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. Reflective aluminium foil was used under particle board flooring during the 1980s.
The creation of the national Building Code in 1992 shifted building rules from simple prescriptive lists to performance-based standards. Reflective foil was draped under almost every 1980s timber floor. But as performance standards increased in the 1990s and 2000s, councils stopped accepting single-layer foil because dust and draughts destroyed its thermal efficiency. Foil was finally banned completely in July 2016 for safety reasons after electrocution risks from metal staples hitting live wiring. Foil was replaced by fibreglass batts (which needed plastic strapping to hold it in place), rigid polystyrene foam, and eventually modern self-supporting polyester.
From 2007 Nelson/Tasman ceilings required a minimum of R 3.3, walls R 2.0 and suspended floors R 1.3.
In 2007, Nelson/Tasman requirements were increased substantially (R3.3 ceilings, R2.0 walls, R1.3 subfloor).
In 2023, the building code update pushed roof insulation targets up to an R6.6 construction rating (requiring thick R7.0 batts or double-layer insulation), with subfloors moving to R2.5+. Walls remain at R 2.0 to fit within 90 mm thick stud walls.
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 and timber trusses.
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 fibreglass insulation in place.
Note that clearance must be maintained between any recessed incandescent or 12V halogen lighting fitting and 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 old recessed lighting with IC-rated LED lighting or surface-mounted light fittings that do not need transformers. Modern IC-rated LED lighting allows bulk insulation to be laid directly over the fittings without safety risks or thermal gaps.
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. 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 all plasterboard 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 it 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. Current best practice is to remove the Insulfluf by vacuuming and then fit new insulation.
Fibreglass is cheap but has a large energy requirement in its manufacture. Various toxic chemicals can be used to bind the fibres more rigidly, and it cannot be easily recycled. Fibreglass has improved by now being bonded, so it keeps its bulk and also binds the fibres together so it’s easier to handle.
Polyester, usually having a high recycled component, does not have 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.