About Green Unit

Frequently asked questions

ARC buildings

What type of buildings does Green Unit offer?

We design and build modular buildings for a range of uses across commercial, community and private sectors. We are experienced working in healthcare, education, leisure and hospitality, offices and commercial, accommodation and private residential developments. See our case studies to find out more about some of our recent projects.

What are the sizes of ARC buildings?

The modular design of our ARC buildings means that the widths of the units are fixed (optimally designed for road transport), and the buildings can be built to practically any length.

Our two width building options – the ARC I and ARC II – have fixed widths of 4m and 6.4m respectively (internal footprint). Find more detailed information and more dimensions about our ARC I and ARC II modular buildings.

Why are ARC buildings curved?

The curved structure is a unique feature of our ARC buildings. The curves mimic the beauty of the natural landscape, and creates a unique experience for the people who use the buildings as the curved space creates a wonderful sense of calm and inspiration. An innate human instinct is to be drawn to natural and organic shapes. 

How much do ARC buildings cost?

Our pricing structure is based on the footprint of each modular building. Initially, we provide a budget indicative guide price based on the general brief from the client. Later, we engage in a design consultation and site survey to review the particular requirements in detail. It is at the design consultation stage that we can provide an accurate quotation based on the project requirements. See more about our pricing.

Where can I view an ARC building?

We run regular open days at our offsite factory. Book a space on an upcoming open day at Green Unit

Unfortunately, many of our client buildings are not available to the general public, but we have a few options available depending on the type of building you’re interested in. The best thing to do is contact us with information about your interests, and we’ll speak to you about the options.

Where can I see your past work?

We have a few examples of our previous work on our case studies section of our website.


What are the design options of ARC buildings?

There is a lot of flexibility in the design and build of our ARC buildings. This means that every client we work with has options for different internal configurations including interior walls, doorways and different options for windows including the glazed end. There is also a choice on fixtures and fittings, kitchens and WCs (where relevant), options for renewables, internal colour schemes and interior styling (supported by our partnership with an interior design firm).

No two ARC buildings are exactly the same, as our in-house design team works with each client on a design consultation to discuss the different design approaches available. Find out more about our design principles

Can you design for bespoke requirements?

Yes! We are experienced in the design and build of a range of buildings with very different requirements, including healthcare units, classrooms, visitor centres, retreats, and offices. For example, some of our healthcare projects have stipulated requirements such as fire retardant finishes and wheelchair-friendly access.

What is the building structure made of?

The ARC is a CNC timber engineered building with timber internal and external cladding. The structures sit on a steel sub-frame to ensure a stable delivery to the customer’s site.

What type of foundations are required?

Our buildings are designed to only require a low-impact, low-cost modular system such as pad or helical pile foundations. We conduct a site survey to assess each building project on a case-by-case basis to determine the correct foundation system. Should the building need to be re-sited in the future these foundations can be relocated too! Green Unit will always specify the foundation system, and this can either be installed by a Green Unit contractor as part of a turnkey service, or instructed by the client to use their own preferred contractor.

How are ARC buildings insulated?

We use a minimum of 220mm of high grade recycled wood fibre insulation in all our walls, floors and ceilings that exceeds building regulations. High levels of insulation are important in maintaining a thermally efficient eco-building.

Can ARC buildings be placed on top of existing buildings?

Yes, ARC buildings can be craned into place on top of flat roofs, in what is often called airspace development. Every airspace development would be assessed on a case-by-case basis. Find out more about airspace developments.

What is the acoustic performance of an ARC building?

ARCs can be designed and built with acoustically insulated walls and doors to prevent sound transfer between rooms. The ARC buildings are well insulated from external noise and internal noise transfer is minimized by the special profiling of the timber internal cladding.

Materials & options

Do ARC buildings have a green roof? Are there other options?

Our standard roofing option on our ARC buildings is a green roof. It is a living sedum – a type of succulent – and the colours change from greens to reds over the course of the year. The green roof adds an additional layer of insulation that helps to keep the building cool in summer and warm in winter. It creates a biodiverse habitat for bees and insects, and performs low-level carbon sinking. We usually recommend a thorough maintenance of the green roof twice a year (Spring and Autumn), and additional irrigation may be required during hot, dry spells. We also offer a curved solar PV panel roofing option.

How are ARC buildings heated?

Our standard heating option is electric underfloor heating. Renewables, such as air source heat pumps are available where desired. Other options are available, and we discuss in detail with each client during the design process.

ARCs can be heated by different means, but we prefer under-floor electric heating systems and air-source heat pumps (ASHP). For extra cosiness, we recommend a wood-burning stove if used with clean and properly seasoned dry wood. All electrical and ASHP heating systems are zoned and can be internet-linked with passive ‘smart’ controls and individual room thermostats.

How are ARC buildings lit?
We opt for efficient LED lighting which can be incorporated with internet-linked ‘smart’ controls and individual room thermostats, if desired.
How are ARC buildings ventilated?

Ventilation is assessed on a case-by-case basis based on the usage requirements of each building. We often use mechanical ventilation heat recovery systems (MVHR) to mechanically recover the heat from warm, stale air and deliver fresh, filtered air into the ARC building.

What type of windows do you use?

We offer a range of windows, including glazed ends and roof, wall and picture windows on our ARC buildings. We discuss all options with you during the design consultation process. All ARC windows, including the glazed ends, are triple glazed to minimise heat loss.

What flooring options are available in ARC buildings?

We often opt for timber flooring in our ARC buildings, but there are various options including carpet or vinyl. We discuss the options available for our ARC buildings with every client during a design consultation.


Are ARC buildings net zero carbon?

Not yet. We are actively working on achieving net zero status for our ARC buildings by 2025 (although we hope to do this sooner). There is a delicate balance between using what are environmentally-friendly or low carbon materials and creating a highly efficient, future-proofed building. We’re also developing standard solutions for renewables (solar PV and air source heat pumps) that will help to pay back the embodied carbon in construction.

Are ARC buildings Passivhaus certified?

No. There are two reasons for that our buildings are not currently Passivhaus certified. Firstly, the Passivhaus certification process is suited to two (or more) storey buildings, and most of our buildings are single storey, which means that the calculations just don’t work out according to the Passivhaus PHPP software system. Secondly, the certification process isn’t compatible with our curved structure as it assumes straight walls in its calculations.

The design of our ARC buildings, however, is based on Passivhaus principles and we achieve extremely high levels of operational thermal efficiency and human comfort levels. See our technical information for more detail.

Is your factory powered by fossil fuels?

No. From day one it has been incredibly important to use 100% renewable energy to power our factory and other operations.

Where can I find out more about Green Unit’s sustainability approach?
Find out more about our sustainability approach here.

Delivery & installation

What access is required to deliver an ARC building to site?

We require access for an articulated lorry with an on-board Hiab, or for a mobile crane transporter to deliver our ARC buildings. A minimum 4m delivery access width is generally required. We can also lift up and over any obstacles such as existing buildings or trees.

How long does it take to install an ARC building onsite?

Our ARC buildings are approximately 95% complete when they leave the Green Unit factory, meaning that there is not much required to complete when the buildings arrive onsite. We are usually onsite for just a day for a very small unit, or about a week for larger projects.

What does Green Unit do onsite after delivery?

We install the road-transportable ARC building sections onto pre-prepared foundations, and contractors then rapidly make their utility connections to the ARC which are all ready to go! The individual ARC sections are joined before the roofing membrane is sealed and greened, and then we hand over the keys! At this stage, some clients also start landscaping works around the building. In some cases, floor finishing works are completed at the client’s site.

Do you ship overseas?
We don’t usually supply overseas (outside of mainland UK) because our buildings are manufactured offsite (in a factory) and delivered to site virtually complete, so it’s not very efficient or environmentally-friendly to transport entire buildings abroad. It also adds significantly to transport costs. That said, we’re happy to discuss plans with you!

Planning & funding

Do I need planning permission for an ARC building?

Yes, in most cases you will need to gain planning permission for your modular build project – just as with any building project. Planning consent often favours sustainable development and how the appearance of the ARC buildings fit with the surrounding environment. Planning permission is managed on a local basis, and ultimately is the decision of the local planning authority.

We recommend consulting with a planning consultant whose advice and expertise can be invaluable in navigating the planning process. The Planning Portal has a lot of useful information.

Can Green Unit apply for planning permission on my behalf?
We normally recommend that planning permission is left to professional planning experts who know the local area of your site. However, if you’d prefer for Green Unit to manage it for you, we can do so for an additional cost.
Can I obtain funding for an ARC building?
Yes. Our ARC buildings can be financed through hire purchase or leasing through our panel of external funders.
What is a payment schedule to purchase an ARC building?
A typical payment schedule starts with a small fee for a design consultation and site survey.

Quality & maintenance

How do you ensure quality of build?

Our offsite design and build process is a very high-quality modern Method of Construction. We use precision production processes – such as computer numerically controlled machinery (CNC) – to ensure the highest quality levels within a controlled, factory environment.

Do ARC buildings comply with building regulations?

Yes. All of our ARC buildings comply with and exceed building regulations. We use a national firm of Building Regulation consultants who know and understand our modular building system for building control approval on our projects.

What maintenance do ARCs need?

ARC buildings are no different from other buildings in needing a little maintenance from time to time, for example checking gutters for fallen leaves (which is much easier on a single storey building)! The green roof will require weeding and watering in very dry seasons to keep it in top condition, and we recommend a thorough maintenance of the roof twice a year. Other elements of the building are generally low maintenance. We provide a detailed Operations and Maintenance manual to every client that outlines all maintenance recommendations for every part of the building.

Modular construction

What is offsite / modular construction?

Offsite manufacturing or construction is the process of building within a factory-controlled environment, rather than on a traditional construction site. Modular construction is the process of constructing parts of a building in sections – or modules. The two terms are often used together because modular construction usually takes place offsite. Find out more about modular construction in our article ‘What is modular construction?’.

What are the benefits of offsite construction?

There are lots of benefits of offsite construction! Constructing our buildings in a factory-controlled environment means that we have excellent control of our quality and wastage levels, as well as the Health and Safety of our staff. We also have the benefit of working all year round as the factory is not impacted by poor weather. We also deliver a virtually complete building to site, meaning that any disruption onsite is kept to an absolute minimum. Find out more in our article ‘What is modular construction?’

Contact us

Speak to the team

01865 682707

[email protected]

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