Objective – Lambda value, u-value and moisture regulation.


Process – Cast application, ratio and density.


Materials – Bio-aggregate shiv and specially formulated lime binder.


Aberystwyth University: Beacon Project, Institute of Biological Environmental Rural Sciences (IBERS). Dublin Institue of Technology (DIT)


Peer to peer, on-site training


Open days


Assessing risks in insulating retrofits using Hygrothermal software tools. Heat and moisture transport in internally insulated stone walls.

I can well believe the resulting assembly has a beneficial sanitary effect on the internal environment.


The reduction of energy consumption and management of internal moisture.

Casting onto a traditional solid brick wall or masonry construction, with for example an existing U-value of 1.7 W/m2K, at a thickness of 100mm and applied with the quantified methodology for Plaster as well as Paper and paint. The resulting U-value for the retrofitted wall can be calculated. U-value 0.3.

Additionally, latent heat of condensation is energy released when water vapour condenses to form liquid droplets. An identical amount of calories (about 600 cal/g) is released in this process as was needed in the evaporation process. (gaining ~600 calories of energy for every gram of water at room temperature). The system surpasses the predicted performance 

As part of a Neighbourhood Construction specified framework of systems, the bio-aggregate installation also requires completion with our specification for Plaster as well as Paper and paint. It requires undertaking within the context of a Home audit, that begins with a home tutorial, and a programme of works that also include no-cost and low-cost interventions.

For the love of our traditional and heritage building.  Dry walls are more thermally efficient. Attaching a synthetic insulation board is highly damaging to the original fabric. Mechanically fixing wood fibre over historical unknows is costly complex and unsympathetic.




Retrofitting bio-aggregate and lime internal wall insulation to a tradition solid brick wall or masonry construction.

Rather than application by trowel, casting presents various advantages to retrofitting. By removing the existing smörgåsbord of inappropriate materials, that trap moisture in the wall, the problem is removed whilst creating more room is created for better improvement.

With the use of the right bio-aggregate, with an appropriately formulated lime binder and the right process, it is possible to create a lightweight composite that improves insulation values, interaction with moisture, recalcitrance and thermal performance.

The Neighbourhood Construction Bio-aggregate system is cast to the original masonry using a traditional method of dooks or dochans to attach shuttering formwork. This allows the material to be installed quickly at the optimal lightweight density and ratio. Retrofitting heritage building fabrics have a practical limitation of space, therefore, it is essential to optimise the performance of the material applied.

Mixed by weight, at a ratio of one part shiv, one part binder and three parts water. 1:1:3. Achieving a density of – 200kg per cubic metre, (200 grams per litre) and a Thermal resistivity – Lambda (λ) value, of 0.056 W/mK. Carbon sequestering and zero waste.



Bio-aggregate shiv and specially formulated lime binder.

Bio-aggregates are plant-based materials used to replace the quarried mineral aggregates used in construction. The addition of a bio-aggregates can greatly improve the desired properties of the material.

Insulating bio-aggregate plasters, typically hemp plaster, have been researched and developed for the more appropriate use in new build construction. Applied as a thin coat, the benefits include reducing surface temperature and therefore reducing the risk of moisture drop out condensation.




With support from Dublin Institue of Technology (DIT) and the Beacon project – Institute of Biological Environmental Rural Sciences (IBERS); Aberystwyth University. Neighbourhood Construction has researched a variety of bio-aggregates for construction use. These include Miscanthus (Elephant grass) and Oil Seed Rape (OSR) straw as well as Hemp shiv (Cannabis Sativa). 

Playing with plaster

Measuring heat flux in situ. Determining the impact of varying mixes, ratios and densities on u-value, and their implications for best practice and performance.

Insulating solid-wall houses using plant-based materials




Up-coming workshops can be found here

Previous training opportunities are documented here

Bio-aggregate stories can be found here



Practitioner David Copeland: Hawkland Ecological Construction, describing the experience of attending a Neighbourhood Construction Bio-aggregate workshop.



Traditional brick walls perform better than first thought.

DECC has commissioned a significant amount of work looking at wall U-values over the last few years after earlier studies found that in-situ wall U-values did not always agree well with those assumed in SAP calculations1, potentially leading to a significant‘performance gap’. This is particularly relevant when it comes to calculating the savings from wall insulation, which appear to have been overestimated in the past, at least in part due to the use of pessimistic U-values for uninsulated walls and optimistic U-value for insulated walls. This has resulted in the application of large ‘in-use’ correction factors being applied to modelled savings in schemes where savings from energy efficiency measures are calculated, like Green Deal and the Energy Company Obligation.”

“The default wall U-values in RdSAP calculations are based on either building regulations requirements for particular eras, or typical building practices at the time of construction. In the former case (i.e. for pre-1976 dwellings) standard thermal properties of construction materials are assumed in order to calculate the U-values. The materials data this relies on was derived a number of years ago, and appears to have been intended originally for use in ‘design heat loss’ calculations for sizing heating system components. For such calculations, it is generally preferable where there is uncertainty or variability in material performance to assume conservative (higher) U-values to avoid under-sizing. Therefore it is thought that thermal properties at the worse end of the range would have been chosen which then became established as normal. This was a reasonable assumption to make at the time, but the data is now being used for a different purpose, such that median values may be more appropriate.”—Wall-U-values-for-existing-dwellings—V1_0.pdf

Bio-aggregate practitioner board – login required



Tradical Hempcrete – brochure

Tradical Thermo – technical data sheet.pdf



Bio-aggregate – casting to existing masonry.
20 seconds


Insulating the walls of our traditional building is not without its problem.

Bio-aggregate – casting to existing masonry solves damp problems with the secondary effect of improving the thermal efficiency of older buildings. The principles and materials used in traditional architectural detailing prevent degradation whilst regulating temperature and humidity by capturing and recycle energy from moisture.

Improved loft insulation and double glazing make walls the coldest surface in the room, increasing the risk of condensation. External insulation is costly, complex, unsympathetic and retrofitting leave cold spots internally. Walls insulated internally with foam board lose the capacity to buffer temperature, humidity and incorrectly installed causes interstitial condensation. Bio-aggregate is more than internal wall insulation, it retains thermal inertia increases hygroscopic capacity and prevents condensation. Quicker, cheaper and better – from cold and damp to warm and dry.



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