7 Gaps in our Building Code
Architectural Designer New Zealand
Over the Course of my career I have relied on our New Zealand Building Code. And confession here, I have used it as a Architectural performance and design guide. And this is why that was a mistake.
Our New Zealand Building Code is a legal document. All building work, whether requiring a building consent or not, has to comply with the Building Code to be legal. Legal building matter, not for the Council or for Architects and Designers, but for homeowners. Illegal buildings cannot be sold without disclosure, don’t qualify for financial lending and aren’t insurable. The NZBC is there to provide protection for the homeowner. It is effectively the set of legal minimums that must be achieved.
When people proudly say their home is Code Compliant, all that means it is legal, it has to be. Not healthy, not comfortable, not affordable, not energy efficient. Just legal, insurable, sellable and financial.
Next month I am covering how Passive House fills these 7 gaps, so if you aren’t already subscribed to my monthly newsletter / blog / Vlog release, I have put the link below so you can get this sent direct to your inbox. Otherwise follow me on social media, I do short little videos on this topic throughout the month, so there will be some gold nuggets for you there too. Those social media accounts are listed below.
So it’s fair to say that there are gaps between a good home and a legal one. Here are 7 gaps in our Building Code and why they matter.
Ventilation
The part of the building code that talks about ventilation is G4. This part of the Code sets out minimum requirements for natural ventilation, extract systems and subfloor ventilation.
We need to replace the air with an air change rate of 0.35 to 0.5 ACH in a healthy space. What that means is that 35 to 50% of all the air in our homes needs to be completely replaced every hour to create a healthy indoor environment for us to breathe in.
The minimum standard in our building code relies on opening windows and doors. The base line legal standard is set by specifying that for any habitable room, the opening area of doors and windows must be at least 5% of the floor area of that room.
And while we say things like, “its stuffy in here, you need to open the windows.” The problem is it doesn’t always work.
Historically this wasn’t as much as issue as it is today because ventilation didn’t just happen through the windows, Our building code works in what they call infiltration too, which is air that comes into your home through cracks and crevices. This creates other issues which I will cover later, but as our construction get more and more air tight (I often say our minimum just code compliant buildings are accidentally air tight as it’s not an deliberate intention) that infiltration rate is less. There are advantages to this, but it does mean that the 5% floor area calculation which has been in our code for decades is less effective. Our codes assumptions are very outdated.
Another big issue is that air needs differences in temperature or pressure or both to move. Its how we know a front is coming in when we watch the weather report. We look for the distance between the highs and the lows around our country. The same thing happens in our homes. So we need a pressure difference from one side of the house to the other, with opening windows and a clear ventilation path or a temperature difference from one side of the house to another to move air through the spaces. We don’t control the weather, so this is entirely reliant on theory and not the actual reality of the external conditions our homes are built in. So air flow is dependent on the weather differences and user behaviour because this needs windows and doors to be open to the right amount and on the right sides to be effective.
Coupled with safety and security requirements, we don’t sleep with doors and windows wide open generally and we also don’t leave our homes unsecured when out at work or away on holiday. So, our homes only get ventilated when its safe to do so. We also don’t heat our homes in the middle of winter with doors and windows open. Our homes only get ventilated with its warm enough outside to do so. Also windows often have security stays on them for safety from falling or from home security reason. This reduces the area of opening windows. Real life senarios aren’t covered by 5%.
A study by Kara Rosiemere took data over the course of a year from carbon dioxide sensors put in various homes around Auckland to test to see how effective our Code is at natural ventilation performance. Carbon dioxide levels are high in a poorly ventilated space as one of the key requirements of adequate ventilation is to remove toxic air, and we breath oxygen of course.
Her study revealed that generally we can only rely on natural ventilation to healthy minimum levels for 10% of the year. That’s a whopping 90% of the year we get to breathe unhealthy air legally.
So using our code as a design guide with 5% of floor area in opening windows is not creating healthy homes and our building code is pretty much ineffective here at creating a quality space for you and your family.
If you listened to last month’s vlog, you would see that I recommend a mechanical heat recovery system, so if you want to know a bit more about who to talk about that, go back and listen to that Vlog
Energy Efficiency
There has been much talk about insulation recently. There is insulation and there is insulating. The entire reason for insulation in a building is to create a temperature buffer between the interior and exterior of a building, through what we call the building envelope. Insulation slows down the transfer of heat. Temperature like pressure wants to equalise, so heat will move from its hot spot to a cooler spot naturally.
This buffer works from inside out and outside in. This is why we need that fluffy stuff. The part of the Code that deals with insulation is called H1 Energy Efficiency. But here is why we have an issue with the minimum in this standard.
There are 3 ways to demonstrate compliance with H1, called H1 Calculations. The schedule method which divides the country up into 6 climate zones and the sets out minimum Construction R values for each element in each zone. Seem straight forward right. At this point I just want to point out, its H1 Energy Efficiency, not H1 Insulation in buildings, but we are so focused on insulation that it seems we miss the point. And we only have to provide evidence of H1 compliance at Building Consent stage with these H1 Calculations. So the schedule method only focussed on Insulation Values.
Then there is the calculation method, which uses a reference building and calculates the heat loss of the building by quantifying the areas of the wall, floor, window and roof/ceiling elements with their construction R Values. More in detail, but again only focusing on heat loss not energy efficiency.
The third way to demonstrate compliance is to do Energy Modeling. Seems like the right way determine energy efficiency right?
Energy Modeling takes the specific design of the building, its construction R Values, its Areas, window sizes, installation and specification, its air change rate, its airtightness, its orientation and its location using Niwa climate data with desirable internal conditions like minimum and maximin internal temperatures and calculates heat loss, heat gain and also gives us figures about how much energy or power that building is going to use.
That is energy demand and then energy requirement. Not just heat loss.
Because we have the schedule method which can be used by just about anyone because it is so simple, and because energy Modeling is more involved, most homes in New Zealand just focus on insulation. And that why it’s such a hot topic right now. But insulation doesn’t make energy and is only a part of energy efficiency
Our building code allows easy options to keep creating power hungry unhealthy homes. I believe our Code needs energy Modeling as compulsory if H1 Energy Efficiency is to do what it sets out to do which is.
“This clause requires enclosed spaces where temperature or humidity are modified to provide adequate thermal resistance and to limit uncontrollable airflow in certain buildings. It also sets out physical conditions likely to affect energy performance, and requirements for hot water systems, artificial lighting and HVAC systems.”
And yet all we need to do is provided Insulation calculations as minimum to show compliance. It is not setting a minimum standard that is in alignment with its aspirations. As a result, most homes don’t meet the aspirations.
Overheating
Overheating is another hot topic (excuse the pun) right now in New Zealand. So what does our new Zealand building code do about overheating.
The minimum temperature a home should not drop below in our Code is 16 degrees Celsius accord to legal standards. I would argue that even in New Homes constructed last year to code minimums may drop below this.
There is no maximum temperature……..
I loved the movie Garbage Warrier. The architect Mike Renolds builds earth ships, sustainable housing made from garbage basically. He started in the New Mexico desert areas. One of his stories was that he build a house with a large conservatory on it to the kitchen and then had a man with a typewriter stay in the house for a while. The conservatories are used to grow food, as these homes are self-sufficient in the desert. He got a call from this man to say that it got so hot at the kitchen that the typewriter had started to melt. Mikes comment was that “thank god we didn’t fry a baby.”
Well, its legal to fry a baby in a new home according to our New Zealand Building Code, because there is no legal max for how hot our homes can get.
The only way to quantify and then mitigate overheating is with Energy Modeling. Making this the minimum requirement is the only way we can address overheating.
And the World Health organisation says that a healthy home should stay between 18 and 22 degrees year round to be healthy. Our NZBC doesn’t recognise that.
Internal Moisture
This part of our NZBC is called E3. It has 20 pages in this section and these pages focus on wet area detailing to stop water from leaking into the structure and causing rot, mould and decay. It also calls for bathroom extracts and kitchen rangehoods for intermittent ventilation.
Now, remember 35-50% ventilation rates for healthy homes. Ventilation not only gives us fresh air to breath, it also removes water vapour from our internal spaces. We breathe out 3 Litres of water a day in our breathe, and its not just cooking and showering that generate water vapour. Our bodies need a healthy humidity. Not too humid that we sweat and are uncomfortable and not too dry that we feel dehydrated.
Intermittent ventilation relies on user behaviour and while these systems need minimum flow rates 50litres per second for a kitchen extract and 25 lires per second for a bathroom extract, those rates are not tested once installed, they are just for capacity of the fan. Duct length, material and path can affect ventilation rates hugely.
Humidity is one of the key triggers for asthma. We have one of the highest child asthma rates in the Developed world. We are world champions at child asthma. The minimum standards in the NZBC don’t do enough to address the healthy humidity levels in a home. There are legal minimums or performance criteria that is specified here.
And as our new homes are more airtight, the humidity levels in new construction is higher than the leaky old villa. So our Building code is effectively getting better at creating asthmas conducive homes because of minimum outdated standards.
Air Tightness
Now I am going to confuse you, but there are no requirements for airtightness in our Building Code. This affects both E3 internal moisture and h1 Energy Efficiency.
Firstly, I did say our new build construction is more airtight. I call it accidentally airtight. Healthy homes have an airtightness strategy and layer. Its intentional, any joints are sealed up. And it can be tested with a blower door test on site. So the air leakage can be quantified.
Our building code doesn’t call for this. You might say, well if new buildings are more airtight why worry about it.
Air moves from a place of higher temperature to a place of lower temperature. And warm air can hold more water vapour than cooler air. It’s the concept of the water / rain cycle. When we have air gaps in our construction and when the interior is not ventilated enough, has a high humidity and is warmer inside that outside, that air can move through those cracks and gaps and get trapped in the wall, floor and ceiling structures. Remember G4, the only ventilation requirements to spaces outside our internal spaces is to the subfloor space, there are no ceiling space ventilation requirements.
When this warmer humid air touches a cooler surface, we get condensation. Now in the case of a wall, we have a weatherproofing layer call building paper. Building Paper allows moisture for move through it to the exterior, as our timber framing when constructed can be a maximum 20% moisture (only needs to be 80% dry) and moisture needs to be able to move out of the construction cavity. But it doesnt allow water to move through it, as it’s a weatherproofing layer. Any condensation in this space, gets trapped. The only way to stop this is with air tightness and adequate ventilation.
Our code doesn’t call of either of those. Do B2 Durability has a bit of an issue as our homes need to stand structurally for a minimum of 50 years. Timber rots very quickly and homes without an airtightness strategy run the risk of what is called interstitial condensation which is trapped water in our structure basically.
It also affects H1 Energy efficiency because when we install ventilation, heating and cooling systems, if the thermal envelope allows air movement through it, those systems particularly the ventilation system, has to work harder for the same level of performance. Airtightness assist ventilation systems by supporting the pressurization that is needed for ventilation to work effectively.
You don’t want to spend money on a ventilation system to pay the price for higher than needed power bills.
Insulation
I know we have talked about Insulation but we have assumptions in H1 Energy Efficiency about timber content and thermal bridges.
Thermal bridges are interruptions in our insulation layers. Our construction elements generally ask that insulation, services and structure all share the same space. So, any space taken up with services and structure reduce the amount of insulation and there reduce the effectiveness of it.
This is an issue because our Schedule method and calculation method assume a timber content in their methodology. That is 12% timber.
There is no way of verifying this in the design and there is no way of checking it on site. Just a nice assumption that makes figures work.
Energy Modeling uses timber contents in workings. So working out how much timber in a wall for example, with specified stud centres (required for structural stability), cladding specific nogs (required for cladding fixing) single or double top plates (which affect bracing) is possible. One project might have 2.7m high studs at 400 crs, nogs at 600crs and a double top plate. Another might have a 2.4m high studs at 600 crs with nogs at 800 crs and another one might have no nogs.
So back to our 12%, that means effectively we assume 88% insulation in our walls, floors and roof elements.
A study by Beacon Pathways showed that the reality is that timber content on acutely building sites is around 34%. That’s 66% insulation. 22% less that what our Building Code assumes. Given we put so much attention on insulation, it seems even that is not working.
We aren’t even insulating our buildings to the minimums of the building code, because the assumptions of timber content don’t match reality. Thermal bridging needs to be designed out. There is no requirement or minimum standard legally required for that.
Window Installation
I mentioned that our Building Code is treated generally as a design guide, and this is particularly evident in a section called E2/AS1 which is called External Moisture. Now we had a time in New Zealand when we leaky buildings. And after this this section was updated to new details around weatherproofing details. These details are called acceptable solutions. So many cladding, window and roofing manufactures use these details for their manuals and compliance and many Architects and Designers use these details for Building Consent. On the surface that seems like a good system. But………
The window details are for Aluminium, which is a poor preforming material and also hang the window over the drainage cavity. What this means that the typical and common window installation detail is easy heat transfer path. As we spend more and more money on better windows like thermally broken aluminon and better performing glass, now mandatory as a minimum for new buildings in NZ, and we talk about affordability, we are putting a higher performing unit into a lower preforming installation detail. As the cost of building comes into focus yet again, if we are spending money on good preforming elements but not installing them in a good preforming way, we aren’t building for affordability. We are missing out on capitalising on better products.
There are systems like Starkes recessed Ambiance uPVC range that are code marked, meaning that we can use do a different installation detail. But if the minimum is still to hang windows over the cladding, we will still be allowing for a poor preforming installation detail to be minimiun and probably common standard. There is no requirement for manufacturers or Architects to consider alternative better installation detailing.
I hear many builders, designers, architects, developer say that when the public ask for building better, then they will provide it.
And I also hear the same people say, that until legislation raises the standard, they will continue to do what they always done.
I am big on change, and doing better and I also have this determined streak to make it happen. We have the tools, systems and skills to do better, but when we ask the public to push change we use you as an excuse for status quo. Because its not your role or job to know about how to build better, that’s why you rely on Architects, designers, builder and developers. But, if you don’t know better, you cannot ask for better.
And it would be naïve to think that is legalisations job to set quality, when it is concerned with legal obligations. If we don’t do better and set the standard independent of the building code, better won’t be expected or common.
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