Underhill ‘The Stealth House’

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 29^th 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.

Key figures:
Air tightness:	n50 = 0.22/h; q50 = 0.23m3/(m2h)
Heating demand:	13 kWh/(m²a) according PHPP
Heat load:	9 W/(m²) according PHPP
Primary energy demand:	62 kWh/(m²a) for heating, DHW, electrical consumption for appliances, etc. (according PHPP)

The house is achieving 90% energy savings over that of an average house. Most of the concrete structure is exposed internally and using this thermal mass from the concrete structure alongside highly-durable insulation has resulted in a highly energy efficient building.

'Out of the Blue' Passive House Wicklow

The family home of Tomás O’Leary in Wicklow was the first Passive House to be built in Ireland consisting of two-storeys, an area of 4000sq ft and was purpose-built to heat and cool itself, without the need for any active heating or cooling system. The house was MosArt designed, specified and supervised while being constructed, also the house is officially certified as a Passive House by the German Passive House Institute.

The house is constructed with block clad and 315mm of EPS with its orientation south facing. The U Value of the building envelope is 0.10W/m2K. Greenspan supplied the external insulation and plaster system for the house and it was installed by external insulation contractors from the UK Insulclad. For the windows contained in the house they have a U Value of 0.67W/m2K and were supplied by Optiwin Ireland. The heat exchanger is certified > 90% heat recovery within the house and was supplied by Produkt Ltd. There is 7.5m2 area of solar panels attached to the building and they were supplied by Eco-NRG from Wexford who also carried out all the plumbing in the house. the airtightness for the house allows for 0.55 air changes per hour and the air-tight tapes and membranes where supplied by Ecological Building Systems in Meath. All of the domestic appliances used in the house are A rated or higher and as well as this there is a wood pellet stove system installed. The main benefits of the Passive House is the low CO2 emissions and no heating bills for the owners.