A modelled method on a proposed five level contemporary home being constructed using good passive solar design and clay construction blocks.
This article is about a modelled method on a proposed five level contemporary 520m² home being constructed in R25Th+ Porotherm clay construction blocks, concrete floors and concrete roof structure. There is no timber framing or other timber construction element in the building.
This describes not only the compliance with Clause H1 of New Zealand Building Code (NZBC), but also much higher energy-efficient design using good passive solar design — incorporating appropriate areas of glazing, orientation and thermal mass. In combination with a well-insulated thermal envelope and reduced thermal bridges, an efficient use of energy minimising heating and cooling costs will be easily achieved.
This use of good passive solar architectural design and energy-efficient performance of Porotherm is not just about compliance documentation for territorial authorities, but is a living philosophy achieving generational sustainability, comfort and high level indoor air quality.
To achieve compliance with Clause H1, a building must be constructed to facilitate efficient energy use for functional requirements (e.g. modifying temperature, providing hot water and artificial light) and to provide an adequate building envelope performance to minimise energy loss.
The general requirements on energy efficiency of housing and small building envelopes is described in New Zealand Standard NZS 4218:2009. This standard specifies the following three different verification methods to demonstrate compliance with Clause H1:
- Glazing area is 30% or less of the total wall area
- The combined area of glazing on the East, South and West facing walls is 30% or less of the combined total area of the walls
- The skylight area is no more than 1.5m² or 1.5% of the total roof area
- The total area of decorative glazing louvres is 3m² or less.
- A glazing area greater than 30% but less than 40% of the total wall area
- A reduction in the construction R-Value of some building elements if this is compensated for by increasing the construction R-Value of other building elements.
- May be used for any proposed building design and all buildings where the glazing area is more than 40% of the total wall area.
The proposed new dwelling will be in Climate Zone 2 and will be constructed with high thermal mass Porotherm walls. To demonstrate the compliance with Clause H1, R-values listed in Table 1 will be achieved.
NZS 4218:2009 does not distinguish the R-Values for types of floors against different exterior conditions such as ground, ambient or unheated spaces. Therefore, we applied the same required R-Value for all types of floor in any proposed building.
From Table 1, we can see that the proposed building elements easily achieve the required minimum R-Value for Climate Zone 2 using the Modelling Method.
Furthermore, the proposed building demonstrates an excellent passive solar design incorporating appropriate areas of glazing and solar orientation. The glazing area is more than 40% of the total wall area and therefore the Modelling Verification Method was used.
The calculation method follows the European Standard EN 13790 and demonstrates a heating energy demand of this proposed building at 9 kWh/m2a. The upper limit for the specific annual heating demand for Passive House certified buildings is 15 kWh/m2a. To design the heating system the calculated heating load of 10 W/m² is used.
The extent of the glazing in this design creates overheating (>25°C). An active cooling system or solar shading has been specified. This overheating is controlled by exterior louvred shading and passive cross ventilation incorporating a three level stairwell and tilt-in joinery units. The design has resulted in zero energy demand for cooling which minimises the total annual energy demand of the building.
Using the reference building R-Values according NZS 4218:2009 in the same modelling method this building in timber frame results in a heating energy demand of 123 kWh/m2a.
Based on our calculation, we can conclude that the proposed building easily achieves the requirements of New Zealand Building Code Clause H1. This building will easily meet and exceed Passive House criteria.
See the design over at MacPherson Architecture or on our site under 'In Progress'