Bio-aggregate – internal wall insulation system

Scott and Soren – 1 minute

Peer to peer on-site training

Apprenticing Chris and Scott, hosted by Soren, and David.


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

How: Methodology – Casting to existing masonry, ratio, density and system.

Why: Objectives – Lambda value, u-value and moisture regulation.


Research: Beacon Project – Institute of Biological Environmental Rural Sciences (IBERS).

Advice and support: Peer to peer on-site training – Brief-Design-Programme-Schedule-Team.


Materials

Bio-aggregate shiv and specially formulated lime binder.

Miscanthus, Elephant grass, growing at the Institute of Biological Environmental Rural Sciences (IBERS); Aberystwyth University.

Bio-aggregates are plant-based materials used to replace quarried mineral aggregates. The addition of a Bio-aggregate can greatly improve the desired properties of the building fabric. Neighbourhood Construction is looking at the workability, performance and agronomy of a variety of plant-based aggregates. These include Oil Seed Rape (OSR) straw, a co-product from food production and Miscanthus Giganteus, a high yield crop that can be grown on marginal land unsuitable for food production. Cannabis Sativa, industrial Hemp, is well established and commonly used as a Bio-aggregate.

Bio-aggregate: hemp-lime, a bio-composite pictured here wet prior to casting.

[Proprietary product photo]

When mixed with a specially formulated lime binder it creates a bio-composite material called Hemp-Lime, sometimes referred to as Hempcrete. The use of the term Hempcrete is to be avoided for it implies that the resulting composite is dense like concrete when in fact it can be cast as a lightweight insulation material.

The use of a proprietary product has been essential in the development of the process for casting onto the existing masonry of the traditional building fabric. Developed for use in new-build construction; increasingly denser mixes can be used to construct monolithic walls, floors or as a trowel applied plaster. The manufacturer describes insulating wall linings as achieved using a heavy 1 part shiv to 3 parts binder by weight ratio. However, with no requirement for compressive or racking strength, the following methodology enables optimal thermal performance to be achieved by using a 1:1 Tradical ‘roof’ mix.

This achieves twice the thermal resistance or halves the thickness required. Using less binder reduces material and labour cost as well as carbon input.

Tradical Hempcrete – brochure

http://www.bcb-tradical.com/wp-content/uploads/2018/02/Tradical-Hempcrete-brochure.pdf

Tradical Thermo – technical data sheet

http://www.bcb-tradical.com/wp-content/uploads/2018/02/Tradical-Thermo-technical-data-sheet.pdf


Methodology

Casting to existing masonry, ratio, density and system.

Miscanthus, Elephant grass, growing at the Institute of Biological Environmental Rural Sciences (IBERS); Aberystwyth University.

Retrofitting internal-wall-insulation to a tradition building fabric.

By using the proprietary product the resulting assembly reduces heat-loss and improves thermal-comfort, it is breathable and hygroscopic, reducing the risks of condensation while capturing energy from moisture vapour. Rather than application by trowel, casting presents various advantages to retrofitting. As a retrofit solution for the tradition building fabric, this system is high-performance, zero-waste, provides carbon sequestration and is installed as a system.

[Formwork attaching rails with Dochans]

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

Bio-aggregate: hemp-lime is best mix in a Tombola not a concrete mixer. Like tossing a salad not stirring porridge.

[Tombola mixer – tossing a salad; not stirring porridge – David, Chris and Matt]

The lightweight ratio 1:1 of shiv and binder do not combine well in a concrete mixer. Instead, they are efficiently blended in a tombola. With a closed lid exposure to dust is minimised, the water is measured and introduced gradually during the short mixing process.

Each mix is subdivided into boxes, each containing a known volume and cast into the predetermined volume of the rising formwork. The mixture must NOT be ‘tamped’. A thin bamboo cane is used to evenly distribute the mixture while seeking out hollows and encouraging particles to disorientate. This ensures the material is open to drying, strong and light.

The internal-wall-insulation system – Bio-aggregate, is part of the Neighbourhood Construction framework undertaken in conjunction with the systems – Plaster; Paper and Paint.

During the preconstruction phase, an audit of the existing property is undertaken with advice and support with achieving other no-cost and low-cost projects within the NC framework.

The Process is open source – analytics are collected on in-situ performance as well as delivery costs to inform future works with up to date costings and performance analysis. This delivers affordable best practice and facilitates real-world academic research opportunities.

https://www.neighbourhoodconstruction.org/category/research/

https://www.neighbourhoodconstruction.org/category/workshops/


Objectives

Lambda value, u-value and moisture regulation.

Joseph Little

There are two available methodologies for conducting hygrothermal risk assessments: steady-state condensation risk assessments, using the Glaser method, and transient hygrothermal performance analysis, using numerical simulation.

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.

Water* – volume can vary dependent on particle gradient, each batch is tested to ensure the mixture is neither to wet or to dry.

Casting onto a traditional solid brick wall or masonry construction, U-value of 1.7 W/m2K[Further information]. 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.

[PENDING – table with varying masonry types and a variety of thickness added]

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. Tradical Thermo 1:1 Lambda (λ) value – 0.056. Neighbourhood Construction supported research Measuring Heat Flux In-situ Lambda (λ) value – 0.054. 

With support from Dublin Institue of Technology (DIT).

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

Historic Environment Scotland Technical Paper 15

Joseph Little, Calina Ferraro & Beñat Arregi

https://www.engineshed.scot/publications/publication/?publicationId=8a2a7b9d-e3b2-4c7d-8c17-a59400a8387b


Joseph Little

https://www.neighbourhoodconstruction.org/author/joseph/

https://www.neighbourhoodconstruction.org/2018/06/18/i-can-well-believe-the-resulting-assembly-has-a-beneficial-sanitary-effect-on-the-internal-environment/


Research

Beacon Project – Institute of Biological Environmental Rural Sciences (IBERS).

Research

Building test panels for controlled testing at the University.

In-situ heat flux measuring is also undertaken ‘real-world’ traditional building fabric insulation projects.

Neighbourhood Construction has researched a variety of Bio-aggregates for construction use. These include Oil Seed Rape (OSR) straw, Miscanthus and Cannabis Sativa, industrial Hemp. With support from the Beacon project – Institute of Biological Environmental Rural Sciences (IBERS); Aberystwyth University.

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

Dr Judith Thornton

http://beaconwales.org/en/blog/view/insulating-solid-wall-houses-using-plant-based-materials

https://www.lowcarbonbuildings.wordpress.com/2018/10/12/insulating-solid-wall-houses-using-plant-based-materials/


Judith Thornton

https://www.neighbourhoodconstruction.org/author/judith/

https://www.neighbourhoodconstruction.org/2018/10/12/insulating-solid-wall-houses-using-plant-based-materials/


Advice and support

Peer to peer on-site training

Bio-aggregate

Brief-Design-Programme-Schedule-Team

Peer to peer on-site training, structured tuition and open format learning. Hosted by an experienced Neighbourhood Construction trained and accredited – Bio-aggregate practitioners.

Pre-construction phase, costings and analytics.

Workshops

We’ll be working alongside experienced practitioners on a real project, learning how to design and plan, as well as the practical delivery.

We’ll consider the underlying objectives of the installation within the broader context of energy and moisture in the home.

We’ll look at the preparations that are required to the walls and how these affect the quality and speed of the installation.

We’ll use a small scale mixing process to accurately proportion, whether by weight or volume and how much water is required for a successful mix.

We’ll calculate the casting volumes and density before getting the project moving efficiently with a little system thinking and team building.

Lunch will be provided.

The content will be covered on days one and two, day three is optional providing an opportunity to practice, demonstrate and re-visit aspects of importance to you.

https://www.neighbourhoodconstruction.org/category/workshops/


50 minutes – Materials module at CAT. MSc Sustainability and Part 2 Architect students.


Bio-aggregate

https://www.neighbourhoodconstruction.org/category/bio-aggregate/


 


Further information

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.”

https://www.bre.co.uk/filelibrary/SAP/2016/CONSP-16—Wall-U-values-for-existing-dwellings—V1_0.pdf