Existing building compliance level after retrofitting insulation

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Means of escape from fire and accessibility

When a building is being retrofitted with insulation in exterior walls, section 112 (1)(a) of the Building Act requires that the entire building’s means of escape from fire be upgraded to comply as nearly as reasonably practicable with the Building Code. For certain buildings, accessibility needs to be similarly upgraded. These upgrade requirements do not apply if a TA has issued a specific exemption from obtaining a building consent.

A BCA must not grant a building consent for the alteration of an existing building (including retrofitting insulation to external walls), unless the BCA is satisfied that after the alteration the building will comply, as nearly as it is reasonably practicable, with the provisions of the Building Code that relate to means of escape from fire and, where applicable, accessibility.

Upgrading the means of escape in standalone housing is likely to require, at a minimum, ensuring it has a suitably located and working smoke alarm system. In larger buildings, upgrading could involve assessing and potentially modifying features such as alarm systems, internal fire separations, fire doors and escape routes. In buildings used by the public, upgrading of accessibility could involve assessing and potentially installing or modifying features such as accessible parking, entrance and access routes, and sanitary facilities.

Protection from fire – Fire affecting areas beyond the fire source

A Group Number is a classification for a finishing material by its behaviour in fire. Within household units, outbuildings and ancillary buildings, there are no requirements for the behaviour in fire of retrofitted insulation exposed to the building’s interior. For interior spaces of other buildings, and in any common spaces of attached housing (eg shared corridors of apartment buildings), insulation materials would commonly be covered with lining that meets C3.4(a) requirements. If left exposed, the insulation material itself should have the appropriate Material Group Number.

Retrofitted insulation material may be part of the external wall cladding materials and could contribute to vertical fire spread. Refer to C/AS1 Part 5.3 or C/AS2 Part 5.8.

Retrofitted insulation material in external walls may contribute to the fire risk from the wall if the distance to the property boundary is closer than 1m. Refer to C/AS1 or C/AS2 Part 5.

Other Building Code performance criteria

Other Building Code performance criteria also need to be considered, to ensure they are not compromised by the building work associated with retrofitting insulation.

If you are altering an existing building by installing new insulation into external walls, sections 42A (2)(b) and 112 (1)(b) of the Building Act require you to ensure the building will comply with the other requirements1 of the Building Code at least to the same extent as it did immediately before the building work began.

Retrofitted insulation may affect the way existing parts of a building perform, particularly those parts that are adjacent to the insulation such as wall frames, cladding and linings. The Building Code provisions described in the remainder of this section can be used to help assess whether an existing building’s performance is affected by retrofitting insulation.

*‘Other’ meaning Building Code requirements other than those relating to means of escape from fire and access and facilities for persons with disabilities.

Structure

Retrofitted insulation could affect the structural performance (ie B1.3.1) of an existing building if moisture were to accumulate in a wall cavity and cause timber framing to decay and lose support. This could occur if the weathertight performance of an existing building is compromised, as discussed below in relation to the effect retrofitted insulation has on compliance with the Building Code performances E2.3.2 and E2.3.5 for External Moisture.

The performance of structural claddings or linings may be affected if they are altered as part of retrofitting insulation. Any holes, patching or reinstatement of structural claddings or linings will need to be done in a way that both complies with the Building Code (see Section 6) and that doesn’t reduce the overall structural performance of the building.

Durability

The durability requirements in the Building Code only apply to the extent that other Building Code performance requirements apply. Effects that retrofitted insulation could have on the building’s durability are considered in the discussion of the other Building Code performance requirements in this section.

Protection from fire – Prevention of fire occurring

Retrofitted insulation can affect compliance of an existing building in relation to outbreak of fire if the insulation covers or is too close to appliances that generate heat, such as recessed luminaires or a flue penetrating through the wall. Sufficient clearance must be provided between thermal insulation and a heat source to prevent an undue build-up of heat.

NZS 4246 provides recommended safety clearances between thermal insulation and such heat sources for common residential construction. Further requirements for luminaires can be found in AS/NZS 3000.

Moisture penetration

The penetration of water through wall claddings is unlikely to be affected by insulation unless the cladding is damaged and compromised by poor installation.

The effect that retrofitted insulation has on compliance of an existing wall with E2.3.2 will depend largely on the construction and condition of the existing wall and the physical properties of the insulation.

Walls with porous claddings, with multiple regular laps or joints in the cladding, with poorly maintained claddings, with pre-existing leaks or moisture problems, and with high exposure to wind and rain, are more likely to have water penetrate through the cladding.

Insulation has potential to reduce the penetration of wind driven water through claddings by increasing the air tightness of the wall and reducing the pressure differences that are generated across the cladding. However, any increase in air tightness may adversely affect the drying rate within the wall cavity, as discussed below in relation to E2.3.5.

Insulation materials that are porous or hydrophilic will tend to hold and transfer moisture through the insulation. In these situations, retrofitted insulation may cause or exacerbate the transfer of moisture from the back of the cladding to other building elements, thereby reducing compliance with E2.3.2.

The biggest potential problem for retrofitted insulation in relation to E2.3.2 is that the insulation material will create a pathway for external moisture on the inside of the cladding to migrate further into the wall cavity, to the framing and the lining. This bridging effect may be mitigated where the insulation is separated from the cladding or from the framing and lining.

• Small, well-defined, gaps between the insulation and the framing, cladding and/or lining will act as a physical barrier to moisture transfer, like the drainage cavity that is designed into new timber framed walls. However, such gaps can be difficult to reliably construct, and generally lower the thermal effectiveness of the insulation. They should be avoided when insulation is retrofitted unless they are specifically designed. As a result, any mitigation from small gaps in the insulation should not be relied upon when assessing the building’s performance for a building consent, unless specifically designed.
• A wall underlay (eg building paper) which forms a continuous layer between the cladding and framing will help to mitigate the effects of any moisture bridging by retrofitted insulation, as it physically separates the cladding from the insulation and will reduce the amount of moisture reaching the insulation.

Walls with well-maintained non-porous claddings with minimal laps and joints, with no leaks or moisture problems, which have low exposure to wind and rain, and which include an intact wall underlay behind the cladding, are unlikely to have water penetrate to the framing cavity. In this situation retrofitting the insulation will not reduce compliance with E2.3.2.

Moisture accumulation

There are many factors that contribute to condensation, fungal growth, and the degradation of building elements. This complexity means it is difficult to provide simple rules for assessing compliance with E2.3.5 and E3.3.1. Installers, designers and BCAs need to consider the merits of each installation when assessing the effects of retrofitted insulation on the compliance of existing walls with E2.3.5 and E3.3.1.

Retrofitted insulation has potential to cause or exacerbate the accumulation of water in wall cavities, causing condensation, fungal growth or degradation of building elements.

Insulation will reduce the air movement in the wall cavities where it is installed, and in doing so will reduce the rate at which they dry out. However, the drying rate depends on several factors, including climate, wall design and the vapour permeability of the claddings, linings and insulation, as well as the air permeability. The net effect on drying rate will depend to a large degree on the design and condition of the existing wall/building, the climate and the physical properties of the insulation.

The resistance of the materials used to construct the wall to fungal growth and degradation, can also impact on compliance with E2.3.5 and E3.3.1.

On the other hand, retrofitted insulation is likely to lessen the risk of surface condensation within habitable spaces, bathrooms, laundries and spaces where moisture is generated. Insulation will reduce heat loss through the wall, and in cold weather will help its interior surface temperature remain higher than that of an uninsulated wall.

Factors that will tend to avoid or lessen any reduction in compliance of an existing wall with E2.3.5 or E3.3.1 when insulation is retrofitted include:

• non-porous claddings with minimal laps and joints, that are well maintained
• no leaks or moisture problems,
• low exposure to wind and rain (eg wide eaves and low wind)
• continuous wall underlay behind the cladding
• treated timber framing, or galvanised or aluminium-zinc coated steel
• vapour permeable wall linings, insulation, underlay, and cladding
• dry climate
• good exposure of the wall to sun and some wind to improve drying
• the installation of drainage plane mesh as part of the wall insulation retrofit in walls without building paper.

Factors that will tend to cause or exacerbate a reduction in compliance of an existing wall with E2.3.5 and E3.3.1 when insulation is retrofitted include:

• porous claddings
• claddings with multiple regular laps and joints
• claddings with leaks or moisture problems
• poor maintenance of claddings
• lack of wall underlay, or wall underlay that is no longer intact
• high rain exposure
• high wind exposure
• untreated timber framing and cladding, including native sapwood
• low vapour permeability of wall linings, insulation or cladding, or the presence of a vapour barrier in the wall
• high humidity climate
• poor exposure to sun and some wind.

Noise performance

Insulation will have no effect on the compliance of an existing building in relation to noise (ie G6.3.1), because the Building Code only controls sound transmission through walls when they are common between occupancies (i.e. G6.2), and therefore not through external walls.

Only when insulation is retrofitted to intertenancy walls is there potential for it to affect compliance with G6.3.1. In these unlikely situations, the insulation materials and the installation will have a large bearing on the noise transmittance performance of the wall, and so must be considered on a case-by-case basis.

Electrical safety

Retrofitted insulation in external walls can affect the continued electrical safety of an existing building if the thermal insulation:

• Reduces the heat dissipation from the wires
• Reduces the current-carrying capacity of the wiring
• Is incompatible with the electrical insulation that protects the wires
• Causes electrical circuits to short

The safety of electrical systems may be compromised by retrofitted insulation if electrical wires that lie within a wall cavity are encased or enclosed by the insulation.

Both the current carrying capacity of the wiring and the heat dissipation from the wires will be reduced by the thermal insulation. The effects of these reductions in performance will depend on:

• the original rating of the electrical circuit,
• the electrical load on the circuit, and
• the proximity of the wire to combustible building elements.

The current-carrying capacity of electrical wires surrounded by thermal insulation is half that of wires surrounded by air.

The compatibility of thermal insulation with the electrical insulation protecting the wiring must also be checked. The common material incompatibility is polystyrene thermal insulation and PVC insulation on electrical wires. Care must be taken to avoid contact between these materials, as polystyrene has the potential to embrittle PVC.

Liquid-applied and loose-fill insulation may cause short-circuits if it migrates into unsealed electrical flush boxes or contacts surface mounted electrical switches and fittings. If the retrofitting of insulation inadvertently causes or exacerbates moisture accumulation in the wall (see the earlier subsection on moisture accumulation) near the back of electrical switches, outlets or junctions within a wall, this could also create an electrical safety risk.

Old electrical circuits which use VIR (vulcanised India rubber) or TRS (toughened rubber sheathed) cables may also short-circuit if insulation is pushed onto and around these old cables. This is because the electrical insulation on VIR and TRS cables tends to degrade and become fragile and brittle over time.

If water accumulation occurs near the back of electrical switches, outlets or junctions within a wall, it could also create an electrical safety risk (see moisture accumulation earlier in this section).

When the safety of electrical circuits is likely to be compromised by retrofitting insulation, or when electrical wiring is modified, a registered electrician should check and certify the electrical safety.

Where older hard-wired fuses are present, miniature circuit breakers can be used to improve protection from overload currents on circuits when the electrical wiring is surrounded by thermal insulation. Alternatively, the thickness of electrical wiring may be increased to safely carry the current and limit temperature build up, or the electrical load may be divided by rewiring some outlets to additional subcircuits. VIR and TRS cables may need to be replaced, depending on their condition.

Residual current device (RCD) protection can also be added to subcircuits at the distribution board, to mitigate against any short-circuits.

Energy efficiency

The retrofitting of insulation must not reduce the extent that the building envelope complies with clause H1.3.1. Retrofitted insulation will improve both the thermal resistance and the airtightness of an existing wall, so will not adversely affect the compliance of an existing house in relation to H1.3.1.

For example, the thermal envelope of an old timber framed house would comprise the weatherboard cladding, the air in the framing cavity and the interior wall linings.

Installing insulation into the framing cavity will not alter the thermal performance of the weatherboards or linings and will improve the performance of the air within the framing cavity, which will by and large be replaced by insulation.