Piha House, Auckland
Principal Architect - Darryl Sang Project Leader - Janice Au Target Certification - EnerPhit
Passive House Designer - Sustainable Engineering Certifier -
EnerPhit has been developed for refurbishments of existing buildings as it is not always possible to achieve full Passive House standard, as it is for new constructions. EnerPhit is the Quality-Approved Energy Retrofit with Passive House Components Certificate.
This house is due for completion December 2021. Check below for building updates.
Background
Located on the outskirt of Auckland City, the house is a mid-2000s 2-storey 4-bedroom 345-sqm house on an elevated site on Auckland’s West Coast, facing west with expansive views of Piha and Lion Rock. There are 2 wings connected by the entrance staircase. There are 3 bedrooms in the quiet wing where guests have their own area under the master bedroom. The other wing has an open-plan kitchen, lounge and dining area on top of the double garage. The existing house has the barest and minimal insulation causing mould, found in the roof space and wall cavities. The renovation will allow for another bedroom and an enclosed terrace which will give shelter from the prevailing wind. The renovation allows the bush and sea views to take precedence.
The existing construction is plastered concrete blockwork walls on a concrete slab with a suspended concrete mid-floor (including mid-level concrete terraces), aluminium single-glazed window joinery and a membrane roof. Being on an exposed, west facing site the house over heated in the summer and was too cold and draughty in the winter. The renovation will be within the existing building footprint
The initial brief was for a limited renovation to upgrade the single-glazed aluminium window joinery, kitchen and bathrooms, add an extra guest bedroom and add some extra internal insulation.
When the internal linings were removed mould was discovered throughout the structure, particularly in the cold membrane roof cavity and on the inside faces of external block work walls. There was remarkably very little internal insulation to the walls and slab.
The owner has a particular health sensitivity to mould so it was decided to undertake a full renovation aiming for Certified Passive House EnerPHit standard to stop this recurring after removing the existing visible mould and sealing all internal surfaces to inhibit the spread of any mould spores.
How
Passive House focus on five components to deliver a healthy home without condensation and mould. They are: Passive house windows, ventilation, no thermal bridging, airtightness and insulation.
The building envelope was upgraded with an external insulated plaster system on block wall, a warm membrane roof and high performance Passive House certified timber-aluminium joinery with high performance double-glazed low-E low G-value (high shading coefficient) glass. High performance double glazed joinery has been chosen with an interior timber frame which has insulating properties and aluminium exterior face which add protection and reduce maintenance. This double glazed joinery is airtight (along with the wall roof, and floor components also being airtight), this is a point of difference that Passive Houses have over standard builds.
Ventilation will be controlled through the use of a mechanical heat recovery ventilation system. This will control the internal temperature and comfort level of the occupants.
Particular attention was paid to remedying or reducing the effect of the thermal bridges in the existing structure including concrete terraces over internal habitable spaces, the concrete floor slab and cantilevered steel and timber roof structure. Thermal bridge is like a tunnel that creates an easy path for heat to escape from the warm interior to colder exterior.
Draft will be kept to a minimum, which will be proven by undergoing a Blower Door Test. A Blower Door Test is a machine used to measure the airtightness of buildings and to help to locate air leakage sites in the building envelope.
A pre-line provisional Blower Door Test during construction, measured air-tightness at 0.8 air changes per hour. This will improve as the project heads toward completion. The Passive House EnerPhit target is an air-tightness of 1.0 air change per hour. Conventional building code house is 5.0 air change per hour.
Other sustainable building features include:
Rainwater harvesting
Both solar hot water and solar photovoltaics with battery storage and electric car charging
Mechanical heat recovery and ventilation (MHRV) system with integrated dehumidification
Heat pump split-system for active cooling
Heat pump domestic hot-water system with hospital grade stainless steel potable water system pipework
Overhead operable louvre roof to provide extra shading to the exposed living areas
Passive House suitable fireplace for night time ambiance - not required for heating.
Continuous Insulation Warm membrane roof over existing roof, rendered cladding system with insulation installed to the external face of the existing blockwall and extended slab edge to perimeter of existing slab
Ventilation Centralised mechanical heat recovery system with integrated dehumidifier in addition to active cooling through air conditioning
Airtightness Exising butynol roofing, existing blockwork plaster, and exisitng concrete slab as the primary airtightness layers
High Performance Windows High performing wood aluminium window joinery with low - e double glazing
Minimise Thermal Bridges Insulation positioned external to the structure assists in minimising the quantity of thermal bridges in the building. Though common with retrofit projects, eliminating thermal bridges all together is not always possible.