It’s all in the Specs

Without getting too airy-fairy about it, good house design is creating spaces (rooms, hallways, open spaces and combinations of these) that function well individually, but then also come together in a cohesive, intuitive way.  You can say the same about the design of anything I guess (cars come to mind), in the sense that you aim for a synergy of these constituent pieces, where the collective effect of the whole is greater than the sum of the parts.

Part of doing this well is selecting the right materials, from the functional aspects of construction I discussed last post, through to the purely aesthetic choices.  What I’m getting at here is that designing a house really is just a massive decision-making process, where you evaluate a bunch of options, and (hopefully) come up with a compelling choice.  Sure, you can take a path of least-resistance, and not concern yourself with things beyond how they look, making sure you only pick from materials that are code-compliant, but it does limit your options.

I’ve previously mentioned how certain design choices can (and should) have a flow-on effect to other decisions you have to make, and I often describe our house specifications as ‘having it where it counts’ in terms of spending the money on things you can’t necessarily see, but will come to appreciate once the house is being lived in

In that regard, C and I spent a lot of time looking into certain things, and not much time on others, but pretty much every item we’ve picked so far was chosen for a reason, which I’ll delve into as we go!

So what’s the Plan?

C and I have always had a pretty clear vision of how the house would look in terms of it’s form – clean, minimalist look with Scandinavian-style touches: whites, concrete, timber, lots of natural light etc.

What perhaps took a bit longer to come together was the function, but that’s to be expected – you don’t know what you don’t know, and one of the reasons I wanted to do this blog was offer the insights I didn’t find when I started researching construction methods.

So in term of function, what did we want?  Because we’d already settled on having polished concrete in the living area/kitchen/bathroom etc, we’d also decided in pretty short order that we needed underfloor heating.  As a result of that, it became pretty obvious we needed to spend our money on a solid level of insulation to protect the ‘thermal envelope’:

  • 70mm Expol ThermaSlab H (under-slab insulation)
  • Expol Expol-X (slab-edge insulation)
  • All exterior walls are 140mm framing (R4.0)
  • Ceiling insulation is R6.0
  • Downlights are all LED, and IC-rated (as are the drivers)
  • Joinery is all double-glazed, thermally-broken, argon filled, with Planitherm XN (Low-E) glass in the living area and bedrooms

Based on my research, the most crucial factor to effectively mitigating thermal loss when running an underfloor heating system is actually the one I see done the least: insulating the edge of the slab.  The so-called Second Law of Thermodynamics states that heat will always flow from an object of higher temperature to that with a lower temperature.  People seem to go way overboard with underslab insulation, and leave the edge of their slabs exposed – underslab insulation is important to be sure, but with a damp-proof membrane down first, and an assumption that there’s no water source running under the slab, the ground temperature directly under the concrete changes very little.

Consider what can happen then if your slab is being heated to 18 degrees, but the outside ambient temperature drops to -5 (as it does where I live).  This is why it’s often stated that ~75% of heat loss occurs through the slab edge.

The problem however is that there seems to be very few effective, reasonably-priced and compliant systems.  Maxraft have a nice system that friends have used to good effect, but I opted for Expol’s solution, as it’s simple to apply, and sufficiently waterproof.  An important point to note, Extruded Polystyrene, (XPS), is much more preferable for this application than Expanded Polystyrene (EPS) due to its closed-cell construction, which means it absorbs much less water, and conducts heat much less readily.

Beyond that, we wanted a robust, clean cladding which fits in with the aesthetic we were after, so we’re using Sto’s Render system over AAC (lightweight concrete).  This gives a significant thermal advantage over standard 70mm brick, the AAC can be installed quickly, and gives much greater impact resistance than polystyrene-based plaster substrates.

One other structural product we’ve opted for is RAB Board, a James Hardie product which is applied directly onto the framing prior to installing the AAC panels  This has a few nice advantages over conventional building wrap, in that it provides necessary bracing elements, it’s easy to fit, and when fitted to spec, it’s weathertight, which allows the builder to crack on with ‘first fix’ tasks without being dependent on a block layer.

The north corner of the living room will be clad in Firth stack bond 10-series veneer block, which is purely for aesthetics.

The house also features a ‘sail wall’ façade of vertical shiplap cedar, that effectively comes inside into the foyer, creating a nice transition from outside to inside.

 

The Long(er) & Winding(er) Road

So 2016 turned out to be an equally productive and frustrating year; we’d finally overcome all the twists and turns in getting sign-off to build a bespoke home with a few design details that separate it from others, but we lost our builder due to delays.

2017 rolled around very quickly, and soon we were meeting with the builder to get a project plan in place.  Or at least I thought it would be that simple – until we started trying to finalize our finance.

I’m not going to go into too much detail here about how painful it was dealing with our bank (who we ultimately ended up staying with), but as the purpose of this blog is to help others I’ll say this – going down the path of a bespoke design, where you pay a builder to manage the construction/sub-trades/and basic landscaping, but want to pick all soft-furnishings, plants etc is likely going to be the painful route.

For whatever reason (I suspect it’s primarily risk-aversion), banks massively favour the showhome companies, as they deliver a turn-key product, with (in theory) franchise backing, and a contract/project plan that locks down exactly what they deliver, when it needs to be paid for, and what the client will get at the end.

Note, this is not a dig at showhomes; there are a lot of very reputable ones out there doing great work, and if you’re the sort of people that don’t like having to make 1,001 decisions, they’re a great fit.

The Long & Winding Road. . .

So it’s been a while since my last post huh?  There are a few reasons for this, which I’ll delve into as we go along, but it’s probably suffice to say that doing a bespoke design which bends (breaks?) a few district planning rules as your first house build is pretty ambitious.

We actually had our plans into council for consent in early-September, and made it through without issue until our application landed in Planning. . .

Just to back-track a few steps, we’d already applied for and received a Land-Use Consent (or LUC – in other words a Resource Consent) to build our house as:

  • We were closer than is normally allowed to our neighbour’s house
  • We required a retaining wall closer to the boundary than is normally permissable
  • We were building over the set-backs prescribed for our subdivision

When we’d submitted the Resource Consent application, we’d taken the area of the house from the slab, as it was still in the concept phase at that time.  Planning took the view however, that our roof area was the more ‘correct’ way to measure the house’s size, so determined we were in breach of our section’s Maximum Site Coverage figure.

The long and short of it was that (despite our protests) they won the argument and we had to apply for yet another LUC.  This took sufficiently long that we ended up losing our builder to a ‘keep-busy’ project for the rest of 2016.

Needless to say, it was a frustrating old time!!