Home insulation history and materials. 2023 changes

It wasn’t until April 1978 that wall and ceiling insulation became required building elements in all newly built New Zealand homes. Before 1978, ceiling and wall insulation was installed in fewer than 20% of houses, although Christchurch City Council started compulsory use in new houses in 1973.

Us Kiwis were tough, considering there was usually inadequate heating and plenty of ventilation. You just wore more clothes inside.

The early insulation installations were minimal: R 1.9 in the ceiling, R 1.5 in the walls and R 0.9 for the sub-floor.

From 2007 Nelson/Tasman ceilings required a minimum of R 3.3, walls R 2.0 and suspended floors R 1.3.

A major change was made in May 2023 to significantly increase insulation requirements in the ceilings, underfloor and windows of all new houses built in New Zealand.

Building standards are higher now. A standard pitched roof in a new house in Nelson/Tasman needs an R 6.6 minimum rating with 245 mm thick batts. Walls remain as R 2.0 to fit within 90 mm thick stud walls. Sub-floor insulation has increased to R 2.5.

There is a benefit to increasing the R rating for older homes. This is often done as a double layer with the layers perpendicular to each other to minimise heat loss from gaps.

40 to 50% of heat loss in a house is through the ceiling. If you want to reduce the cost of heating a house, extra insulation in the ceiling is the place to start.

If the insulation thickness is less than 120 mm, the ceiling insulation should be increased, and it is usual to keep the existing insulation in place.

Note that clearance must be maintained with any recessed lighting from the insulation to avoid the risk of heat buildup and fires. 12V ceiling lights are a particular problem due to the considerable heat produced and the need for a transformer for each light. Thermal efficiency is increased by replacing recessed lighting with IC-rated LED lighting or surface-mounted light fittings that do not need transformers.

Insulation is fairly easy to retrofit in the ceilings of houses built before 1978. You pass the batts up through the ceiling access panel and spread them out.

Sub-floor insulation in new buildings now has a minimum rating of R 2.5. Maintenance-free materials are rigid polystyrene foam, polyester batts or rockwool. Reflective aluminium foils are unsafe due to the possibility of staples penetrating electrical cabling and the entire subfloor area being electrified. Yikes!!

Fibreglass batts under floors have two significant issues: they are not self-supporting and need to be held firmly in position, usually with plastic strapping, which deteriorates in time; and they are affected by moisture, they are considerably less effective when wet. Fibreglass batts can become displaced due to gravity or by air movement. Polyester batts are more stable and self-supporting when stapled into place.

Installing insulation in walls is clearly awkward. The interior wall lining to the exterior walls must be removed, you might as well remove it all due to the dwangs, install the insulation, then re-line the walls, seal, and paint. Not so easy. Few houses built before 1978 have wall insulation unless this has been subsequently installed.

Also, there was a period when Insulfluf, macerated paper insulation with fire retardant added, was “blown-in” between the ceiling joists. Over time this loose-fill insulation settles or is blown around by draughts in the ceiling space, making it much less effective. It is generally better to ignore any existing insulation and fit new insulation straight over the top.

Fibreglass is a cheap but unhealthy material: installation, or popping your head into the ceiling space, requires a good mask to avoid breathing in the fibres of glass blowing around. Fibreglass slumps over time, losing its insulating rating. It has a large energy requirement in its manufacture, various toxic chemicals can be used to bind the fibres more rigidly, and cannot be easily recycled.

Polyester, usually having a high recycled component, does not have these health issues and maintains its insulating properties. Naturally resistant to moisture, vermin, insects, mould, bacteria, and fire, but will burn if ignited with sufficient heat. It can be recycled.

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