BROOK-MILLER HUDDLESTON HOME | LAUDER ROAD, LAUDER
What is interesting about Lauder, other than the rail trail passing right by the southern boundary, is that NIWA have a weather station here, which is used for one of the Passive House Climate Zones.
Damien went to Lauder to meet Dunstan & Abi, visit the site and carry out geotechnical bearing tests in September 2023.
The Power of the Passive House Planning Package
Dunstan & Abi wish to build a healthy home, preferably a passive home (uncertified) in Lauder, Central Otago.Their site is on the edge of the township, with the Otago Rail trail on their southern boundary. They are used to living in small spaces, as their current home is just 54m2. As Abi says, they want to build a better home, rather than a bigger home.
Adrian Taylor of Candence Architectural Design was engaged and provided a design for a 100m2 cottage with wide verandas on the north and west elevation. The thermal envelope consists of a MAXRaft slab with NZSIP structural insulated panels as walls and ceilings, with triple glazed PVC windows.
It was thought by all involved that this would be an energy efficient home that should be close to achieving Passive House Low Energy levels of performance. However, we were concerned about the climate, altitude and site constraints.
Energy Modelling Software
We energy modelled the design including site constraints using the Passive House Institute’s modelling software called Passive House Planning Package, (PHPP). This is a large Excel spreadsheet, made in Germany, but once adjusted for climate and location, is used right around the whole world.The beauty of PHPP is that a good idea of the performance of the home can be gained well before it is built and adjustments can be made to optimise this performance, without making costly alterations down the track. The PHPP software provides comparison calculations for
– Heating demand in kWh/(m2a)
– Peak heating load in kW
– Final Electrical Energy in kWh/(m2a)
– The frequency of overheating. (Internal temperatures over 25°C)
A DesignPH model of the thermal envelope was created, along with immediately adjacent context and terrain. This was employed to analyse the shading coefficient for each window pane.
Fig 1. Model view looking from the south with future water tanks and garage adjacent to the building for true shading context.
Fig 2. Model view looking from west - with example window radiation/shading analysis (blue highlighted window).
Five different scenarios were modelled, with scenario 1 providing a baseline comparison with the minimum Building Code requirements for H1.
The results were higher than what we initially set out to achieve for this healthy home, just because the climate is harsher and the altitude higher than many other parts of New Zealand.
A series of recommendations were made for Abi and Dunstan to consider, the main one being the removal of the verandas from the north and west elevations. Also suggested, was making all the windows on the north and west elevations full height to improve solar gain. This is unusual for a high performance house project, where we are often trying to make the windows smaller to reduce overheating in summer!
Following discussions with Abi & Dunstan, a compromise was reached, in that the verandas would be reduced in width to 1.5m. Panel pricing became available, which indicated that the thermal spline options were beyond their budget, as support rafters were still required.
The model was then amended for the new veranda and window layout, with the results provided below.
Scenario 1 & 3 align with the previous modelling. Scenario 2 & 4 show the difference reducing the size of the verandas make; 21.5kWh/(m2a) for a code minimum house and 12.7kWh/(m2a) for this house. Considering that the maximum total heating demand for a Passive House Classic home is 15kWh/(m2a), reducing the veranda size makes a huge difference to overall performance.
Option 5 allows for Dunstan to add an insulated ceiling cavity under the SIP panels at some point in the future, when the budget allows. This provides another 2.9kWh/(m2a) of energy savings.
The benefits of energy modelling can be clearly demonstrated by this exercise. Reducing the veranda width will save money from the front end build budget, and reduce long term heating demand.
Unfortunately, we were not able to take this home to Passive House levels of performance, but on paper at least, we have a healthy home that is 4.2 times more energy efficient than a house built to the minimum legal standard. This is a significant win for Abi and Dunstan, and particularly important for an off grid home.