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Sun-stack Grow Homes - a blueprint for resilient & sustainable communities in 2030.

In the wake of COP 26, GreenTrace Architect have been busy working on a new type of housing model; a model for resilient, adaptable, and inclusive communities with a healthier relationship with nature and minimal impact on the planet:

Social interaction, connection & cohesion

The proposal illustrates a thriving community where residents are encouraged to connect with each other and nature. It is a place for every stage of life; for play, work and retirement. The vision is a new type of street, encouraging interaction at many levels. Lines of movement converge at a central plaza where seating and communal facilities are located. The public realm extends into the spaces between houses where shared space may evolve into retail units or workshops. Community cohesion is encouraged by providing communal facilities: such as the common green and common room that may be used for recycling, information, or performance. Roof-top gardens provide private spaces to socialise whilst bringing activity and greenery street-side and enabling visual connections to the street at all levels.

Accessibility & practicality

In recognition of the extra space required for disability, elderly care, as well as work and play, additional shared internal space is provided at ground floor level between each home. As well as enabling the homes to become more space-efficient (reducing cost and carbon), the shared spaces have multiple social and functional benefits for occupants. Residents could agree how these public spaces evolve to benefit the community to bring life, purpose, and welfare, whilst fostering neighbourliness. The homes are designed to Lifetime Homes guidance. Parking lots could be located near to the entrance ramps, away from the street. Vehicular access to homes for emergency, refuse and drop-off is achieved via the common green where cellular grassed pavers provide adequate hardstanding whilst allowing drainage and green space.

Outdoor space & connection to nature

The proposal understands the importance of a connection to nature for health and well-being. In addition to the roof-top gardens and balconies, communal green infrastructure is provided with green walkways and park space. The raised walkways have a light touch on the earth, allowing nature to grow under and around them. Avoiding hard, impermeable surfaces such as concrete reduces overheating risk and allows natural, inexpensive drainage. Timber structures can be re-used and remodelled unlike carbon-heavy and permanent concrete.

Internal Environment

  • Ventilation & air quality -The homes adopt Passive Ventilation with Heat Recovery. Instead of mechanically moving air, the natural air current of rising hot air generated within the building is encouraged by wind power and natural buoyancy to expel damp and pollutants while drawing in fresh air from outside. A heat exchange unit at the top of the house transfers the energy in the expelled air to the incoming fresh air. The house has been designed to encourage this stack effect with a large atrium placed central to the plan that is also heated by solar gains.

  • Thermal comfort -The passive ventilation system can be coupled with a ground source heat pump and earth storage system to enable heat transfer to water pipes for space heating and cooling. In summer, excess heat recovered from the heat exchange and PVT solar panels (explained below) is stored in an Earth Energy Bank (explained below) for recovery in winter. In winter, adequate space heating is achieved without the need for any additional fuel source (explained below).

  • Healthy fabric & moisture control - Natural building materials have clear benefits for health and wellbeing. The proposed construction system is made from straw, wood, wood fibre, and clay and hemp plasters. These materials allow the fabric to breath, controlling moisture effectively to eliminate the risk of damp and mould. Combined into a panel, the fabric provides extremely good levels of acoustic and thermal insulation, are non-toxic, have thermal mass, and are carbon sequestering. The fabric build-up has been inspired by the ModCell Core straw panel system in addition to the ISOBIO research project into natural building materials.


  • Flooding - The homes are raised off the ground on stilts (galvanized screw-piles) allowing flood water to pass below.

  • Water scarcity -Communal rainwater storage tanks are provided below the raised walkways.

  • Overheating - The scheme proposes natural, passive and mechanical cooling strategies. Natural cooling via planting that provides shade in summer as well as natural surfaces to diffuse solar gains and avoid the heat island effect. Deciduous trees run alongside the external walkways providing shade for the circulation areas as well as the south facing fenestrations of the dwellings. Planting the roof gardens would be provide further shade and cooling. Passive cooling of the dwellings is achieved by the stack effect and night cooling coupled with the thermal mass of clay plasters. Mechanical cooling is employed if required via the ground source heat pump cooling incoming fresh air.

  • Fuel scarcity - The homes of 2030 are completely self-sufficient with regards to fuel, relying wholly on solar energy.

  • Home working - The shared spaces between each dwelling may be used as a home office.

Energy Efficient fabric with low and embodied carbon

The construction system is carbon negative with positive environmental impact. The fabric meets PassivHaus requirements for U-values, airtightness and thermal bridging with U-value in excess of 0.11 W/m2K and airtightness levels below 1m3/(h.m2). The panel is used for wall, floor, and roof applications with adjustments to internal or external layers for waterproofing and ventilation, etc.

Design for deconstruction (re-use)

A strategy to avoid concrete has been adopted. Concrete is very high in embodied carbon and is difficult to re-use. Instead, foundations are designed with screw piles and steel ring beams which are bolted together (instead of welding) to enable easy deconstruction. Screw-piles can be easily removed from the ground for re-use. The roof covering is powder coated steel which, like the substructure is high in embodied carbon but can be re-used indefinitely. The roof structure is simple with no awkward shapes which allows the roofing sheets to be laid whole and therefore more re-useable.

Prefabrication & Flying Factories

The panels are prefabricated in a local ‘Flying Factory’ such (as local farmer’s barn) keeping much of the project’s value within the local economy and reducing CO2 emissions. Panels are entirely manufactured and assembled under controlled conditions. The aim has been to reduce the amount different sized panels for increased manufacturing efficiencies. There are also no openings in the panels to speed up processes. Digital technologies, such as a CNC machine could be employed to cut sheathing boards to size, whilst local labour could be up-skilled to assemble the panels and provide quality control.

Diagram of the Caplin Solar system that stores heat in an Earth Bank for us in the colder months (source: Caplin Solar)

Low-carbon technologies

Caplin Solar Ltd have developed a complete integrated renewable system, in which three core technologies are brought together to solve the fundamental renewable energy dilemma: seasonal imbalance. By collecting and storing summertime heat for use during the winter, efficient running is maintained all year round. According to the company, “the system out-performs all other conventional combinations of renewable technologies, finally making it practical and affordable to achieve zero carbon status for new homes and low-rise commercial developments.” The system consists of three core components:

  • Photovoltaic Thermal (PVT) panels - combine conventional photo-voltaic electrical generators with thermal energy collectors to produce both electricity and useable heat from one panel. These combined PV-Thermal generate more energy over a year than the equivalent area of PV, and collect more heat energy than solar thermal panels

  • Earth Energy Bank – heated fluid is pumped from the roof through a series of pipes underneath the house, warming the surrounding earth. When a ground source heat pump is paired with an Earth Energy Bank the earth is “charged” with thermal energy and the ground temperature rises above ambient. Consequently, when heat is extracted, the minimum temperature stays significantly higher, increasing the efficiency of the heat pump.

  • Ground Source Heat Pump - The heat pump is powered by electrical energy from PV-T panels and is used to extract heat from the Earth Energy

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