cracked wall using hempcrete spray (9.24 – 11.20). 

Modern Styles

Due to the precise requirements, Graham found that more modern designs, with long, hard and sharp lines, take longer than old builds. One method of overcoming this is to black out the windows and set up a laser with clingfilm over the laser level on the opposite side of the space where Graham is spraying with hempcrete. He then follows the green line of the laser, which enables the accurate application of hempcrete. However, lasers cannot be used outside due to light levels (18.07 – 20.07). 


Graham has completed several hemp experiments at his home, proving the durability of hempcrete. He heard early on that ‘once hempcrete starts to break down, the sugars break down, and there’s a problem.’ Graham tested this out on his property, using mouldy hemp as the base material on a project’s roof. The building has been standing for four years, and Graham has only had to scrape a tiny 25mm layer where the rain had been gathering over this four-year period. This project shows Graham how resilient hempcrete is to limitations, even when using pre-used fibre. (13.15 – 14.40).


Graham offered a clear answer on using hemp insulation in roofing, which indicated why a contractor might not always recommend it.

“It makes very good roofs, but you’re putting in a relatively heavy insulation material, so you have to structure up for that’ You are also putting in a wet material. This means you need a way of covering it to prevent it from getting even wetter from rain, ‘but you also need to get airflow. Otherwise, it is not going to dry out.’

However, this is also climate dependent. Graham offered the south of France as an example, where hempcrete brilliantly helps keep indoor temperatures down. With global temperatures only rising, hempcrete roofing may become more applicable in northern Europe. (22 – 23.15).

Hempcrete Performance: General Info
Thermal Capacity

Similarly to Tom and Jeremy, Graham provided great insight into hemp’s thermal capabilities, which continued to shine compared to conventional alternatives. 

‘Where hempcrete, I think, really wins out is the way you get this wonderful mix of thermally massive materials, which are much better with thermal mass, and there are insulators that are much better as insulators, but hempcrete sits in that middle sweet spot.’

‘So what enables is enough heat to go into the fabric of the building, warming it up. Yet, if you imagine most modern buildings with their plasterboard and insulation behind them, the problem is that the only thing ever warm in those buildings is the air.’

‘There is no thermal mass, and there is no building fabric that the heat can get to, as it is just insulation behind the plasterboard. Whereas with hempcrete, the actual fabric of the building warms up, so if you open a window or a door, the room temperature takes ages to drop down, whereas I assume we have all been in houses where the heating goes off at 10pm, and the room is freezing cold by half past 10 or 11.’

With hemp, heat will stay in the building till the following day (30 – 34.15). This, of course, reduces the urge to use electrical heating for prolonged hours.’

Moisture Management

All buildings get moisture spikes simply from breathing, but especially our homes, where we take showers, do the dishes and wash and dry clothes. This is because we ‘all produce humidity’, which raises the relative humidity. Hempcrete houses absorb those moisture spikes, so they keep your humidity really steady’ (36.20 – 40.49). 

Fire Protection

Graham also reinforced hempcrete’s fire durability, which was discussed in Tom and Jeremy’s presentations, mentioning yet more experiments involving hemp being burned with blow torches to no avail (40.50 – 41.50).

Electro Magnetic Interference

This aspect might bother people, but as long as they are aware, problems can be averted. Graham revealed that hempcrete could block wifi signals, especially when laid on thicker (41.23 – 42). 

Main Drawbacks

Graham finished up with a few bullet points of the main drawbacks to hemp in his own experience.

  • Lime-based – so the temperature is important
  • Messy
  • Drying time for thick walls can be an issue.
  • Lack of understanding of the material
  • Hemp production barriers – obviously, Hemspan are making headway in remedying this!
  • Lack of expertise

If you want to find out more, please get in touch. We’re here to help.

Graham Spraying hemp