Minimal Design NZ
Hawea Grove - a project in achievable sustainability
Updated: Mar 31, 2021
Hawea Grove is the vision of a passionate, outstanding local bloke who goes by the name of Keith Stubbs. We were lucky enough to meet him at the initial stages of this project by chance, on a chair lift in Ohau Ski Resort. Within ten minutes, we were discussing Minimal Design principles and arranging another meeting over a cold brew.
We were instantly struck by his goal of becoming a sustainable living and visitor sanctuary among established flora, and he liked our ethos ‘to simplify the design, building and maintenance process with thoughtful planning, logical solutions, basic shapes, quality materials and a consideration for the environment’.
A match made in Minimal Design heaven and it wasn’t long before we were onsite and onside. During the following meetings, we created a concept design including Keith’s initial ‘must have’ list;
Hydronic underfloor; an efficient air-to-water heating system, designed to keep the concrete slab at a consistent temperature all year round.
Hempcrete; a concrete substitute made from hemp, with a little concrete and lime mixed in. Quite possibly one of the most environmentally friendly building materials on the planet.
Charred cladding; A Japanese technique known as Yakisugi (or Shou Sugi Ban), where a timber cladding is sealed through charring techniques to lengthen the lifespan and make it more durable.
The design of the main house of Hawea Grove follows a few of the ‘passive house’ principles, although becoming a certified passive house was never Keith’s goal. Fortunately, his energy model returned an efficiency rating of 28.2 kwh / m2a. This means that for every meter of floor area, the house will use 28.2 kilowatt hours annually.
A passive house requires a rating of 15 kwh / m2a to gain their certification, so Hawea Grove is not far off - and we’re doing it using natural materials. Here’s how the different design elements achieved this:
With any building, corners and joins are a point of weakness. This is where air leaks out and heat is lost. Put simply, the more corners your building has, the less efficient it is. Keith went with a simple rectangle shape for this reason, broken up with an outdoor area on the north side, a carport on the south side next to the entrance, and a dual single pitch roof line to help mix up the aesthetic and steer warm air to the upper living area.
Soaking in the sun
There are views to both the north and east of this property, while it loses the sun a little early in the west during winter due to nearby mountains. In the summer, the afternoon sun is fierce in Hawea and can often lead to overheating with west facing windows. With this in mind, we decided to put some big east-facing windows to catch the morning sun, harnessing some early morning energy and holding it in a thermal mass. Which in this case, is our rammed earth floor. We also placed some big windows and slider doors on the north side to keep the sun coming until mid afternoon.
Eaves shade your windows in peak summertime and protect the exterior of the house from rain, but they also require more work from your builders and push up the cost of construction.
At Hawea Grove, Keith chose a large eave on the north side of the house shading the upper level windows and is planning to grow a grape vine over the slider doors on the ground level. The beauty of this is that it will shade in the summer when the leaves are green but allow the sun to beam in during the winter months.
The Hawea Grove goal is to use timber 100% grown right here in New Zealand. One of the challenges we face down in Central Otago is the powerful sun. For this reason, many people choose to use cedar claddings on new builds, due to its strength and durability. Unfortunately, almost all cedar is imported so it has a higher embodied carbon than anything grown domestically.
For this reason, Keith chose to go down the route of thermally modified timber. This process typically uses New Zealand grown pine (which is incredibly sustainable) and cooks it in a large kiln. This changes the molecular structure of the wood and makes it amazingly strong and durable.
Like any commercial or residential building project, the consent process can be a tricky one. But, with a unique project like Hawea Grove and the uncertainty of Covid-19, Keith expected a frustrating few months. He was pleasantly surprised, as this sustainable oasis is considered an ‘alternative solution’ by our friends at Queenstown Lakes District Council. This meant that a specialist was assigned to our project, who we have a direct line of contact with.
Here are a few of the things we needed to adjust or detail more clearly in our application:
Hempcrete uses a lime binder to help it bond and set. We had to make sure that the lime binder came from a recognised source and had the historical data to back up its standards. At that point in time, we weren’t able to find a reputable source of lime binder within New Zealand so we had to source this from Australia. It’s a good thing the hemp itself will be sourced in New Zealand, as that’s 90% of the hempcrete makeup and we’re trying to keep our embodied carbon low in this build.
As we’re using a rammed earth floor in the living area, the details of how this works with the foundations and the hempcrete walls needed to be well documented. We’ll be using a timber edging in between the rammed earth and the concrete foundations to help with thermal efficiency and minimise shrinkage.
Part of QLDC regulations for the classification of land Hawea Grove is on (Rural Residential) means we have to maintain 20,000 litres of water for fire fighting purposes.
Two of the windows in our upper floor have an opening that is larger than 1000mm wide with a sill sitting 900mm above floor level. We either had to make one of the panes fixed or put a small guard rail across the outside of the window. Keith liked the idea of opening both panes of glass, especially as we’re using the European style tilt and turn windows, so they act as a guard rail.
If you’d like to find out more about the Hawea Grove project, Keith has also been creating an epic video series detailing each phase of the design and build and all his learnings along the way - all from the perspective of a self-proclaimed ‘consumer with little experience’.
His objective is to showcase the twists and turns of creating and managing a sustainable, eco-focused building project, and to help promote the products and practices of the partnering suppliers. Check it out.