Designing Warm Roofs for Performance

[Shane Clarke] Welcome guys, thanks for coming. Today's topic is how to specify a robust warm roof solution. Warm roofs are becoming more and more common — they're really becoming the norm — and it's important that we specify a robust system. With me on the panel today I've got Scott Squire, our Specification Manager for Nuralite, and Thomas McLaughlin, Managing Director of ILD — International Leak Detection. Thomas, you've been doing this since 2013, so you've seen a lot of changes in the membrane space and some of the things that trip people up over and over. Your job is purely to go out and inspect membrane roofs — you don't install them, you just see what's left after everybody leaves. Why we think today's webinar is important: recent changes to the New Zealand Building Code around H1 thermal efficiency have driven designers towards warm roofs. Ten years ago they were probably about 5% of our business. Today they're about 50%. On top of that, MBIE are planning significant changes to legislation around accountability — moving from joint and several liability to proportional liability. There are also changes around professional indemnity insurance, disciplinary penalties, and even the fees to be an architect are increasing. So if there's one message to take away from today, it's that Nuralite can de-risk your warm roof. We're going to touch on three aspects: mechanical fixing, insulation choices, and electronic leak detection. But first — Scott, what is a warm roof? [Scott Squire] Historically, with membrane flat roofs, you'd put the membrane onto a plywood substrate and fill the roof cavity with fluffy insulation. With a warm roof, we take that insulation layer and put it on top of the roof, with the membrane on top of the insulation. So we're moving insulation from inside to outside — where the science shows it should be. That does a few things: it helps manage condensation risk, and it gives you a really uniform layer of insulation so you get good thermal performance. Thinking about H1 — H1 is about insulation, but it's also about limiting uncontrollable airflow. Part of our system includes a vapour barrier that goes under the insulation, so it ticks both of those boxes. The build-up from bottom to top is: the metal tray or substrate, then the self-adhering silver vapour barrier, then the PIR insulation board, then the two-layer membrane on top. It's all about control — the membrane sheds water, the PIR is your thermal control layer, and the vapour barrier is your air and vapour control layer. [Thomas McGlocklin] Warm roofs aren't new to us either. But what we see — because we're involved after the design phase, during construction and post-construction — is the interaction between the construction site and the membrane. It goes down so early in the process, and then the whole site works around it. [Shane Clarke] Right. So the first key aspect of designing and building a robust warm roof is the type of fixing. Scott? [Scott Squire] Our preferred method is mechanical fixing, 100%. If you download any of our details from the website it shows the IKO Fix fastener. We offer adhesive fixing as well, but 99% of the time we recommend mechanical fixing — it de-risks the installation during construction. The only situation where we'd advise gluing is something like a heated indoor swimming pool where you need to eliminate every single point of thermal bridging, but that's few and far between. The IKO Fix fastener has a thermally broken flange. If you start putting plain metal fixings through the insulation layer you're eroding the thermal performance it's there to provide, so the thermally broken flange offsets a degree of that thermal bridging. The screw fixing is a standard size, but the beauty of the flanges is we can get them in very long lengths to accommodate really thick PIR build-ups — so whatever your target R-value, you've got the flexibility. It's fast and easy to install, and the installer just follows a standard pattern without having to deal with adhesives. [Thomas McLaughlin] Shrink-wrapping buildings is pretty common now — it doesn't carry that stigma of the leaking building anymore, it's just the way we build. That helps a lot, because if you're trying to install a warm roof in exposed conditions you've got dust, temperature fluctuations, all of that. Adhesives are affected by curing conditions — there are certain months of the year you simply cannot use them in the South Island, for example. [Shane Clarke] Another benefit of mechanical fixing is that if water ingress does happen during construction, you can simply unscrew the boards and replace the damaged ones. You can't do that with a glued system. And thinking about wind pressure — with climate change, facade engineers are designing for really significant wind uplift. Our standard mechanical fixing pattern gets you to 4 kPa. Anything over that, you just add more fixings. One thing to be aware of is that with a full-length screw, if someone impacts on it during construction, they can push the screw up through the membrane. We saw that at a building where people had been standing around a fixing — the membrane had dished up around it like a toilet seat and then come back down, and it was completely hidden under the ballast. With PIR you've got better compressive strength, so that's much less of an issue now. [Scott Squire] Exactly. The compressive strength of PIR is one of its big advantages. [Shane Clarke] Alright, the second key factor in designing a robust warm roof is insulation type. Scott? [Scott Squire] In our system we use PIR insulation board 99.9% of the time — it's a foamed plastic. The benefits are really good thermal performance per unit of thickness, excellent compressive strength, and compared to other foamed plastics like EPS or XPS, PIR has improved fire performance. When you're loading a roof with a significant volume of foamed plastic — which is technically combustible — you want to make sure it won't spread and propagate a fire if the worst happens. EPS — the stuff packed around your TV when you buy a new one — we don't advocate that at all. Our PIR is imported from Belgium and we've got a lot of test data to back up its performance. In terms of where it's been used, a good example is the Somerset Aged Care development up in Mildale — a large all-CLT project with a flat upper roof deck and a tapered PIR warm roof. Quite a lot of PIR on that roof given the design ridge running through it. On that particular project the fire engineer introduced ROCKWOOL at the inter-tenancy firewall junctions. Rockwool is non-combustible — wool made from rock, so it doesn't burn. The theory is that in the event of a fire breaking out in one of those fire cells and getting up into the roof, it won't pass over the firewall. It creates a controlled fire cell, giving people time to get out of the building. The limitation of ROCKWOOL is that it has lower compressive strength than PIR — think of a dense yoga mat versus a wooden table. And you can't put membrane straight onto it like you can with PIR boards, so a dense gypsum-based cover board goes on top to give it grunt and a surface to membrane onto. The IKO Fix fasteners pin the cover board down through the PIR into the substrate below. [Thomas McLaughlin] Where that creates a challenge for electronic leak detection is that the Rockwool and cover board zone doesn't have the foil facing that the PIR has, which is what we use as the conductive element. In that situation we'd design in a 50 by 50 mm stainless steel mesh underneath the cover board and a conductive ribbon on top. It's not 100% coverage, but it still gives the ability to test electrically — with slightly reduced accuracy, but a test all the same. [Shane Clarke] Our third key point is integrating electronic leak detection. We call it ELD — your company is ILD, International Leak Detection. Thomas, can you explain what ILD is and how the technology works? [Thomas McLaughlin] International Leak Detection is a company started in Germany. The technology is called EFVM — Electric Field Vector Mapping. We operate in New Zealand, and Roberto looks after Australia. It started off primarily on concrete substrates, which are your conductive material. What EFVM does is put a current on top of the membrane. We wet the surface — not flood it — then run a conductive wire around the perimeter of the membrane and connect it to a generator. That generator pulses roughly 40 volts through the moisture on the surface. We can then read the electricity within that perimeter. If there are no breaches, the electricity has nowhere to go — it's held, insulated by the membrane. On a small surface like a balcony you can tell almost instantly that everything looks good. The voltage is 40 volts at very limited amperage, so it's safe — it gives you a little tickle if you touch it, but that's about it. If there is a breach in the membrane, the current starts to move — it has somewhere to go. It leaves via the water as the conductive medium and travels down to the conductive substrate below, whether that's the foil face of the PIR board, concrete, or the conductive mesh over the Rockwool zone. From the direction of that movement, the team can triangulate and pinpoint the exact breach location. The process is like mowing the lawn — walking the roof in a pattern. It's not just about the equipment though. The team's experience and their eyes pick up a lot. It's a skill you develop, not something you just buy off a shelf. [Shane Clarke] We now write electronic leak detection into our specifications as standard. If you download a Nuratherm warm roof spec from Master Spec or our website, it automatically includes ELD. What we changed to make that possible is simple — the installer gets a roll of conductive tape that we supply, and they run it perpendicular to the board butt joints, connecting the foil faces of all the boards together into one continuous conductive element. The joint tape goes over the top. You'd have to physically remove it from the spec, and I'm not sure why you would. [Scott Squire] You're 99% there already with the foil facing on the PIR. Adding the tape and the test tags is all it takes. The test tags — little dog tag connectors, about $17 each — are recommended at one per 500 m². They're stuck to the aluminium foil and the wire runs up through a penetration or upstand to give Thomas's team something to connect onto on the outside of the membrane. That completes the circuit — on concrete you're connecting to the reinforcing steel, here you're using the tag. Think about where to locate that exit point at the design stage, because often architects want a clean roof with no penetrations, but there are usually pipe stacks, solar, or a skylight flashing you can dress it through. [Thomas McLaughlin] ELD has been around for just over 40 years. It's a big thing in Europe — you see it on Grand Designs UK from time to time. It's been available in New Zealand since 2009. [Shane Clarke] We've moved away from flood testing for this build-up. There is a proper standard for flood testing, but the last thing you want to do is fill that cavity with water and try to get it out again. Keep moisture away from the warm roof, particularly during construction. Thomas, you've tested millions of square metres over the years. Where are you typically seeing the failure points? [Thomas McLaughlin] There's a stigma — and I'm not sure where it came from — that the waterproofing, the waterproofer, the product, is always the issue. We thought that too at first. But the more we saw the test results, over and over again, it's the construction phase. The traffic. And where's the waterproofer when that's happening? They've finished and handed it back to the main contractor. [Shane Clarke] So when's the best time to do an ELD test? [Thomas McLaughlin] At practical completion. There's value in a handover test from the waterproofer, but if you've got a limited budget and you can only do one test, do it right at the end — after every other trade has finished using the roof as a workbench. That way you draw a clear line in the sand: these things were found, they've been fixed, and we're handing over a watertight membrane. Once the ELD infrastructure is installed, you can test at any point in the building's life. Pair it with your regular visual inspections and it becomes a really powerful ongoing maintenance tool. [Shane Clarke] It's also worth noting the context of E2 and the allowance for failure. The building code recognises through sequencing — clause 3.7A and B — that the membrane will be installed first and it's nearly inevitable it will get trafficked on. Allowing for that failure to be located and fixed is the point of ELD. It mitigates that construction phase risk and extends into the maintenance life of the building.