Croft103 by Mackays

The Property

Croft 103 are low energy, highly sustainable buildings constructed using all natural materials.

The buildings benefit from the following characteristics:

  • High levels of insulation: The building is constructed with a thick blanket of sheep’s wool insulation wrapping the wall and roof construction. Externally, wood-fibre sheathing provides a complete thermal break to the outside of the structure. The floor has 250mm of polystyrene below a thick concrete ground slab.
  • Breathable construction: The insulated building envelope is constructed to be breathable, this means that any moisture within the construction can pass through the insulated envelope virtue of a vapour permeability gradient from inside to out such that moisture will always migrate to the external face of the wood-fibre sheathing where the inclusion of a ventilated cavity results in moisture being wicked away with the passing air.
  • High levels of air-tightness
    The building achieved an air-tightness result of 0.83 ACH (Air changes per hour). This represents levels of air-tightness. The result is that the building has no drafts and loses minimal amounts of heat through air infiltration.
  • With the high levels of air-tightness, mechanical ventilation is required to provide fresh air to the building in a controlled fashion. The cottage benefits from a very efficient MVHR (Mechanical Ventilation Heat Recovery) unit. This extracts stale moist air from the kitchen, utility and bathroom and supplies fresh drier air to the living and bedroom spaces. In the process, the unit exchanges the heat from the outgoing air into the incoming air with 93% efficiency.
  • The building envelope is completed by large amounts of south facing glazing. This glazing provides unique drama, allowing all types of weather to be enjoyed from the comfort of the cottage. This glazing also provides a generous amount of solar gain to the building (although it also loses heat at night and on days with less sun) on particularly sunny days there can be an excess of solar gain. To contend with this, the thick concrete floor slab (we have simply power floated the surface of the structural slab) provides a large amount of thermal mass to the building. The floor is able to absorb large amounts of heat, helping to regulate the temperature of the building. The slab will absorb excess heat during the day, and then release it again during the night.
  • The concrete floor slab provides the medium for supplying heat directly to the building. Under floor heating pipes are set within the concrete slab. On days when heating is required, this is provided by pumping low temperature water (e.g. 25 degrees) through the UFH pipes, warming the slab which then radiates heat into the building. Given the thickness of the slab and the amount of thermal mass. As a result, this means of heating the building is not very responsive. This is because of the high thermal mass of the slab. Before this heat can be radiated to the room, the slab needs to be warmed.
  • With high levels of insulation and air-tightness and high levels of thermal mass in the slab, the buildings work best when they are kept at a consistent temperature. The thermostats are set at a fixed temperature and there is no time clock, the building is intended to remain at a comfortable warm temperature at all times.
  • The warm water that feeds the under floor heating is supplied from two large thermal stores housed within an insulated service space behind the building. The water in these thermal stores is heated, whenever possible by the solar panels behind the building. During the winter months there is often not enough sunshine to provide all of the required hot water to run the system, at these times, an electric immersion within the thermal store provides the balance of heat to the tank. Some of the time, this electric will come from the 6Kw wind turbine located towards the entrance to the croft. This turbine produces, on average, 16,000Kw hours electricity per annum. As a result of the energy generated by the solar panels and the wind turbine, the cottages are carbon neutral overall.
  • The domestic hot water is also supplied from the thermal stores via a heat exchange coil; as a result, the hot water is fresh mains water.
  • Additional heat can be provided by lighting the wood burning stove. This also provides an attractive focal point. The stove benefits from an external air supply. Since the building is air-tight, without an external air supply, the stove could effectively starve the area of oxygen, but with the external supply, the stove is effectively a closed system.

The Property

All in all, the cottage may well function and perform quite differently to the house that you are used to, and this may take a little getting used to, as may the feel of the internal atmosphere. Rest assured that the buildings have been set up to be as comfortable as possible and to regulate themselves for heat and ventilation.