Settled on Auckland’s waterfront on the end of Princes Wharf, is the eight-storey 187-room 5-star Hilton Hotel.

It was in need of a new roof to replace the old metal one; only this time, the client was looking for more thermal efficiency along with the usual requirements for water tightness, salt spray corrosion resistance, durability and the ability to withstand high wind pressure. The decision was made to have a membrane roof installed.

The building roof design was such that the large ceiling void with its myriad of reticulated services did not lend itself to a typical ‘cold roof’ insulation system where glass wool insulation had proven problematic; so installing a warm roof system was the preferable option.

It was also critical that the roof was to be replaced without upgrading the original steel portal frames or purlins, as the extra time and cost to replace those would have been prohibitive.

It was important to the architect, Babbage Consultants Ltd that this luxury hotel took advantage of one of New Zealand’s simplest, most energy-efficient and cost-effective warm roof systems — Viking WarmSpan. Additionally, being avid fans of bitumen-based membrane products because of the service history in New Zealand, Viking Torch-On was specified as the waterproofing layer.

What is Viking Warmspan?

Viking WarmSpan is a warm-roof-on-steel roofing assembly for low-sloped roofs. With its rigid foam and trapezoidal steel tray base, Viking WarmSpan gives the system a spanning ability between purlins of up to 3.6m (versus the 400mm centred joists required under a heavy 17mm plywood substrate for a traditional membrane roof).

Additionally, being a lightweight system (less than the 20kg/m² maximum), it has the ability to be installed in half the time of a traditional membrane roof, saving on construction costs. The wide-span capability and speed of installation allows for a 30% saving in material and labour costs to achieve the same R-value rating of more conventional membrane roof solutions (cold roofs).

The Installation

Viking Roofspec systems can only be installed by Viking Approved Applicators; companies that have put their installers through a stringent licensing programme. Once the project went to tender, long-time Viking Approved Applicators, Mohan Roofing Services were awarded the contract.

With the steel purlins being part of the original framework, after some minor modification, it was straight to work with fixing down the trapezoidal steel tray substrate. Having the building shrink-wrapped also allowed for trades to continue working no matter the weather conditions.

Being a simple three-layer warm roof system, Viking WarmSpan removes unnecessary, superfluous components that can be found on other warm roof assemblies.

The steel tray sheets were sealed during installation, and proprietary flashing tapes were then used to seal any transitions or junctions to complete a ‘built-in’ vapour barrier.

Next, the insulation layer: 75mm Kingspan polyiso panels. Viking WarmSpan uses a proprietary two-component, polyurethane adhesive to bond the Kingspan polyiso panels to the steel tray. This fully adhered system using F.A.S.T technology, provides greater strength and wind uplift resistance than mechanical fixing, while avoiding thermal bridging at the same time.

Lastly, Viking’s two-layer Gemini APP Torch-On membrane was installed over the polyiso boards, providing the waterproofing layer(s).

Viking Gemini APP consists of a 3mm thick sand finish base sheet as the first waterproofing layer, and a 4mm ceramic chip cap sheet installed on top.

The result

The Hilton Hotel is now completely watertight, with the Viking Approved Applicator completing this project to a very high standard. The roof looks great and will withstand the gusty conditions that the Auckland waterfront is prone to. Surrounding buildings higher than eight storeys, now look down on the Hilton Hotel’s tastefully installed, watertight and energy-efficient roof which is backed by a 20-year warranty from Viking Roofspec.