Building Consent Challenges

Building consent applications for unique designs such as ours are processed through what’s known as “alternative solutions” with Queenstown Lakes District Council. This means that a specialist is dealing with it and you have a direct line of contact to them. We had a sit down meeting at the start of the process to identify any areas of concern and had regular emails to work out the details.

Here are a few of the things we needed to adjust or detail more clearly in our application…

1. 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 NZ so we had to go offshore for this over to Aussie. It’s a good thing the hemp itself will be sourced in NZ as that’s 90% of the hempcrete makeup and we’re trying to keep our embodied carbon low in this build.

2. 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.

3. Part of council regulations for the classification of land we’re on (Rural Residential) means we have to maintain 20,000 litres of water for fire fighting purposes. Herein lies a problem! We’ve designed the location of the house to fit snugly right next to the council setbacks (areas that you’re not allowed to build in due to the land classification). This is 10m from a road boundary and 6m from any internal boundaries. It makes sense to help preserve the rural residential feel, but it also means that you can’t build anything bigger than 5m2 (or 2m high) within these setbacks. Unfortunately, a 20,000 litre water tank is quite a bit bigger than 5m2. So we’ve gone with two smaller 10,000 litre tanks and set them a little lower than the normal ground level. Check – council were happy with this!

4. 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. Unknown to us, this meant that we either had to make one of the panes fixed or put a small guard rail across the outside of the window. I like the idea of opening both panes of glass, especially as we’re using the European style tilt and turn windows, so a guard rail it is. No kids are gonna be falling out of our windows!

The Design

The design of this house follows a few of the “passive house” principles, although becoming a certified PassivHaus was never the goal. Fortunately, the energy model we discussed in episode 03 returned an energy 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.

PassiveHaus require a rating of 15 kwh /m2a to gain their certification, so we’re not far off. And we’re doing it using natural materials too! Here’s how the design shaped up to achieve this …

The Envelope

With any building, corners and joins are a weakness. This is where air leaks out and you get heat loss. Put simply, the more corners your building has, the less efficient it is.

We went with a simple rectangle shape for this reason. Rectangles are pretty boring though, so we chose to break it up with the 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 aesthetics (and help to steer warm air to the upper living area).

Maximising the Sun

We have views to both the north and east on this property, and we lose the sun a little early in the west during winter due to nearby mountains. In the summer, the afternoon sun is fierce in NZ 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 – in this case 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.

To Eave or not to Eave

Eaves serve a few different purposes. They can shade your windows in peak summertime and they can protect the exterior of the house from rain. It also means more work for the builders and pushes up the cost too.

We have chosen to use a large eave on the north side of the house for sun shading for the upper level windows and are planning to grow a grape vine over the slider doors on the ground level. The beauty of this is that is will shade in the summer when the leaves are green but allow sun to beam in during the winter months.

Cooked Timber

Our goal is to use timber that is 100% grown here in New Zealand. One of the challenges we face down here 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 meaning it has a higher embodied carbon than anything grown domestically.

For this reason, we’ve chose to go down the route of thermally modified timber. This process typically uses NZ 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.

What’s Next?

We’re hoping to break ground within the next few weeks and start pouring the foundations. We will start shooting episode 05 at the same time.

In the meantime, we’d like to say a huge thanks to Minimal Design for their creativity and patience throughout the design phase. It’s full steam ahead for the build now!