Spray foam insulation from Huntsman Building Solutions forms part a project to transform a collection of derelict Cumbrian industrial buildings into a striking self-build house and office.

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The external combination of Lakeland stone and larch cladding blends beautifully with its surroundings

Dating back to the late 18th century, the original buildings were part of a mill producing blacking, a material used to coat the insides of casting moulds. Architect Robert Glass and his partner Ruth Grimshaw, who practice at Tape Design in Ulverston, had decided to move back to the South Lakeland area of Cumbria following years in the city. Robert had known about the site since his early 20s and had always wanted to build a home there. In January 2015, they approached the owner, and after finally gaining planning approval, bought the site in November 2017.

The site was challenging with narrow single-track access. A fast-flowing beck, which originally provided power for the mill, ran through the site and the surrounding land was completely overgrown, almost reclaiming the tumble-down stone structures that had laid abandoned since the 1950s. Despite this, the potential was clear to Robert and Ruth, and plans were drawn up to transform the buildings into a four-bedroom, 218-square-metre house and a 90-square-metre workshop and office. A roof terrace was incorporated into the house, providing a recreational space and views over the surrounding woodland.


The original stone buildings had almost been reclaimed by the landscape

High-performance insulation to minimise heat loss
A key criterion in the construction of the buildings was control of the internal environment to minimise heating costs. Achieving a high degree of airtightness and incorporating a mechanical ventilation and heat recovery system into the structure was therefore required. It is estimated that around 40 per cent of a building’s heat loss is caused by air leakage – essentially draughts – so an insulation system that works to prevent air leakage, effectively creating a sealed environment was essential in order to minimise heat loss.

Following detailed research, an open cell spray foam insulation solution from Huntsman Building Solutions (HBS) was chosen. The company’s H2 Foam Lite product not only provides outstanding levels of airtightness and thermal efficiency, but also allows the building to ‘breathe’ and move with the timber framed inner structure.


The site runs through a steeply wooded valley with a fast-flowing beck that provided water power to the mill

Huntsman supplies its products exclusively through a trained and authorised contractor network, and the spray foam installation was handled by Preston-based contractor Heatlok Insulation. Greg Raby of Heatlok explained that HBS spray foam insulation systems were developed in Canada to cope with severe winters and are now widely used in the UK in both the residential and commercial sectors. He also said that spray foam insulation is an inherently elastic material so it moves with the building without cracking and causing gaps. Furthermore, it is also able to fill the small voids in the structure where conventional rigid board insulations are almost impossible to fit effectively.


Huntsman H2 Foam Lite was sprayed to a depth of 230mm in the timber-frame external wall and roof structure, and 300mm at the roof/wall perimeter area

Minimal environmental impact
Unlike the urethane foams of 20 years ago, modern spray foams, such as HBS H2 Foam Lite, use water as the blowing agent. This means that the reaction between the two components produces a small amount of CO2, which causes the foam to expand. The foam cells burst and the CO2 is replaced by air.

According to Huntsman Building Solutions, H2 Foam Lite E is currently the only spray foam insulation system to carry the prestigious British Board of Agrément (BBA) certification. From an environmental perspective, H2 Foam Lite claims a Global Warming Potential of 1 and an Ozone Depletion Potential of 0 (zero). In addition, it doesn’t emit any harmful gases once cured – another important factor in the choice of insulation. “Ruth is very sensitive to chemicals in the air; the fact that H2 Foam Lite becomes inert after a few seconds, with little or no off-gassing after installation, made it the perfect choice for us,” said Robert.


A completed section of the building prior to trimming back the breathable foam insulation to accept the plaster boarding

Thermally-efficient structure
H2 Foam Lite was used in the external wall and roof areas to create a highly thermally efficient structure. The external walls comprise a 250mm outer leaf of Lakeland stone, facing with a 140mm thick timber frame inner leaf with spray foam filling. Inner 50mm thick battening allows an extra 90mm thickness of foam insulation, giving an overall thickness of wall insulation of 230mm.

Where timber cladding was used to visually soften the exterior appearance, wall sections comprise 22mm thick larch cladding, facing a 140mm thick timber-frame supporting structure with foam insulation infill. Similarly, 50mm thick inner battening allows an extra 90mm thickness of foam insulation, giving an overall thickness of wall insulation of 230mm.


The Mill reconstruction gradually comes to life – the 90-square-metre roof terrace will provide recreational space and stunning views over the surrounding tree canopy

The roofs also received high-levels of insulation. Pitched roof areas are timber clad over a glass fibre waterproofing layer that overlays 18mm oriented strand board (OSB) fixed to 145x50mm rafters with foam infill. Foam-filled 50mm thick inner battening gives an overall thickness of insulation of 230mm. The flat roof areas beneath the roof terrace have 300mm thick foam sprayed around the perimeter where the roof and walls meet, to fully seal any potential gaps.

Robert and Ruth acted as both designers and main contractors for the reconstruction process – a huge task – while also continuing to run their architectural practice and engage and manage trades as required over the Covid disrupted build programme.

Grand Designs project
The mill transformation began in January 2018 and is due to complete in spring 2022. The four-year project was the subject of a Channel 4, Grand Designs programme presented by Kevin McCloud, which was broadcast last autumn.

Contact Details
For more information, please visit the Huntsman Building Solutions website. Click here for more information about HBS H2Foam Lite products. The author is grateful to Tape Design for their considerable help in the preparation of this article.