New building work - Building Code performance requirements for retrofitting insulation

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Protection from fire

Most types of insulation must be protected from being heated to over 90°C by nearby appliances. This can be achieved by having sufficient distance between the appliance and the insulation, or by protecting the insulation with fire retardant material such as fire rated plasterboard.

Although there is no Acceptable Solution covering fire hazards associated with insulation, Part 7 of either C/AS1 or C/AS2 may help in determining compliance for the placement of fixed appliances near combustible building materials.

Energy efficiency and Internal moisture

Clause H1.3.1(a) of the Building Code has a requirement for the building envelope of many buildings to provide adequate thermal resistance. However, that clause applies to the overall performance of the building envelope: for a timber framed wall, thermal resistance is determined by how the interior linings, framing, installation, underlay, cladding cavity (if any) and cladding all interact. The compliance of wall insulation alone, whatever its thermal resistance (R-value), cannot be evaluated against the requirements of clause H1.3.1.

Similarly, although clause E3.3.1 has a requirement for the provision of an adequate combination of thermal resistance, ventilation and space temperature, the compliance of wall insulation alone cannot be evaluated against clause E3.3.1.

This means that there is no minimum R-value required by the Building Code for the retrofitted insulation.

However, the retrofitting of insulation must not reduce the extent that the building envelope complies with clauses H1.3.1(a) and E3.3.1. This is discussed in Section 7. It is easily met, as retrofitting insulation generally improves the R-value of a previously uninsulated wall.

While the thermal performance is not relevant to issuing a building consent, it is likely to be fundamental to any contract between a homeowner and the supplier/installer. The thermal performance of retrofitted insulation can vary considerably, depending on the type of insulation, the quality of installation and the in-service conditions.

Structure

Removing and reinstating structural wall linings when retrofitting wall insulation, or drilling holes through studs, would require compliance with Building Code clause B1.3.1. However, the insulation work itself is not part of the structural system of a building, and therefore does not need to (and in fact cannot) be evaluated for compliance with B1.3.1.

Durability

The durability requirement in the Building Code applies only to the extent that other Building Code performance requirements apply.

The Building Code requires 50-year durability for building elements that are difficult to access or replace, or where failure of the building element to comply would go undetected.

In most situations, insulation retrofitted into a wall cavity can be expected to remain substantially protected from common causes of degradation such as dampness, vermin, and ultraviolet light, when appropriately designed and installed. In such conditions, common types of insulation are likely to meet the 50-year durability performance criteria B2.3.1(a). Unusual types of insulation or very harsh environments may cause insulation to degrade over time, reducing its effectiveness (thermal resistance) and perhaps producing hazardous materials or creating new risks. Such possibilities can only be assessed on a case-by-case basis.

External moisture

Insulation retrofitted into a wall cavity will not form part of a wall’s weathertightness protection, and so cannot be evaluated for compliance with most parts of Building Code clause E2 External moisture.

However, clause E2.3.6 deals with construction moisture, and is relevant to some types of insulation retrofitting work.

Most types of insulation are designed to be installed dry and therefore have acceptable moisture levels
when installed.

However, some less common types of insulation may be designed to be installed wet. Compliance of insulation that is installed wet with Building Code E2.3.6 will be difficult to assess given the variability in drying rates that occur, and the variability in susceptibility to moisture of nearby materials. Compliance would need to be assessed on a case-by-case basis that could involve an extended series of moisture measurements. There is no Acceptable Solution for the dissipation of construction moisture from retrofitted insulation.

Factors that will affect the drying potential of insulation in a cavity wall include:

• the vapour permeability of the wall linings and claddings (including any building wraps, paints and surface coatings)
• the rain and wind environment (ie the wetting potential)
• the ground conditions and foundation connections to a wall
• the condition of the existing cladding (eg cracks and gaps)
• the ventilation rate within the wall cavity
• temperature of the external and internal wall surfaces.

Hazardous materials

Provided insulation is sourced from a reputable manufacturer, then handled and installed in accordance with manufacturers’ instructions, it is likely that it will comply with Building Code clause F2.3.1.

There is no Acceptable Solution covering material hazards for wall insulation. However, off-gassing and small airborne particles are the primary material hazards to consider.

A number of different chemicals can be used to manufacture various types of insulation materials or used in the binders that hold them together.

While some such chemicals can be hazardous in high concentrations, generally the concentrations that are associated with thermal insulation are not high enough to be considered problematic to building users. Formaldehyde is such an example, and while relatively common in many different building products it is generally not found in sufficiently high concentrations in insulation to be considered hazardous.