| Planned occupancy | The houses being retrofitted are both currently occupied by tenants that have requested transfers, therefore the planned occupancy is currently not known, as new tenants, totally engaged and committed to the retrofit monitoring, will be selected during the retrofit process. However, as the houses are 3-bedroom, we envisage families of 4-6 members occupying the properties. |
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| Space heating strategy | The existing gas-fired central heating system will be removed. Space heating demand will be minimal once the retrofit is complete, and therefore simple wall-mounted electric panel heaters in strategic locations will provide any occassional top-up space heating requirements. This is a simpler, lower maintenance and more cost-effective approach than retaining a central heating system. Additionally, as this is a retrofit for the future, aimed to make the homes future-proofed for 2050 and beyond, retaining a heating system based on a finite and non-renewable energy source, is contradictory to this aim. |
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| Water heating strategy | A high volume, super insulated temperature efficient thermal store, heated by electric immersion, will provide all the hot water demand for the house. This system is one that has been designed by HHP and successfully deployed in a number of homes we have designed and/or built. Actual hot water energy use is 40% of that predicted by SAP. |
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| Fuel strategy | The homes will be all-electric. This future-proofs the homes for the 21st century and beyond, assuming decarbonisation of grid electricity. However, as total decarbonisation of the grid is some way off, the proposed solution to ensure the homes are zero-carbon from day one is to make a sufficient investment in a local community wind turbine to cover the predicted primary energy consumption of the houses. |
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| Renewable energy strategy | Our renewable electricity generation strategy is to invest in an off-site community wind turbine project in the local area, sizing the investment to purchase sufficient capacity to cover the predicted annual energy consumption of the homes. This strategy is a far more cost-effective approach than building integrated solutions. In addition, it removes a maintenance headache for the social landlord; it removes any operational overhead for the tenant; it generates an annual income for the social landlord to cover other maintenance costs of the home; and most importantly it is actually cash-positive, as the original investment will ultimately be returned to the social landlord. |
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| Passive Solar strategy | This is key to our design. We are adding a 1.5 storey sun space that will harvest the passive solar energy for positive input to the house. In addition, this sun space will also shelter a significant amount of the building fabric from the external climate, acting as a buffer zone. Evidence from HHP houses shows that this buffering equates to a reduction of around 10 degrees of temperature difference between the internal and external air temperatures. As heat loss is a function of temperature difference, this reduces heat loss, and hence space heating demand, but is totally ignored by SAP. The sun spaces are thermally separated and unheated; tenant education and fused electrical circuits will be used to prevent use of plug-in heaters. |
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| Space cooling strategy | There is no active space cooling strategy proposed. The high levels of internal mass within the insulated envelope will act as a passive space cooling system, absorbing excess natural energy flows as the air temperature rises. |
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| Daylighting strategy | Daylighting will be provided by traditional windows and glazed doors. Daylighting calculations have been carried out for all rooms in the house, and openings have been re-sized appropriately to ensure sufficient daylighting whilst minimising heat loss. |
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| Ventilation strategy | A Vent Axia Sentinel Kinetic unit will provide a whole house mechanical ventilation solution with heat recovery. This is an accredited system with a 92% heat exchange efficiency rating. |
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| Airtightness strategy | Detailing, build quality and high quality openings will ensure a high level of airtightness; design air permeability rate is 2. This will deliver a significant improvement over the current air permeability of no-fines concrete, which when tested in these homes in the early 1990s was found to be very poor. |
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| Strategy for minimising thermal bridges | The newly applied wall insulation (in a retrofitted cavity) will be taken right down to the exisitng footings and then up into the roof space in a continuous layer. Internally, the existing, uninsulated solid floor will be removed, and replaced with an insulated solid floor; the insulation layer will be placed below the new high density concrete floor, again right down to the bottom of the existing footings, and 50mm of edge insulation will be incorporated. The new openings will be fitted within plywood box liners that span the new cavity; there will be no lintels or masonary returns spanning the cavity. |
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| Modelling strategy | Standard SAP and the supplied whole house extension spreadsheet were used for modelling. Adjustments were then made to predicted figures to account for: a more efficient hot water system; sheltering provided by the sun space; heat capacity of the thermal mass. |
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| Insulation strategy | High levels of insulation will be applied in the floor, walls and roof. The existing solid wall will become an internal high-mass skin of a new cavity wall, with the outer brick skin being retrofitted. The cavity will be 250mm and fully filled. The existing 250mm insulation in the loft will be doubled to 500mm. The existing uninsulated solid floor will be removed, and replaced with a high mass solid floor (150mm) on top of 250mm of insulation, and incorporating 50mm of edge insulation. |
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| Other relevant retrofit strategies | Tenant education in the design principles and how to maximise the energy-efficient performance of the home. |
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| Contextual information | NOTE: uploading of some of the design sketches has distorted them, which is why the footprint of the ground and first floors look radically different! They are both in fact 6.5m x 6.5m square. |
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