This extravagant looking Underhill Passive House Project is situated in a very prominent location at the top of a hill in the Cotswolds Area in West Central England. On the 29th of Jan 2010 the project passed Passive House Certification, and is therefore the first certified domestic Passive House in England. Being dug into the hill to be invisible from the surrounding countryside, it is essentially a stealth house, with absolute minimal visual as well as environmental impact on landscape. The house is entirely glazed to the south, and the rest of it being earth-sheltered and therefore highly insulated creates the perfect passive solar design. The structure of this underground house is entirely concrete, much of which is left exposed internally to exploit the benefits of its thermal mass. It is insulated and waterproofed externally for the same reason.
The extension is joined to the existing old barn which also was partly renovated with the total treated floor area being 358m². The construction method consisted of externally insulated concrete walls, floors and ceilings. All the insulation used in the house came from Dow Building Solutions in England. The external walls are 220mm thick with the underground U-Value being 0.117 W/ (m²K), also containing Fosroc drains with 310mm Perimate DI-A insulation. In relation to above the ground it has a U-value of 0.153 W/ (m²K) with 250mm insulation and Lotusan acrylic render finish. The floor slab is 250mm concrete; screed and resin finish over 250mm Floormate 300-A insulation and a U-Value of 0.146 W/ (m²K).
The ceiling consisted of a 250mm hollow core concrete slab and screed with 360mm Roofmate SL-A insulation, also some of the earth has the ceiling partially insulated and the U-Value is 0.085 W/ (m²K). The windows installed in the house are Optiwin Alu-2-Wood which had an overall Uw of 0.74 W/ (m²K) and a G-Value of 50%. Optiwn Frostkorken also provided the front door with a U-Value of 0.72 W/ (m²).
Ventilation in the house is produced by a Paul Campus 500DC balanced mechanical ventilation system which is a Passive House heat recovery unit with 83% efficiency and 0.28 Wh /m³ energy consumption. The heating is from a Woodfire F12 wood burning stove with a back boiler, sealed to room air. 2 post heaters (water based) in air supply ducts distribute the heat. For the domestic hot water a Solex solar thermal roof with 40m² collector area was installed with a 2000 litre accumulator tank; in winter via back boiler from wood stove, it will be backed up through the electric immersion heater.
n50 = 0.22/h; q50 = 0.23m3/(m2h)
13 kWh/(m²a) according PHPP
9 W/(m²) according PHPP
Primary energy demand:
62 kWh/(m²a) for heating, DHW, electrical consumption for appliances, etc. (according PHPP)