The new floors have now been laid. The floor slab is 150mm of dense concrete, which sits on top of a new layer of insulation which is 250mm thick. Around the side of the floor slab is 50mm of edge insulation.
Floor insulation being installed, which will be below the new concrete floor
The new floor slab will act as a heat store to help keep the house warm through winter, with heat loss from the slab to outside of the house minimised by the insulation below and around it. The heat then only has one way to go; back into the house as the air temperature drops below that of the floor.
The new concrete floor slab being poured over the insulation layer
In summer the floor slab will act in reverse as a cooling mechanism, because as the air temperature rises above that of the floor, the excess heat will be absorbed into the dense concrete.
The mass of the original solid walls will act as a heat sink in a similar way, helping to cool the house in summer and heat it in winter, once it is fully encased in insulation, which is the next major phase of the retrofit.
Although we believe we’ve come up with a very energy-efficient retrofit design, and combined with the energy offset provided by the investment in the community wind turbine will deliver a zero carbon solution, there is still one critical element over which we have limited control – the tenants.
In highly energy-efficient houses that combine high thermal mass and significant levels of insulation to remove the need for a space heating system, it is vital that the occupier appreciates the design concepts and how to live in the house; if you leave a window open in winter the house is going to get cold!
Therefore we will be working with the tenants moving into the retrofitted houses, to help them understand how the houses are designed, and more importantly how they need to occupy the house to ensure this design is effective.
In order the take advantage of the thermal mass of the existing solid concrete walls, and turn them into a heat store for the houses, we are building a new external wall and incorporating a large (250mm) cavity fully-filled with insulation between the two walls. This significant layer of insulation will stop the heat absorbed by the existing solid walls transferring to the outside of the houses and being lost, as it does at present.
Before we build these new external walls, a couple of steps are required first:
Removal of the existing bays on the houses to make it easier to build a single wall right across the front
Addition of new foundations on which to build up the new walls
The video below shows the houses with the bays removed and the new foundations being laid. The new foundations were combined with underpinning for the existing walls to make the overall structure more secure.
The houses currently have solid concrete floors with no insulation underneath them. As a part of the retrofit we are excavating these original solid floors, and replacing them with a combination of insulation laid under a new concrete floor. Putting the insulation underneath allows the mass of the concrete to store heat and then give it back up as the air temperature in the house cools, thereby helping to keep the house warm.
Effectively the floor is then acting as a storage heater. The heat absorbed into the floor is from a combination of passive solar gain and incidental gains from occupants, cooking and appliance use. Basically whenever the air temperature in the house exceeds the temperature of the floor slab, the floor will absorb that excess heat. The insulation under the floor slab stops the heat escaping to the ground below, storing it to be returned to the house as the air temperature subsequently cools.
The existing solid walls will act as a heat store in a similar way once the new external wall is built up with the insulated cavity outside the existing wall.
The video below shows one of the houses with the old floor excavated and Nick summarises our plans for the new floor.