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Construction and materials

Making a rental property warmer and drier

08 February 2018

Modifying windows in a flat has resulted in a warmer home with happier tenants.

The owner bought the 100-year old weatherboard house in Wellington’s eastern suburbs in late 2016. Built on a hill, the two-storey house had been split into three flats several years earlier – two on the top level and one below.

While two flats had heat pumps the third had a flued gas heater. In winter the tenants in this flat used the gas heater for several hours each evening. Despite leaving windows open for ventilation during the day, mould and condensation became a problem.

Pitfalls of acrylic sheets

Most of the windows in the flat had single glazing, so to retain heat the previous owner had installed acrylic sheets over the wooden-framed windows. While this slightly improved heat retention, mould grew as condensation was trapped between the glass and acrylic, and moisture caused the paint around the wooden frames to crack and peel. The acrylic also meant the sea views from the windows were blurred.

Wanting to ensure the flat was warm, dry and healthy for tenants the new owner decided to improve the windows and frames – while ensuring the view was not affected.

Mould grew between and around the acrylic sheets and the window glass.

Insulation film applied to existing windows

Double-glazing the windows was too expensive, so the owner considered window insulation options (or secondary glazing), deciding on a film that is installed on the inside surface of the glass. The film (known as a low emissivity film) reflects heat, reducing the amount of heat that escapes outside through the glass.

Sanding back the frames prior to repainting, and then applying the insulation film.

The owner sanded back the frames, filled cracks with a repair filler and repainted. A professional installed the window insulation in one day ensuring minimal disruption to the tenants. The flat looks smarter with the repainted windows – and the view is great.

The window insulation is almost invisible and will keep the home warmer in winter and cooler in summer. The owner is also planning on installing a heat pump in 2018.

These small improvements have made a big difference, with happier, healthier tenants and an owner who is protecting her investment.

The insulation film is almost invisible against the window.

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Note that this document is published by the Ministry of Business, Innovation and Employment Chief Executive as Guidance under Section 175 of the Building Act 2004. This is a guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case.