Passive Design

The correct installation of insulation is critical. Both bulk insulation and reflective insulation perform poorly if incorrectly fitted. Insulation must remain dry through out its life to maintain its insulating performance.

In framed walls, 18% to 22% of the area is made up of framing members with a lower insulation value than the insulated cavity. It is critical that the insulation in the remaining 80+% of the wall is fitted correctly and performing at full capacity. Thermal bridging through the framing and uninsulated gaps can reduce the insulation efficiency by up to 20% for timber framing and 50% for steel framing.

For steel wall framing, a thermal break must be used to obtain satisfactory insulation. A minimum of 20 mm-thick expanded foam board strip should be use to batten out the external cladding.

General tips for specifying insulation installation

Follow the manufacturer’s recommendations for safety and handling. Wear recommended protective clothing and masks.

Insulation must be installed:

• without edge gaps
• clear of downlights unless zero clearance downlights are specified
• clear of hot fixtures such as flues, and transformers (refer to Electrical Code of Practice ECP 54)
• clear of water tank overflow trays
• for polystyrene insulation, isolated from PVC sheathed wiring.

Do not pack insulation tight around electric cabling. And leave a minimum 25 mm gap between the insulation and roof underlay or sarking.

Installing segments and mats

These must fit tight between framing with no gaps, and they must not:

• be compressed
• have folds or tucks
• in walls, sag within the framing cavity – preferably the mat or segment should be the same thickness as the cavity
• be installed in timber framing with a moisture content of over 18%.

Loose fill

Loose fill insulation must be installed so that:

• it cannot be shifted by the wind
• it is of even thickness throughout
• it is sufficiently deep to allow for settlement
• it is not compressed.

Perforated foil

Perforated foil insulation must:

• only be used under suspended timber floors (not in walls or ceilings)
• have a sag of at least 100 mm when draped over floor joists
• not be damaged during construction
• be sealed or stapled at boundary joists
• be enclosed by a sheet lining when the sub-floor is not enclosed
• remain clean and shiny.

Rigid boards

Rigid polystyrene board insulation must:

• be laid over a damp proof membrane when used under a concrete slab on the ground
• be separated from internal spaces by a lining material
• be fitted tightly between cavities
• not come into contact with PVC (such as TPS wiring)

When used as a cladding, rigid board insulation should be installed in accordance with NZS 4246 and the manufacturer’s instructions.

Insulating plaster

Insulating plaster must be applied to the design thickness of the plaster mix. When applied externally, it must be protected from the weather by a suitable weatherproof coating.

EIFS

EIFS cladding systems are to be installed in accordance with the system supplier’s recommendation. Guidance of the design and specification of this cladding system is given in the BRANZ publication Good Practice Guide Textured Coated Claddings.