Sustainability for modhouse: this has been a very large part of the project in order to create a very healthy, warm and comfortable house to reside in.
Factoring in environmental considerations started with the actual house size purposefully mid-sized (it is not a large house) but which utilises all the space. Approximately 95% efficient with <6sqm hallway.
Then the placement of the plan modules to suit the orientation of the house to its site (north facing light, wind direction, local weather conditions) and the number and size of openings were all considerations.
The plan shape being rectangular also aids in maximising usable space and reduction in material use with a very simple roof shape being a long gable and a single ridge which makes water collection easy from both ends.
The extensive use of timber was also no accident, much of the timber is NZ grown sustainable plantation pine which supports the local economy (#logsforjobs) and the many people employed in the forestry sector as well as minimising transport emissions from importation of materials.
Thermal Comfort + Air and Light Quality
The house is very well insulated with a slab raised off the ground (cupolex system) with an insulated slab edge and high wall R values achieved which was made possible through using 150x50 framing wherever possible and extra high insulation blankets throughout R3.6.
Also the roof SIP panels which are a 150mm thick PIR cool store type product with very high R values from Metalcraft ensure the thermal comfort creates a house that is a joy to live in. Cool in summer, warm in winter. The placement, size, scale and extent of openings and glazing for modhouse was another very well-considered element of the build.
Aware that we needed to allow not only for the correct amount of natural light into the house but also to include a lot of openable doors and windows to allow for good cross-ventilation. APLs Metro series joinery suite incorporated double glazing which was always going to be the minimum requirement in terms of heat loss but we also looked at joinery that included thermal suites for greater efficiency.
The joinery on modhouse has been a great success. The doors are almost 2m wide (the entire ground floor openings are sliding doors) which also slide past each other over the walls. This allows the ability to break down the solidity and mass of the house and open the end walls of the house to the outside which is both functional and also quite dramatic.
"In any house, the joinery is one of the largest single-ticket items in terms of costs."
The added benefit environmentally was the joinery supplier Twin City are located approximately 1km from the site reducing the freight footprint. And with a long-standing interest in environmental sustainable design (ESD) and in this case energy consumption; we avoided the requirement for energy-high and costly air conditioning and heat pumps. The sole form of heating is from a locally manufactured wood burning pyroclassic fireplace which burns the media very slowly and at intense heat such that there is very limited ash for the garden. A convection fan atop the fireplace pushes the heat out to the lower floor before it rises to the bedrooms above.
Photovoltaic (PV) panels
modhouse has 8 PV panels capable of producing 2.48kw of power. This feeds the daily use and extra power is stored into a 5.5kw battery via an inverter for use later (i.e. when it is dark and the panels don’t generate power). Any additional power is then fed back to the grid as you will only export once the battery is full and all your home loads are met.
July 2019 facts:
$4.40 only export.
This gets deducted from the bill and seems low, however the savings are what you have not consumed from the grid, not your export at 8c/kW. modhouse have only used 225kWh in the month whilst the NZ average is 800kWh.
Generation - 159kWh
159kWh - 55kWh export = 104kWh consumed x 0.26c/kW = $27
$123 kWh of battery stored energy used = 123 x 0.26c/kw = $32
$32 + $27 + $4.4 = $63.40 total savings for the July month.
If you take away the lines charge modhouse saved more then we spent on power in the middle of winter!
Note: We would recommend future houses to have 24 panels to maximise output, and also to source a retailer that offer time of use rates.
Rainwater from the main modhouse roof is collected into a 3000l tank supplied by Bailey Tanks. This water is used for watering the garden and external use such as carwashing and house washing.
Note: we would recommend future houses couple this to a small pump to increase the water pressure.
We used both Dulux and Resene paints and wherever possible waterborne paints to reduce voc.s – both these brands are strong SUSTAINABILITY advocates and for environmental purposes allow recycling of paint cans and returns; refer to Specifications for brand and colour. Osmo was used extensively for whitewashing the plywood walls and floors and is also A waterborne system.
modhouse sought to reduce the extent of hard external surfaces and cement use by replacing the standard concrete driveway with the use of concrete pavers supplied by Firth. We filled these with 10mm stone pebbles from Winstone’s quarry. This allows for permeability and soakage on site rather than directly into the City’s stormwater system.
We have minimised hard external surfaces (refer driveway above) and planted ready lawn (prefabricated grass!) which works well on our flat site. We have attempted to attract birdlife and bees by planting 18 flowering feijoas and also used natives for hedging (70 griselinias). We are yet to build the raised vegetable garden and plant citrus (lemon and lime tress) and a further 3 Magnolia Grandiflora for sun shading in the summer months.