Frequently Asked Questions

For us, sustainable architecture means designing buildings that prioritise health, comfort, and minimal environmental impact. We combine low-energy design, renewable materials, and innovative technology to create timeless architecture inspired by the Cornish landscape.

Yes. All our projects use Passivhaus principles – exceptional insulation, airtight construction and ventilation with heat recovery — to achieve outstanding comfort, low energy demand, and minimal running costs. We also have 3 in house certified Passive House Designers.
We tailor the level of performance to your brief, whether you’re targeting certified Passivhaus, EnerPHit, or a high-performance low-energy home.

Our studio is in Bodmin, Cornwall. While most of our work is across Cornwall and Devon, we also undertake selected projects further afield when the ethos and design ambitions are a good fit.

We typically work on projects with a construction budget exceeding £1 million, specialising in bespoke, high-quality, sustainable new builds, refurbishments and replacement dwellings.

The first step is a conversation. Get in touch by phone or email to tell us about your site, ideas, and ambitions. We’ll arrange an initial consultation to discuss your brief, budget and timescales, then outline how we can help — from concept through to completion. Book a consultation

If available: site address, sketches, photos, surveys, or any planning history. If you don’t have drawings, that’s fine — we can help assess your site from first principles.

Yes. We can assess potential plots or existing properties and advise on their potential for development or refurbishment before you commit to purchase.

In most cases, new dwellings in open countryside are resisted by planning policy. However, if your proposal could be considered “infill” or “rounding off” development — or qualifies under Paragraph 84 (for exceptional design in the countryside) — there may be scope.
We can advise on feasibility and guide you through the most appropriate planning route.

Paragraph 84 of the National Planning Policy Framework allows for exceptional new dwellings in the open countryside — if they demonstrate truly outstanding design quality and innovation.

Read more in our blog

Most new houses, replacement dwellings and extensions require planning consent.
We’ll review your site, advise on policies and constraints, and prepare and manage your planning application — including pre-application discussions where beneficial.

Absolutely. Many of our projects are located in stunning coastal and countryside settings, often within or adjacent to protected designations such as AONBs, AGLVs and SSSIs. We specialise in designing contemporary, sustainable buildings that respond sensitively to their surroundings — respecting the landscape, local heritage, and planning constraints. Our careful approach to visual impact, scale, materiality and siting helps ensure that new architecture enhances, rather than detracts from, these exceptional environments.

Yes. We have extensive experience working with listed and sensitive sites, carefully balancing conservation principles with contemporary, sustainable design.

In many cases, yes. The National Planning Policy Framework promotes sustainable development, and demonstrating high environmental performance can strengthen your planning case — especially when supported by sensitive design and a well-evidenced sustainability strategy.

Every project is unique. We offer tailored fee proposals — either fixed fees for smaller packages, or phased/proportional fees based on the construction cost for most projects.
We’ll explain your options clearly in our engagement letter before work begins.

Every project is unique. We offer tailored fee proposals — either fixed fees for smaller packages, or phased/proportional fees based on the construction cost for most projects.
We’ll explain your options clearly in our engagement letter before work begins.

Costs vary by site, specification, and delivery method.
As a guide, a high-performance, low-energy new build designed to ARCO₂ standards typically costs £5,000–£5,500+ per m² with a main contractor.
Hands-on self-builders may achieve lower rates if contributing labour.

New dwellings are zero-rated for VAT. Refurbishments and extensions attract VAT at 20%, although reduced rates may apply if the property has been vacant for over two years. Self-builders can reclaim VAT upon completion.

Timeframes vary depending on complexity and planning authority workloads, but typically:

• Concept Design: 4–8 weeks
• Pre-Application Determination Period: 5 weeks
• Planning Development & Submission: 4-12 weeks
• Planning Application Determination Period : 8–12 weeks
• Technical Design & Tender: 12–18+ weeks
  We’ll provide estimated timescales within our appointment letter.

Construction generally takes 12–24 months, depending on the size and complexity of the project.

Yes. We can guide you through tendering, contractor selection and contract administration.
Our in-house construction company, ADD Sustainable Construction, ensures a seamless process from start to finish, maintaining quality, performance, and shared values.
Alternatively, we can work with trusted external contractors experienced in sustainable build methods.

Yes, we coordinate a full team as needed, including planning consultants, structural engineers, energy assessors, landscape and interior designers, and more.

A Passive House is a highly energy-efficient building standard that minimises heat loss and maximises comfort.
It relies on five key principles: superior insulation, thermal bridge-free detailing, airtight construction, high-performance glazing, and mechanical ventilation with heat recovery (MVHR).

Yes, but only a minimal amount — often just towel rails or small radiators — as the building retains most of its heat naturally.  However, many of our clients prefer the comfort and feel of underfloor heating.

Mechanical Ventilation with Heat Recovery (MVHR) continuously supplies filtered fresh air while extracting stale air and recovering up to 90% of the heat.
It ensures excellent air quality, reduces humidity, and helps create a comfortable, healthy indoor environment.

es. MVHR is designed to work efficiently with windows closed, but you can open windows whenever you wish — especially in summer when systems include a “bypass” mode for cooling.

A healthy building is one that promotes wellbeing through clean air, natural light, low-toxin materials and stable humidity.
We use breathable construction methods, natural insulation, and non-toxic finishes to create calm, comfortable and uplifting spaces.

Initially, yes — high-performance materials and detailing cost more than meeting minimum Building Regulations.
However, the long-term savings in energy bills, maintenance, and health benefits far outweigh the upfront cost.

Yes. We design off-grid and-zero-carbon homes using technologies such as solar PV, battery storage, wind turbines, and  ground or air source heat pumps.

Absolutely. Heat pumps are highly efficient, reducing CO₂ emissions by up to 70% compared with fossil fuels.
When combined with renewables, they offer one of the cleanest heating options available.

Timber is renewable, quick to build, and enables excellent airtightness and insulation.
It also allows breathable construction and flexibility in design, with a low embodied carbon footprint.

Masonry offers strength, durability, and high thermal mass, helping to maintain steady internal temperatures.
When built with super-insulated cavities, it can achieve excellent performance while using local skills and materials.

ICF combines strength, speed, and airtightness, providing excellent acoustic and thermal performance.
It can be cost-comparable with timber frame and offers long-term durability.

Yes. We support clients after completion with snagging, maintenance advice, and warranty coordination.
We can provide Professional Consultants Certificates (PCCs) or assist with structural warranties where required.

Where clients are happy to host visits, we can arrange viewings. You can also explore our completed projects on our website and social media.

Yes — we can provide in-house design input or coordinate trusted specialists as part of your project team.

Trust; feeling of wellbeing; far exceeded our expectations; unique quality; great team to work with and felt in safe hands all the way through; delighted with the results; working with ARCO2 has been a delightful experience; we could not be happier; an excellent service from start to finish; relaxed yet attentive approach; amazed and delighted; imaginative; full of ideas with a professional ethos; owning a building designed by ARCO2 is both unique and in my opinion timeless; complete empathy with the project; would not hesitate to recommend ARCO2; a stunning, light and airy home; ARCO2 fulfilled all the original criteria with a brilliant sustainable design in good time with no trouble, in fact we enjoyed the experience.

Generally this would be considered a development in the open countryside and is likely to be resisted by the planning department. If the proposed development could be considered to be rounding off or infill then you may have a better chance. You should also check to see whether your Parish has a Neighbourhood Development Plan, which may dictate where development is considered acceptable. If you have an existing barn or even a modern agricultural building there is scope within planning policy to convert it into a home.

We are often faced with this dilemma. When taking VAT into account a replacement dwelling often looks more favourable as you will not need to make so many compromises, especially with regards to heat loss, thermal comfort and airtightness; however, a replacement dwelling is likely to provide less usable floor area than a refurbishment and extension for the same budget. New dwellings have zero-rated VAT, while refurbishments and extensions are charged at 20% VAT.

It is possible to self-build for approximately half of what a main contractor will charge. This is very dependent upon using as much of your own labour as possible. Approximately 60% of the cost of a construction project is labour.

We normally recommend that the design, drawing work and costings from the contractor will take between 12 and 18 months+, while the construction of a new property will take between 10 and 12 months, depending upon the size and complexity of the project.

This depends if you are comparing apples to apples! A sustainably built low-energy building will cost more than a building that only meets Building Regulations minimum standards; however, a low-energy building should be considered a longer-term approach that will save energy, CO2 emissions, and money while providing better comfort levels and making you feel good.

A healthy building consists of many factors. In terms of air quality, good ventilation such as a mechanical ventilation and heat recovery system combined with a breathable construction will help to moderate humidity and provide clean filtered fresh air, preventing condensation and mould. Selecting materials that do not emit volatile organic compounds (VOCs) or other harmful chemicals is crucial, and natural materials are always encouraged. Some materials, such as sheep wool insulation and earth and clay plasters, will help to reduce airborne contaminants. Airtight construction will enhance comfort by reducing draughts and external pollutants. Natural daylight is another important factor in a healthy building, as is the creation of views, especially of green spaces and vegetation which help with mental wellbeing.

The short answer is yes. You would probably be surprised by the total area of glazing on your low-energy building, which can be quite large especially if you have lovely views. If you compare the thermal efficiency of the walls to the glazing you will realise that the walls are around four times more efficient than triple glazing, or six to seven times more efficient than double glazing. This equates to a lot of heat loss, which in turn equals a lot of additional CO2 emissions and energy costs. Triple glazing will also provide better acoustics and thermal comfort than double glazing. The inside pane of glass will not be cold to the touch, meaning you will be able to sit next to a large window on a cold day but not feel cold.

We work with a variety of consultants. Here are a few you may require along the way:

Topographical Surveyor, Contamination Consultant, Ecological Consultant, Planning Consultant, Energy and SAP Assessor, Passive House Consultant, Arboriculturalist, Landscape Architect, Lighting Designer, Interior Designer, Mechanical and Electrical Designer, Kitchen Designer, Quantity Surveyor, Structural Engineer, Air Pressure Tester, Asbestos Surveyor, and Party Wall Surveyor

Of course you can; however, the system is designed and balanced to work efficiently with the windows shut to minimise heat loss and save on energy bills. In the summer months you can open windows and doors and use the summer bypass function to turn off the heat recovery. You can also increase the ventilation rate if desired, or purge the building at night by introducing cooler air.

A mechanical ventilation heat recovery (MVHR) system provides pre-warmed filtered fresh air into most rooms 24 hours a day. These systems extract moist air and smells from bathrooms, wet rooms and kitchens and recover the heat from the extracted air via a heat exchanger, resulting in minimal heat loss and pre-warming the fresh incoming air. The system constantly extracts moisture, maintaining internal humidity levels at a healthy level of between 45–55% by carefully balancing the system. A well-designed and installed system will be quiet and, as a result of not having trickle vents, you will not hear noises outside. The filters catch pollen and other allergens to help allergy sufferers. Most systems automatically sense humidity and will boost when someone is cooking or showering. One of the many benefits is that the system can bypass heat recovery in the summer months and purge-ventilate at night to cool the building, meaning you don’t have to open windows.

No, airtight houses still require ventilation to comply with the Building Regulations Approved Documents. In low-energy houses, trickle vents in windows and doors and mechanical extract vents are not used as they are very leaky, resulting in heat loss and draughts. A mechanical ventilation and heat recovery system is normally specified to provide a whole-house ventilation strategy.

A ground source heat pump (GSHP) uses similar technology to a fridge. Fridges take the heat out of the food and transfer it into the room. A GSHP takes heat from the ground or water source and transfers it into the building. The heat pump circulates glycol and water around a pipe or ground loop, which is either buried or contained within a large water source such as a river or lake. The fluid in the pipes absorbs the heat, which passes through a heat exchanger into the heat pump. An air source heat pump (ASHP) works in much the same way, but uses the heat from the air instead of the ground or water. As the climate in Cornwall is fairly mild throughout the year, an ASHP works very well. A GSHP is more efficient than an ASHP because the temperature in the ground or water is normally constant. A GSHP is approximately 400% efficient, providing 4kW of heat for every 1kW used, while an ASHP is approximately 300% efficient.

Yes, a heat pump will greatly reduce CO2 emissions and environmental impacts in comparison with using gas or oil. You must remember that using a heat pump for hot water and space heating means that you will be reliant upon electricity; however, approximately 50% of electricity is already produced using renewable energy, with this set to rise year on year. If you are also generating your own electricity using photovoltaic panels or wind technology then the CO2 emissions associated with your heat pump will be very low. This is a very clean way of heating your building and providing hot water, and is specified in most of our new buildings.

Cavity blockwork construction is considered a traditional build technique; however, we tend to use extra-wide cavities to provide super insulation, bringing this method into the 21st century. Masonry construction is very robust and there are many contractors and masons locally with the skills to build with blockwork, which needs to be laid in dry but not cold conditions. Keeping the cavities clean is also a challenge during construction. Masonry buildings are relatively easy to make airtight and are considered to have high thermal mass, acting as night storage heaters to store and displace heat over a longer period to provide a steady internal temperature.

Blockwork structures are much harder to adapt than timber buildings and normally incorporate concrete or steel lintels and beams. Block and beam floors are often used to create a very dense and solid construction. The drying out process can take a long time, and plastered walls and ceilings crack more often than they do in timber frame buildings. The use of cement in the blocks and mortar results in higher CO2 emissions than timber, although the blocks are made locally.

Yes, over half of the power generated in the UK now comes from low-carbon sources. The CO2 emissions associated with grid electricity are now extremely low, and are now only slightly higher than from a 90% efficient gas boiler. Any kind of heat pump is at least twice as good as a gas boiler from an emissions perspective.

Yes, but the practicalities and cost may be prohibitive. As battery storage options for electricity and heat batteries evolve this will become a viable option.

Timber sourced from sustainable forests endorsed by the Forest Stewardship Council (FSC) or the Programme for the Endorsement of Forest Certification (PEFC) can be used to achieve a low carbon footprint for your building. The use of timber framing normally enables the faster construction of a watertight building envelope and provides flexibility throughout the construction process, including in the depth of insulation used. Timber can be used to create a breathable building fabric, subject to the correct insulation materials and further construction layers, and can last for centuries if kept dry and allowed to breathe. Timber frame buildings are often considered to have a low thermal mass, and are therefore responsive to both heating and cooling; however, it is possible to incorporate thermal mass and achieve a very comfortable building fabric. Timber frame buildings also allow for some movement and are therefore not as rigid as masonry buildings, which is why many buildings in earthquake zones are constructed using timber. The acoustics of a finished super-insulated timber frame building are very similar to a masonry frame building.

Passive House is the fastest-growing energy performance standard in the world. Originating in Germany, its primary aim is to reduce energy and improve comfort. Designing requires intelligent design and a technical approach using the standard’s own PHPP software. The five Passive House principles are thermal bridge-free design, superior windows, ventilation with heat recovery, quality insulation and airtight construction. Passive Houses require minimal heating; often only a few radiators or heated towel rails are all that is required.

For a building to be considered a Passive House, it must meet the following criteria:

1. The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year which relates to 10 W per square meter peak demand.

2. The Renewable Primary Energy Demand, the total energy used for all domestic applications (heating, hot water and domestic electricity), must not exceed 60 kWh per square meter of treated floor area per year for Passive House Classic.

3. In terms of Airtightness, a maximum of 0.6 air changes per hour at 50 pascals pressure should be measurable with an on-site pressure test (in both pressurised and non-pressurised states).

4. Thermal Comfort must be met for all living areas during winter as well as in summer, with not more than 10% of the hours in a given year over 25°C.

Yes, but likely only to raise the temperature by a few degrees. Underfloor heating is desirable but can be more than is necessary. Often, a few radiators or heated towel rails are all that is required.

This is a tricky question to answer as it is often somewhat out of our hands due to the planning department, other consultants and of course you the client. Most projects will take between 3–6 weeks for the initial concept and design stage. This is often an exciting time where we will present initial ideas to you and evolve the design. Design is, after all, a process, and should be enjoyable. Once we are both happy with the design, we will often submit a pre-application submission to the planning authority to test the water and receive written feedback. We may or may not consult the Parish Council and other bodies. Assuming that the pre-application process is positive, we would then look to develop a planning submission, which often takes 2–5 weeks depending upon the size and complexity of the project. The planning authority determination period is normally 8–10 weeks or 10–12 weeks for major applications, which also allows for the registration process.

The concept of every building we design is derived from the careful site analysis we undertake. Our buildings are designed to be site-specific and bespoke. They belong in their environment; if you were to put the same building on another site it would not work. This means that the design of every building is different, but the process is the same.

This is a difficult question to answer as construction costs vary depending upon the work and location. The design, services, access, ground conditions and site constraints will all impact the cost. Material and labour rates also fluctuate. We would expect to build an interesting new low-energy building incorporating super insulation, airtightness, triple glazing, mechanical ventilation with heat recovery, renewable heating, attractive finishes and mid-range kitchen and sanitaryware for £5,000 – £5,500+ per square metre. This is based upon using a medium-sized contracting firm with dedicated project management and site management. Smaller contractors with lower overheads may be able to construct similar buildings for lower rates. Self-project managing would also lower the rate, but will increase your workload and mean you take on the responsibility. Hands-on self-builders could build for rates from £2000+ per square metre if undertaking the majority of labour themselves. As a rule of thumb, labour equates to 60% of the construction cost and materials represent 40% of the costs.

In short, the answer is yes. The National Planning Policy Framework states that there is a presumption in favour of sustainable design; however, there are many more considerations that may influence the planning process including principle of development, impact, highways, design and whether the site is located within a sustainable location, to name but a few.

If you are building a new house the main contractor will not charge you VAT. If you are a self-builder you will be able to claim back VAT. If you are converting, refurbishing or extending your property you will pay VAT at the prevailing rate, currently 20%. You may be able to undertake some works at a reduced VAT rate if the property has been empty for more than two years. Please visit here to find out more.

We have worked as far afield as Dorset but prefer to work in Cornwall and Devon.

We work on projects exceeding a construction budget of £1 million+.