To understand the need for sustainable architecture it is necessary to delve back into the past for a bit. For centuries building in Cornwall, especially in close proximity to the coast, has always presented a unique set of challenges that are not found in other parts of the country. Exposure to the elements is the obvious one but ironically the favoured use of the available local building material is another – for what’s below ground is what appears above; hence the predominance of granite structures in this part of the world. It is a challenging material to work with and only its naturally occurring abundance has meant that it pops up in the local building stock from Land’s End to Bude.

Contrary to popular misconception it is impermeable – it does not absorb rainwater and moisture cannot flow through it. It should be the ideal choice. However, it is in the mortar joints that all moisture movement occurs. Herein lies the problem. This is compounded by wind driven rain and sea spray with its corrosive companion – salt. So, although granite has been the material of choice for centuries for external walls due to its ubiquity, it has always been compromised due to its bonding partner.

Other factors are also coming into play that bring into question its use as building matter. During the winter months it can be a very cold substance necessitating unnecessary use of heat generating appliances to keep a building at a comfortable temperature. It is a very expensive choice because it must be mined and transported from quarries and requires facing by experts. Installation of granite is complicated, involving the employment of experts which in turn is laborious and time-consuming. It is very heavy thus increasing its transportation cost and by extension its environmental impact. It is also difficult to repair.

We cite this because it is a prime example of one of the reasons why new materials and practices will have to be adopted in order to meet the challenges faced, not just by the building industry but the world in general. Everything is up for re-assessment in light of the environmental impact of all we do, hence the emergence of sustainable architecture and the part it will play in our future.

Keynvor Bedroom
Credit: Matthew Heritage

What is sustainable architecture?

As a concept the Center for Our Common Future (a sub-organisation of the United Nations), defined sustainability as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs,” (attributable to its then leader Gro Harlem Brundtland).

Sustainable architecture manifests itself in materials specified, methods of construction, the use of resources, the building’s thermodynamic efficiency and general design. It places a charge upon architects to produce designs and explore and use technologies that adhere to a principle of minimal environmental impact in both the short and long term.

Keynvor view through house to sea
Credit: Matthew Heritage

Passivhaus approach

At ARCO2 our raison d être is couched in the idea of sustainability and the methods advocated by the Passivhaus standard that can trace its origins back to May 1988. In September 1996, the Passivhaus-Institut was founded in Darmstadt to promote and control passivhausstandards. We follow these evolving standards.

Keynvor, sustainable architecture built by ARCO2
Credit: Matthew Heritage

Implementation of these principles at Keynvor, Mawgan Porth

Our recent new build in Mawgan Porth is a dual but interconnected development that exemplifies a sustainable approach. The project represented a clear opportunity for our client to obtain a low energy luxury property that incorporates an abundance of character and architectural merit.

Key to the project are several areas that are worthy of mention. As with many of our builds that are close to the sea, a high level of insulation is necessary, so priority was given to wall thickness with recycled newspaper blown into the wall structure to a width of nearly 400mm. A high level of thermal insulation was specified, one that removes direct heat transfer between the outside and the controlled internal environment, resulting in a lower heat load to the internal spaces. By reducing the amount of temperature change the level of interstitial condensation risk was lowered. This has measurable positive benefits for the longevity of the property, as material degradation is lessened due to moisture generation and retention being reduced to a minimum.

The property utilises a 500mm cavity, blockwork external walling where the structure is ‘subterranean’ with an independent external & internal timber frame structure. And, where the roof joists require a depth to generate the spanning lengths required, we included a ‘counter batten’ solution,  above and below the rafters to limit thermal bridging through materials.

Keynor views, sustainable architecture built by ARCO2
Credit: Matthew Heritage

External Joinery

All External joinery includes thermally separated glazing and frames that combine to improve the thermal separation and heat load. A solar coating with argon filled cavities between the glazing panes all culminate to provide an excellent thermal solution. The detailing, implemented by Nathan Davis, has been meticulously considered to make the windows wind and water tight. This is imperative to the coastal location where winds can reach 90mph.

Kitchen in Keynvor
Caption: Matthew Heritage


Keynvor has an air source heat pump to provide the primary space and water heating requirements. The main use of the property will be during the summer months when a heat pump solution is most efficient. We would expect the air source heat pump to provide a coefficient performance of above 3 during the warmer months of the year. This means for every 1kW of electrical energy consumed the heat pump is capable of providing at least 3kW into the living space or for heating water. What is particularly innovative is the capital investment into a single heating system for both properties. A carefully planned super-insulated heat loop pipework system had to be installed deep into the ground to reduce the heat losses to a minimum.

Mechanical heat recovery and ventilation (MVHR) solutions are essential in maintaining a healthy living environment. They are a ‘must have’ to each and every ARCO2 sustainable architecture design. The location of the MVHR with a short pipework run to the outside is an essential to gaining the best efficiencies in heat recovery. 

External shot of Keynvor
Credit: Chris Hewitt

Construction materials

The materials that are selected for our sustainable architecture designs to become tangible have a hierarchy of credentials that dictate our choices. We would always seek out those that are sourced locally first. The stone and cut timbers in the case of Keynvor were acquired locally with more specialist materials imported from as near to the site as possible.

Living area in Keynvor, sustainable architecture
Credit: Matthew Heritage

The details

The light and airy first floor is open plan, benefitting from a continuity of materials with timber panelling and micro-cement floor tiling throughout. The ground floor is linear in arrangement with segmented private bedroom spaces.

A green roof, achieved by the planting of sedum, was implemented to minimise the impact of the foreground building on the site line and to integrate with the view of the headland beyond.

Virtual reality (VR) simulations allowed us to work out the positions for the windows to maximise the sea view and orchestrate the cast of natural light within the building. It also facilitated seamless and efficient on-site construction with off-site 3D modelling prior to commencement of the build.

Keynvor lit at night
Credit: Matthew Heritage


This project was very much a collaborative effort by the team of James Huxley and Nathan Davis. The end result was the culmination of a synthesis of energy and ideas by both partners. As Nathan acknowledges, ‘It’s the most enjoyable outcome to see the success of a well thought through design being physically realised.’

It also hit many sustainable targets. High levels of insulation and airtightness were achieved with quick response underfloor heating mitigating the impact of warming a property in a more traditional and energy demanding way.

By flipping the day area to the first floor we maximised access to the views that are on offer from this site too.

Keynvor - sustainable architecture
Credit: Matthew Heritage

Client feedback

The client is delighted and overwhelmed by the quality and comfort that he has been gifted in Keynvor, coupled with the ability to provide a combination of holiday rentals to cater for the thriving market in Mawgan Porth.

The separation of the two properties is sufficient for each building to be used independently, or if a larger group books up then the external spaces can be used as a communal area. The client is also delighted that he can let one of the properties and still enjoy a family holiday in Mawgan Porth at the same time.

In summation he has received a financially future proof asset that has low energy demands designed upon passive house principles and that can also cater for his family’s needs. It will provide a passive income coupled with the ability to support multigenerational living all wrapped up in a sustainable well considered design bundle.

If you have a similar project in mind, please get in touch with our team! We’d love to help bring your idea to life.