Insulation

Bungalows were typically constructed without insulation. Even with modifications, most fall below current insulation standards.

Bungalows were not insulated when they were built. While some may have had roof space and sometimes underfloor insulation added, they are still likely to fall well short of current insulation requirements. 

Where floors may have had insulation installed, the insulation is likely to be reflective foil fixed to the underside of floor joists, or if installed after 1990, it may be polystyrene boards fitted between floor joists.

Even if the original timber lining has been removed from inside walls, it is unlikely that insulation has been installed unless the renovation work has been done very recently.

Although there is no mandatory requirement to upgrade the insulation of existing houses, all new work is required to meet current standards. New work can easily be insulated to the required levels, but difficulties in interpretation of requirements can arise where renovated spaces comprise both existing and new construction, such as the extension of a particular room.

Roof insulation 

Where there is reasonable access into the roof space, the installation of insulation does not pose a problem. Where access is limited, it may be more difficult. The options available include installing:

  • segment or blanket material – glass wool, wool, polyester
  • rigid and semi-rigid board (expanded polystyrene)
  • loose fill – macerated paper (cellulose), wool.

Blanket

Blanket or segment insulation is available in a range of thicknesses and R-values. It is fitted between roof framing members, and blankets may also be draped over the framing to increase the effectiveness of the insulation. They must be fitted snugly between framing without gaps, tucks or folds and must not be compressed or packed tightly around electrical wiring. A 25 mm gap must be maintained between insulation and flexible underlay.

Expanded polystyrene

Expanded polystyrene boards must be fitted tightly between roof framing members and are only suitable where the access and roof space are generous. Polystyrene should be separated from PVC electrical cables with waxed paper strips.

Loose fill

Loose-fill, macerated paper or wool is blown into the roof space to the thickness and density required to achieve a particular R-value. 

It should be installed with extra thickness to allow for settlement and can also give total coverage across joists.

It can be blown into inaccessible corners of the roof space but must not be compressed. It is the only suitable option for very low-pitched roofs and must be installed by a professional installer. 

Keeping insulation dry

Insulation generally must be kept clean and dry. It should be clear of water storage tank overflow trays and flues. Clearance around downlights installed in the ceiling must be in accordance with the New Zealand Electrical Code of Practice (NZECP) 54:2001. 

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Skillion roof insulation

It is more difficult to install insulation in a skillion roof. These were not a common roof-type in bungalows, but may be part of a subsequent addition. Options available are to install insulation:

  • from below by removing the ceiling lining
  • from above by replacing the roofing.

The lower pitch of skillion roofs tends to cause the metal roof to deteriorate more quickly than a more steeply pitched roof, so access from the outside for insulation installation may be a more viable option and one that also allows roof underlay to be installed. 

The amount of insulation able to be installed is dependent on the rafter depth as there must be a 25 mm gap between the insulation and the underside of the flexible roof underlay. 

An alternative way to insulate a skillion roof is to install a foam-backed sheet material over the existing interior lining. The R-value achieved depends on the material used and the thickness but there are also difficulties in incorporating the additional thickness into the existing detailing.

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Wall insulation

It is more difficult for to install insulation in external walls where exterior cladding or interior linings are not being replaced. 

If the weatherboards are sound, removing the cladding to install insulation is unlikely to be economical – it is estimated that more than 50% of the boards are likely to be damaged during removal as old native timbers are usually dry and prone to splitting. 

Options for insulating walls:

  • Where the exterior cladding is in need of replacement, the insulation can readily be installed. New wall underlay can also be installed if it has not been installed or if it requires replacing
  • Where walls are already plasterboard-lined, assess their condition. If in poor condition, it may be more economical to remove the lining, install insulation, and replace the wall lining.
  • If the internal lining is match lining, remove every second or third board and insert flexible insulation. (Boards may split or be otherwise damaged, but they will be covered.) Where there is no underlay behind the cladding, install polystyrene insulation and leave a gap between the insulation and the back of the cladding or fold wall underlay into the framing before installing the insulation material. 

Drainage paths

A problem with installing insulation from the inside is that it can be difficult to ensure that the drainage path on the back face of the weatherboard cladding is maintained as it is not visible. 

If a clear drainage path is not maintained, water may be trapped by the insulation causing timber weatherboards and/or timber framing to remain wet. Options to avoid this include to install polystyrene insulation or a proprietary bulk insulation with a water-repellent face.

In most cases, retrofitting insulation to walls requires a building consent. 

Blown-in insulation for walls

There is a range of blown-in insulation options for retrofitting insulation to existing walls. Currently none of the available systems hold a BRANZ Appraisal. Key considerations when retrofitting blown-in wall insulation are:

  • Only use this option if it is appropriate for the existing construction – for example, such products should not be installed into walls that do not have a flexible wall underlay (building paper or building wrap) installed behind the cladding.
  • For brick veneer construction the insulation must not fill the drainage and ventilation cavity between the bricks and the framing. It was common for brick veneer houses to be constructed without a flexible wall underlay fixed to the outer face of the framing.

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Brick bungalow wall insulation

The walls of double cavity brick bungalows cannot easily be insulated. Insulation must not be inserted between the two skins of brick as this will provide a route for water to move across the cavity to the inner skin. 

If necessary, the internal walls may be strapped, insulated and lined, but this will negate any benefit of thermal mass to store heat that the inner brick skin may provide to the interior of the house.

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Floor insulation

If the floor has had reflective foil installed underneath, the foil should be removed and replaced with a polystyrene or bulk insulation suitable for use in subfloor spaces. This will reduce the amount of air leakage through the floor as well as increasing the floor’s R-value. 

Retrofitting or repairing foil insulation under floors was banned from 1 July 2016. This practice can be dangerous – the risk is that people using staples or nails to attach the foil to timber members accidentally pierce a live electrical cable. There have been five electrocution deaths and one non-fatal shock reported in New Zealand from installation of foil insulation under houses.

If there is any moisture in the subfloor space, it can be reduced by laying polythene over the ground. By keeping the air drier, this will effectively make the house feel warmer.

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Window insulation

Original window units are likely to be relatively inefficient. There are several options for improving thermal performance, from curtains to installing insulating glass units (IGUs).