Home Grown Homes

COP 26 Scottish Home Grown Homes

The COP26 house is a one-bedroom unit with mezzanine studio, with an internal floor area of 70m2. The original low carbon, low energy, affordable house was designed by Peter Smith of Roderick James Architects, based on their traditional oak frame barn style. The concept was updated by Peter for the COP26 House, aiming for zero carbon impact in construction and operation, and to offer a modern, comfortable, affordable means of delivering housing at scale, using ecologically responsible materials. The design of the COP26 House has been adapted from earlier built versions of this style, with a proven track record in both materials use and construction methodology.

The COP26 House is the first house of this type, however, that has been specifically designed to be zero carbon. The house employs many of the Passive House principles, using a fabric first approach, with the ambition to create a building where the heat losses of the building are reduced so much that it hardly needs any heating. It also incorporates Heat Recovery Ventilation to Passive standards. In addition the COP26 House places great emphasis on reducing embodied carbon in the building to the absolute minimum, using natural, non-toxic and ecologically responsible materials.

Energy efficiency and expected running costs

The building is designed to run using very small amounts of energy, and is significantly more energy efficient than standard new build houses. Heating demand is mitigated through high levels of insulation, and ongoing energy costs for heating and hot water can be reduced even further – as required – by incorporating solar PV and/or solar thermal, or by installation of an air source heat pump. The target energy cost is £150 per annum, although will vary depending on the amount of on-site renewable energy generation.

Heating demand has been designed to be very low, only likely to be needed at the coldest times of the year. Heating for the COP26 House is provided by infra-red panels which heat objects and people directly, rather than heating the air. Infrared panels are an efficient, low-cost electric solution which can be provided by a renewable energy source or tariff. The panels are also almost entirely recyclable at the end of their life.

All the usual options are available for water heating: solar thermal, air source heat pump or direct electric immersion (potentially using solar PV).

The house uses a Mechanical Ventilation with Heat Recovery system – MVHR. This system provides fresh filtered air into a building whilst retaining most of the energy that has already been used in heating the building. It goes hand in hand with a fabric first building approach, and provides excellent indoor air quality.

Compared to alternative ventilation strategies and systems – extraction fans, trickle vents in windows or simply opening windows and doors, MVHR cuts out almost all the ventilation heat losses, which make up to 30% of the heating demand of a dwelling. The use of MVHR therefore has a significant positive impact on primary energy use, heating costs, and overall carbon footprint related to operational energy.

Structure

The whole structure of the house is made from timber, and wood derivative products, locally sourced as much as possible. The windows and skylights have timber frames, with aluminium coating on the exterior. Both the roof and floor are also timber structures, with wood fibre insulation and timber cladding (external and internal) on the roof.

The principle of the foundation design is to minimise the use of concrete as much as possible, and ideally avoid it altogether. For the COP26 House in its current location, we have used timber sleepers laid directly onto an existing tarmac surface, avoiding all concrete or groundworks. In general, there are several options for the foundations for the house, including: steel screw piles, which can be removed and recycled at the end of life; recycled concrete pad foundations, which are readily available everywhere in the UK; paving slabs, if building off existing tarmac or concrete.

If a concrete foundation is required, we would use a low carbon cement such as GBBC, and look to replace at least one layer of steel mesh reinforcement with fibre additives, to reduce embodied carbon further (both materials and transport related carbon).

Most of the construction for the COP26 House has been done off-site for on-site assembly, but construction can vary depending on site and client. No specialist factory is required for off-site construction: any space with enough room to handle the timber sections will do. In fact, utilising local commercial units would be actively encouraged, as it will help reduce transport-related carbon, and employ local trades.

The highest performing windows are recommended to complete the integrity of the building shell, ensuring optimum thermal efficiency.

All the materials used have been deliberately chosen so that they are readily available, standard specification. This is a fundamental feature of the design to keep costs down, speed up the construction process and broaden the potential for delivery across the maximum area of the UK.

Other Sustainability Issues

We opt for natural, non-toxic and ecologically responsible materials wherever possible, and avoid known pollutants from the house structure, such as cement, petrochemicals and steel. We also specify products with low levels of VOCs (volatile organic compounds), which together with use of the MVHR system ensures healthy indoor air.

Industry Standard lifetime calculations for modern houses are based on 60 years, although if well maintained and cared for, our houses will last considerably longer. The house has also been designed using circular economy principles, so at the end of its first life, it is easily deconstructed. It is based on 1.2m panels which are screwed together, not nailed, enabling the house to be disassembled and moved elsewhere, or split into its individual elements and reused wherever possible or recycled.

Suitable for self-build

This is an ideal solution for self-build and community build. The house has been specifically designed with construction based on a 1.2 metre grid, enabling it to be easily handled on site by two people. The house has been designed so it can be built using existing standard skills and well-established building systems.

The smallest units can be built in approximately 8 weeks (as for the COP26 House), and up to 24 weeks for the larger units. This is the time from starting on site with timber kit to handing over the keys. Obviously, different sites will have different time and work requirements to complete groundworks and foundations prior to the timber kit erection. For straightforward sites, groundworks and foundations usually take around 4 weeks.

The house can be built without a crane, but they save a lot of time if they can be accommodated. A forklift or telehandler for on-site materials handling will be required, (especially for products that are delivered on pallets, both for unloading and moving on site). Scaffolding and a hoist may be required to safely install the roof.

As guide price we would expect the cost to be between £1,800 per square metre (for self-build) up to £2,500 per square metre, dependent on size, location, builder, and final finish specification.

Beyond Zero Homes

As a group, Beyond Zero Homes, we have a single mutual goal that goes beyond achieving zero carbon (in construction and operation) – we want to demonstrate how beautiful, affordable, healthy and comfortable homes can be delivered with minimal impact on the environment, throughout their lifecycle. And to do this using materials and technology that are available today. Hence why the ‘beyond zero’ name.

In addition to the one-bedroom COP26 House, we have four standard house designs based on the same build system: the largest is a 4-bed semi-detached unit with internal floor area of 140m2. All our houses are based on standard designs but can also be adapted to suit individual clients and local planning requirements.

You don’t need an architect to build one, but you will need to secure planning permission and building warrant/regulations approval. We recommend using Roderick James Architects for this.