BERA has been conducting Section J (DTS) assessments under NCC 2019 for over six months now, so we thought it would be a good time to put down some thoughts on how it’s going. If you’re a fellow Energy Efficiency assessor, we’d love to hear how you’re going with it to.
We’re sharing our experiences to encourage designers, certifiers and assessors that NCC2019 Section J DTS assessments are very do-able. We’ve heard many stories of people saying that NCC 2019 Section Js are now too hard and that you have to do a JV3. We respectfully disagree and have found, with a bit of familiarity with the new code and some in-house tools, that completing NCC2019 Section Js (and the associated design requirement outputs) is pretty straightforward.
BERA has now done about 50 Section J jobs under NCC 2019, including a 4 storey care building, plenty of multi-storey education buildings, a fish hatchery (that was interesting), a large mine laboratory and, at the smaller end, a couple of fish and chip shops.
Here’s some thoughts so far on assessments using NCC 2019:
- One of the huge leaps forward in NCC 2019 is the ability to average the performance of wall/glazing constructions across all four orientations. This make a huge difference for large buildings, or buildings with complex glazing on one or two sides. The code has been changed to allow assessors to use either of two ‘methods’ – one assesses each orientation separately, the second takes an average of the four orientations. It’s a (little) bit like a JV3, and has given us much more flexibility in coming up with compliant solutions. [In fact, when we spoke to ABCB (Australian Building Code Board) about this, they said the purpose in making this particular change in NCC 2019 was to reduce the number of JV3 assessments that were needed].
- Wall insulation requirements have gone down for most designs – yes, down, and we mean dramatically! Instead of the requirement for a wall to have say R 3.3 under NCC 2016, the maximum R value required for most climate zones is now R 1.4. Even when you include thermal bridging, we now typically see wall bulk insulation requirements of R 1.5, whereas under NCC 2016 wall bulk insulation requirements were often R 2.5 or more in Climate Zone 2. This likely has to do with averaging walls and glazing under the new “Wall-Glazing Construction” approach to assessment – though we haven’t discussed that directly with ABCB.
- Under-slab insulation is catching everyone by surprise. J 1.6 requires smaller buildings (very roughly, less than ~500m2 footprint) to have underslab insulation to limit the amount of heat loss/gain into the ground. A surprising number of our commercial clients have never even heard of under-slab insulation, so it’s led to some fun conversations. The most useful tip we have is that sub-slab insulation goes between concrete beams/piers, not underneath them – in accordance with J1.2(a)ii. We also had a useful conversation with a Kingspan technical contact – Kingspan seem across the details about how to design/install sub-slab insulation.
- ABCB Support – There’s always a learning curve with a new code, as you get familiar with the details of the legislation. A hugely helpful resource for us in this has been the authors of the legislation, the Australian Building Codes Board. We just submit a question via their website and a few days later there will be a very helpful phone call from someone there, usually Michael Dowd. They have been very patient as we’ve peppered them with lots of tiny detail questions, and their answers have made a big difference in helping us and our clients identify solutions.
- The ABCB Window-Glazing Calculator – As much as we appreciate the work of ABCB in providing a new calculator to assess “wall-glazing constructions”, sadly the calculator was not exactly up to the task. We found it quite restricting in its workflow, un-necessarily complicated, tried to do too much, and most concerning of all it had a number of pretty serious bugs. So instead we built our own wall-glazing calculator, putting all the details of the legislation into some cool formulas that do all the work in the background. Without this, there’s no way we could have kept doing DTS assessments. We hear that at least the bugs in the ABCB calculator are being fixed – but we won’t be going back.
- Thermal Bridging – it was always there in the old legislation, but now allowance for heat loss through a wall or roof frame (thermal bridging) needs to be incorporated into wall performance calculations. There are plenty of TB calculators online, but we built one into our spreadsheet. In the early stages, to get the inputs needed to calculate heat loss through TB, we kept asking clients for every last detail of their wall design (i.e. material, thickness, steel gauge, stud spacing, # noggins, top plate, bottom plate etc). Most clients didn’t have this level of detail at the time of assessment, so now we will typically just ask frame thickness and “steel or timber?” and then assume a “worst case” framing design for the assessment – if that doesn’t pass, we’ll go back to our clients to get more detail.
- Roof colour – we thought more clients would object to being restricted to just light colours per J1.3(b), but in fact we’ve had no objections from any clients on this. The only time it has been an issue has been where for a refurbishment job where there is an existing dark roof. In one of these cases, we used a Performance Solution (see below for more on this), and in the other, the certifier was willing to exempt the roof from NCC2019 compliance on the basis of Section 61 of the Queensland Building Act.
- Performance Solutions now require quantification, in kJ/m².hr, of “hourly regulated energy consumption, averaged over the hours of operation” (JP1(f)). This is new, and not straightforward to determine without modelling the building using something like a JV3. We have done just the one performance solution under NCC 2019 (see a previous point), where we replaced the DTS requirement for a light roof with an additional (excess) R 1.5 insulation in the ceiling – because the roof ceiling and roof colour are on the same part of the conditioned envelope, we argued that the substitution would satisfy the kJ/m².hr requirements, without actually quantifying it. If the substitution/offset was on another part of the conditioned envelope, we would need to model it with JV3, defeating the purpose of using the Performance Solution – so for us, Performance Solutions have become much rarer.
- Lighting requirements have certainly got tighter, but we’re yet to find a design that doesn’t comply. The difference is that we now often need to make use of factors in the calculations (for e.g., where a motion detector is used) to get some designs across the line.
Overall the transition to NCC 2019 DTS has been pretty smooth, or at least much smoother than expected! Requirements have not skyrocketed in the way some of the talk would make you think, and we haven’t had a spike in clients grumbling about what the code is asking them to do (with the possible exception of J1.6 under-slab insulation!). There is a little bit more complexity in some parts of the assessment, but the “outputs” (i.e. requirements for designs) are in a similar league to NCC 2016.
We have spent the last six months carrying out NCC 2019 Section J DTS Assessments, and want to assure fellow assessors, clients and Certifiers that they are not all that complex and are almost always a more cost-effective method of assessment for suitable buildings that the JV3 modelling. A JV3 will usually give you the most flexibility to develop solutions for complex designs, but for most buildings a DTS should be considered first. If you have a project that you have been advised is not suitable for Section J DTS Assessment, feel free to ask us to have a look to see if a Section J DTS will work – we don’t charge for this kind of review.
We really like the flexibility of averaging wall/glazing requirements across all orientations, so from an energy efficiency assessors point of view, our verdict after 6 months is actually a big thumbs up for NCC 2019.