Building Science and the Building Code; Part 1
Last week we raised the challenges of integrating Building Science into the New Zealand Building Code without causing contradictions between various clauses;
The current New Zealand Building Code is organised into several clauses that cover various aspects of building performance, see full list here:
And a quick recap of what building science is roughly about:
· Heat protection
· Moisture protection
· Acoustics
· Fire
· Structure
Considering the recent discussions surrounding changes to Clause H1, which primarily governs energy efficiency and therefore heat protection, made the decision easy to start here.
Heat Protection
Of course you already knew it’s affecting Clause H1 and Clause E3, internal moisture - Easy!
But before we go into what other clauses are actually affected by heat protection we should probably cover the aspects of heat protection – What is it, what is heat flow and where it occurs.
Heat flow is occurring at the external boundary of our buildings. Mostly outward in New Zealand, but works both ways.
If you think thats your external walls floors, roofs windows – you are on point! Yes, Thermal bridges, too. Although we are not quite sure what they are mostly....
Thermal bridges are the connection details which we are currently ignoring entirely.
But where else could heat flow play a role?
G5 - Interior (or shall we rename it "Inferior"?) Environment
Ah yes, of course. There is a reference to heat flows and R-Values, but only really for isolated spaces within buildings (and for elderly and children only…). I mean why would you want to heat the whole building when you can focus on one room to achieve 16ºC at 750mm floor height, right? Super energy efficient.
I mean the idea is there. Make it comfortable cheap.
We could look at using ASHRAE55, or ISO7730 and actually define what internal comfort means. Things like:
Temperature: 20°C to 24°C (68°F to 75°F) in winter, 23°C to 26°C (73°F to 79°F) in summer (ha, wonder what distance from the floor this is measured...)
Humidity: 30% to 60% RH.
Air Speed: 0.1 to 0.2 m/s (higher speeds can be comfortable in warmer conditions).
Clothing Insulation: 0.5 clo to 1.0 clo depending on the season.
Metabolic Rate: Typically around 1.0 to 1.2 met for sedentary to light office activities.
Does this affect H1?
Well, Acceptable Solutions isn’t really looking at any of this, but Verification Method 1 and 2 do actually set temperature boundaries for the calculation of heat loss (Energy Modelling).
E voila! – 20-25ºC is what is typically used for energy models for residential buildings. For theoretic compliance of course. That’s pretty good so far – That is IF you choose to use the modelling method for compliance.
Most people still use Acceptable Solutions however. Can we upgrade acceptable solutions to roughly get there?- I think so. Maybe not by raising one construction R-Value into the echelons of absurdity (yes, roof R-Value… talking to you!). A more balanced approach would be welcome. And an updated calculator maybe for standard heating sizes, if you must. Something that is at least referencing to the latest R-Value requirements.
What should really be improved is the direction for G5 - Air quality? Air temperature? Sizing for heaters? Pick a Lane!
The parameters for internal environment can easily be copied, or referenced to existing standards (ASHRAE, or ISO) and while we’re at it – please ad pollutants/contaminants to it (CO2 levels, particles, etc.). They’re currently hidden deeply in G4 (VM, which doesn’t apply for acceptable solutions).
G4 - Ventilation
Heat flow interacts with ventilation systems by influencing the efficiency of heating, ventilation, and air conditioning (HVAC) systems. Properly managing heat flow ensures that ventilation systems can effectively control indoor temperatures without excessive energy use.
Is there a reference to R-Values in G4? Nope. It is largely about moving air and its doing a pretty poor job at that to be honest…Have you ever looked at the math of trickle vents? Ha - wait till we cover that!
Do we need to worry about ideal insulation levels and thermal bridge free designed buildings? What does that have to do with ventilation?
Yes, more insulation leads indirectly to higher moisture loads! - Hear me out. The inside of buildings become warmer and can hold more humidity in the air. Thicker/denser insulation leaves fewer gaps in the building fabric making buildings more airtight. Meanwhile we still carry on to produce large amounts of moisture inside of buildings – just with every day activities. Like we always have, no change here.
But overall this leads to overall higher moisture inside our buildings – which means we need to look at managing that. Spoiler alert – ventilation is key!
While we might not need to reference R-Values in G4 per se - the current compliance with G4 should really look at effectively meeting the parameters we mentioned in G5 earlier (humidity, air speed, effective minimum air exchange) to combat the by-product of better insulation – increased airtightness and increased moisture loads.
H1 - Energy Efficiency
Where to start… the H1 changes and rollback discussion aside. Can we just acknowledge the Swiss Cheese of a clause were dealing with?
You may remember our 2022 H1 Overview a few years back when we put our 2 cents worth into the update submissions. Her a quick recap:
proposed H1 changes 2022
Whether we agree with Acceptable Solutions R-Values or not (we all know energy modelling should be the only Method...), where are the thermal bridges? We should really add those to the mix – even under Acceptable Solutions.
The heat loss might not be a huge factor for mediocre performing buildings but if we want to move into a cleaner greener future with higher R-Values we have to integrate these as a standard. Because thermal bridges and the relative heat flow increases with the R-Values and also they impact on E3.
And what about the control of airflow? Without getting into the details of it can we all agree that an air leaky building - no matter how insulated it is - is not going to meet the performance target. The end.
So why cant we implement targets for the control of air flow? Blowerdoor tests are a quick and easy way to confirm that on site. Just add this to the Compliance Process. Im not saying we need to implement targets yet. Lets just start testing. Collect some data. Don't scare the builders :-)
Solar Heat Gain - the next building crisis after internal moisture (has that started yet?)
Does improved insulation affect overheating? Damn straight it does! but this one is tricky, because the science behind overheating is much more complex and can't just be distilled into an Acceptable Solutions format. Could R-Values in the acceptable solutions be tied to solar heat gain coefficients in glass? Maybe - that could be an entire study in itself. But this would also have to involve the thermal mass of the building, and the shape of the building, and the ventilation strategy of the building. What was thermal mass again? - read here.
Easy way out would be energy modelling, or H1, VM1, or 2. This may have been raised as a solution before...
E3 - Internal Moisture
Does improved insulation affect internal moisture? Not currently. Only a lack thereof is mentioned. But yes, sometimes directly, and sometimes indirectly.
Lets start with the indirect consequences - like I said earlier - if buildings are more insulated there is less opportunity for unwanted infiltration (drafts) and the internal air can hold more moisture. While E3 says its good enough to ventilate and keep inside temperatures just 5-7 degrees C above external temperatures for moisture control we would assume that is not really comfortable across the country. But lets assume that we have a fantastic ventilation system that keeps all of that in check. We spent the money on a really nice Heat Recovery Ventilation with supply air and extract air balancing and did all these passive principle (...Ye I, know) things to our building.
We end up with perfect temperature and humidity at all time in our building! Hurray!
Or is it?
Heres what E3 doesn't cover in any shape or form - what happens behind the plasterboard?
Yep, stuff happening right where you cant see it. Its called diffusion and is pretty much like you imagine it. Not obvious like a vapour diffuser, some use for ambience, but in principle.
The water vapour in the air in the drawn to the cold. This can be cold surfaces in your house, or where it can migrate into the areas hidden behind the plasterboard. The easiest way for it to get there is by air gaps but it can just migrate straight through the porous structure of the material itself.
This is a direct consequence of increasing insulation. The increase in insulation creates a bigger difference between inside temperature and outside temperature which creates a stronger force for the water vapour to want to go to the cold parts.
And now what, E3?
No acceptable Solution, or Verification method to tackle this yet.
Our idea here is to look at what other countries have done - because there are standards that cover this problem. Its not unique to New Zealand.
Acceptable solutions could look at typical construction methods and connection details, like the German Beiblatt 2 document, or a calculation, similar to calculating the R-Values but the output is a condensation value. Or, what we currently use as Alternative Solution Verification Method - a hygrothermal Analysis or WUFI Model.
In Part 2 we will be looking at Moisture Protection in much more detail.
