The curved double glazed green windows challenge


Window and door joiners AliWays travelled a new learning path when they installed curved windows for a house with a stunning view over Lake Taupo.

Architectural designer James Thomson, of JT Design, specified precision curved windows to capitalise on the premier location to fully capture the lake and mountains of the Central North Island.

The house was built in a Zone 3 area where Energy Efficiency was introduced in 2007. To achieve its thermal performance, this house used double glazing throughout. However, to complicate matters, several of the windows are curved double glazed units.

To achieve a successful result, templates were provided to the glass supplier, Glasshape, and the aluminium extrusion curver, Fabtech. The first lesson learnt was that the double glazed curves were never going to bend to suite the extrusion, so the curved extrusion had to be perfectly curved to the agreed radius. No margin for error here!

AliWays had to overcome the technical difficulties of coupling curves to flat faced sidelights at the interface. AliWays owner Mark Stringfellow performed all sorts of calculations based on dissecting angles, but conceded that the best result was achieved through the sheer skill and great eye of one of the guys on the factory floor.

Double glazed curved windows are a marriage between the house, the aluminium frame fitted to the house and the glass fitted to the aluminium frame.

The concrete rebates — top and bottom — provided by builder Penny Homes had to be of a constant radius throughout and vertically aligned top and bottom throughout the curve, while the curved aluminium and glass also needed to be absolute to the agreed radius.

The whole radius puzzle was a bit of a mind bender for AliWays and Penny Homes due to radius changes between the inside of the reveal, the upstand on the window frame and the position of the double glazed bead.

Installation also had its own difficulties. For those who have squeezed a standard flat window or door up the side of a house between the scaffolding and the house framing, give a thought to doing the same with a curved window.

Each curved double glazed unit weighed more than 100kg, and had to be lifted by six men with strops, as standard glass suckers are useless for gripping on to curved glass.

The tolerances were minimal so, despite a high degree of care in the manufacturing, problems were encountered in fitting the double-glazed bead and wedging.

Mr Stringfellow maintains the only reason they got there in the end was the positive attitude of the Metro glaziers.

Penny Homes and AliWays have achieved their own curve during the building of this home — a huge learning curve — and must now be the acknowledged Taupo experts at building and installing double glazed curved windows!

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